Astrophotography is a specialised type of photography that entails making photographs of astronomical objects in the night sky such as planets, stars, and deep sky objects such as star clusters and galaxies.
Astrophotography is used to reveal objects that 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.
Astrophotography poses challenges that are distinct from normal photography, because most subjects are usually quite faint, and are often small in angular size. Effective 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 and/or multiple exposures (often more than 20 per image).
- Tracking the subject to compensate for the rotation of the Earth during the exposure
- Gas hypersensitizing of emulsions to make them more sensitive (not common anymore)
- Use of filters to reduce background fogging due to light pollution of the night sky.
