Has anyone seen this effect

[Tom OD]

This is pretty odd. My first thought was a filter wheel had not rotated fully, blocking some of the chip, mainly due to the different amount of the dark band from the initial pic to the Rosette one. I have not seen anything like this on any set up I have used, but it sure looks like a physical obstruction rather than a camera effect. Is the mount flipping between the objects where it comes and goes? Like what Carol is saying, is gravity shifting something?

Tom

 

[JSeaman]

No filter wheel, it is just a QHY8L

Both Rosette and Leo were done with the scope on the same side but there was no problem on Leo (only 40 mins)...

 

[philherbert]

I'm no expert, but could it be a very slight gap allowing light to leak into the OTA somewhere when in a particular orientation, perhaps in line with nearby lights? The fact that you can apparently see stars in the background is also odd - are they the right stars in the right location (can you compare to any previous subs of the same target)? Be worth checking that everything is tightly coupled.

[JSeaman]

I thought exactly that, it was the first thing I checked but no sign of a gap

The forecast doesn't look good for following up on this any time soon!