Amp glow location changes w number of stacks?

[vineyard]

Hello,

Hope everyone is safe & well.  I've started playing with some lights I took on Sat night, and noticed something weird.  I spent a good two hours on M81.  Attached below are 2 JPEGs.  I haven't done any processing other than stacking in DSS and then doing ABE in PI.  One image (where the amp glow is top right hand corner) is 10 lights stacked w darks, flats & biases.  The other image (where the amp glow is bottom left hand corner) is 55 lights stacked w the same darks, flats & biases.

Why does the direction of the apparent amp glow change depending on how many lights are used?  When I look at the darks & the individual lights, the amp glow is in the top right hand corner w nothing like that in the bottom left hand.  So how come something is being subtracted from the bottom left hand if more lights are stacked?  (With more lights stacked, the amp glow form the top right hand goes which would make sense since the darks are subtracted but how come something weird is happening on the bottom left hand too?).

Thank you for any insights!

Vin

 

[andrew s]

Was a meridian flip involved? It's the only thing I can think of.

Regards Andrew 

[vineyard]

Hmm, interesting idea Andrew.  I can't remember for sure but I think there was one. And yes I guess depending on how the camera orientation to M81 changed, the top right hand corner of the chip would be move to a different orientation to the galaxy.  Maybe I need to find the pre- & post- flip images and stack them separately.  Now, to figure out how to find out which were pre- and post- flip FITS!  Cheers, Vin 

[andrew s]

@vineyard the images should have a time stamp and a planetarium program will tell you when it transits. 

Regards Andrew 

[vineyard]

Thanks Andrew.  I was playing with the Blink function in PI and that's great b/c it shows the flip happening - and it was exactly after the 10th light!  Will try stacking in two batches and then try combining the two images.  Cheers again - you called it spot on, Vin