calibrating flats with bias only

[herman]

My flats are usually around 5 seconds and I do not make 5-second dark-frames.  Instead, I want to just use bias frames to calibrate the flats.  I first use the BatchPreprocessing Script to create master dark, bias, and flats and I do not have any lights loaded into it... i.e. this step is just to get master darks, bias, and flats created.  My darks are 900-seconds (because my lights are 900-seconds).   Will the script attempt to use the 900-second master-dark that gets created early in the process to subsequently calibrate the flats?  I hope not since that would be a massive scaling of the dark given it's 900-seconds and the flats are 5-seconds? i.e. is the script smart enough to know I do not have matching darks for the flats and to just use the bias instead?

The reason I ask is I noticed different results in the master-flat that gets created when I have "optimize dark frames" checked.  If I don't have it checked I noticed many dark pixels in my master-flat.  If I check it, there are very few dark pixels.  i.e. it almost seems like "optimize dark frames" is telling the script to not use the 900-second dark-frame for the 5-second flats.  I don't think the script should attempt to use the dark-frame regardless of this setting since it clearly doesn't match the flats.

Thanks in advance for any insights.

[pfile]

i don't think calibrating flats with bias frames is supported by the script. if it is supported, it's news to me... this is basically the reason why i never use BPP.

hopefully i'm wrong about this.

rob

[Carlos Milovic]

I should read the code... but my impression is that BPP is using the bias frames for the flat.

[Geoff]

The BPP script will use any darks it can find and will scale them accordingly.  If you don't want to use darks in your flats, the easy workaround is to just enter bias frames and flat frames in the BPP script.  There will be warnings about no lights and darks, but they are only warnings and BPP will happily generate a master bias and master flats calibrated only with the master bias frame, all of which you can use in subsequent runs of the BPP script.