Quote:
Originally Posted by Hagar
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.
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What do you mean by "better results", if you have vignetting, then the flats should show this, so that it can help fix it in the light exposure. The more vignetting, dust motes etc showing in the flat the better, its supposed to image the faults. The worse flats you can get is a uniform grey with no imperfections, thats useless, waste of iime, and of no "correction" value at all.