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I made a stack with and without flats, without it it looks much better, with flats I have a very strong brightening especially on the right and at the bottom of the edge.
What could be the reason for this?
The flats are exposed for 0.5s and are also nicely centred in the histogram.
The lights are 20x300s with gain 101 on an Askar Apo with reducer at F3.9 and Antlia Dual Narrowband Filter...
Camera ASI 533MC
without flat
with flats
Histogram seems ok
thanks for your 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
4th screenshot is with neutralized Background
Thanks! I failed to notice that.
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.
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.
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?
@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.
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.
