Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 10/08/2020 - 16:18

Not sure if this post belings here or the Photometry forum.

Camera: ASI183 mono cooled, BVI filters. Scope: 80MM APO. CMOS experience level: Zero. CCD experience level: going on ten years.

Given lack of shutter and milisecond exposures, how do CMOS observers take flats? In my CCD world twilight flats are taken with 3 second exposures to deal with the shutter. Given the millsecond capabilities of these shutterless cameras I am wondering what the rules are for exposure time for flats and when it is appropriate to take them. I could imagine that the rules are quite different.  In addition, suppose you are taking sub-second flats, how do you calibrate them? With bias only, with darks of the same integration?

Thanks for the feedback,

Ed

Affiliation
American Association of Variable Star Observers (AAVSO)
Given lack of shutter and

Given lack of shutter and milisecond exposures, how do CMOS observers take flats?

I own an ASI183MM and I can take millisecond exposures.

Affiliation
American Association of Variable Star Observers (AAVSO)
Same here, ZWO ASI 178mm . ms

EDIT:

Ah sorry, after reading the original post, I think I got the question wrong the first time :-).

Yes, the rolling shutter allows CMOS cameras to work with shorter exposures for the flats because we don't need to worry about the shutter movement creating artefacts on the flats for short exposures. So yes I think sub-second exposures are the usual exposure times e.g. when using flat panels etc, unless working with very narrowband or UV filters (I take flats for each filter separately because...just to be on the safe side..that is another discussion)

Calibration: I do this with darks of the same duration and gain, but of course at sub-second exposures, darks and bias frames really kind of converge.

CS

HB