User:JohnOwens/Pet Projects/astrophotography

Astrophotography is a specialised type of photography that entails taking photographs of items in the night sky such as planets, stars, and deep sky objects. Astrophotography is used to reveal objects which are too faint to observe with the naked eye, as both film and digital cameras can accumulate and sum photons over long periods of time.

Professional astrophotography
Astrophotography poses challenges which are distinct from normal photography in that the subject is usually extremely faint, and often small in angular size. Effective professional astrophotography requires the use of many of the following techniques:
 * Mounting the camera at the focal point of a large telescope
 * Emulsions designed for low light sensitivity
 * Very long exposure times (one hour or more is common)
 * Tracking the subject to compensate for the rotation of the Earth during the exposure
 * Gas hypersensitizing of emulsions
 * Use of filters to reduce background fogging due to light pollution of the night sky.

Since the early 1990s, most professional observatories switched to using CCD devices for astronomical imaging. They have numerous advantages, with increased sensitivity and more linear response. The principle disadvantage is a significant reduction in the field of view. CCDs require specific modifications for best effect in the low light conditions of astronomy, such as:
 * cryogenic cooling to reduce thermal noise
 * compensation for non-uniform pixel sensitivity
 * biasing

Amateur astrophotography
Emulsion based astrophotography remains popular with amateur astronomers, but even here CCD imaging is becoming relatively cheap and is starting to replace wet photography.



Main types of differences

 * altazimuth mount vs. equatorial mount w/ drive
 * digital camera vs. photographic film camera or photographic plate
 * single-lens reflex camera vs. integrated lens

Equatorial mount
Ideal for long exposures.

Altazimuth mount
Includes camera mounted directly to tripod, with no telescope/binoculars involved. Can be used for long exposures, with a GOTO and a rotating erector prism. Also useful for short exposures (typically <10s) or star trail images.

Single images
Taking one image with a long exposure time.

Compound ("stacked") images
Taking many images and "stacking" them together to create a single brighter, clearer (hopefully) image.

Film or plate
Single image only.

SLR
Afocal with lens and eyepiece, or focal with neither lens nor eyepiece.

Focal field of view/angle of view:
 * Approximate: $$\alpha = {d \over f} \times {180 \over \pi} \equiv {180 d \over \pi f}$$
 * Precise: $$\alpha = 2 \arctan {d \over 2 f}$$

Integrated lens
Afocal with eyepiece only.

Specialized astrophotography camera
You got an instruction book with that, didn't you? What are you looking here for?

Software

 * IRAF

Software

 * Microsoft Windows
 * Registax
 * Un*x/Linux
 * GCX
 * SImg
 * AstroMosaic (in French)
 * BabelFish translation
 * AstroMosaicGUI
 * ESO-MIDAS
 * IRAF
 * Linux Astronomy CCD Imaging
 * Apple Macintosh
 * Lynkeos

Category:Astronomy Category:Astrophotography Category:Photography by genre