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Ok, just wondering, I don't see gain 0 a lot. But things like the offset I didn't see in the header, what did you set that at?
Gain is 0 and offset 50
Ok thanks for checking, that all seems fine. I'll continue investigating as well.
So indeed, seeing the same. I think it must be lying in the way the flats are shot. Over-correction usually is caused by a difference between how the light enters the setup normally and when the flats setup is used. Like Wouter also mentions, it may also be worth it to shoot at a higher ADU.
Thanks Vincent, ok i will try higger adu.
Hi Marc @marc68,
I am investigating your data.
Regarding the Lum data that you uploaded:
After data calibration I see the same, the vignetting profile is overcorrected in the corners. It seems that the gain and sensor offset are all okay and the same for the lights and the bias, darks and flats.
So I had a good luck at the actual calibration data and I see several issues which can and probably will explain why calibration is not working optimally 😉
First have a look at the bias and darks, this is a single dark frame where I set the Black slider to zero to see if the sensor offset is set high enough :
Clearly it isn't because the histogram is clipping on the left side. The Same holds for your bias frames. So that needs to be fixed and can easily be done by using a higher sensor offset using your camera's driver.
Now if I look at your Luminance flats, I see immediate problems I think, the vignetting profile is not uniform from center to the corners, it has ripples in it and that will never be okay I would expect.
So.. probably you will need to change/improve the way in which you make your flats for this setup. But first try to fix the sensor offset and check if things have improved 😉 already.
Will check your green data as well now.
Hi Marc @marc68,
Just had a look at the green flats. I see the same issue as with your lum flats, they show ripples in the vignetting profile and that needs to be solved/fixed. You expect a smooth illumination profile in the flats from the center to the corners without those ripples superimposed on it.
Hi Mabula, thanks a lot for having looked into this. Got your points and will apply. I was not sure about those "circles" in my flats, i guess this is what you name ripples. I will try to find out why my alnitak flip flat device does produce this and also increase offset.
Just to confirm something, your flats were shot at 0 gain as well? I recently had a very similar issue with my ASI2600, flats shot carefully at 100 gain (Sky flats and with a panel) looked fine and the master flat looked fine but it over corrected the corners. I reshot really rough flats at 0 gain by just guessing exposure times as the sky darkened and they corrected really nicely, so I reshot proper sky flats at 0 gain. The illumination is quite flat to begin with and all I can think of is that the 5ADC/e of 100 gain (About the same as your 6200) introduced too much quantisation uncertainty for the flats to work well.
I didn't do that until after I spent quite some time looking for light leaks of course!
Hi, yes gain 0 and offset 50 for all flats. I will try the points from mabula, what i dont yet get i where those ripples on my flats are coming from. Need to check my setup. Thanks