Astrophotography

This page explains what astrophotography is, a beginners guide to astrophotography is located here.

When the photographic plate was invented the astronomers at the time quickly realized it's potential. Instead of manually drawing the appearance of an object, they could capture it photographically thus removing any bias from the astronomer. This enabled astronomers to scientifically present their findings.

Amateur astronomers quickly followed, and with the invention of the CCD/CMOS sensor it's now relatively easy to take photo's of the night sky with quality similar to that of professional observatories only 30 years ago.

Deep Space Objects
Most of the popular nebulae are quite big in the night sky and don't require a lot of magnification. In fact, there are quite a few that are bigger than the full moon howevever they are very faint and the camera needs to be exposed for long periods of time to reveal them. Depending on the telescope and the object, this can be anything from 30 seconds to 1 hour. Because of earth's rotation the stars appear to move along with any faint nebula and the like, which means that the mount has to precisely track the movement of the sky. Often the mount itself is not sufficiently accurate and a secondary camera is used to observe the motion of a star and sends small corrections to the mount to prevent the target from shifting in the field of view while an exposure is taking place.



Signal and noise
In a single exposure a faint nebula will often be swamped by noise created by the camera itself. This noise is purely random yet the stars and any nebula are constant which means that multiple exposures are combined to smooth out the noise. The more exposures that are combined the smoother the noise will be and thus the more detail you will be able to see. Another way of revealing faint details is to increase the signal. This is done by increasing the exposure time of each individual exposure. In other words, the longer the telescope is gathering light the more detail will be visible.

Our own solar system
Unlike nebula the planets in our own solar system are much smaller in the night sky and are also much brighter. This allows the astrophotographer to take very short exposures of 1/15th of a second or less depending on the object and distance to it (see List of Oppositions). This will have the effect of 'freezing' the blurring effects of the atmosphere (seeing) and makes it possible to capture an image during brief moments when the atmosphere is calm. Programs such as RegiStax are then used to automatically sort these exposures and discard the ones where the atmosphere has distorted and blurred the image. It is then possible to combine the sharp exposures together to reduce the noise (just like with faint nebula as explained above) and allowing some sharpening to be applied.