DSLR Astrophotograpy….. 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 consume less power than CCDs Provide excellent color
One shot color (Bayer Matrix) http://www.cambridgeincolour.com/tutorials/camera-sensors.htm
How color is created Debayering the matrix….. greyscale data converted to RGB image http://www.cambridgeincolour.com/tutorials/camera-sensors.htm
Processing after demosiacing Irreversible process 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)
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 plus JPEG or TIFF) Usually 3-4 minute unquided exposures Total exposure time usually 1-2 hours (15-30 exposures) Dark site is important
Image processing Images Plus Dark subtraction Debayering conversion to color FITS Grading File conversion to 16-bit TIFF Could do everything in Images Plus
Images plus
Registar Use for aligning and combining (usually) Fool proof and very flexible
CCDStack Use for digital development (non linear stretch), creation of luminance image, deconfolution of luminance
Photoshop for the rest of processing