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DSLR AstrophotograpHy …. My way

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

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DSLR AstrophotograpHy …. My way

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  1. DSLR AstrophotograpHy…. My way

  2. My camera

  3. 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

  4. Creating a color digital image

  5. One shot color (Bayer Matrix) Filtered sensors convert photons to electrons which can be measured http://www.cambridgeincolour.com/tutorials/camera-sensors.htm

  6. Bryce Bayer (1929-2012) http://image-sensors-world.blogspot.com/2012/11/bruce-bayer-died.html

  7. How color is created Debayering the matrix… greyscale data converted to RGB image Each pixel contributes to the luminance image which gives detail http://www.cambridgeincolour.com/tutorials/camera-sensors.htm

  8. Processing after demosaIcing Irreversible processes best done on a computer and not in the camera http://www.cambridgeincolour.com/tutorials/raw-file-format.htm

  9. 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

  10. Why modify the canon sensor? Stock IR cut filter limits Ha response of sensor

  11. Modified camera is a must

  12. 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)

  13. Comparing Canon Cameras

  14. APS-C sensor (advanced photo system)

  15. 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

  16. Connecting to the telescope

  17. 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

  18. Backyard EOS focusing

  19. 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

  20. 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

  21. 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 • Deconvolutionof luminance PHOTOSHOP (CS5) • Use LRGB method (Adam Block) • Carboni’s Astronomy Tools, Gradient Xterminator, Noise Ninja, HLVG

  22. Monitor calibration • Important if others are looking at your images online • Spyder4 Express (~$100)

  23. Slides on website www.geoandpat.com

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