DSLR_Astrophotograpy..

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

P
ROCESSING 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