Question on flat frame calculation for OSC cameras

For some months now I have been having Voyager shoot dawn flats (Since I bought a new camera, an ASI2600 which allows the use of Bias frames to calibrate flats instead of dark-flat frames)

When shooting flats with an OSC, what value does Voyager use to calculate and compare to the target ADU? Is this the mean of the red/green/blue channels overall? If that is the case I should be able to determine a new ADU target based on having good red but poor green and blue response.

Voyager do not debayer data so there is no concept of color in flat in adu mean.

All the best

Thanks Leonardo, I should have though of that. So the “Mean” in flats is the mean of all pixels.

I should be able to simply reduce the requested mean ADU by something approaching 75% and get a good result with the red at something like my original target ADU and the two green and one blue of each RGGB “super pixel” reading dark current and whatever small amount of HA signal leaks through into the green and blue pixels.

Just some feedback, I reduced my target ADU form approx 40K to approx 12K and the flats come out very nicely with the HA filter in the train.

It was a bit of work to get it focusing as the un debayered data with “Holes” for the missing green and blue data making things tricky, but I got it going, it just takes a while to focus, and plate solving takes a lot longer as it requires at least 15 second exposures versus 3 seconds without the HA filter. But, last night was successful. An image before and after introducing the HA attached here.

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Dear Paul,

flat can be done in all the linear part of response of the camera, get it higher in ADU is possible is the best solution to get less noisy flat. This is if you dont have internal reflection to the flat light that adding in not linear way light to flat (mechanical parts , particular filters), in this case you must reduce the ADU mean to enter on the linear part also for the reflections added (usually this is true for fast instruments like in Takahashi Epsilon and some newton)

You must just check the color histogram no overtake or be lower than the linear part response of your sensor for each colors.

Very nice image !

All the best

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Shooting through both a HA filter and bayer matrix made it a little harder to work out. I had to find an overall mean value which resulted in the red pixels having a mean of approx 40K ADU (Out of 51K full well) which had the green and blue pixels having a mean of approx 3K ADU. That seems to work nicely.

I will be buying a mono camera in the future but being able to do this means I can spread the spend over a much longer time as I now know that I can buy a filter wheel and fit it along with NB filters and be able to use it successfully, I just can’t shoot LRGB and NB on the same night without some compromises, not until I buy a mono camera.

You got a very nice result, Blue! Congratulations.



Thanks, I am happy to see it works well as it extends the capabilities of the camera while I save up to go mono.