[Shiraz (Ray)]

Probably time to summarise.

The following steps should deal with practical issues that have been raised. It assumes that the acquisition software allows you to sample pixel values under or near the cursor during acquisition. If you can think of any way to simplify/enhance this process, please chime in.


1. Take a short dark sub with your camera in whatever mode you normally use for acquisition. Using your acquisition software, move the cursor to sample the ADU levels at a few points around the centre of the image - estimate the average signal. This is "Bias" in the calculations.

2. Obtain the Read Noise (electrons RMS) and gain (electrons/ADU) data for your camera, either from the manufacturer's data or by measuring.
Calculate the target ADU using:

targetADU = Bias + 10*RN*RN/gain

You only need to do this once for your camera - remember the number, it's all you need to know.

3. From now on, when imaging with the calibrated camera, sample a few background sky regions (in a sub) with your acquisition software and adjust your sub exposure times so that the average background sky ADU levels are fairly close to the targetADU. You use the same targetADU for any scope, filter or sky conditions.

That's all you need to do.

If you use your camera in a binned mode, you will need to use the Bias, RN and gain data for the binned mode in the calculation (as you would for the online calculators). The targetADU for binned mode will be different from that for 1x1.