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

Filtered sensors convert photons to electrons which can be measured

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 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 unquided 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)