Doing science via photometry – Bias images

Forums Variable Stars A beginner…. Doing science via photometry – Bias images

Richard Miles

Glad you are looking to go one step further …

Can I just point out about the need (or not as the case might be) to take Bias frames. Professionals do this because lots of people use the same instrument and they all probably want to use different exposure times. For the amateur, I would recommend NOT taking Bias frames. After some investigation, I decided it was a pointless exercise. Better to take a series of Dark frames using the SAME EXPOSURE TIME as your Light frames. A good compromise for a standard exposure time is 60 seconds but that will depend on your mount’s tracking performance.

More important is the need to average a good number of Dark frames (and Flats) so that you achieve a satisfactory SNR. How much SNR you need in the Flatfield depends on what you are trying to target for observation. Say 20 frames of each are a good compromise. Also – Don’t forget to take the Flat-Darks with the same (short) exposure time as your Flat frames. HTH

P.S/ Nick James mentions Comet 29P – you might find you will have to sit on that target for say 30 minutes with your 6″ Cass. to build up enough SNR. Feel free to try.