SKILLS FOR STARGAZERS

Get the best from your astro camera

- Peter Jenkins

How to optimise your CCD or CMOS settings for great imaging results

CD and CMOS astrophotography cameras have been on the market for many years and allow amateur astrophotographers to produce stunning image results. But to get the best from your astro camera, you need to really understand and master its settings.

If you've just bought one or you've had one for a while but you're not getting the results you hoped for, it's time to learn all about it - and learn from examples of good (and bad!) imaging results. We'll run through how to judge your settings both during and after a 'first light' session. Much can also be learned in post-processing, meaning you can tweak settings on the next clear night.

There are four main settings to focus on: exposure, binning, gain and offset. Exposure is how long (in seconds) each frame is. Finding your camera's ideal exposure length depends upon many factors, including device sensitivity, sky conditions, light pollution and your astronomy target. Longer exposures can lead to more signal and detail, but also introduce noise. This could be system noise (created by the electronics) or shot noise. While system noise is reduced by taking calibration frames, shot noise can be reduced by taking multiple frames to stack together later. A careful examination of the histogram curve in your capture software will show if an exposure is too long or short. If the curve is fully towards the left axis, shadow detail may be lost in post-processing, whereas a curve that extends to the right will clip highlights, leading to blown-out areas.

Binning, gain and offset