Flat Problem... without Flat Result much better..? please help...

@brazzo229 Hi!

The histogram of the flats looks different from the 3rd to the 4th screenshot. What is the difference between them?

Also, I am sure that the answer is yes but the flats were shot with the filter as well, right? What other calibration data do you use?

Thanks, Wouter

@wvreeven  4th screenshot is with neutralized Background

yes the flats are shot with the filter as well 

Integration , Calibration etc. is automatic

I use 20 Bias Frames and Darks as well,

the integration is completely identical except for the flats

Posted by: @brazzo229

4th screenshot is with neutralized Background

Thanks! I failed to notice that.

Posted by: @brazzo229

The flats are exposed for 0.5s and are also nicely centred in the histogram. Camera ASI 533MC

The only thing that comes to mind is that 0.5 sec is very short for this camera. CMOS cameras like this one work better with flats of at least 1 sec because of the rolling shutter. This is an electronic way of mimicking a physical shutter and it takes a while to read out the sensor. During the read out, pixels that have not been read out yet keep on collecting light potentially leading to subtle illumination differences between the edges of the sensor. This could explain the red edge.

@wvreeven ok thanks, i will try a longer exposure

@wvreeven :

Now Flats with 3s exposure time... 

unfortunately no improvement

Just as a thought; it looks like the flat is overcorrecting the right-hand and bottom side. It could be that the way you take the lights doesn't fully represent the vignetting of your setup, sometimes caused by an extra light leak.

@vincent-mod

Hmm... I don't know where the light leak should come from, the camera etc. is screwed tight and the lights actually look normal.

Lightframe normal stretch

Lightframe over stretch

Doesn't seem to be the case in the lights indeed, it's just a thought. Could also be a calibration issue perhaps with the bias/darkflats. But when you take the flats, you have no other light sources around? Could you specify how exactly your setup is?

@vincent-mod 

the darks are not photographed with the filter maybe that is the reason ?

@brazzo229 Darks do not require light so it doesn't matter if the filter, or even the telescope, was installed. It is perfectly fine to take darks with the camera completely disconnected.

@wvreeven

i left out the darks and now it looks perfect...

I bought the camera used and the seller sent me the masterdarks, but apparently they don't fit somehow.

@brazzo229 That's great! So it is a matter of shooting new darks and creating a master dark from it and you're set.