Mon, 01/09/2023 - 03:09
A question for well-experienced CMOS photometrists:
How long do you find that CMOS dark frames (dark masters) remain valid for photometry? (I'm probably most interested in the 4040 chip.)
With CCD, we've been accustomed to needing to take darks only every few weeks or months, so taking darks never used very much scope time per year.
But is the same true of CMOS darks? How long do they last? How often do you take darks? (If the requirement is "every night", then I can never buy a CMOS camera, leaving my photometry future in serious doubt.)
On their own forum, senior staff at SBIG report that their newer CMOS cameras have settings tuned so that new darks are only needed every few weeks or months, which is similar to CCD practices. Good to know. Thought I would pass that along here, in case others have the same question.
It's not clear to me how broadly their advice can be extended to other cameras, but at least the situation isn't nearly as hopeless as nightly darks would be. With less expensive cameras, and certainly when used for photometry rather than guiding etc, I would surely rely on my own experiments to judge how long dark frames stay valid (unfortunately that advice is pretty useless to those considering buying a CMOS camera model without already owning it, which is why I was compelled to post).
I guess my question might be how ambient temperatures (of the electronics, not the detector) affect the darks, winter versus summer, say. The obvious test is to use some daytimes to take the necessary frames.