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Sorry Leon, my flats comment maybe unjustified. Its just that when I looked over your data I noticed what appeared to be a centered radial gradient. I've attached a diagonal line profile which shows the histogram increase. This could simply be wispy nebulosity, but I have not seen this before. If there is a calibration process that is going to cause you grief - it will be with your flats!
The FSQ-ED with its large flat wide field doesn't have a huge light drop off in the corners. Tests performed by Don Goldman with the KAF16803 (16mp) chip showed a very minor drop off of 2,500 ADU (22,000 ADU at center and 19,500 ADU in the corners) - impressive. Flats are still required though (for obvious reasons).
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