model st-4 star tracker imaging camera operating manual · 2020-06-05 · sbig st-4/0490 page 1...

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Santa Barbara, CA 93150Phone: (805) 969-1851 • FAX: (805) 969-4099Email: [email protected] • Web: www.sbig.com

Model ST-4 Star TrackerImaging Camera

Operating Manual

Table of Contents

Instrument Overview ............................................................................. Star Tracking Operation......................................................................... Page 4Imaging Camera Operation ................................................................... Page 8Host Computer Software Overview...................................................... Page 10Using the ST-4 with an IBM PC or Compatible ................................... Page 18Using the ST-4 with a Macintosh........................................................... Page 28Observing Suggestions with the ST-4 Imaging Camera...................... Page 37Problem Solving with the ST-4 .............................................................. Page 38Appendix A............................................................................................. Page 39

SBIG ST-4/0490 Page 1

Model ST-4 Star Tracker / Imaging CameraOperating Instructions

INSTRUMENT OVERVIEW

The Model ST-4 Star Tracker / Imaging Camera is a multipurpose instrument. It can be used asan automatic star tracker to take long guided exposures of the night sky, or, in conjunction witha personal computer (PC), as a highly sensitive imaging camera. This manual describes thetechnical concept of the Model ST-4, the interfaces to the telescope and computer, and generaloperating instructions.

Tracking OverviewThe Model ST-4 uses a charge coupled device(CCD) detector to detect star images. Thedetector can be understood by examining Figure1. An array of 192 by 165 detector elements,called pixels, is arranged as shown in the figure.We refer to the horizontal axis as X, and thevertical axis as Y.

X

Y

165 Pixels

192 Pixels

Enlarged View Showing Pixels

Figure 1 CCD Configuration

In operation the pixels convert photons intoelectrons, and store them until read out by theST-4's microcontroller (the ST-4 has memory fortwo images, one for light frames, and one fordark frames, as explained further below). Forexample, if a star's image is present at pixel

position 121,132 the computer will determine itsposition by noting the increased signal from thatpixel. If the star is drifting due to guiding errors,it will appear at a different position in the nextexposure, say at pixel position 123,132. Thecomputer then calculates how far the star hasdrifted from the original exposure, and togglesthe telescope drive accordingly.

The microcontroller (in the ST-4) can take anexposure (called integration), read out all thepixel values, and calculate the necessarytelescope correction in less than a second. Thetremendous sensitivity of the CCD enables guidestars as faint as 8th magnitude to be tracked witha 1 second exposure and a 60 mm guidetelescope.

The calculating power of the ST-4 enables thestar's location to be determined to a fraction of apixel accuracy, enabling very accurate tracking.

Imaging Overview

The Microcontroller referred to in the trackingsection is built into the ST-4. This microcontrollercan communicate to an XT or AT compatible PC,or a Macintosh* , over the ST-4's RS-232 seriallink (the serial interface of the ST-4 is alsocompatible with the RS-422 ports used on theMacintosh).

A full image can be transmitted at 19.2Kbaud within 18 seconds and over a distance of100 feet. Data transfer rates as high as 57.6K

* Macintosh is a registered trademark of AppleComputer, Inc.

SBIG SANTA BARBARA INSTRUMENT GROUP

Page 2 SBIG ST-4/0490

baud are supported, and work very well overshorter cable runs. A partial image transfermode is also supported which sends 1/4 as manypixels (one value for each group of four adjacentCCD pixels) in 5 seconds. This mode ofoperation is very handy for focussing thetelescope and finding objects. Finding faintobjects is easy using this method; the outline ofthe Ring Nebula is clearly seen in exposures asshort as 10 seconds with an 8" SchmidtCassegrain Telescope (SCT) operating at f/10.

In imaging mode, the microcontroller in theST-4 is told to take an exposure by the PC. Itdoes so, and stores the resulting data in memorywithin the instrument. This data is then relayedover the serial link to the host computer. Thedata is retained in the ST-4 until the nextexposure is captured or power is turned off. Thehost does all of the extensive data manipulationrequired by the user, such as contrastenhancement, and also can store data on disk forlater study. This is a very attractive feature; thecomputer allows a quick look to be taken at theimage, within seconds of the event, and a moredetailed look at any later time, such as a rainynight or during the day.

The CCD can be exposed for integrationtimes longer than five minutes. The pixels slowlyfill-up in the dark due to a phenomena calleddark current, and they saturate at about the fiveminute point when the CCD is cooled to atemperature near -30 °C using the single stagethermoelectric cooler used in the ST-4. The wasteheat of the thermoelectric cooler (about twowatts) is dissipated into the air by convectionaround the CCD head. The CCD has a sensitivitycomparable to ASA 20,000 film, if such a filmspeed were available. The CCD has a limitedresolution due to the small number of pixels;much greater resolution would be degraded bythe limitations of most computer graphicsscreens.

Note:With the CCD running at lower than ambienttemperatures, you will wonder why dew andfrosting aren't a problem. First of all, thechamber containing the CCD is small, andonly a small volume of air surrounds theCCD. The small volume minimizes the totalamount of water vapor in the air, which willfrost onto the coldest surface inside the head(which is the bottom of the CCD). Althoughfrost may initially form on the top of theCCD, in a matter of minutes it will migrateand be trapped at the back of the CCD.

System Interfaces

The following equipment is a prerequisite torunning the ST-4 CCD Star Tracker / ImagingCamera.

1. A Telescope with pushbutton or joystickslow motions in at least Right Ascensionand and hopefully also Declination.

2. A guide telescope, 50mm aperture orlarger, or an off axis guider arrangement.

For pushbutton type controllers the ST-4 trackercontrols the telescope the same way you do;through the RA and Declination slow-motionadjustment switches, the interface to which isshown in Figure 2. Four relays in the ST-4 areused to operate the switches. Most telescopedrives have two Declination motor adjustmentswitches which are normally in the 'open'position. Pushing the button or closing the relayboth apply voltage to the motor. Study Figure 2carefully, along with your pushbutton control, todetermine the correct configuration.

Most telescopes have one Right Ascensionswitch which is normally closed; opening thisswitch slows down the drive. The other RightAscension switch is normally open; closing thisswitch speeds up the drive. It is apparent thatthe relay contacts which are brought out on thecable, 4 groups of three (normally open, normallyclosed, and common) are all that is necessary tocontrol the telescope. The cable pinouts aredescribed in Appendix A.

When the ST-4 tracker is connected to thetelescope, the hand controller is not disabled, and



still operates normally. If the telescope control ismodified for the ST-4, and the ST-4 is unplugged,the drive may not run since the normally closedconnection in the ST-4 has now been removed. Ifthis situation is a problem it is best to build up amating connector to replace the ST-4 box that hasthe appropriate pins shorted together (usuallyjust two are required to enable the RA drive towork).

For joystick type controllers, the four relaysin the ST-4 are used to simulate the joystick beingpushed to its limits. Two relays are used for eachaxis or rheostat of the joystick as shown in Figure3. For the Right Ascension rheostat you woulduse the +X and -X relays, and for the Declinationrheostat you would use the +Y and -Y rheostat.

c

nonc

switch

common

normally opennormally closed

A: Standard Hand Controller Switch

B: Modified Hand Controller Switch

normally opennormally closed

c

nonc

relay

commonc

nonc

Figure 2 Pushbutton Interface

rheostat nc

c

no

nc

c

no

relay

A

B C

A

B C

A: Standard Joystick B: Modified Joystick

relay

Figure 3 Joystick Interface



STAR TRACKING OPERATION

The instrument panel is illustrated in Figure 4.The ST-4 instrument is furnished with a powercable, a cable to the CCD, and a third cable forthe telescope's hand controller. There is nopower switch; plugging in the power turns theinstrument on. The instrument will come-up inFIND AND FOCUS mode, which displays thegreatest pixel value found in the readout of theCCD array, and the location of that pixel. Thegreatest pixel reading will drop as the CCD coolsin temperature. After about 2 minutes, the CCDwill have cooled to its optimum temperature.

Note:The display values range from 0 to 99corresponding to percentage. Pixel X and Yvalues of 50 correspond to a pixel centeredwithin the CCD, while a brightness value of99 corresponds to a completely saturatedpixel, i.e., the star is too bright for tracking.

Instrument Startup for Tracking Purposes1. Insert the CCD head into the eyepiece tube

such that it seats accurately against the tube.The CCD will not be damaged by light whenpowered, so it can be easily handled.

2. Begin calibrating the CCD by completelyblocking the open end of the telescope toremove all light (the CCD is very sensitive -it will saturate in very low ambient lightlevels).

3. Observe the VALUE reading. This readingshould fall to a reading of around 10 andstabilize within two minutes of theinstrument being powered-on. Press theINTERRUPT button to halt the FIND ANDFOCUS mode (or any other mode for thatmatter).

4. Push the TAKE DARK FRAME button. Themicrocontroller will readout the CCD and putthe data in the dark frame memory.

VALUE X Y

89 45 37SBIG ASTRONOMICAL INSTRUMENTS

STAR TRACKER/IMAGING CAMERA

TAKE DARK

FRAMEFIND AND

FOCUS

CALIBRATE DRIVE

TRACK

MODE SELECT

INTERRUPT

MENU

ADJUST

Figure 4 Instrument Panel

5. Push the FIND AND FOCUS button anduncover the telescope to begin the collectionof light by the ST-4. The instrument willautomatically begin taking frames of CCDdata, subtract the dark frame stored inmemory, and display the maximum value.Direct the telescope to a star and adjust thetelescope's position to approximately center

the star image on the CCD by noting thereading on the X and Y displays.

6. If the star is too bright (VALUE reading 99)then either the exposure must be reduced, ora fainter star chosen for tracking. In order tocorrect this condition, press the INTERRUPTbutton to stop the collection of data, and



return control of the ST-4 instrument to thekeyboard.

Push the MENU button. The brightnessdisplay will then read "EA" (exposure adjust)and a "1" will appear on the X pixel display(indicating a default exposure time of onesecond).

Repeatedly pushing the ADJUST key willscroll through a list of exposure times, from0.1 second, to 20 seconds. Adjusting theexposure time to shorter times will reduce thestar brightness, while choosing a longerexposure time will increase star brightness.When the desired exposure time has beenchosen, press the MENU button again (theST-4 will display "CA" (Calibration Adjust),and then press it several more times until yousee a bA displayed in the value box. bAstands for brightness adjust; two modes areavailable, A for average, or F for faint. Fincreases sensitivity by 9 times. You shouldset this parameter to A for initialfamiliarization. Press the MENU buttonagain until you see the boost (b) parameterdisplayed. This is a boost factor, wheregreater values mean greater gain. Initially setthis value to 1. Press the MENU button againto return to the normal operating mode (afterbeing interrupted "HELLO" appears on thedisplay).

Note:You must take a new dark frame if youchange the exposure time, the brightnessadjust, or the boost factor.

7. When the brightness level has been adjustedto an acceptable level, focus the telescope byturning the focus knob and observing theVALUE display. At best focus, this numberis maximum. Be careful to take your hand offthe telescope between adjustments or thetelescope vibration will smear the star imageover multiple pixels within the CCD,reducing the brightness. Atmosphericturbulence will also tend to smear the image,so it may be helpful to watch severalsequential exposures when criticallyfocussing the image.

A table of typical VALUE readings fordifferent magnitude stars is shown below in

Table 1. This assumes a 1 second exposureand a typical response of the CCD. Use thisas a reference for determining whether thesystem is properly focussed.

Star ST-4 VALUE ReadingMagnitude 60mm Refractor 8 inch SCT

4 99 995 60 996 24 997 9* 808 4* 329 1* 13

10 - 5*

Table 1 Typical VALUE readings

8. When the focus is adjusted, remove the CCDand insert an eyepiece into the tube, slidingthe eyepiece in the tube until the image is insharp visual focus. With a knife or othersharp object, scribe the eyepiece on its side atthe end of the tube. This eyepiece can then beused to quickly center and focus the CCD inthe future Place the CCD back into the tubeso that it seats against the tube as before.

9. Position the star image approximately in thecenter of the CCD (X=50, Y=50) using thetelescope controls. Push the UP, DOWN,LEFT, and RIGHT buttons for a few secondsto make sure that each relay control iscorrectly interfaced to the telescope hand-held controller unit. If the buttons areworking correctly, the star image will movein four different directions (but notnecessarily up, down, left, and right).

10. Push the CALIBRATE button. The ST-4 willautomatically drive the telescope in eachdirection, determine which directioncorresponds to +X and +Y, and calculate thecorrection speed of your drive in all fourdirections (in pixels moved per second). Thisprocess takes about 30 seconds. This is afour-step process with the ST-4 exercising thefour relays, and after each step the ST-4 willmomentarily display the location andbrightness of the brightest object in the fieldof view. If the image moves too little (less

* Use an increased boost factor and the faint starmode when working at these levels.



than 2 units) or too far (greater than 30 units)the relay closure time should be adjusted bypressing the MENU key twice to get to the"CA" option, and then repeatedly pressingthe ADJUST key to scroll through the timeadjustment values (1 to 20 seconds).

11. If no errors are displayed at the end of theCALIBRATE procedure (E1 or E2 in theValue display), then position the guide staron the center of the CCD, adjust the exposuretime if necessary, and then press the TRACKbutton. The ST-4 will automatically guide thetelescope until the INTERRUPT button ispressed.

Note:The ST-4 constantly corrects driveadjustment times to try to improve tracking.The visual X and Y displays show thetracking error seen during each exposure inunits of 0.2 pixels (i.e. a displayed Y value of-3 indicates that the star moved 0.6 pixels inthe -Y direction during the exposure). Thenumber displayed after the A in the valuelocation is the average error for the last 16correction periods.

If the star is completely lost during an exposure,the unit will stop tracking and the display willdisplay the brightness and location of thebrightest object in the field of view (like the FINDAND FOCUS mode), and the track lost relay willbe activated for one second after 5 consecutivemisses. The telescope will not be corrected againuntil the star reappears.

Calibration steps 10 and 11 should berepeated whenever the telescope is substantiallyre-positioned in Declination (to correct for longerRA adjustments near the poles). Calibrationshould also be repeated if the telescope mount isof German Equatorial design and the telescopetube flips from one side of the mount to the other(reversing adjustment directions). Care shouldbe taken to orient the CCD head so the RA andDeclination axes line-up with the sides of theCCD head (you can tell by looking through theglass window at the CCD or by noting theorientation of the Serial Number tag on the rearof the head which is oriented like the CCD). Thisadjustment is not critical. The tracker will work

in any orientation. It just makes it easier to makesense out of the x and y readings and to use thepushbuttons if the axes are lined up to the RAand Declination axes.

Explanation of Menu Items

The menu choices which can be adjusted to aparticular telescope's configuration can beviewed by pressing the MENU buttonrepeatedly. The different menu items have thefollowing effect:

Note:For each menu item, pressing the ADJUSTbutton repeatedly will scroll through thechoices, finally jumping back to the lowestvalue choice. There is no way to back up.

EA: Exposure AdjustThe exposure (integration time) used by theST-4 in the tracking mode can be set to befrom 0.1 to 20 seconds. The readout time ofthe array is 0.14 seconds; the smearingproduced by the readout time for shortintegration times is not significant in thetracking mode.

CA: Calibration AdjustThe amount of time (in seconds) the drive isleft on during each move when theCALIBRATE mode is executed. If the time istoo short the move will not be accuratelydetermined. If it is too long the star willmove off the array. Set this parameter suchthat a move of 5 to 30 units result.

SA: Scintillation AdjustThe ST-4 modifies the correction factorsdetermined in the CALIBRATE mode, ifnecessary, to improve the tracking. Thismodification is performed only if errorsgreater than the SA factor are seen (the SAfactor is in pixels). Telescopes with extremelylong focal lengths (>10 feet) may find thetracking is improved if this value is increased.Also, its setting should be increased if the ST-4 shows any tendency to "run away" duringtracking.



bA: Brightness AdjustmentSetting this to A is the normal mode. If thisparameter is set to F the ST-4 will set eachpixel equal to the sum of the 3 x 3 pixel boxcentered on that pixel prior to performing thetracking calculation. Since star images areoften smeared over several pixels, thiscollects more light from a faint star. A newdark frame should be taken after altering thisvalue.

H1: Hysteresis (backlash) Adjustment, X-axisThis parameter sets the amount of extra timethat the drive is operated when the directionof adjustment is changed. Many telescopeshave severe backlash, and the star image maynot move for several seconds after acorrection is made. The parameter is thenumber of tenth second increments added tothe calculated move when the move directionis reversed from the previous move.

H2: Hysteresis Adjustment, Y-axisThis parameter is identical to the H1parameter above except for the Y-axis.

b: Boost factorThis parameter boosts the internal gain of theST-4, enabling fainter stars to be tracked withshort exposures. Care must be taken thatthermal variations of the CCD head do notcause the star to be lost when working withvery faint stars. If this value is altered a newdark frame must be captured.

Please review the problem section at the end ofthis manual if problems are encountered duringtracking.



IMAGING CAMERA OPERATION

The ST-4 works quite well as an electronicimaging camera when connected to either an IBMPC or compatible or an Apple Macintosh. Somedetails concerning the operation of the CCD inthis mode are necessary to understand all thecontrols and features available in this mode.

CCD Pixel Dimensions

The CCD pixels are not square. Their dimensionsare 0.01375 millimeters wide in the X-directionand 0.016 millimeters tall in the Y-direction.Note that the CCD active area is therefore 2.64 by2.64 millimeters, or exactly square (about onetenth inch on a side).

Caveats of CCD Readout

The CCD is read out electronically by shiftingeach row of pixels into a readout register at theY=0 position of the CCD, and then shifting therow out through an amplifier at the X=0 position.The entire array shifts down one row when a rowis shifted into the readout register, and a blankrow is inserted at the Y=165 position. Note thatthe CCD elements are still collecting light as theystep down to the readout register. Mostcommercial CCD cameras use a more expensiveCCD which has what is known as a frametransfer readout mode, where all active pixels areshifted very quickly into a pixel array screenedfrom the light by a metal layer, and then read outslowly. The SBIG ST-4 CCD minimizes the effectof not having a frame transfer buffer by readingout the array very quickly, in about 0.14 seconds.As long as the CCD exposure is greater thanabout one second this technique will reducestreaking of the stars to acceptable levels.

Planets pose a particular problem to the CCDsince they are so bright that exposures of 1second at f/10 are badly overexposed. The ST-4has a Half Frame mode for planets and brightstars to solve this problem. In the Half Framemode the upper half of the CCD is used as aframe buffer for a bright image positioned in thelower half of the CCD. A short exposure can betaken (down to 0.01 seconds) and the bottomhalf of the array shifted rapidly up to the upper

half. The 82 lines of short exposure data can thenbe readout at the normal rate. This methodworks quite well, and uses enough pixels suchthat 0.5 arcsecond per pixel scale factors can beachieved while viewing an entire planet.

Unfortunately, this technique does not workfor the moon, since the moon's image typicallyfills the CCD. The only way to image the moon isto use neutral density filters to attenuate the lightdown to where the CCD can be used for a 1second exposure without saturating. The sameholds true for images of terrestrial scenes duringdaylight.

When a long exposure is taken, a glow will benoticed in the upper left corner of the image, nearpixel (1,1). This is apparently due to heating ofthe array by the readout electronics increasingthe dark current. This glow can saturate thearray in the corner in exposures several minuteslong and cause a blank region to appear in thesubtracted data. Using exposures short enoughthat saturation does not occur in the corner willreduce this cosmetic problem to acceptable levels.

Dark Current

The CCD can not take an unlimited exposure.During an exposure in the dark the pixels willslowly fill up due to an effect known as the darkcurrent of the device. This dark current isreduced by cooling, and this is why the CCD ismounted on a single stage thermoelectric coolerin the CCD head. The window is used over theCCD to keep moisture from the CCD while it ispowered. If the window is removed the CCDwill frost rapidly (in seconds). In a roomtemperature environment the cooled CCD pixelstake about 5 minutes to fill up due to darkcurrent. At lower ambient temperatures the CCDwill take longer (maximum exposure timedoubles for roughly every 20 °F drop intemperature) until around 32 °F, where the coolerpower is reduced to avoid damaging the CCDwith excessive cold. The dark current can besubtracted from images as described in a latersection, but the effects of the dark current fillingthe CCD can not be avoided.

CCD vs Film

The CCD is very good at the most difficultastronomical imaging problem; imaging small,



faint objects. For such scenes long exposures aretypically required. The CCD based system hasseveral advantages over film; greater speed,quantitative accuracy, ability to increase contrastand subtract sky background with a fewkeystrokes, the ability to co-add multiple imagesto increase sensitivity without tedious darkroomoperations, wider spectral range, and instantexamination of the images at the telescope forquality. Film has the advantages of a muchlarger format, color, convenience, andindependence of the wall plug (the ST-4 can bebattery operated in conjunction with a laptopcomputer, though). After some use you will findthat film is best for producing sensational colorpictures, and the CCD is best for planets, smallfaint objects, and general scientific work such asvariable star monitoring and positiondetermination. It is for this reason that wedesigned the ST-4 to support both efforts, as astand-alone tracker, or as an imaging camera.Our reliance on serial communications slowsdown the image update rate, but allows the useof portable laptop computers which seldom willaccept a PC card.



HOST COMPUTER SOFTWARE OVERVIEW

This section describes the features of the hostsoftware used to interface the ST-4 to either anIBM PC or compatible or a Macintosh. You willwant to read this section independent of the typeof computer you have, and will also need to readthe section below dealing with the type ofcomputer you own.

Displaying Images

One of the obvious features of the software is itsability to display the images taken with the CCDcamera. There is much latitude in the processingof the images due to the "digital" nature of theimages and the availability of personal computerswith graphics displays.

Adjusting the ContrastAny image taken by the ST-4 consists of an arrayof 192 x 165 pixel values, with each pixel valuehaving 8 bits of accuracy or in other words valuesfrom 0 (completely dark) to 255 (saturated).Although any one pixel can have this dynamicrange, typically the interesting aspects of animage will be constrained to a more limitedrange.

There will usually be a background levelassociated with the image, which is like aspatially uniform intensity level, due to darkcurrent, sky background, or uniform luminosity.In addition, the bright stars in an image maysaturate, or you may be interested in examininglow-level luminosity (such as nebulosity). Forthese reasons, the image's contrast can beenhanced with the use of two parameters:Background (sometimes abbreviated as Back) andRange.

The Background parameter specifies anintensity level at which any pixel below thatintensity will appear black in the image.Increasing the Background parameter will havethe effect of masking or hiding the uniformbackground, or low-level intensities. The Rangeparameter is then used to specify the range ofpixel values above the Background level that willcause the image to saturate on the display. As anexample setting the Background parameter to 25and the Range parameter to 50 will cause any

pixels with intensity less than 25 to be displayedas black, any pixel values between 25 and 75(25+50) to be displayed with a gray scale, and anypixels above 75 to be completely white.

You will want to experiment with the settingsof the Background and Range parameters to get agood feel for how they affect the image. Theseparameters do not physically change the imagedata, but only affect the way the image isdisplayed. We will refer to the processing of thedata to increase the contrast as "stretching thedata".

The software can automatically pick anappropriate set of values for the Background andRange parameters using an Auto-Contrastfeature. It does this by noting the number ofpixels at each of the 256 possible intensity levels(called a Histogram) and setting the Backgroundand Range parameters based upon thatcalculation. This works quite well for images ofextended objects (nebulae, the moon, etc.). Forimages of star fields you can try Auto-Contrast,but will probably get better results by manuallyadjusting the Background and Range parameters.

One other feature of the host software in theimage display mode is Presentation Mode, wherethe image is centered on the screen (horizontallyand vertically) and the non-image areas of thescreen are blacked-out. This Presentation Modeis quite handy for taking photographs of thescreen for presentations, etc.

Image Smoothing and InversionAnother image processing technique available forthe displayed images is image smoothing.Visually, image smoothing reduces the effects ofnoise by smoothing out rapid variations in pixelbrightness. This is accomplished by making eachpixel in the displayed image be a weightedaverage of its own pixel value and the values ofits eight neighbors. Finally, the displayed imagescan be "Inverted", meaning black areas becomewhite and vice versa. Visually this is like lookingat a negative, and can produce good results withimages showing subtle nebulosity. Also, it seemsthat you can push the contrast harder on Invertedimages without the saturated regions detractingfrom the image appearance.

Crosshairs and Photometric AnalysisDue to the linear properties of CCDs and thedigital nature of the image data, photometric



analysis of CCD images is easily achieved whencompared to techniques used with film. Thissection discusses the photometric capabilities ofthe ST-4 and its host software.

Scope FactorsSeveral telescope and calibration factors arerequired by the computer software to correctlycalculate star brightnesses and separations. Thetelescope focal length in inches and aperture areain square inches are required, as well as acalibration factor. The focal length is usually justthe focal length of the telescope, but can beadjusted for such things as barlows and imageprocessing techniques such as image zooming.The calibration factor is the reading that wouldbe produced from the CCD by a zero magnitudestar focused onto one pixel by a lens with 1square inch of area, with an integration time of 1second (with a gain factor of 1). Its value istypically around 12000, but will vary due toatmospheric and telescopic transmission, andCCD device variations. The calibration factorshould also be scaled with the gain (described inthe "Baseline and Gain Parameters" sectionbelow), doubling it for a gain of 2x, tripling it fora gain of 3x, etc.

Note:Atmospheric transmission varies with theelevation of the star, so careful work willrequire attention to this detail as well as tothe stellar temperature.

Pixel Coordinates and IntensitiesThe CCD is configured as illustrated before inFigure 1. An array of light sensitive detectors,called pixels, are arranged in an array of 192 by165 pixels. In this manual and in all otherreferences we will refer to the 192 pixel widedimension as the X-direction and the 165 pixeltall direction as the Y-direction (see Figure 1).When an image is displayed on the computerscreen pixel number (1,1) refers to the pixel withthe (x,y) location corresponding to the upper lefthand corner of the screen. X increases to theright, and Y increases toward the bottom of thescreen. The position of pixel 1,1 on the CCD canbe physically determined by referring to the

placement of the serial number tag on the rear ofthe CCD head as shown below in Figure 4.

Pixel 1,1

Figure 4 Pixel 1,1 location

The host software allows a crosshair to bemoved across the image, and the coordinates ofthe crosshair (in pixels) and the brightness of thepixel under the crosshair are displayed.Additionally, a weighted average intensity of thepixel under the crosshair and its eight neighborsis also shown. These values of the coordinates,intensity, and average intensity are the simplestform of photometry available in the hostsoftware. They are quite handy for setting theBackground and Range parameters and fordetermining the image background level (due tosky background or dark current) anddetermining the optimum exposure time.

Magnitudes and SeparationsThe host software can also measure stellarmagnitudes as well as diffuse magnitudes andangular separations between objects.

The determination of stellar magnitudesinvolves measuring the total light emitted by astar, or in other words adding the intensitycontributions of all the pixels illuminated by thestar. Star images will rarely be constrained to asingle pixel, hence the requirement foraccumulating the intensity from all illuminatedpixels. In practice, a 5 x 5 box of pixels is used indetermining the magnitude although other sizeboxes (3 x 3, 7 x 7, etc.) can sometimes bespecified. Since the magnitude scale islogarithmic (an increase of 1 magnitudecorresponds to a star which is roughly 2.5 timesas faint) the calculation of stellar magnitudeinvolves taking the log of the accumulated pixelintensities. Finally, to accurately measure



magnitudes the background level must besubtracted. This is done by moving the crosshairto a dark area of the image and specifying thatregion as being typical of the backgroundintensity for the image. This specification of thebackground allows the magnitude calculations tobe independent of effects such as dark current orsky background. The factors that affect thecalculation of stellar magnitude are: Exposuretime, Aperture area, and Calibration factor.

The diffuse magnitude (also called surfacebrightness) of diffuse objects is the magnitude persquare arc-second, and is calculated identically tothe magnitude calculation discussed aboveexcept that the accumulated pixel intensities aredivided by the area of the 5 x 5 box in squarearc-seconds. The factors that affect thecalculation of diffuse magnitude are: Exposuretime, Aperture area, Focal length, and CalibrationFactor.

The host software also allows you to measurethe angular separation between objects in animage. This is done by moving the crosshair tothe first object, establishing that position as areference position, and then moving the crosshairto the second object. The software then displaysthe angular separation and orientation (indegrees, clockwise of vertical) of the crosshair'sposition relative to the fixed reference position.The calculation of the separation between twoobjects is only dependent on the dimensions ofthe CCD pixels and the focal length of thetelescope used (which must be accuratelyentered). This usually requires experimentaldetermination using known double stars forprecision. The direction corresponding to east-west in a setup can be determined by taking animage of a star, letting the image drift for a fewseconds, and taking another image. The imagescan then be co-added and the line between thetwo images of the same star delineates the East-West direction.

Other Image Processing Techniques

The host software uses other image processingtechniques besides contrast enhancement,smoothing, inversion, and photometric analysis.These other techniques are discussed in thissection.

Flipping the ImageSome inspection will reveal that the screen imageis flipped about a horizontal axis relative to theCCD. The horizontal and vertical flip commandsenable a picture to be oriented correctly nomatter what combination of telescope and prismsis used to form the image. Also, the flipcommands are quite useful for making an image'sorientation match that of published images.These commands actually modify the image data,and hence the results of using these commandsare retained if the image is saved after thesecommands are applied to an image.

ZoomingThe host software allows you to zoom in on anarea in the image by moving a zoom-box over theimage until the zoom-box is positioned at thedesired region where the zoom may becompleted. The zoom-box is quarter sized (48 x41 pixels), and the pixels within it are thenzoomed to a full 192 x 165 sized image andinterpolation used to fill in the "missing pixels".The zoomed image can then be used with all thephotometric analysis software, etc., and can alsobe saved. Depending on the amount of hostmemory available when the zoom is performed,the zoom either writes over the original imagedata (you are warned first) or the original data isretained and the image can be un-zoomed later(unless the zoomed data is saved on disk inwhich case the original un-zoomed data isdiscarded).

Zooming can be quite handy for examiningclose binary stars, and small detail, but is nosubstitute for higher magnification images sincethe zooming process doesn't contain any moreinformation than the original 192 x 165 pixelimage contained.

HistogramsThe host software can also calculate and displayan image's histogram, which is a count of thenumber of pixels at each of the 256 possible (0through 255) intensity levels. The histogram canbe useful for determining the settings of theBackground and Range contrast parameters (likethe Auto-Contrast does), for determining thedark current or sky background level, and fordetermining the optimum exposure time.



DitheringAlthough the images from the CCD camera canhave 256 possible intensity levels or gray-scales,not all computers have the ability to display sucha wide range. Some graphics displays can onlydisplay two colors; black pixels and white pixels(Hercules adapters and Mac Pluses for example).Something must be done on these displays or elseimages would not look good due to their ultra-high contrast or lack of gray scale. In these casesa technique called dithering is used to increasethe number of gray scales available.

Dithering involves using a cell of displaypixels (2 x 2, 3 x 3, etc.) for each image pixel, andstrategically turning on combinations of pixelswithin that cell to simulate the gray scale. Thisworks well because the eye does a good job ofaveraging the intensity over the entire cell. Thetrade-off is that you require a larger number ofpixels for an image, or must decrease the spatialresolution of the image to accommodate a fixednumber of pixels.

Dithering can also be used to increase thegray-scale capabilities of displays with more thantwo but a limited number of gray-scales or colors.For example, a 2 x 2 dithering cell gives 61different gray scales on a display adapter withonly 16 shades of gray (such as the high-res VGAmode and some Macintosh II video cards).

Making the Camera Connection

An important aspect of the host software is itsability to interface to and communicate with theST-4 over the serial port. If you have ever dealtwith serial interfaces you should be happy toknow that much effort has been given to makethe host to ST-4 interface as easy as possiblewhile maintaining a high degree of compatibilityand flexibility.

On power-up, the ST-4 wakes up at 9600baud, which is quite safe in terms of being able toestablish a reliable communications link with thecamera, but which as also a bit taxing of yourpatience in terms of image download times. Thehost can however program the ST-4 tocommunicate at any baud rate from a lowly 1200baud to the highest rate of 57.6K baud. Theactual baud rate used will depend on how youconfigure the host program and/or theenvironment in which the host and ST-4 exist

(mainly the cable length between the host and theST-4). The host software can be configured totalk to the ST-4 at the fixed baud rates of 1200,9600, 19.2K, and 57.6K or can be configured forAuto Baud mode.

In the fixed modes, the host software willprogram the ST-4 to the selected baud rate andalways attempt to communicate at that rate. Insome circumstances it may be possible to pick toohigh a baud rate for reliable communications, anda lower rate may need to be selected. This isdescribed further below.

In the Auto Baud mode the host software willsequentially program the ST-4 for the highestpossible baud rate (57.6K baud), and then test thecommunications link, lowering the baud rate asnecessary to establish a link with the camera. Theonly times this "auto baud" process will occur iswhen the host software is first run or when theEstablish link command is executed under usercontrol. Another feature of the Auto Baud modeis that if the host ever looses the communicationslink with the ST-4, it will search around (in baud)until it finds the camera or gives up. In this casehowever, it will not try to change the ST-4's baudrate, but will continue to communicate at thediscovered rate.

We suggest you use the Auto Baud mode,and let the computer determine the bestcommunications rate. If you do, you shouldalways make sure the communications link isestablished with the ST-4 prior to downloadingimages, by either having the ST-4 connected tothe selected port and powered-up when the hostsoftware is first run, or by explicitly establishingthe communications link using the Establish linkcommand. Also, if you ever turn off the ST-4 orloose contact with it you will need to use theEstablish link command to re-program thehighest possible communications rate. Ifhowever you always use the same configuration(cable length, environment, etc.) then selectingone of the fixed rates may slightly speed up thestart-up phase of the host software since it won'thave to run the "auto baud" process.



Important Note:The ST-4 sends a check digit with each line ofdata. The host software verifies the datausing this check digit. If it does not agree,the computer requests that the line be sentagain. After four sequential failures acommunications link failure is indicated.Under no circumstances will garbage data betransmitted and displayed without theoperator knowing it.

Images and Image Modes

This section discusses the different types ofimages you can take, and the different imagemodes that the host software and ST-4 support tomake it easier to take images of the variety ofcelestial objects.

Light and Dark FramesTaking a typical long exposure requires severalsteps. The simplest technique is to take a longexposure of the object, save the image, and thentake an exposure of identical length with thetelescope blocked, and save this image also. Theimage of the object will be referred to as the lightframe, and the blocked frame as the dark frame.

When the dark frame is subtracted from thelight frame (using the host software) the randomvariations in the dark current from pixel to pixelare eliminated and the picture quality improvesconsiderably, becoming much smoother and lessnoisy. Exposures longer than 10 seconds cangenerally be improved by this technique. Theonly drawback with this technique is that therange of the data is reduced. The 8 bit readoutelectronics produce a value ranging from 0 to 255for each pixel, and if the dark scene has anaverage value of 191, only 64 units of range areleft in the image. This is more than adequate forproducing an attractive image, but betterperformance can be achieved by boosting thegain as discussed in the "Baseline and GainParameters" section below.

Co-Adding ImagesIn addition to subtracting dark frames from lightframes, the host software allows you to addimages together. You will typically use this on

long exposure images to reduce the noise orsmooth the data by increasing the signal level.

As previously mentioned, you can not takeinfinitely long exposures because the CCD willeventually saturate from the effects of the darkcurrent. You can however add several longexposures (after subtracting the dark frames fromeach of the light frames) to make an image which,while not exactly the same as a longer exposure,will have the added benefits of greater signal tonoise (S/N) and show less graininess.

In practice, you will typically add three orfour images together. Adding more is not muchhelp because the improvement in S/N goes as thesquare-root of the number of co-added images;two co-added images increases the S/N to 141%,three increases it to 173%, four increases it to200%, and nine would increase it to 300%. Alsoyou will typically only be able to add a fewimages before large areas of the image saturatesince the sum of the images is still restricted to an8-bit number (0 through 255).

When co-adding images, you must tell thehost software how much (if any) to offset the 2ndimage by (in both X and Y) to correctly line upwith the 1st. You can determine these offsetamounts by noting the pixel position of somestar or particular feature on each of the imagesyou wish to co-add.

The Anti-Blooming GateCCDs suffer from an effect called blooming thatoccurs when photons continue to strike pixelsthat are saturated. The effect manifests itself asstreaking around objects which are roughly fivetimes as intense as a star which just saturates thepixels (for a given exposure time). This effectvaries from device to device, and the CCD usedin the ST-4 has some special electronic circuitry toreduce the effects of blooming. The ST-4 and thehost software allows an "Anti-Blooming Gate" tobe selectively enabled during exposures whichwill inhibit blooming of objects up to 100 timesthe saturating brightness level.

You will typically want to use the Anti-Blooming Gate on long exposures. It bleeds offcharge from the CCD pixels, and reduces theCCD dark current, allowing longer exposures.Its only deleterious effect is that it tends toslightly broaden bright objects (such as stars),which is far more appealing than the detractingstreaks associated with bloomed objects.



The Baseline and Gain ParametersAs previously mentioned, long exposures willreduce the dynamic range of images with thebackground level due to dark current taking up agood portion of the overall dynamic rangeavailable. Again, this is because with the darkcurrent background using say 191 counts, only 64remain for the image data itself. This can beavoided using a technique where one first takes adark exposure of the intended duration, sets theelectronic readout baseline level (referred to asthe baseline in the host software) slightly lowerthan the background level value in the darkimage, and then boosts the gain by 2, 3 or 4 timesto reduce the effects of digitizing the data. Thelight frame and dark frame are then captured andsubtracted as before.

This technique is also useful for shortexposures of faint objects, which do not begin tosaturate the CCD (levels of 255). Set the baselineto the dark sky level, and boost the gain by 4 ifshort exposures are unavoidable due to driveerrors, etc. The noise of the CCD is greater athigher pixel values; a boost of four is useful forimages in which the CCD pixel does not reachone quarter of saturation, while a boost of two isall that is useful at pixel levels near saturation.

Note:The CCD has occasional "hot" pixels whichsaturate first in a long exposure. These hotpixels can show up in a subtracted image as ablack pixel, since the saturated value is thesame in light and dark exposures. Keepingthe maximum exposure below that requiredto fill the CCD pixels 50% of the way willeffectively eliminate this problem.

Automatic Dark Frame SubtractionAs mentioned previously, the ST-4 has memoryfor two image buffers, a light buffer and a darkbuffer. The host software allows you to capture adark frame and retain it in the ST-4, then onsubsequent light images, you can have the ST-4subtract that dark frame from the light imagesimmediately after the image is readout from theCCD and prior to it being sent to the host.

As always, you must manually cover thetelescope when you ask the host software to take

the dark frame. This is handy for searching anarea for an object of interest, but for your finalimages (the ones you really want to keep) youwill want to capture and download both lightand dark frames and let the host software do thesubtraction. This is so the time differencebetween the light and dark frames will be assmall as possible and hence any possible changein the CCD's temperature and dark current willbe minimized.

Focussing and Special Imaging ModesTo facilitate focussing, imaging planets using thehalf frame mode alluded to above, taking a seriesof images and selecting the best, etc., the hostsoftware supports the following image sub-modes in a grouping under a mode of operationcalled the Focus Mode:

Full Frame ModeIn this mode the host software continuallytakes full frame images, and downloads themfrom the ST-4 and displays them.

Half Frame ModeThis mode allows using the upper half of theCCD as an image buffer for bright objects asdescribed in the "Caveats of CCDReadout"section before. Because only half ofthe image is downloaded from the ST-4, thedata transmission time is only half as long asin the full frame case. Finally note that theonly way you can take Half Frame modeimages is through the Focus Mode.

Quarter Frame ModeIn Quarter Frame Mode, the host softwarefirst takes and downloads a full frame image.The user then specifies an area of the fullimage equal to a quarter frame by positioninga square on the full frame image. The hostsoftware then takes full frame images butonly downloads the pixels within the quarterframe specified by the user, resulting in atransmission time which is 1/4th as long asfor full frame images.

Low-Res ModeThis mode, also called one of four mode, isalso faster that the full frame mode at the costof image resolution. After each image istaken, the ST-4 reduces the image to 1/4th the



number of pixels be replacing each group of 2x 2 pixels by the average of the group. Thehost software then downloads that 1/4 sizedimage, which only takes 1/4th thetransmission time of a full frame image. Priorto displaying the image, the host softwareexpands the image up to its full size byinterpolating between pixels. The resultingimage has 192 x 165 pixels but has lowerresolution than a full frame image due to theimage reduction and expansion. This mode isvery handy for finding faint objects since theentire field is transmitted and the update timeis fast.

Spot Frame ModeIn this mode, after each image is taken, theST-4 searches through the image and locatesthe brightest pixel. It then reports that valueto the host, which in turn downloads a smallsubset of the image pixels surrounding thebright spot (33 x 27 pixels). The greatlyreduced number of pixels drastically reducesthe data transmission time which is quitehandy for focussing on stars.

Track Frame ModeLike Quarter Frame Mode, in Track FrameMode the host software first takes anddownloads a full frame image. The user thenspecifies an 33 x 27 pixel area of the fullimage by positioning a square on the fullframe image. The host software then takesfull frame images but only downloads thepixels within the 33 x 27 pixel area specifiedby the user, resulting in a short transmissiontime and hence a rapid frame update rate.The image is displayed with a cross hairdrawn through the center, and while thescreen is in the continuous update mode you(through the host software) can move thetelescope (if the relays in the ST-4 are hookedup) or the telescope can be moved manually.The telescope can be guided on a faint star byviewing the screen and making corrections,which is much less fatiguing than guidingthrough an eyepiece in an awkward position.This mode can be used to guide on stars toofaint for the ST-4 to lock on, since the eye-brain combination is better at recognizing afaint stellar image in the presence of grainyreadout noise.

In all the Focus sub-modes described above, thehost software displays the coordinates andintensity of the brightest pixel in the CCD.Additionally the host software can be configuredto pause between images, until the user gives thego-ahead, and the host software can beconfigured to use the Auto-Contrast featurewhen displaying the data or can use Backgroundand Range values set by the user. Although thehost software has commands for simply taking anexposure and downloading the image you willfind yourself using the Focus mode the majorityof the time. Table 2 below shows typical pixelvalues you should see for various magnitudestars for a well focussed image. These assume a 1second exposure and typical value of 10000 forthe CCD calibration factor.

Star Star IntensitiesMagnitude 60mm Refractor 8 inch SCT

4 255 2555 150 2556 60 2557 24 2088 10 839 4 33

10 1 13

Table 2 Typical Star Intensities

Capturing and Viewing an Image

Capturing and viewing an image at the telescopeusually requires the following procedure:

1) Find a bright star.2) Focus the star.3) Center the telescope on the desired object.4) Grab an exposure of the object.5) Grab a dark exposure if desired.6) Subtract the dark exposure from the light.7) Display the image and optimize the

contrast.

Start by inserting the CCD camera head into theeyepiece tube of the telescope and entering theFocus Mode. Configure the Focus Mode for anexposure time of 1 second, full frame, automaticupdate, no auto-contrast, and set the Backgroundto 0 and the Range to 255.



The computer will begin displaying the field,updating the screen about every 10 seconds.Position a bright star (magnitude 3 to 5) in thecenter of the field and focus the image to achievethe smallest spot. It is usually best to maximizethe peak value of the star image, which isdisplayed in this mode, rather than rely on thesize of the spot to define the best focus.

Some difficulty may be encountered infinding the star in the field of view. Use aneyepiece in the tube to center the star beforeinserting the CCD head. The CCD is quite small,so try to position the star within the center 10% ofthe field of view of a low power eyepiece. Whenthe star has been found, centered, and focusedtake the time to accurately center the star in theguide scope to make finding objects easier in thefuture. Also, remove the CCD head, insert aneyepiece in the tube, and focus the eyepiece bysliding it within the tube. When best visual focusis found scribe the side of the eyepiece so thetelescope can be quickly set close to the optimumfocus the next time. Replace the CCD head,taking care to always seat it securely against thetube.

Now that you have found an object, exit theFocus Mode, and vary the Background and Rangeparameters to modify the display. Small valuesof Range have the effect of increasing the contrast.Stars get fatter due to the fact that the stray lightnear the main image is being seen, but nebulardetail becomes more visible. The Backgroundshould typically be set to correspond to the levelsof the black regions in the image (these levels canbe determined using the crosshairs).

Try out the different frame modes. Positionthe star in the bottom half of the display screenand then try the Half Frame mode. You will notethat the star image appears in the upper portionof the screen. Move the star off the screen to thetop by moving the telescope and you will notethat the star reappears, but badly smeared (for abright star). This is important. If, in the HalfFrame mode, you have a badly smeared image itmeans that you need to move the star or planetdown in the field to correctly position it foroptimum imaging. Finally try out the QuarterFrame and Low-Res modes, and try out the two33 x 27 pixel modes.



USING THE ST-4 WITH AN IBM PC ORCOMPATIBLE

This section describes the PC host software forusing the ST-4 as an imaging camera. You willwant to read it if you plan on connecting the ST-4to an IBM PC or compatible computer. Also,prior to reading this section you should read the"Host Computer Software" section above.


The ST-4 is connected to the computer using theserial cable provided with the unit. The cableshould be connected between the ST-4 and thecomputer serial port, either COM 1 or 2. RS-232serial connectors on PCs and compatiblesgenerally come in 2 varieties, with either a 25 or 9pin connector. Hopefully you specified the typeyou require when you placed your order and youhave the necessary adapters in the box. If youdid not, please contact SBIG or go to your localRadio Shack, and obtain the necessary adapters.

Note:As the software comes on the distributiondisk it is configured for using COM 1. IfCOM 1 is available you should initially usethat port. Otherwise you can use the COM 2port but the software will have to beconfigured for it (described later but for nowdon't worry about it). Also the softwareremembers the port for which it has beenconfigured and will only have to be changedif you switch COM ports.

Running the Program

Before running the ST4 program, please make abackup copy of it following the proceduresdescribed in the DOS manual, and save theoriginal in a safe place. After successfullyconnecting the ST-4 to your computer, power upthe ST-4 and computer, and run the program.

Note:The PC version of the ST4 program(CCD.EXE) requires several other files foundon the floppy disk to run. The CGA.BGI,EGA.BGI, etc. files are graphics drivers forthe various types of graphics cards supportedby the program, and the CCD.CFG fileretains the settings of key parameters(exposure time, etc.). If you wish make anadditional running copy of the program (sayto run on your portable computer, etc.) makesure you copy these files in addition to theCCD.EXE file.

After you have made a backup copy of theprogram and stored the original away you mayrun the program by doing the following:

If you do not have a hard disk:

Insert the program disk into the disk drive, andget into the drive directory by typing:

A: (and then hit enter)

You can then run the program by typing:

CCD (and then hit enter)

If you have a hard disk:

You can transfer the program and configurationfiles to your hard disk using the DOS copycommand as described in your DOS manual.

After copying the files to your hard disk youcan run the program by first getting into thedirectory that contains the CCD.EXE file, andthen typing:

CCD (and then hit enter)

Once you are in the program, the programautomatically initializes the serial port, andsearches for the ST-4. Since the software has beenconfigured (by the factory) for the Auto-Baudmode, if it finds an ST-4 it increases the baud rateup to the maximum the hardware will accept. Ascreen message will then inform you thatcommunication has been established and showthe baud rate.



If you get a communication failure message,recheck your cables, make sure the ST-4 ispowered on (red numbers should appear on thedisplay). Ignore any problems until you haveread the section below describing the PCcommand. Then check the configuration of theCOM port and use the Establish link command.

Elements of the User Interface

This section describes the user interface of theCCD program. We hope you will find the userinterface to be both friendly and efficient.

When you first enter the CCD program youare put into the Command Mode. The top line ofthe screen displays the main menu of commandsand is referred to as the menu bar. A commandcan be selected by moving the highlighted menucursor to the command name using the left andright arrow keys. The selected command maythen be invoked by pressing the Enter key. Analternative to using the arrow keys to select thecommand and pressing the Enter key (to invokethe command) is to simply press the first letter ofthe desired command. To help you rememberthis, the first letter of each of the commands hasbeen highlighted for you.

Below the menu bar towards the bottom ofthe screen are two boxed in areas called theStatus box and the Data Buffer information box.The Status box is used by the CCD program tocommunicate passive information to the usersuch as the introductory message presentedwhen the program is first run. The Data Bufferinformation box indicates whether any imagedata is currently held in memory, whether thatdata has been saved on disk or not, and whetherthe image has been zoomed (and thus could beun-zoomed).

The blank area between the Status box andthe menu bar is used for interacting with thecommands from the menu bar through pop-upcommand screens and for important messagesfrom the CCD program which are also shown inpop-up message boxes.

Become familiar with the screen by looking ateach of the commands shown on the menu bar,and by invoking the commands to examine theirassociated command screens. You can exit froma command screen and return to the menu bar bypressing the ESC key. If you hit the ENTER key

within any of the command screens, thatcommand will immediately execute.

Each command screen consists of severalparameters which can be changed by moving tothe desired line and changing the setting. Youmove the flashing cursor up and down throughthe command screen parameters using theUP ARROW and DOWN ARROW keys or usingthe TAB and SHIFT-TAB key combinations. Alsonote that the descriptive text to the left of eachparameter contains a single highlighted character.The highlighted character indicates that you canmove directly to that parameter by pressing theALT key in conjunction with the highlightedcharacter.

The method used to change a parameter'ssetting depends on the type of parameter, ofwhich there are two: Ones where you select asingle choice from a list of choices and oneswhere you type in some number or text. Toselect a specific setting use the LEFT and RIGHTarrow keys to highlight your choice. To changethe setting of an entry type item you type in thevalue or text. You can use the BACKSPACE keyto edit a value, or the DEL key to completelyerase all the text entered in the parameter.

The Grab, Focus, Display, and Image I/Ocommands are routinely used in acquiring andviewing images, while the Camera/Scope and PCcommands are used to control the computer andST-4 configuration. Please keep in mind whenusing the command screens that the cursor keysor the TAB key are used to move around withinthe screen. Hitting the ENTER key will cause thecommand to immediately execute, and the ESCkey will get you out of the screen and abort mostcommands.

Image Processing and Analysis

This section describes the commands used forimage processing and analysis; the Image I/O,and the Display commands as well as someportions of the PC command.

The Image I/O CommandAs its name implies, the Image I/O command isused for storing and retrieving images to andfrom disk, and is also used for co-adding images,subtracting dark frames, and editing thetelescope factors and calibration value used when



capturing an image and saved with the image ondisk.

The path parameter tells the computer whichdirectory to look in for files used in the Image I/Ocommand. The path should be blank (or set to".\") to load and save files to the default directory(the one you were in when you ran the CCDprogram). Typically you will have a computerwith a hard disk, or one with just floppy drives,and should follow the directions in the next twoparagraphs:

If you have a hard diskYou will probably have the CCD program ina directory called CCD. You could save yourfiles in another directory called DATA (thatyou had previously created) by using a pathdefinition of C:\DATA\. You could save thefiles to a floppy disk drive by using a path ofA:. Floppy disk drive operations are slowerthan hard disks, so it is best to save to thehard disk, and later save the valuable files toa removable floppy.

If you do not have a hard diskFirst load the CCD program into memoryfrom the A: drive, then remove the CCDsource disk and insert a formatted blank diskfor data storage. Use a path of A: or B:,whichever is appropriate. If you have twodisk drives you can keep the source disk in A:and store the data in B:. Remember toreinsert the source disk into the A: drivebefore exiting the program (if you only haveone drive) so that the configuration data canbe saved upon exiting.

You can also set a filter in the Image I/Ocommand. A filter tells the computer to onlylook for files with a certain name or extension. Afilter entry might be *.PIC or *.ST4, where theasterisk is a wild card character. You can anyany filter that is valid for MS-DOS, just like withmost of the MS-DOS commands like copy, erase,etc.

To load a file with the Image I/O command,use the cursor to highlight the Load operation,and hit ENTER. You will be presented withanother command screen showing the files in thespecified path matching the filter parameter.Select the desired file using the cursor keys, andhit ENTER again. The file will be loaded, the

Status box will show an annotation attached tothe image, and the values of the telescopeparameters associated with the image, and theData Buffer information box will be updated toreflect that fact that an image has been loaded.After loading an image you would typically usethe Display command to display it.

Note:The directory command screen shows amaximum of 40 files. The files are sorted intoalphabetical order, and you can move thecursor by hitting the starting letter of a filename. For example, hitting the "T" keypositions the highlighting cursor on the firstfile name starting with "T". This samedirectory command screen is used when everthe CCD software asks you to pick a file fromthe disk. Since you will not be able to accessany files beyond 40 in each directory, youshould try to keep you images arranged witha maximum of 40 per directory.

To save a file that has been downloaded from thecamera or has been changed, select the Saveoperation and hit ENTER. You will be asked forthe name of the file, and the file will be saved inthe directory specified by the Path parameter. Ifyou pick the name of an existing file, the softwarewill ask you if you wish to overwrite the filebefore it actually performs the Save operation.

The Add image operation can be used toco-add an image on disk to the one in memory.Upon invoking this operation you will bepresented with the same command screen usedin the Load operation where you can select thefile you wish to add. After selecting a file youwill be presented with a third command screenwhere you can specify an X and Y offset. The Xand Y offsets are the offsets of the image to beadded from the one in memory.

The Dark subtract operation can be used tosubtract a dark frame stored on disk from thelight frame currently in memory. A value of fouris added to the light image before the subtractionis performed to insure that clipping of the imagedoes not occur due to slight offsets between thetwo exposures.

Selecting the Edit parameters operationallows you to change the file annotation, and edit



the telescope factors (aperture area, focal length,and calibration factor) saved with the image.

Note:Magnitude corrections made in the crosshairmode described below modify the calibrationfactor automatically.

The Display Command

The Display mode (accessed through the Displaycommand) is used to examine the image stored inthe computer's memory by a previous Focus,Grab, or Image I/O operation. Each of theparameters in the Display command screen andtheir effects are discussed below:

FormatThis item allows you to select whether theimage itself is displayed (Image option) orwhether the image's Histogram is displayed(Histogram option).

If selected, the Histogram is shown in atabular format, with the Average intensitylevel and the 1% intensity levels shown. TheAverage intensity can be helpful in setting theBackground parameter for adjusting the imagecontrast. The 1% Level can be used todetermine the proper setting of the Baselinelevel to increase the dynamic range of longexposures as discussed in the The "Baselineand Gain Parameters" section above. Finally,if the Histogram is selected in the Displaycommand screen, the settings of the otherparameters have no effect, and needn't bechanged.

If the Image option is selected, then theimage is displayed using the graphicscapability of your display adapter. In theImage mode, the other parameters in theDisplay command screen affect the imagedisplay as described individually below.Also note that some settings in the PC com-mand will affect the image display, whichwill be discused later.

Auto contrastSetting this item to Yes enables the Auto-Contrast mode where the computer sets theBackground and Range parameters based uponthe image's histogram. If you do want Auto-

Contrast, don't change the setting of theBackground and Range parameters below orthe software will automatically deselect Auto-Contrast before displaying the image. Thisfeature allows you to specify manual contrastmode by merely changing the setting of theBackground or Range parameters and notworrying about whether you forgot to turnAuto-Contrast off.

BackgroundThis is the Background parameter whichdetermines the "black level" of the image.

RangeThis is the Range parameter which controlsthe contrast of the image.

SmoothingSetting this item to Yes causes the image to besmoothed prior to display, a feature whichreduces the graininess of faint nebula, andbrings out very faint stars. The smoothingprocess slows down the display processslightly and blurs the image slightly, so it isnot desirable when close double stars arebeing examined, for example.

Negative imageSetting this item to Yes causes the image to bedisplayed as black on a white background,similar to a photographic negative. This canalso be used on LCD type displays popularon portable computers to make the imageappear as a positive, negating the effects ofthe LCD display's inherently "negative"graphics display (pixels turned on are blackon an LCD vs white on a CRT).

Display modeWhen this parameter is set to Analysis theimage is displayed with its annotation, andseveral other pieces of textual information,including a Display Mode menu. In thismode you have full access to the crosshairroutines, image zooming, etc., as discussed indetail below.

When this parameter is set to Photo thespecial Presentation Mode is activated, andyou can not access the crosshairs, etc. InPresentation mode, the horizontal axis of theimage is expanded or compressed by the



amount specified in the Aspect ratio item inthe PC command. Once entered, PresentationMode is exited by hitting any key.

Color select (VGA systems only)In color mode, images are displayed with 60hues using a color table which is like colortemperature, using blues for dark colors,progressing through reds and yellows up towhite. In monochrome mode (this item set toGrey scale), images are displayed with 60shades of grey. This works correctly even ona color monitor.

Display Analysis ModeIn Display Analysis Mode, the image is shown tothe right of the screen with the image annotationdisplayed above the image, a Display Menubelow the image, and a block of text to the left ofthe image showing the settings of the Backgroundand Range contrast parameters and whether theimage has been smoothed or zoomed.

The Display Menu has four commandsdescribed individually below. Each of thecommands can be accessed by pressing the firstletter of the command which has been capitalizedto help you remember.

X-HairsExecuting this command enters CrosshairMode used for examining pixel brightnessesand magnitudes. The Crosshair Mode isdescribed fully below.

Horiz flipExecuting this command causes the image tobe flipped about a horizontal axis, andredisplayed with that new orientation. Thiscommand actually flips the image data, andthe effect will be remembered if the image issaved after this command is executed.

Vert flipThis command is identical to the Horiz flipcommand above except that the image isflipped about a vertical axis.

ZoomExecuting this command does one of twothings, depending on whether the image hadbeen previously zoomed or not (shown in theupper left of the screen). If the image had

been previously zoomed and was not savedon the disk, executing the Zoom commandrestores the image to its un-zoomed state.Otherwise executing this command entersZoom Mode where a portion of the image canbe enlarged to the full size of the image, andis described in more detail below.

EscHitting the ESC key while in Display Modereturns you to the Command Mode and re-draws the menu bar, Status box, etc.

Crosshair ModeWhen Crosshair Mode is entered, the DisplayMenu below the image is replaced with theCrosshair Menu, the block of text in the upperleft corner of the screen is replaced by 8 lines ofCrosshair Parameters, and a '+' shaped Crosshairis shown superimposed over the image.

The Crosshair Parameters are updated as theCrosshair is moved around the image and aredescribed individually below. You should referto the "Crosshairs and Photometric Analysis"section of the host software description above fora description of the the Magnitude and DiffuseMagnitude calculations:

PixelThese are the X and Y coordinates of theCrosshair. Location 1,1 is in the upper leftcorner of the image.

ValueThis is the intensity of the pixel directly underthe Crosshair as recorded by the ST-4, and isa number from 0 to 255.

Sm-ValueThis is the average value of the pixel directlyunder the Crosshair and all the pixels inside abox centered under the Crosshair. The size ofthe box can be changed and is shown in theBoxsize parameter.

MagThis the magnitude of the star underneath theCrosshair. This value is calculated from thepixel values within the box, and telescopeand calibration data stored with the image.In most cases an accurate calculation ofmagnitude requires the sky background to be



subtracted. The Crosshairs should be movedto a dark region of the image, and the B keyhit (executing the Background command) totake a background reading. The Magparameter then displays a 99. The Crosshairshould then be moved to the desired star; thebackground will be automatically subtractedand the correct magnitude displayed.

DifmagThis is the diffuse magnitude, and is used tomeasure the brightness of diffuse objects suchas nebulae or galaxies in units of magnitudeper square arcsecond. Using a large box sizeimproves the accuracy of this reading(provided the box is smaller than the object),enabling extremely low surface brightnessobjects to be measured.

Sep and AngleThese are the separation (in arc-seconds) andthe angle (in degrees, clockwise of vertical)between the current position of the Crosshairand the reference position fixed using theCentroid or Star commands in the CrosshairMenu.

The crosshairs can be moved using the cursorkeys, or moved faster using the 2, 4, 6, and 8 keyson the numeric keypad (if you have one). The I,J, K, and M keys are also treated as a "pseudo-keypad", and will move the Crosshair in additionto the SHIFTed versions of those keys. All in all,we find it easiest to keep one hand on the SHIFTkey and use the other to work the cursor keys.

Each of the commands in the Crosshair Menuand their effects are discussed below. Eachcommand can be executed by pressing the keycorresponding to the first letter or character inthat command.

StarExecuting this command fixes the referenceposition for the Separation and Anglemeasurements at the current position of theCrosshair.

CentroidThis command is like the Star commandabove, but higher accuracy positioning of thereference is achieved for stellar objects bydetermining the center to subpixel accuracy.

BackgroundThis command records the background levelused in the magnitude calculations to theaverage value of the pixels inside the boxcentered under the current position of theCrosshair.

Toggle box sizeExecuting this command toggles the boxsizeused in the average pixel, magnitude, anddiffuse magnitude calculations through thepossible values of 3 x 3 through 11 x 11. Theprogram goes back to the image point wherea background measurement was last madeand makes another reading at the new boxsize when this command is executed.

+Mag, -MagThese commands modify the image'scalibration factor so that the calculatedmagnitude can be corrected as required forstars of known magnitude. The SHIFT + andSHIFT - keys change the magnitude by 0.01magnitude, while the unshifted keys (= and -)change it by 0.1 magnitude. The keys on thenumeric keypad work differently. Thecalibration factor can be expected to varyslightly with the transparency of the night, orthe elevation angle of the stars. Atmosphericabsorption is a significant factor whenaccurate measurements are desired

EscWhen the ESC key is pressed in CrosshairMode the program exits that mode andreturns to Display Mode.

Zoom ModeWhen Zoom Mode is entered, a zoom-box isdrawn superimposed on the image and theDisplay Menu is replaced with the Zoom Menu.The zoom-box can be moved around on theimage using the same keys used to move theCrosshair (cursor keys and 2, 4, 6, and 8). Whenthe zoom-box is positioned appropriately,pressing the ENTER key causes the image datawithin the zoom-box to be expanded to the sizeof a full image. The newly zoomed image isdisplayed, and Display Mode is entered.Pressing the ESC key while in Zoom Mode



merely cancels that mode and returns to DisplayMode without performing the zoom.

Zooming actually replaces the image data inmemory with the zoomed image. If the CCDprogram has enough memory, the un-zoomedimage is retained, and the image can be un-zoomed later by invoking the Zoom command asecond time (unless the zoomed image is saved todisk in which case the un-zoomed image isdiscarded). If there isn't enough memory, youwill have been warned when the CCD programwas first started.

Fine Tuning - The PC CommandThe PC command contains items for configuringthe serial port used in communicating with theST-4 and for fine tuning the graphics softwareused for displaying images. The items in the PCcommand are discussed individually below:

Serial portThis item allows you to select which serialport is used to communicate with the ST-4.

Baud rateThis item allows you to select the baud rateused in communicating with the ST-4. Pleaserefer to the "Making the Camera Connection"section above for a detailed discussion of howthe host software uses the setting of this itemin communicating with the ST-4.

Graphics cardYou can usually leave this item set to Autoand the CCD software will automaticallydetermine the graphics capability of your PCand use the best graphics mode fordisplaying images. Some combinations ofPCs and graphics adapters aren't fullycompatible with this auto-detection software,and in those cases you can set this item to totype of graphics adapter you have. Strangeand unusual results can occur if you specify agraphics card type that you don't have.

Note:Some graphics adapters will support multiplemodes such as VGA adapters that will alsodo CGA and EGA emulation. These adapterscan be used in any of their supported modes.Also, each supported graphics adapterrequires a BGI file in the same directory asthe CCD program. For example CGA moderequires the CGA.BGI file. All the necessaryBGI files are contained on your master CCDprogram disk.

Color displayIn general you will set this item to Yes if youhave a color display or monitor attached toyour graphics adapter. The setting of thisitem affects whether the Command Modescreens are in color or not, and affects theDisplay Mode as shown below for the varioustypes of graphics adapter:

EGAIn color mode (this item set to Yes),images ares displayed with 32 hues usingblues for dark colors, progressingthrough light blues and greens up towhite. In monochrome mode (this itemset to No), 60 shades of gray are used.Due to the way EGA cards display colors,monochrome mode will only workcorrectly with a monochrome monitor.

CGAImages displayed on CGA monitors aredisplayed using 4 colors. In monochromemode (this item set to No), the order ofthe colors are rearranged to correspondto gray scale when used with amonochrome monitor.

HerculesWhen used with Hercules adapters thesetting of this item has no affect on thedisplayed image.

Aspect ratioThis item is used in the Presentation Mode ofthe Display command, and specifies howmuch the horizontal axis of the image shouldbe shrunk (values < 1) or expanded (values >



1) to produce a square image on the monitor.The required settings will vary depending onthe type of graphics adapter and monitor youhave.

Taking Images

This section describes the commands used fortaking and downloading images from the ST-4,i.e. the Camera/Scope, Grab, and Focuscommands.

The Camera/Scope CommandThe Camera/Scope command screen allows theuser to setup the ST-4 and computer for optimumperformance in taking images, and for indicatingthe telescope parameters. The items in thiscommand screen affect images taken with boththe Grab and Focus commands, and aredescribed individually below:

Camera Setup Parameters

Establish linkSetting this item to Yes and executing thiscommand causes the CCD program to try toestablish the communications link with theST-4 as described in the "Making the CameraConnection" section before.

Anti-Blooming gateThis item allows enabling or disabling theAnti-Blooming gate during exposures asdescribed in "The Anti-Blooming Gate"section before.

Dark subtractThis item enables or disables the ST-4's darkframe subtraction at the end of exposures asdescribed in the "Automatic Dark FrameSubtraction" section before. Enabling thisitem does not cause the camera toautomatically capture the dark frame. Thatmust be done manually using the Grabcommand.

Camera baseline levelSet this item to the desired baseline level asdescribed in the "Baseline and GainParameters" section before.

Gain expansionSet this item to the desired gain as describedin the "Baseline and Gain Parameters" sectionbefore.

Telescope Setup Parameters

Focal lengthEnter in this item the focal length (in inches)of the telescope you are using. When imagesare downloaded from the ST-4 the settings ofthis item and the two shown below arecopied to the image.

ApertureEnter in this item the aperture area (in squareinches) of the telescope you are using.

Response factorEnter in this item the desired setting of thecalibration factor for the CCD. A typicalvalue is 12,000.

NoteEnter in this item any desired annotation forthe image. The note can be up to 78characters long, but note that imagesdisplayed on CGA monitors will only showthe first 40 characters.

The Grab CommandThe Grab command allows taking a singleexposure, downloading, and displaying thatimage and is most convenient for long exposures.The exposure is taken after the command isexecuted (you hit ENTER), and pop-up messageboxes indicate the progress of the exposure andimage downloading. The parameters in the Grabcommand screen are discussed individuallybelow:

Exposure timeThis is the exposure time, and allowedsettings range from 0.01 seconds through 10minutes. The value is always entered inseconds.

Take dark frameSetting this item to Yes causes the CCDsoftware to have the ST-4 take an exposureand store it in the ST-4's internal dark frame



memory (The image is not downloaded).This dark frame can then be subtracted fromfuture images if the Dark subtract item in theCamera/Scope command is enabled.

Auto displaySetting this item to Yes will cause the image tobe displayed after it is downloaded from theST-4.

Auto contrastSetting this item to Yes enables the Auto-Contrast feature if the image is automaticallydisplayed after downloading.

Background and RangeThese items are the Background and Rangeparameters used in displaying the image if itis automatically displayed after downloadingbut the Auto-Contrast feature is not enabled.

Exposure delaySetting this to any non-zero value causes adelay to occur after the Grab command isexecuted and prior to the exposure takingplace. The software will beep every seconduntil the last three seconds where it will beepevery half second.

Skip exposureSetting this item to Yes causes the software tonot take a new exposure, but download theimage in the ST-4's memory (from theprevious exposure).

The Focus CommandThe Focus command allows taking a series ofexposures. It is the recommended mode to usewhen taking short exposures of planets or doublestars, since many frames of data can be examinedand the best one, least corrupted by atmosphericseeing, saved to disk. The parameters in theFocus command screen are discussedindividually below:

Exposure timeThis is the exposure time, and can range from0.01 seconds to 10 minutes. The value isalways entered in seconds.

Auto contrastSetting this item to Yes enables the Auto-

Contrast feature when displaying the imagesdownloaded from the ST-4.

Background and RangeThese items are the Background and Rangeparameters used in displaying the imagesafter downloading when the Auto-Contrastfeature is not enabled.

Frame sizeSet this item to the desired frame mode asdiscussed in detail in the "Focussing andSpecial Imaging Modes" section before.

Note:The CCD software will only let you saveimages captured in the Full Frame, HalfFrame, or 1 of 4 (Low-Res) Frame modes.

Update modeSetting this item to Manual causes the CCDsoftware to pause until the SPACE bar is hitafter each image has been downloaded anddisplayed. This is quite handy when you aretrying to select one good image from a seriesof images, waiting for a stable atmosphere,etc. The CCD software will only let you savea complete image, not one that was paused inmid-frame. Since in some frame modes it isdifficult to exit the Focus Mode at just thecorrect time, using the Manual optionalleviates this problem. Setting this item toAutomatic enables Auto-Update mode wherethe software does not pause unless instructedto by the user.

After all the parameters have been set as desiredand the ENTER key has been hit the CCDsoftware goes into Focus Mode.

The Focus Mode screen looks similar to theDisplay Mode screen and shows a block of text inthe upper left corner, a menu at the bottom, andas images are downloaded they are shown on theright edge of the screen, with a white boxencompassing the image.

The block of text includes items displayingthe frame mode, whether the Automatic updateis enabled, the settings of the Background andRange parameters, and the value and X and Ycoordinates of the brightest pixel (Peak) from theCCD. The Peak parameters are updated after



each exposure, before the image is downloadedand displayed.

The menu bar and image will vary dependingon the frame mode selected in the Focuscommand screen. In general the commands inthe menu allow the frame mode to be changed(without exiting the Focus Mode), and the Auto-Contrast and Auto-Update features to be toggledon and off. Hitting the SPACE bar momentarilypauses the Focus Mode until it is hit again, andhitting the ESC key exits the Focus mode andreturns to Command Mode. Finally, some of theframe modes require some more detailedexplanations given below:

Quarter FrameWhen Quarter Frame mode is first entered, afull frame image is down-loaded anddisplayed. The Focus Mode then pauses, anda quarter frame sized rectangle is drawnsuperimposed over the image. The rectanglecan then be positioned as required using thesame keys used with the Crosshair ( cursorkeys and 2, 4, 6, and 8). After positioning therectangle, hitting the ENTER key causes theFocus Mode to resume, taking anddownloading the quarter frame images. Ifthe position of the quarter frame image needsto be changed at any point you should switchto Full Frame mode and then back to QuarterFrame mode, starting the process over again.

Track FrameInitially this mode works like the QuarterFrame mode described above, except that therectangle is not quarter frame sized but 33 x27 pixels in size. After the rectangle ispositioned, hitting the ENTER key causes theFocus Mode to resume, taking anddownloading the 33 x 27 pixel images, shownwith a crosshair superimposed over theimage. Zooming the images 4:1 can beinvoked using the Zoom command in theTrack Menu displayed at the bottom of thescreen. Zooming makes it easier to see theimage but slows down the display process, souse it as required. Finally, the cursor keyscan be used to control the relays in the ST-4,where each key press causes one of the fourrelays to close for 0.2 seconds. Be careful tonot hold the keys down too long or else the

keyboard's auto-repeat feature will make ittough to control.

Note:Although each cursor key will close one relayin the ST-4, the orientation of the cursor keys,compared to the direction the star will moveas a result of closing the relays may not becorrect. Essentially it's like using the handcontroller; you will have to determine whichcursor key is require to move the image inthe correct direction.



USING THE ST-4 WITH A MACINTOSH

This section describes the Macintosh hostsoftware for using the ST-4 as an imaging camera.You will want to read it if you plan on connectingthe ST-4 to an Apple Macintosh computer. Also,prior to reading this section you should read the"Host Computer Software" section above.

Running the Program

Prior to running the Macintosh software (calledSBIG ST4), please make a backup copy of thedistribution diskette and put the original away ina safe place.

After the backup has been made, you shouldconnect the ST-4 to your Modem port using thesupplied serial cable, being careful to note theorientation of the cable since it has the same typeconnector on both ends. The cable supplied withthe ST-4 will mate to the older style 9-pinconnectors, and if you have a Mac Plus or latermodel computer you will need one of the mini-din to 9-pin adapters which can be purchased atyour local Apple retailer if required.

At this point, the software can be run just likeall other Mac programs; by double clicking on theapplication icon (the one with the telescope) or bydouble-clicking on any of the image icons (suchas the Dumbbell image file). The later ispreferred for now so you can try out a few of theimage processing commands.

When the program is first started, it willdisplay the About Dialog which can be dispensedwith by clicking in the dialog or hitting theReturn key. The program will then go out andlook for a ST-4. It will tell you whether it findsone or not. If it didn't find one and it shouldhave don't worry for now, but after you read thesection dealing with configuring the serial portyou should use the Establish link command toestablish a communications link with the camera.

If you didn't double-click on one of the imagefiles, use the Open command in the File menu toopen one of the image files such as the Dumbbellimage file.

Elements of the User Interface

This section describes the basic elements of theuser interface for the SBIG ST4 applicationprogram. We hope you'll find the programworks like all other Mac programs, taking fulladvantage of the Mac's user friendlyenvironment.

The Standard Windows and DialogsA good portion of the user interface of many Macprograms, and this one in particular, involves thevarious windows used to let the usercommunicate with the program. The windowsfound in the SBIG ST4 program are introducedbelow and discussed in more detail later:

PictureThe Picture window is where the image isshown, and the title of the window is thename of the image file. Although thiswindow has no size-icon in the lower-righthand corner, the image and hence thewindow can be resized using the Expand 2xCheck Box in the Contrast Window.

Note:Those users with Mac IIs and gray scale orcolor graphics will achieve the best imagedisplay. The older monochrome Macintoshes(Plus, etc.) produce interesting images, butthe lack of gray scale does not allow all thedetail in the image to be seen. Thephotometric capabilities of the device arereadily available, though. Also note the thesoftware determines the color or gray scalecapabilities of your system when it is firstrun. If you have a color display card andwant to access the gray scale capabilities youwill need to make sure your card isconfigured for more than 2 color or Black &White mode when you start the program.

ContrastThe Contrast window contains controlswhich affect the image display.

CrosshairThe Crosshair window shows several image



factors resulting from the use of theCrosshairs.

HistogramThe Histogram window shows the image'shistogram in a graphical format.

FocusThe Focus window is shown in Focus Modeand displays information about the status ofthat mode, and gives the user some controlover focussing operations.

General Purpose MenusThe other half of the user interface of anyMacintosh program is the menu bar and itsmenus. This section describes a few of thestandard menus in the SBIG ST4 program.

The menu gives you access to all the deskaccessories you have installed in your system,and an About SBIG ST4 command which showsthe information about the program, including theversion. Knowing which version you are using isimportant if you ever have trouble with theprogram and contact us for technical assistance.

The Edit menu is common to all Macprograms, and probably needs no explainingexcept to say that the commands in this menu areprovided for support of desk accessories only.Finally, the Windows menu allows you to bringan opened but buried window to the top byinvoking the appropriate item in this menu.

Image Processing and Analysis

This section describes the actions and commandsused in image processing and analysis. Thisincludes commands from the File, Image, Dither,and Ops menus, and elements of the Contrastand Crosshair windows.

Loading and Saving ImagesThe commands in the file menu allow you to loadand save images files to and from disk. Each ofthe commands for this purpose are describedbelow:

OpenUse this command to load an image file fromthe disk. When an image file gets opened, theimage is displayed in the Picture windowand the Contrast window is opened. You can

only have one image file open at a time, soyou must close the current one if you want toopen a different one.

CloseUse this command to close an image file,releasing it from memory. If the image isnew or has been changed due to some imageprocessing functions, you are asked if youwant to save the changes or not. Unlike someMac programs that use the Close commandto close the front most window, thiscommand always closes the image,independent of which window is active.

SaveUsing this command saves any changes youhave made to an image, and saves thosechanges in the original file, replacing the oldimage with the changed one. If the file is newand hasn't been saved yet you are bouncedinto the Save As command described below.

Save AsThis command allows you to save the imageinto a different file that the original. If youhappen to pick a name that is used by anotherfile you are asked if you want to replace thatfile with the image file.

Revert to SavedThis command allows you to discard anychanges you have made to an image bydiscarding the image and re-loading it fromthe disk. This command will only be enabledif some change has been made to the image.

If you haven't already done so, you should usethe Open command to open one of the imagefiles to try out with the image processingtechniques discussed in the next few sections. Agood example image is the Dumbbell image.

The Contrast WindowAs previously mentioned, the Contrast windowcontains controls which affect the displayedimage, and will always be open whenever animage is loaded (from the disk or downloadedfrom the ST-4). In order to access any of thebuttons or controls in this window, it must bemade active first. Like any window, it may be



activated by clicking in the title bar (or any otherportion of the window).

Hitting the Do It button by clicking in it or byhitting the RETURN key causes the computer toread the settings of the other buttons and controlsin the Contrast window and re-draw the image inthe Picture window based on those settings. Youwill also have to do this when ever you changethe dithering using the commands in theDithering menu.

Note:While having to hit the Do It button mayseem like extra work, changing the image isnot instantaneous for all display modes andvaries from model to model. You would notbe happy if every time you tried to bump thecontrast up you had to wait a few secondswhile the Picture window was updated.

The Background and Range parameters are shownand allow the image contrast to be adjusted asdescribed in the "Adjusting the Contrast" sectionof the host software description above. Thesetting of these parameters can be changed inseveral ways. First, the value of each can beentered directly by clicking in the appropriate celland typing in the desired value. You can also usethe TAB key to switch back and forth betweenthe Back and Range parameters. Second, there arefour small buttons adjacent to each of theparameters. Clicking in the single or double up-buttons to the right of the parameter will increaseits setting by 1 or 10 respectively. Likewise thedown-arrow buttons to the left will decrease theparameter by 1 or 10. If you continue to hold themouse button down, the parameter willcontinuously be adjusted until it reaches its limitor you release the mouse button.

Clicking the Auto button lets the computerdetermine appropriate settings for the Backgroundand Range parameters (the Auto-Contrastfeature) and updates the image display withthose settings.

Finally, there are several check boxes in the"Processing" section of the Contrast windowwhich are described below:

Expand 2XSelecting this item makes the image beexpanded to twice its normal size.

Note:Since the pixels on the Macintosh are square,and the pixels from the CCD are not, thesoftware transforms the image into a 192 x192 pixel image for display purposes. Thispreserves the image's overall aspect ratio.

SmoothingSelecting this item causes the image to besmoothed prior to display.

InterpolateSelecting this item when both the Expand 2Xand Smoothing options above are selectedenables interpolation whereby the "expandedpixels" between the 192 x 192 image pixels arethe average of their neighboring pixels ratherthan just a copy of the neighboring pixels.This removes a fine graininess associatedwith expanded images.

InvertSelecting this option makes the image appearas black on a background of white, much likea photographic negative.

The Dithering MenuThe commands in the Dithering menu select thetype of dithering done on the image displayed inthe Picture window. Macs with gray scale andcolor capabilities can choose from 16 and 256gray scales, and all models can choose from the 2color (black and white pixels) modes. Each of theoptions are described below:

1 x 1 - 256 ColorThis mode is the highest resolution mode,allowing each of the 256 possible pixel valuesto represented by a unique color. You willprobably want to stick with this mode if youhave an 8 bit video card. Technically a 1 x 1dithering pattern actually corresponds to nodithering at all.

1 x 1 - 16 ColorIn this mode the image is made by assigningone of 16 colors to each possible pixel value.This mode can produce some interestingdisplays, but users with only 4 bit video cards



will probably want to use the 2 x 2 modediscussed below.

2 x 2 - 16 ColorIn this mode, a 2 x 2 dither cell is used, witheach pixel in the cell having one of 16 colors,yielding 61 hues. This is the best mode forusers with 4 bit video cards. Imagesdisplayed in this mode without the Expand2X option enabled will suffer a loss of spatialresolution.

2 x 2 - 2 ColorIn this mode a 2 x 2 dither cell is used, witheach pixel in the cell either being black orwhite, yielding 5 gray scales. This is thefastest display mode for Macs lacking truegray scale capability. Images displayed inthis mode without the Expand 2X optionenabled will suffer a loss of spatial resolution.

3 x 3 - 2 ColorThis is identical to the 2 x 2 mode aboveexcept the dither cell is 3 x 3 yielding 10 grayscales.

4 x 4 - 2 ColorThis is identical to the 2 x 2 mode aboveexcept the dither cell is 4 x 4 yielding 17 grayscales. While offering the greatest gray scaleon black and white displays, the large size ofthe dither cell sacrifices image spatialresolution to provide the increased gray scale.

Photometric AnalysisThis section describes how to access and use thephotometric capabilities of the SBIG ST4program. For reference, the photometriccapabilities were discussed in detail in the"Crosshairs and Photometric Analysis" section ofthe host software description above.

Prior to using the the crosshairs to investigatean image you should become familiar with twocommands in the Image menu: Edit info andNote.

Invoking the Edit Info command brings up adialog containing the telescope parametersassociated with the image (discussed in the"Telescope Factors" section of the host softwaredescription above) as well as some imagecropping parameters. Each item is discussedindividually below:

Focal lengthThis is usually the focal length of thetelescope used to take the image but can bechanged by zooming, etc.

ApertureThis is the aperture area of the telescope usedto take the image.

Exposure timeThis is the image exposure time or integrationinterval.

Calibration factorThis is the calibration factor for the CCD. Atypical value is 12000 and will scale with thegain (24000 at 2x, etc.).

CroppingThese four parameters determine the amountthe image is cropped prior to display in thePicture window. The values correspond tothe number of pixels to crop from each side,and are handy for removing the sometimesunsightly top line from the images.

These parameters are saved with the image, andthe program also has a default set of parametersthat are copied to newly acquired images. Youcan edit the default parameters by invoking theEdit info command and selecting theScope/Default check box at the top of the dialog.

Each image can also have some descriptivetext or annotation saved with the image. Thistext can be reviewed or changed by invoking theNote command. Also, newly acquired imagesinitialize this text to contain the date and time theimage was downloaded.

The Crosshair Command and WindowYou can activate the crosshairs when an image isopen by invoking the Show Crosshairs commandin the Image menu. Doing this opens theCrosshair window. When the mouse pointer ismoved around in the Picture window, it willchange its shape to a crosshair and valuesdisplayed in the Crosshair window will beupdated to reflect the position of the crosshair.Each of the parameters are discussed below:

Pixel Data



X, YThese are the X and Y coordinates of theCrosshair. Location 1,1 is in the upper leftcorner of the image.

ValueThis is the intensity of the pixel directly underthe Crosshair as recorded by the ST-4, and isa number from 0 to 255.

5X5 AveThis is the average value of the pixel directlyunder the Crosshair and all the pixels inside a5 x 5 box centered under the Crosshair.

Stretched Data

ValueThis is the intensity of the pixel directly underthe Crosshair as stretched by the Backgroundand Range parameters to a value between 0and 255.

5X5 AveThis is the average stretched value of thepixel directly under the Crosshair and all thepixels inside a 5 x 5 box centered under theCrosshair.

Magnitudes

AbsoluteThis the magnitude of the star underneath theCrosshair. This value is calculated from thepixel values within the 5 x 5 box, andtelescope and calibration data stored with theimage. In most cases an accurate calculationof magnitude requires the sky background tobe subtracted. The Crosshairs should bemoved to a dark region of the image, and themouse clicked to take a background reading(also, a square will be drawn on the image tohighlight the location of the background).The Absolute parameter then displays a 99.The Crosshair should then be moved to thedesired star; the background will beautomatically subtracted and the correctmagnitude displayed.

DiffuseThis is the diffuse magnitude, and is used to

measure the brightness of diffuse objects suchas nebulae or galaxies.

Geometry

Separation and AngleThese are the angular separation and theangle (in degrees, clockwise of vertical)between the current position of the Crosshairand the background reference marker fixedby clicking the mouse in the Picture window.

Note:The Picture window must be active beforeclicking in it will place the backgroundreference box/marker used in the Magnitudeand Geometry calculations. This is why itappears that you need to double clicksometimes to place the reference marker:The first click is used to activate the window.

If you find that the calculated magnitudes orseparations are in error you can correct them byadjusting the telescope parameters with the Editinfo command in the Image menu. Changing thecalibration factor or the telescope aperture willchange the calculated magnitudes. Changing thetelescope focal length will change the calculatedseparation.

The HistogramWhen an image is open, the Show Histogramcommand in the Image menu can be used to openthe Histogram window. The histogram isnormalized, with the greatest histogram pointrepresenting a vertical value of 100. Also notethat the histogram data points corresponding topixel values of 0 and 255 are never allowed todetermine the scaling factor, so half frameimages, etc. will not have their histogram hiddendue to the large number of zero valued pixels.On Macs with color or gray scale capability, acolor bar is shown under the histogram showingthe effects of stretching the image with theBackground and Range contrast parameters. Thehistogram window can be closed by clicking in itsclose box or by invoking the Hide Histogramcommand in the Image menu.



Image Processing from the Image MenuThis section describes the commands in theImage menu which have not been described yet:Color Table and Presentation.

If your Mac has color or gray scale capabilityyou can use the Color Table command toproduce some dramatic and vibrant imagedisplays. Using the Color Table command youcan select from eight different color tables andmodify or create them as you wish. A color tableis a mapping from the 256 possible pixel values todisplay colors.

Invoking the Color Table command reveals adialog with a box of 256 color table entries orcells, a pop-up menu, and several buttons. Thepop-up menu is used to select an individual tablefrom the 8 (maximum) possible tables. As themouse is moved around in the box of color cells,a white highlighting rectangle as shown, and textin the lower left corner of the dialog indicates thecell number of the currently highlighted cell. Thecell number shows the correspondence betweenthe 256 possible pixel intensities or values and thecolors used to display those pixel values. Thecolor of any one cell can be changed using thefamiliar Color Picker dialog by double clicking inthat cell. Finally, the buttons are describedindividually below:

NewThis button creates and selects a new colortable. The color table is ingray scale color table. This button will begrayed-out if the maximum number of 8 colortables already exists.

DeleteThis button deletes the currently selectedcolor table. This button will be grayed-out ifthere is only 1 color table left.

RenameThis button allows you to rename thecurrently selected color table. Color tablenames can be up to 16 characters in length.

DupThis button creates and selects a new colortable which is an exact copy of the currentlyselected color table. We suggest you use thiscommand whenever you wish to modify an

existing color table since any changes made toa color table can not be undone otherwise.Also this button will be grayed-out if themaximum number of 8 color tables alreadyexists.

RampThis button can be used to create a blend ofcolors between two cells. If you click in a celland drag the mouse, a range of cells can beselected. Once a range of cells is selected,hitting this button causes the cells in theselected range to become a blend of colorsbetween the two endpoints of the selectionrange. If the OPTION key is held down whenthis button is hit, you are first allowed to pickthe color for the two endpoint cells using theColor Picker prior to the cells being blended.

DoneHitting this button dispenses with the ColorTable dialog and uses the currently selectedcolor table for displaying the image in thePicture window.

Note:You may wonder what causes the interestingeffects sometimes visible in the Picturewindow while you are using the Color Tablecommand. Essentially it is the Macintosh'ssystem software. Each window can have itsown color table, and with over 16 millionpossible colors, of which only a small sub-set(such as 256) can be displayed at one time,the system software gives the highest priorityto the front most window. As the systemsoftware juggles the available colors,windows in the background don't getupdated when the Color Table dialog is openand hence show the effects of the changedcolor environment. While this producessome interesting looking displays, it is notlasting or repeatable.

Finally, the Presentation command can be usedto access the Presentation Mode where the imageis drawn centered on the screen, with all thebackground (including the menu bar) beinghidden and blacked-out. You can exit fromPresentation Mode by simply clicking the mousebutton.



Image Processing from the Ops MenuThis section describes the image processingcommands available in the Ops menu.

Note:The commands in the Ops menu modify theimage data in memory, so the file will have tobe reloaded (using the Revert to Savedcommand for instance) in order to return tothe original display (except in some cases ofthe Zoom command).

Images can be co-added to one another using theMem+Disk->Mem command. An offset can beentered to allow two images of the same object tobe registered to increase the image quality. TheMem-Disk->Mem command is typically used tosubtract off a dark background reading (toremove dark current fluctuations).

The Flip Horizontal and Flip Verticalcommands allows flipping an image to matchsome preferred orientation. The Highpasscommand allows a highpass filter to be applied toaccentuate the "edges'" in the image, or theLowpass command can be applied to smooth theimage. The Highpass command will tend tobring out stars from an image showing both starsand nebulosity, but once applied to an image, anymeasurement of magnitudes is not applicable oreven accurate.

The Zoom 4 x 1 command allows a portion ofthe image to be magnified four times. Move thezoom-box which appears in the Picture windowwhen this option is selected to the desiredlocation (the zoom-box follows the motion of themouse), and click the mouse button to update thedisplay. If enough memory was available to savethe un-zoomed image, the Zoom 4 x 1 commandwill change to Unzoom Image which will restorethe image to its un-zoomed state.


Prior to taking and downloading images from theST-4 you need to make sure the physicalcommunications link between the Mac and theST-4 have been established. When the software isfirst run it will try to find the ST-4. If successful

you can probably skip this section unless youdesire to change the communications speed, etc.

The Communications command in theCamera menu allows you to select which of theMac's two serial ports to use, and the baud ratewhich is selected from a pop-up menu. Pleaserefer to the "Making the Camera Connection"section of the host software description above fora detailed discussion of recommend baud rates,etc.

Note:Not all Macs will actually have pop-upmenus, depending on which version of thesystem software you are using. On thoseMacs without pop-up menus, clicking (andreleasing the mouse button) in the shadowedbox to the right of the Baud Rate title willreveal a dialog with a list of items that can beused to select the desired baud rate. Allother pop-up menus will work the same wayon these machines.

The Establish link command in the Cameramenu will cause the software to go search for theST-4 and establish the communications link, re-programming the ST-4's baud rate if necessary.This is a good thing to do if the software didn'tfind the ST-4 when it first started up or if youchanged the serial port selection with theCommunication command.

Taking Images

This section describes the five commands fromthe Camera menu used in taking anddownloading images from the ST-4: CameraSetup, Grab Setup and Grab, and Focus Setupand Focus.

The Camera Setup CommandThe Camera Setup command is used to selectoptions that apply to both the Grab and Focuscommands discussed below. Each item in theCamera Setup dialog is discussed individuallybelow:

GainThis is the gain parameter discussed in the"Baseline and Gain Parameters" section of the



host software description above. The settingsabove 1x can be used to reduce the imagegraininess for exposures where the dynamicrange is reduced due to long exposure build-ups of dark current where short exposuresare necessary.

Camera baseline levelThis is the baseline parameter discussed in the"Baseline and Gain Parameters" section of thehost software description above. Setting avalue slightly lower than the background dueto dark current or sky background andincreasing the Gain can reduce imagegraininess.

Enable Anti-Blooming GateChecking this option enables the Anti-Blooming Gate feature during the exposure asdiscussed in "The Anti-Blooming Gate"section of the host software descriptionbefore.

Dark SubtractionChecking this option enables the automaticdark frame subtraction feature of the ST-4described in the "Automatic Dark FrameSubtraction" section of the host softwaredescription before. Enabling this featureallows you to more easily search for dimobjects with short exposures since the unevenand obscuring background will be removedfrom the image.

The Focus Setup and Focus CommandsThe first operation with the ST-4 is typically tofind and focus on an object. This is most easilydone by first using the Focus Setup commandfollowed by the Focus command from theCamera menu.

The Focus Setup command brings up adialog box which has items which control theoperation of the Focus Mode. The Exposure timeshould be set to the desired value ranging from0.01 to 600 seconds. Checking the Auto Updatecheck box causes the Focus Mode to not pauseautomatically between images. Finally, the FrameMode pop-up menu allows you to select thedesired frame mode as discussed in detail in the"Focussing and Special Imaging modes" sectionof the host software description above. Some of

the frame modes require further discussionbelow:

QuarterIn this mode, a full image is firstdownloaded, and the Focus Mode is paused.You then position a quarter frame sizedsquare drawn in the Picture window andclick the mouse to designate the desiredportion of the image to download onsubsequent images.

TrackLike Quarter Frame mode above, a full imageis first downloaded and the Focus Mode ispaused. You then position a 33 x 27 boxdrawn in the Picture window and click themouse to designate the desired region of theimage to download on subsequent images.The downloaded images are then blown-up4:1 for display and shown with asuperimposed crosshair. Also the Focuswindow is expanded to show 4 arrow shapedbuttons. Clicking in any of the buttons closesone of the relays in the ST-4 for 0.2 seconds,enabling the drive correction for that button.

Note:Although each arrow shaped button willclose one relay in the ST-4, the orientation ofthe buttons compared to the direction the starwill move as a result of closing the relaysmay not be correct. Essentially it's like usingthe hand controller; you will have todetermine which button is require to movethe image in the correct direction.

The Focus Setup command can also be invokedwhile in Focus Mode to change the exposuretime, frame mode, or Auto-Update feature.

The Focus command brings up the Focuswindow and enters the software into FocusMode. The Focus window has two bar graphs inthe "Progress" box which show the progress ofthe Exposure and Download portions of theFocus Mode cycle. After each exposure iscompleted and prior to the image beingdownloaded, the parameters in the "Max.Intensity" box are updated with the position andvalue of the brightest pixel in the image.



The Pause / Resume button can be used tomomentarily pause the Focus Mode. Thebutton's title indicates the function that will beapplied. Hitting the Restart button causes theFocus Mode cycle to start over at the beginning.For most frame modes, this means just restartingthe exposure, but for the Quarter Frame andTrack Frame modes, the entire process is startedover with the downloading of the full image andspecifying the desired region to work with onsubsequent images.

Images captured in the Focus Mode can ofcourse be saved using the Save or Save Ascommands in the File menu. Also, when theFocus Mode is active, several of the otherfeatures are unavailable such as image zooming.You can exit from the Focus Mode by clicking inthe Focus window's close box or by reinvokingthe Focus command a second time. Finally, thereare some items in the Customize commandpertaining to the Focus Mode described below.

The Grab Setup and Grab CommandsIf you have already focussed the system, and justwant to take a single image, fussing with theFocus Mode can be a lot of work. Instead, youmight use the Grab Setup and Grab commandsto take, download, and display a single exposure.

Use the Grab Setup command to set theExposure time and Exposure delay items as desired.Again, the Exposure time can range from 0.01 to600 seconds. Setting the Exposure delay item to anon-zero value causes the software to delay bythat amount prior to taking the exposure, givingyou time to get back to the telescope and preparefor tracking, for example.

The Customize Command

The Customize command in the File menucontains items which allow you to customize theoperation of the software to your personal taste.The items are individually selectable and arediscussed below:

Auto Show CrosshairSelecting this option makes the Crosshairwindow be opened automatically wheneveran image is opened or downloaded from theST-4.

Auto Show HistogramSelecting this option makes the Histogramwindow be opened automatically wheneveran image is opened or downloaded from theST-4.

Auto Contrast on DLSelecting this option enables the Auto-Contrast feature for images downloadedfrom the ST-4.

Don't Ask to Save on DLIf you invoke the Grab or Focus commandswhen you have an unsaved image inmemory, you will be asked if you want toproceed (which will overwrite the image inmemory). Selecting this option makes thesoftware skip the warning and overwrite theimage.



OBSERVING SUGGESTIONS WITH THE ST-4IMAGING CAMERA

The ST-4 lends itself well to many types ofobservations. Even a modest 2.4 inch refractorwith no drive can be used to do scientific work.As an example, taking several images of theplanet Jupiter over a two hour period and thenmeasuring the position of the moons using thecrosshairs will allow the relative motion of themoons to be easily determined. The apparentincrease in the size of Mars can be measuredduring an opposition. The diameter and phase ofVenus can be determined. Double stars down to7th magnitude with separations of 5 arcsecondscan be measured, using exposures only 0.1seconds long to avoid blurring of the star due tothe earth's rotation. Photometry of variable starscan be performed. If a drive is added, allowingthe exposure to be extended to 10 seconds, starsdown to 12 magnitude can be detected.Planetary nebula become detectable, along withthe center of prominent galaxies.

If a more powerful telescope is available,such as an 8 inch Schmidt-cassegrainian, muchfainter stars can be reached. A one secondexposure will reveal 12 magnitude stars. A fiveminute exposure will reveal 18th magnitudestars, and faint nebulosity. Use of a fieldcompressor to reduce the f- number of thetelescope to f/4 or f/5 is recommended, since itnot only increases the field of view but it reducesthe required exposure to see faint nebulosity byat least 4 times. Adding a high quality Barlowlens will allow detail at the limit of the telescope'sresolution to be captured. Quite often closedouble stars can be detected and measured bynoting the elongation of the image, a simplemeasurement when examining an image in thezoom mode at your leisure. The rotation ofJupiter can be easily seen in exposures only a halfhour apart; similar measurements can be made ofMars. Use of color filters improves the contrastof planetary surface features. Not as well knownis that galaxies also change in appearance whencolor filters are used. Old pictures of manygalaxies were taken with blue sensitiveemulsions, and the dust lanes in the arms arevery prominent. At red wavelengths, the dust ismore transparent, and the galaxy takes on adifferent appearance. Stars partially hidden by

the dust may become more visible. Color filterscan also be used to make stellar temperaturemeasurements. This is not mathematicallysimple. SBIG plans to sell a filter set andprogram which will make this measurementautomatic, allowing an entire field of stars to beportrayed in different colors corresponding totheir temperatures, and not their intensities. Thetemperature of a variable star can be plottedalong with its intensity.

The tremendous sensitivity of the ST-4 allowssupernova searches to be conducted with greatersensitivity, and less work. The positiondetermination capability enables motions of theplanets, asteroids, and faster moving stars to bequantified in a short period of time. Relativemotion of double and triple stars can be followedover the years.

Our company philosophy is to put thegreatest astronomical capability in the hands ofthe amateur that we can. We feel thisquantitative measurement power in the hands ofso many enthusiastic individuals can onlyadvance the state of astronomical knowledge,and enable organized observing programsheretofore impossible. This product has onlybecome possible in recent years, due to thefreefall in the price of computers and CCDimaging devices. We intend to upgrade oursoftware often to take advantage of the rapidimprovement in computer graphics taking place.Enjoy using the ST-4, and appreciate that you areusing equipment superior to anything availablewhen man first went to the moon.



PROBLEM SOLVING WITH THE ST-4

This section discusses common problems youmay experience while using the ST-4 anddiscusses possible solutions to those problems.

PROBLEM: Can't find the star!This problem is usually due to the telescope

being badly out of focus. Remove the CCD andput a piece of ground glass or strip of ScotchTape over the end of the telescope eyepiece tube.Point the telescope at a bright object such as themoon or a planet and focus the image on thediffuse screen (this is easiest if you look at thescreen as if you were sighting down the eyepiece,but from 12 inches away. (The CCD opticalposition is actually about 1/8th inch in from theend of the tube). Move to a bright star. Centerthe image in the tube and then insert a highpower eyepiece.

Without changing the focus, adjust thetelescope to center the image in the eyepiece.Then insert the CCD and the star should bereadily apparent in the display values. It is veryhandy to boresight another telescope to the guidetelescope during initial use of the CCD. Thisallows the CCD to be rapidly moved to a varietyof stars of different brightness.

PROBLEM: Error message appears after thedrive calibration step.

MESSAGE: E1 1 (or 2, 3 or 4)This message appears when the instrumentdid not 'see' the star move at all in one ormore of the four directions (+X, -X, +Y, -Y)during calibration. Re-check the drivecontrols using the four drive adjustmentbuttons on the box.

MESSAGE: E2 1 to 4This message appears when the ST-4 did notsee an adequate correction in one of the fourcorrection directions. A correction of at least5 pixels (2 units) must be seen in all fourdirections. If this is not the case, theinstrument assumes these is no correctionequipment for that direction and ignorescorrections in that axis in the future. Thisfeature is helpful, for example, when no

Declination motor is installed on thetelescope mount.

PROBLEM: Star images in photos are not round!First, check to see in what direction the

images are smeared. If it is in Right Ascension,which is most likely, consider the followingpossible problems.

1. The guide telescope focal length is so shortthat adequate tracking is not possible. Theguide telescope should have a focal length ofat least 1/4 that of the primary telescopedoing the photography.

2. The telescope drive is very poor quality orST-4 exposure times are too long. Sometelescope drives produce rather abrupt hopsin their position which create motion toorapid for the ST-4 to follow. Also, somedrives drift so badly that they can not gouncorrected for even five seconds. In thesecases, the tracker exposure time (whichcontrols the time between corrections) mustbe reduced. This may limit the ability of theST-4 to track faint guide stars.

If the error is not only in Right Ascension, it ispossible that differential deflection is occurringbetween the guide telescope and the primarytelescope. The simplest solution in this case is touse an off-axis guider, or the on-axis guideroffered by SBIG.

Note that the ST-4 tracker is capable of bettercorrection than a human because it averages theposition of the star over a period of seconds,while a human sees the star dance about anambiguous central position due to atmosphericturbulence. Also the ST-4 makes precise driveadjustments in response to a guiding error, whilea human stabs away at the pushbuttons until thestar is again centered.

Another error can occur when guiding on astar some distance off-axis with an improperlyadjusted mount. The guide star is trackedaccurately, but stars within the camera field ofview will rotate slightly about the guide star.This effect is small, but significant in carefulwork. A one half degree error in correctlypositioning Polaris could produce an imagerotation in the telescope of 5 minutes of arc perhour. If you were to take a 0.5 hour exposure



using a guide star centered 1 degree away fromthe field of view of your camera this effect wouldcause each star to form a streak about 2.6arcseconds long.



APPENDIX A

The tables below show the pin-outs of the four connectors on the ST-4 and the colors of the wires on thecables supplied with the unit.

Pin Number Function Color11 +X, Common Gray 3 +X, Normally Closed (NC) Pink10 +X, Normally Open (NO) Tan

5 -X, Common Brown12 -X, Normally Closed (NC) Yellow 4 -X, Normally Open (NO) Violet

14 +Y, Common Green 6 +Y, Normally Closed (NC) Orange13 +Y, Normally Open (NO) Blue

8 -Y, Common Black15 -Y, Normally Closed (NC) Red 7 -Y, Normally Open (NO) White

Table A1 Relay Connector/Cable

Pin Number Function Color5 Chassis Ground Green

4 +12 VDC, 1 amp, or 12 VAC Red9 Other side of 12 VAC, or DC ground Black2 Alarm relay1, common connection Orange6 Alarm relay, normally closed Blue1 Alarm relay, normally open White

Table A2 Power Connector/Cable

ST-4 Wire PC Cables Mac Cables Pin Function Color PC/XT(25 pin D) AT(9 pin D) 9 pin D 8 pin DIN

2 Transmit data from ST-4 Red 3 2 9 53 Receive data to ST-4 White 2 3 5 35 Ground Black 7 5 32 43

Table A3 RS232C Connector/Cable

For additional information regarding the operation of the ST-4 Star Tracker / Imaging Camera, pleasecontact the Santa Barbara Instrument Group:

SANTA BARBARA INSTRUMENT GROUP1482 East Valley Road, Suite 601Santa Barbara, CA 93108

1 The alarm relay in the ST-4 can activate an external alarm or light (110 volt).2 Longer cables may require jumpering pin 8 to pin 3 to make the Mac's RS422 compatible with RS232.3 Longer cables may require jumpering pin 8 to pin 4 to make the Mac's RS422 compatible with RS232.



Telephone (805) 969-1851FAX (805) 969-0299



Index

AADJUST button ..................................................... 4Angular separation ............................................. 10Anti-blooming gate ............................................. 13Aperture area......................................................... 9Atmospheric transmission.................................... 9Atmospheric turbulence ....................................... 4Auto baud mode ................................................. 11

BBackground level................................................. 13Background parameter ................................... 8, 15Baseline parameter.............................................. 13Baud rate.......................................................... 1, 11BGI files................................................................ 16Blooming.............................................................. 13Boost factor ............................................................ 4Brightness adjust ................................................... 4Button (ST-4)

ADJUST........................................................... 4CALIBRATE ................................................... 5DOWN ............................................................ 5FIND AND FOCUS........................................ 4INTERRUPT.................................................... 3LEFT ................................................................ 5MENU ............................................................ 4RIGHT ............................................................. 5TAKE DARK FRAME .................................... 3TRACK ............................................................ 5UP .................................................................... 5

CCALIBRATE button .............................................. 5Calibration factor .................................................. 9Capturing images ................................................ 15CCD................................................................ 1, 3, 7

blooming ....................................................... 13cooling ......................................................... 2, 7orientation....................................................... 5pixel dimensions............................................. 7readout ............................................................ 7temperature................................................... 13

Check digit........................................................... 12Co-adding images ............................................... 12COM 1 or 2 .......................................................... 16Connecting to the camera ................................... 11Contrast.................................................................. 8Crosshair .......................................................... 9, 10

DDark current .................................................2, 7, 12

Dark frame..............................................1, 4, 12, 13Dark frame subtraction

host .................................................................. 2ST-4................................................................ 13

Declination......................................................... 2, 5Dew ........................................................................ 2Diffuse magnitude .............................................. 10Displaying images................................................. 8Dithering.............................................................. 11DOWN button ....................................................... 5Downloading images .......................................... 12Dynamic range .................................................... 13

EError messages .................................................... 35Establish link command ..................................... 12Establishing communications link ..................... 11Exposure ................................................................ 1Exposure time.............................................4, 12, 13Eyepiece tube....................................................3, 15

FFilm......................................................................... 7FIND AND FOCUS button .................................. 4FIND AND FOCUS mode .................................... 3Finding a star..........................................2, 4, 15, 355 x 5 box ............................................................... 10Flipping images ................................................... 10Focal length............................................................ 9Focus mode.......................................................... 14Focussing ..........................................................2, 13Frost.................................................................... 2, 7Full frame mode .................................................. 14

G - HGain parameter.................................................9, 13Guide stars............................................................. 1Guiding errors ....................................................... 1Half frame mode ................................................... 7Hand controller ..................................................... 3Hard disk ............................................................. 16Histograms .......................................................... 11Horizontal flip ..................................................... 10Host computer................................................... 2, 8Hot pixels............................................................. 13

IIBM PC................................................................. 16IBM PC.......................................................software

Camera/Scope command............................ 23command mode............................................ 17command screens ......................................... 17



crosshair mode ..............................................20crosshair parameters.....................................20crosshairs .......................................................20data analysis mode .......................................20data buffer info box.......................................17data directory ................................................18directory command screen...........................18Display command.........................................19establishing link.............................................23flip ..................................................................20Focus command ............................................24Grab command..............................................23histogram.......................................................19Image I/O command ....................................17loading images ..............................................18menu bar........................................................17PC command .................................................22presentation mode ........................................22saving imaes ..................................................18special keys....................................................17status box.......................................................17taking images.................................................22telescope parameters ....................................18zoom...............................................................21

Image modes ..................................................12, 13Image transmission................................................1Images

capturing........................................................15co-adding .......................................................12contrast ......................................................8, 15dark frame subtraction .................................12displaying ........................................................8downloading .................................................12flipping ..........................................................10inversion ..........................................................9smoothing ........................................................9viewing ..........................................................15zooming ........................................................11

Imagingfull frame mode.............................................14moon ................................................................7planets........................................................7, 13quarter frame mode ......................................14spot frame mode ...........................................14

Imaging camera......................................................7operation..........................................................7

Integration ..............................................................1Integration time......................................................2Interpolation.........................................................11INTERRUPT button...............................................3Inversion.................................................................9

J - LJoystick interface....................................................3Joystick type controllers ........................................2LEFT button ...........................................................5Light frame.......................................................1, 12

MMacintosh .............................................................25Macintosh software

About dialog..................................................25Auto button ...................................................27Camera Setup command ..............................32Color Table command ..................................30Communications command.........................31contrast window ..................................... 26, 27crosshair window..........................................26crosshairs .......................................................28Customize command....................................33Dithering menu .............................................28Do It button ...................................................27Focus command ............................................33Focus Setup command..................................32focus window................................................26Grab command..............................................33Grab Setup command...................................33histogram window........................................26Info Edit command .......................................28loading images ..............................................26Open command....................................... 25, 26Ops menu ......................................................31photometric analysis.....................................28picture window ............................................26Presentation command.................................31Save As command ........................................27separations.....................................................29Show Crosshairs command..........................29Show Histogram command .........................30

Magnitudes...........................................................10Making the camera connection...........................11MENU button ........................................................4Menu items (ST-4)..................................................6

b (boost factor) ................................................4bA (brightness adjust) ....................................4CA (calibration adjust) ...................................4EA (exposure adjust) ......................................4H2 (y hysteresis)..............................................6SA (scintillation adjust) ..................................6

Microcontroller ......................................................1

N - ONegative images.....................................................9Neutral density filters............................................7Observing suggestions ........................................34



PPC compatible...................................................... 16Photometric analysis ............................................. 9Pixel 1,1 .................................................................. 9Pixel coordinates ................................................... 9Pixels .............................................................1, 7, 12

hot.................................................................. 13Presentation mode................................................. 9Problem solving................................................... 35Pushbutton interface ............................................. 3Pushbutton type controllers ................................. 2

Q - RQuarter frame mode ........................................... 14Range parameter ............................................. 8, 15Relays ..................................................................... 2Right ascension...................................................... 2RIGHT button........................................................ 5RS-232............................................................... 1, 16RS-422..................................................................... 1

SSchmidt Cassegrain telescope (SCT).................... 2Scribing the eyepiece............................................. 5Separations........................................................... 10Serial interface ............................................1, 11, 16Serial port........................................................11, 16Signal to noise ratio (S/N).................................. 12Smoothing.............................................................. 9Spot frame mode ................................................. 14Star tracking

operation ......................................................... 3overview.......................................................... 1

TTAKE DARK FRAME button............................... 3Telescope drive...................................................... 1Telescope factors ................................................... 9Thermoelectric cooler ....................................... 2, 7TRACK button....................................................... 5Typical star intensities ........................................ 15Typical VALUE readings...................................... 5

U - ZUP button............................................................... 5VALUE display ..................................................... 3Vertical flip .......................................................... 10Viewing images ................................................... 15X coordinate........................................................... 9Y coordinate........................................................... 9Zooming images.................................................. 11

model st-4 star tracker imaging camera operating manual · 2020-06-05 · sbig st-4/0490 page 1...

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