AC4040 - Rectangular gradients

I am getting rectangular gradients appearing in different locations depending on filter selected. s this a filter defect?

 

Here is the fits file.

 

Doug, Here are a couple of files pre processing.

 

Doug,
The vertical structure in the center is coming from the dark current. I believe the structures to the top and the sides are coming from the filters since if you rotate the filter they move by the corresponding amount.

 

Yes through the telescope. I have a electroluminescent panel for my flat frames. The pictures I am taking have the same issues unless I take a picture with the filter empty. I bought all this equipment from you guys in December 2o21. Not managed to get an image yet. I have read lots of info on CMOS chips. I have the IMX571 Back-Illuminated CMOS chip on another camera which is awesome but seem to be hitting a brick wall with this new AC4040 on the calibration frames. I really need some help.Here is a dark frame and you can see that it has that vertical line up the middle which is in the frames I sent you earlier.

 

Doug,

Thanks. Should the target be the same regardless of binning?

 

I'm having a similar problem. I've taken a large series of 120s images of M57 in StackPro. I've then got a series of 120s darks in StackPro. We have a panel Neil (though a very large one for the 32" we operate). I took 15 flats, 2s each in low gain mode and then a big round of 100 2s darks (also in low gain). Calibrating through and stacking that square pattern is still present in the final image (in single calibrated images it's almost undetectable but in stacks it obvious). I used both Maxim DL and Pixinsight for the calibration and came to the same result. I'm unsure where the problem is...

 

I was trying to eliminate variables and was mostly testing the red filter (filter was purchased from you). I can confirm whether the effect is there in blue and green.

 

I can confirm that is it there in Blue and Green as well. They were the same exposure (120s) and flatted with their own flats (also 2s)

 

I eventually got to the problem issue. I had purchased the filters from diffraction and there was a coating problem with the filters. I purchased chroma filters and the problem went away.

 

Hi, I have a less obvious middle line in my master flats too, and the obvious quadrant pattern in my darks, but I'm not seeing it in the master light frames after calibration. I've assumed that the issue in the flats and the quadrant pattern in the dark are inherent in the CMOS chip, and as Doug said is part of the reason we do calibration of light frames. The only time I see anything like that in my calibrated light frames is when I've taken a light frame at too short an exposure for the target. In that case, the SNR in the light frame is so low that the artifacts don't calibrate out perfectly. I see this if I take a too short exposure in High mode or using a too short subexposure time in HSP (for example a 1 minute HSP image with 2-4 sec subexposures). I don't see it when, for example, I take a 1 minute HSP with 30 sec subexposures. The issue might appear even with 30 sec HSP subexposures too if the target if faint, but if you think about what subexposure time makes sense for a target with a particular signal strength, I think the issue can be managed. To me, this is just part of the learning curve with the CMOS chips. I'm so burned in (no pun intended) on CCDs that it has been an interesting journey.

I hope this is of some help.

Best,
Mark