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Hello guys! I am relatively new to astrophotography so i still figuring out things. One of those things is flat frames. I’ve been struggling with flat frames and i could never make them work until recently, when through experimentation, i managed to do it. I made sure i have no light leaks in my system as this was an advice i was given at some point. The general advice everywhere i asked and everywhere i looked was that you should try to expose the flats, for a DSLR, around 2/3 or halfway through the histogram, and, for a dedicated astronomy camera, around 20000-30000 ADU. This never worked for me!! Through trial and error i settled at an ADU around 3500-4000. How can this be? Isn’t this too low? But yet it works! I may be doing something wrong but it works perfectly. And this is consistent with different cameras too! So my question is how could this be? How did everybody come up with those numbers? Does it work like this only for me? I use deepSkyStacker. Cant wait to hear your thoughts! |
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| I use (for the large newt) sky flats at fixed exposure so my flats' mean values tend to be very low indeed. I found no real difference and there shouldn't be any as long as you have a modicum of illumination in the corners, IOW the light drop off at the corners is less than 30% (in my experience). Having high mean values allow for lessened risk of numerical clipping of the deep shadows, much more pronounced if you were to use integer maths which I don't think is an issue nowadays. Too high and you are out in the potentially non-linear response range of the sensor and too low and there might variations in bias signal for some sensors as well as response discontinuity for some older sensor too. |
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| If it works, it works. |
