Bizarre exposure problem


sorry for 3rd post. This one is ‘interesting’. In my last post I described my exposure run of NGC281 pacman neb. The mount went to the west side and all went fine for 20 mins until the mount hit the west limit. However, the 4x 5 minutes exposures which were downloaded were reversed left to right and also up/ down.

I found this out when I tried to align and combine the images in Nebulosity 3. It’s the right area of sky no doubt, but the images are reversed both ways. Nebulosity facilitates left right flip and up down flip, so I did that and thought it would be fine. I inspected the images and they seemed to be the same as the remainder of the Reds (I took 4 on West side of mount and 9 on east when I restarted a bit later).

When I aligned them and stretched it was a real mess - difficult to describe, but made you feel dizzy to look at it!!!.

So I scrapped the 4 exposures and used the other 9. I have never seen this or anything like it before. Any ideas? I’m stuck - there were no setting changes at all - everything the same.

It’s an sBIg stt8300 cam with SG filter wheel.

I just hope it doesn’t happen again as obviously it has taken up precious imaging time. Here in the U.K. , I get so few cloudless nights I was out imaging NGC281 on Christmas night…

thanks for any thoughts,


ok to try to help my embarrassment, i have made my own reply, it’s what happens when the mount meridian flips…
however, I still don’t understand why the images were unusable after I flipped them. If I can find out, I’ll post that too.


You should only need to rotate them 180 degrees after the meridian flip. Also it’s likely that the stack wasn’t put together correctly or you may have a couple of bad images with trails that are adding to the “double vision” issue.

I’ve never used Nebulosity for processing so I can’t really commend on the stacking algorithms there. You may give Deep Sky Stacker a shot as I’m fairly certain it can handle the rotation without you needing to do anything.

If all else fails you can upload all of your raw FITs some place and I can take a look.



Most image registration programs such as DSS or PI will auto-flip the images to match when you register them. As I understand Nebulosity (and I never used it much), it’s more of a manual registration thing… just click the stars correctly (2 star?) and it should rotate them to match right?

And, like Jared said, remove the bad ones.