QHY268m - strange ghosting artifact in recent data - Forums

Topic starter

Sep 7, 2023 · Edited: Sep 7, 2023

Hi,

hoping to get some feedback on this issue. I'v been on a forced break for a couple of months (clouds, short nights) and have just fired up the rig again. However, I am seeing a previously unseen issue in my data (HA, OIII and SII all show this, also in the raw images prior to calibration and stacking). There appears a vertical "ghosting" and I have no idea what this could be caused by. Any thoughts? I haven't changed my camera settings - and the only thing that is "different" right now is a pretty intense heat, and the camera is struggling to reach -10 because of it (usually not a problem in these parts).

Anyway, I am a bit lost and am hoping for some suggestions to hopefully fix this...

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Ben Koltenbah

Sep 7, 2023

Sorry to hear about your trouble, Marc.

This doesn't look like a light leak, actually more like a strange reflection, but checking for leaks should be a quick thing you could do just to rule it out.

What happens if you place the target off to the right or left? Does this artifact follow the target or remain down the middle?

Do you see this artifact in dark, flat, bias frames?

Does this only appear when the cooler is running at maximum? I try not to run my camera at maximum cooling, although I've had to do this on occasion. One of my few complaints about the 268M is that its cooling is weak. My 600M, however, is notably stronger.

Best Regards,
Ben

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Brian Clary

Sep 8, 2023

I had something similar to this happen last night and it turned out to be that my off axis guider pick-off was overlapping my sensor by a fraction. After adjusting the vertical band went away.

V/R

Brian

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Marc

Topic starter

Sep 8, 2023

Thanks for the feedback!

No OAG involved, so that probably isn't it. My best guess is that my USB connection is having issues, maybe due to the heat - or maybe the cable went bad over the summer. Will keep looking - but after talking to the tech support from the company where I bought the camera, there probably isn't one most-probable explanation - so I will just have to keep switching around cables; and re-install the QHY driver.

Marc

Topic starter

Sep 11, 2023

Hi, now to the solution of this mystery…

First of all, my eyes played a bit of a trick on me; the artifact does not appear in the raw images.

I turned out to be a problem introduced by Pixinsight, or rather the "linear defects correction" that was apparently switched on in my weighted batch preprocessing workflow. CMOS generally do not have linear defects so the algorithm instead decided to add some into my images… Switching it off complety fixed the problem.

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Ben Koltenbah

Sep 12, 2023

Ah, very good, Marc! Your original post threw me because you said the problem was in your raw frames. Glad you checked again and found the problem showed up during processing. The important thing is that you tracked it down!

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