Quote:
Originally Posted by multiweb
Hi Doug when you say 65ke I assume you mean 65k ADU right? My understanding is that a third of the full well is recommended, the full well being the value at which the camera sensor is starting to have a non linear response which in my QHY8 appears around 45kADU. In practice I shoot flats at 9~10kADU on the brightest pixels of the bayer matrix which with my EL sheet ends up in the red pixels. I tried higher values but anything over 10kADU is giving me reverse vignetting no matter how I scale/normalise to my lights.
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Hi Marc, Thanks for the reply. I also use an EL sheet which has made taking flats a bit easier but my results have been mixed.
I had always done my Flats at about the 9000 to 12000 range and had some very mixed results. Sometimes good, sometimes bad. With the RC having such a long imaging train it does suffer quite a lot from Vignetting and the old settings just didn't cut the mustard on this image. Using a max of 22000 produced much better results. I actually way oversaturaded the original image without flat calibration which showed up the problem areas quite graphically. I then re-did the image after calibration and again way oversaturated the image to find the 22k flats had really carried out the desired job.
I tried this at 7000, 9000,12000,15000 and 22000 and was surprised by the results. The 22000 calibration was well out in front. I will try this on some other targets when the sky clears and I can get some other images. The only scope I can use this test method on is the RC as the FSQ has a much larger image circle and doesn't suffer from any vignetting with the QHY8 CCD.
Just my ramblings of course but I thought it was worth sharing. Others may have experienced the same unreliable application of flats that I have in the past.