1. Intro to CCD Imaging Joe Roberts www.RocketRoberts.com
Astro Photography 101
Intro to CCD Imaging
Joe Roberts

2. Astro Photography 101
Astrophotography has never been easier (but it is still not “easy”)
The challenge: Trying to photograph something (often at significant magnification) that is very dim and moving while using an imperfect detector
No such thing as “point and shoot” for deep sky objects
Equipment can be costly
Figure ~ $1500 in equipment for entry level deep sky work!

3. Astro Photography 101
Basic Requirements to get started (for deep sky work):
Telescope (preferably on equatorial mount) with tracking drive
Bigger scope is not always better!
CCD Camera (entry level imagers start around $300)
Computer (laptop is probably best) for controlling the camera
Software (Maxim DL is common for controlling cameras, PhotoShop good for post processing)

4. Astro Photography 101 What Scope is Best for Imaging?
It depends on what object you want to image!
Many famous deep sky objects are far too large to fit in the field of entry level imagers
For starting out, most any scope will work, however shorter focal length (<800mm) and faster focal ratios (<F7) will make things easier!
Smaller focal length = less tracking accuracy needed
Faster focal ratio = Shorter duration exposures

5. Astro Photography 101 The most difficult parts of astrophotography:
Tracking accuracy
Focus
Tracking errors and bad focus cannot be fixed by image processing!
If errors are not too terrible an image with bad focus and/or bad tracking can be made “acceptable” by reducing the image scale

6. Astro Photography 101
Tracking accuracy requirements go up as focal length increases
My Losmandy G-11 mount was limited to exposures of around 60 seconds at a focal length of 665mm!
Still had to toss many of them...
For your first images, start out with a shorter focal length if possible!

7. Astro Photography 101
Focus is typically accomplished by maximizing star brightness on camera control software display
Focusing can be tricky due to atmospheric turbulence
Bahtinov Mask can be a big help!

8. Astro Photography 101 Focus will drift as ambient temperature changes!
SCTs and MAKs are especially prone to focus drift
Scopes with carbon fiber tubes reportedly less prone to focus drift
Check focus periodically during your session if there are temperature changes!

9. Astro Photography 101 “Nice to Have” items:
Flip Mirror or guide scope: this will allow you to precisely center your subject without the need to swap the camera out with an eyepiece
Motorized fine focuser: will eliminate “jumping” of star while adjusting focus
Bahtinov mask (can make them from templates available on line)
Autoguider: greatly simplifies guiding!!

10. Astro Photography 101 CCD Advantages:
No reciprocity failure (2x exposure = 2x the light, unlike film)!
Much larger dynamic range (ability to simultaneously record both light and dark extremes)
Linear response (compared to film)
No chemicals to deal with
CCDs also have undesirable characteristics, however most of these can be largely eliminated by use of special processing techniques!

11. Astro Photography 101 CCD Basics:
All CCD imagers generate a certain amount of unwanted “noise”
Noise is the signal that results even when the CCD is exposed to total darkness
Noise can be greatly reduce by use of techniques called “stacking” and “calibration”
Noise reduction is possible because the noise from frame to frame is random whereas the light from the image is constant

12. Astro Photography 101 CCD Basics:
Other artifacts (vignetting, dust spots) can be largely eliminated by use of “flat frames”
Flat frame is an exposure of an evenly lit subject (twilight sky, white poster board, etc)

13. Astro Photography 101
Basic Steps for monochrome or single shot color CCD Imaging:
1. Set up scope, acquire good focus (use a star near your desired subject), then center desired object in the imager's field of view
2. Take “light” frames
3. Take “dark” frames
4. Take “flat frames” (optional for starting out)

14. Astro Photography 101 6. Process the raw data:
5. Take “dark frames” for flat frames (optional for starting out)
6. Process the raw data:
First, combine dark frames
Next, calibrate light frames with dark frame composite
Calibrate with flat frames (if desired, not necessary for your first shots)!
“Stack” calibrated frames to obtain final image
Adjust image to bring out detail
Do post processing in PhotoShop if desired

15. Go to web pages
CCD Imaging Fundamentals
Showpiece Image Gallery