Quote:
Originally Posted by gregbradley
I am finding these CMOS sensors a lot harder to calibrate than CCD cameras.
What have you found as a workable approach to calibrating your CMOS images?
Greg.
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Hi Greg, I have the ASI2600 mono and ASI6200 mono. The main point that I would offer is to
not use bias frames when calibrating CMOS sensors. Bias signal with CCD cameras is linear and repeatable but not so with CMOS. Simply take darks of the same exposure length and temperature as the light frames for dark frame calibration (i.e. do not scale/optimise darks to match lights). For flat frame calibration, use flat darks i.e. darks frames with the same exposure time and temperature as the flat frames. That should do the job nicely.
One other point that I would like to throw out there is that I have seen a few forum posts crop up that posit that CMOS sensors can go for longer periods between times when re taking calibration frames such as darks and flats. I found this a little surprising so tried to track down source material that confirmed this. I was unable to find any technical documentation that supported this view and, to the country, found source information that confirmed that CMOS sensors are the same as CCDs in needing to retake calibration frames regularly. In my case I will redo my calibration frames every three to four months, the same as I have been doing with my QSI683 CCD.
Below are links to sources on the SBIG site that talk to CMOS calibration requirements. The first is a paper by Doug Georg, lead engineer at SBIG, that discusses CMOS calibration technicalities. The second link is to a forum discussion where a discussion ensued regarding the length of time between calibration frames. This was in the context of the SBIG Aluma 4040 CMOS camera. These are worth a read as they talk to the issue of bias stability and managing calibration data.
https://forum.diffractionlimited.com...ay-valid.9550/
https://diffractionlimited.com/calibrating-cmos-images/
Clear skies,
Rodney