Re: NGC 7000 with CMOS camera

Robert Chozick <rchozick@...>

The problem is that you cannot use bias on a CMOS camera.  Any exposure less than 3 seconds is not advisable (not an engineer so not sure why).  So if you cannot use a bias frame on your flats you have to use flat darks.

On my CCD camera I took flats that were less than 1 second and used bias to subtract.  I think all of these quirks of a CMOS have to be observed to get good calibration.

On Aug 24, 2019, at 8:09 PM, Mike Dodd mike@... [ap-gto] <ap-gto@...> wrote:

On 8/24/2019 8:47 PM, Robert Chozick rchozick@... [ap-gto] wrote:

> ...make my exposures for flats at least 3-4 seconds
> and take flat darks.

I don't bother with darks for flats. The noise is small compared to a 
flat ADU of 20,000-40,000, so why subtract tiny noise from a very bright 

PixInsight measures pixel brightness from 0 to 1. I just measured a flat 
frame and found an average level of 0.32. A dark used for this 
particular image measured 0.01. So the dark's noise is 3% of the flat's 

(I could/should increase my flat's level to 0.5 or 0.6. I'm still 
gaining experience with dusk flats.)

--- Mike

Robert Chozick

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