DSLR ASTROPHOTOGRAPHY…. MY WAY
MY CAMERA
WHY CANON?
• Provides RAW files• Not directly useable as an image
• “Digital negatives”… unprocessed readout of pixels
• Well suited for dark subtracting and flat fielding… not true of Nikon
• Canon uses CMOS (complementary metal oxide semiconductor) sensor• Less sensitive than CCD, but cheaper to make
• Generally consumes less power than CCDs
• Provides excellent color
CREATING A COLOR DIGITAL IMAGE
ONE SHOT COLOR (BAYER MATRIX)
http://www.cambridgeincolour.com/tutorials/camera-sensors.htm
Filtered sensors convert photons to electrons which can be measured
BRYCE BAYER (1929-2012)
http://image-sensors-world.blogspot.com/2012/11/bruce-bayer-died.html
HOW COLOR IS CREATED
Debayering the matrix… greyscale data converted to RGB image
Each pixel contributes to the luminance image which gives detailhttp://www.cambridgeincolour.com/tutorials/camera-sensors.htm
PROCESSING AFTER DEMOSAICING
Irreversible processes best done on a computer and not in the camera
http://www.cambridgeincolour.com/tutorials/raw-file-format.htm
OTHER REASONS TO USE CANON
• Software readily available
• Acquisition (Images Plus, Backyard EOS, Nebulosity, DigiCamControl)
• Processing (Images Plus, PixInsight, Nebulosity, Deep Sky Stacker)
• Gain from the experience of others
• Yahoo Group Digital Astro
• Yahoo Group DSLR Astro Image Processing
• Cloudy Nights DSLR & Digital Camera Astro Imaging & Processing
• Jerry Lodriguss CCD books are excellent and website
• Books, adaptors, modifications, etc., are widely available
WHY MODIFY THE CANON SENSOR?Stock IR cut filter limits Ha response of sensor
MODIFIED CAMERA IS A MUST
DOWNSIDES OF MODIFYING CAMERA• Must use custom white balance
• Auto mode will not work with custom white balance in older Canons… must use P or M mode
• Canon warranty is void and they will not service the camera
• Cost is $200 - $300 (Hutech, Hap Griffin, Gary Honis)
COMPARING CANON CAMERAS
APS-C SENSOR (ADVANCED PHOTO SYSTEM)
LENSES AND TELESCOPES THAT I USE
• 17-40mm f/4 Canon
• 85mm f/1.8 Canon (image scale 13.5 arcsec/pixel)
• 200mm f/2.8 Canon (IS 5.4)
• Borg 77ED refractor, f/5.5 (IS 2.5)
• TAK FSQ 106 refractor, f/5 (IS 2)
• TEC 140 refractor, f/7 (IS 1.1)
• Importance of image scale… try to stay >2
CONNECTING TO THE TELESCOPE
IMAGE ACQUISITION
• Important to use a computer because it gives the best focus
• Images Plus Camera Control
• Many features… DSLR (Canon and Nikon), CCD, video
• Autofocus control for motorized focusers; temperature compensation
• $240, includes image processing software
• Very good video tutorials
• Backyard EOS
• Only for Canon cameras
• Manual focus aid plus framing aid, drift alignment, video, eclipse mode
• Only $30
BACKYARD EOS FOCUSING
TYPICAL EXPOSURES
• Usually stop down lenses a couple of stops
• Always use ISO1600 (never go below ISO800)
• Always collect RAW images (optional JPEG or TIFF)
• Usually 3-4 minute unguided exposures
• Total exposure time usually 1-2 hours (15-30 exposures)
• Usually take 5-10 dark exposures, but no flats
IMAGE PROCESSING
• Images Plus
• Dark subtraction to reduce sensor noise (no flats)
• Debayering conversion to color FITS
• Grading
• File conversion to 16-bit TIFF
• Could do everything in Images Plus
REGISTAR• Use for aligning and combining (usually median)
• Fool-proof and very flexible; mosaics; aligning different formats
CCDSTACK• Use for digital development (non-linear stretch)
• Creation of luminance image
• Deconvolution of luminance
PHOTOSHOP (CS5)• Use LRGB method (Adam Block)
• Carboni’s Astronomy Tools, Gradient Xterminator, Noise Ninja, HLVG
MONITOR CALIBRATION
• Important if others are looking at your images online
• Spyder4 Express (~$100)
SLIDES ON WEBSITE
WWW.GEOANDPAT.COM
