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Peter,
As a zero second exposure is not possible with SBIG cameras, I am puzzled as to why anyone would want to use them, as they are already contained in the dark frame data.
A bias frame is simply a zero second dark, hence if you take any dark frame it consists of: a zero-second dark + x-second dark.
Also the dark map in SBIG cameras, from what I understand, while superbly consistent, is not truly linear.
Hence best practice to to use a library of darks taken at temperature x, and exposure time T, that obviously need to match your lights.
I've found much more value in simply getting excellent quality flats (I prefer sky flats....in fact they were the only flats that consistently worked with a back-illuminated chip I was running some years back )
Playing with Bias frames can often induce a bunch of artefacts that simply aren't in the data. I personally never use them.
Cheers
Peter
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