astrophotography with a side of raspberry pi
TRANSCRIPT
Rob Pettengill - AAS
Astrophotography With A Side Of Raspberry PiRob Pettengill ([email protected]) Austin Astronomical Society 11 April 2014
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Rob Pettengill - AAS
My Name Is Rob & I Am Addicted To Astronomy
• I am not a professional Astronomer
• Please do try this at home
• Follow your own inspiration & needs
• Have fun
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Rob Pettengill - AAS
AGENDA• Review Basic
Astrophotography • Explore The Intersection Of
Internet Of Things & Astronomy
!1. Quick Context
• Astrophotography (Trade-Offs) • Internet Of Things &
Raspberry Pi 2. What I Built 3. What I Learned Taking &
Processing Images 4. What's Next…
Christos Vasilas of Dash One
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1st afocal RPi Cam astro images
Rob Pettengill - AAS
Sensor Telescope Target MatchWhy not capture everything?
We must match Telescope & Sensor resolutions.
Example 89mm (3.5”) scope: R = 4.56/D = 4.56/3.5 = 1.3 arc sec Dawes Limit at prime focus 1.57º x 1.07º or 4348 x 2963 re or 12.9 MP !Dawes or Rayleigh Criterion gives resolution, you need 2X this to capture "the space between” aka sampling theorem or 12.9 * 2 *2 = 52 MP! !For a 7” scope we need > 200 MP !With practical sensors, we can either maximize field of view or resolution but not both!
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Trading Off FOV and Resolution
• Sensor Choice
• Extended Deep Sky Objects - Large sensors with larger pixels
• Solar System - small sensors with smaller pixels
• Modify telescope Focal Length
• Panoramas (at n squared times the work)
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Sensor Size & Resolution Examples
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Sensor Size mm
Resolution Pixel Size um
Pixel FOV arc sec
Sensor FOV arc min
RPi CM 3.67 x 2.74 2592 x 1944
1.4 0.224 9.79 x 7.3
Sony NEX-5N
23.4 x 15.6 4592 x 3056
5.0 0.8 62.4 x 41.6
Starlight Ex SX814C
12.5 x 10.0 3388 x 2712
3.69 0.59 33.3 x 26.7
Meade DSI Pro III
10.2 x 8.3 1360 x 1024
6.45 1.03 27.2 x 22.1
Orion Starshoot
5.77 x 4.3 2592 x 1944
2.2 0.352 15.4 x 11.5
Philips SOC900NC
4.6 x 3.97 640 x 480 5.6 0.96 10.2 x 7.66
89mm Objective 1280mm FL
ScaleOfViewPrimeFocus=206.3/FLmm arc sec/µm, ResolutionLimitDawes=114/Dmm arc sec
Rob Pettengill - AAS
Astrophotography & FL
Camera (Rule of 500 / tripod, tracking or piggyback mounts)
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Prime Focus Reducer Shortened Focal Length
Barlow Extended Focal Length
Eyepiece Projection Extended Focal Length
Afocal / Digiscoping Extended Focal Lengthdrawings from Televue
Rob Pettengill - AAS
Networked Computers so small and cheap that they can be embedded in everything !Gartner - 26B by 2020 !Astronomers have been pioneers
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Microcontrollers Arduino... Network Connected PCs • RPi ARM $30 • Arduino Due $50 • BeagleBone Black ARM $50 • Intel MinnoBoard Atom $200
Graphic from mobilemarketingwatch.com
Rob Pettengill - AAS 9http://www.raspberrypi.org
http://beagleboard.org/Products/BeagleBone+Black
http://www.intel.com/content/www/us/en/do-it-yourself/edison.html
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Internet Of Things And Astronomy
• Remote Observing downsized & updated.
• GoTo telescope control
• PushTo instrumentation and link to planetarium software
• Automatic focusing.
• Guiding
• Camera control and enhancement.
• Plate solving.
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http://vaticanobservatory.org
http://simonbox.info/index.php/astronomy
http://www.recantha.co.uk/blog/?p=3615
http://astrobeano.blogspot.com/2014/01/instrumented-telescope-with-raspberry.html
Rob Pettengill - AAS
M a k i n g A s t ro p h o t o g r a p h y A f f o rd a b l e P o r t a b l e & F l e x i b l e ?
DSLR (small screen/limited functionality) alternatives require a computer.
• Largest component is the computer / laptop
• Replace the computer with a small low power wireless computer. ARM based machines are powerful yet small and low power.
• Replace the laptop display with a wirelessly connected cell phone or iPad. Better displays than many laptops.
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Terry Belia astrotex.com
Rob Pettengill - AAS
R P i + C a m e r a M o d u l e + Q u e s t a r C a m e r a A d a p t e r
C a n I t Wo r k ?
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https://www.flickr.com/photos/robpettengill/sets/72157635483690850/
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Hang Me ’Til I’m DoneAstro RPi 2.0
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Screw Me Up TightAstro RPi 3.0 Uses a T-ring as a nut to bolt mounting plate for camera to the extension tubes
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Acquisition Software StackIOT based model - smart devices, using web based interfaces on the network, to talk to personal devices.
• On the Raspberry Pi
• Camera Interface (raspicam)
• Web Server - translate camera control from Web requests to raspicam, serve up images for aiming and focusing
• Image storage on local SD card
• Wireless ad hoc WiFi network for communication
• On a smartphone or tablet
• Web browser with camera control interface
• Last still image
• Streaming video
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72 image Astro Raspberry Pi Lunar Panorama made with Hugin
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BerryCam ready for Jupiter imaging
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Jupiter Io & Europa 240 of 500 images stacked & sharpened
Rob Pettengill - AAS
SoftwareMy environment Linux & OS X
Planning
• Stellarium
• AstroPlanner
Image acquisition:
Custom python web server on RPi front end to raspicam application. Motion JPEG & VLC streaming both work.
Web browser or Berrycam app on iOS
Stacking & Preprocessing:
• Lynkeos - fast, powerful, easy to use (occasional crashes)
Nebulosity - powerful, robust, deep-sky oriented (also image acquisition)
Post processing
Photoshop
Hugin - amazing panorama tool
Gimp - powerful but not 16bit clean yet
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Acquisition Lessons
• Good focus is essential! Bahtinov mask!
• It is hard to aim! Getting a bright planet in the field of view of a small sensor imager is hard!
• Image latency from the imager to the display really matters in finding and focusing.
• Use video streaming for aiming and focusing.
• Realtime cropping focusing aids matter.
• Speed of wireless link is important (802.11n or ac needed)
• Use RAW format if you can, but you can do without it for bright Solar System objects.
• Cell phone camera imagers can give excellent Solar System results
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Rob Pettengill - AAS
Preprocessing Lessons
• Stacking “lucky images” gives amazing results.
• Automatic image grading helps, but is not enough
• Ease of reviewing & selecting images is essential
• Dark and Flat frames are essential for deep sky but "not so much" for bright Solar System objects
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Rob Pettengill - AAS
Post Processing Lessons
Post processing balances art and science as you iteratively reveal the data in the image in a pleasing realistic way.
• Deconvolve before stretching.
• Iteratively stretch (mid & dark points) with levels tool more controllable than curves.
• Layers and masks are your friends, learn to use them well. Masks reduce sharpening artifacts.
• Unsharp mask appears to give a sharper image, deconvolution really does.
• Iteratively sharpen and filter noise. Avoid and reduce sharpening artifacts.
• Finish off with color enhancement (gamma, saturation, vibrance) and curve tweaks to enhance contrast.
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Quick Resolution Check
• Calculate angular pixel size
• Down-sample image to reference resolutions
• Up-sample reference images to original size
• Compare original to reference images
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Drizzle - Stacking Of Under Sampled ImagesA Hubble example of a drizzle stack of 12 images from Wikipedia shows recovery of under sampled data
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http://en.wikipedia.org/wiki/Drizzle_(image_processing)
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30sec ISO 6400 APS-C sensor
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7 stacked ISO 6400 30 sec, dark frames, & post
Rob Pettengill - AAS
Rob Pettengill - AAS
What's Next?
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• Lack of drivers for high quality cooled astrophotography imagers is a barrier for now. A few already provide Intel Linux drivers and some ARM Linux (Point Grey).
• High speed wireless network protocols will enable wireless astrophotography.
• Headless GoTo and PushTo telescopes with wireless connections to tablet & smart phone apps.
• Embedded computers have a bright future in Astronomy, with smart phones or tablets replacing laptops for user interfaces. IOT devices like Raspberry Pi make it easier for amateurs to lead the way.
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