I'm just making this post because I'm at a bit of a loss on how to process some data I've recently acquired.
My university was kind enough to let me use one of their telescopes to take some images on. I decided to shoot M 83 because with my own scope, there's no way I'd ever be able to capture this target.
There are two major issues I see with the university's scope though. The first is that it's on an alt-azi mount which isn't ideal, but I can't really change that. The other problem is that the camera (I assume is the cause) is creating this very strange gradient that is split into 4 different sections of the image. I've been able to calibrate out all the defective columns easily enough, but I have no idea how (if it's even possible) to get rid of this strange gradient. I've never really seen anything like it before and I was wondering if anyone here has had experience in dealing with anything similar.
Here's what one sub frame with the gradient looks like:
Here's what the integrated subframes look like:
And here's a precursory (starless) attempt at processing the image according to my normal work-flow:
I've tried to use dynamic background extraction with different parameters, Graxpert with different smoothing factors and Gradient Correction (with default settings because I'm not super familiar with this tool yet) but none of them get rid of the gradient. From what I can tell, Graxpert does the best job, but the gradient is still very evident.
Unfortunately, due to the nature of the telescope and how the university allows users access to their scopes, I can't take any calibration frames myself. All I can do is check a box that activates "automatic subframe calibration upon acquisition". I've been told that flats, biases and darks are subtracted from each subframe if this box is checked so theoretically, each subframe is already calibrated. I'm unconvinced of this given the results I see in the subs, but again, I don't have any control over this so I can only use what I've got.
The only solution I can think of myself is to frame the target such that it is only in one quadrant of the camera's sensor, then Graxpert or DBE might be able to work its magic, but that would require me to retake all my subs which I'm hoping to avoid!
Thanks for reading and if you have any suggestions, please let me know.
Kind regards and clear skies,
Evan
