Ok, so there's a few possibilities. Thanks everyone for your help here
I definitely didn't bump the mount, it's on a pier bolted down hard, the obs is a shed which I can close and lock, off which I can take the roof and observe. I set it to do 4 subs at 4200 seconds each, closed the door and went to sleep
- but that doesn't preclude an animal deciding to 'investigate' it and somehow crawl up the side of the shed, we get a few possums locally and that could have happened. It hasn't before, but it could!
I like the idea that it decided to focus on a hot pixel instead of the guide star, that sounds likely here. Other possibility I've thought of thanks to this thread
is that it might also have hit a slew limit imposed by the software near the end of the exposure. That would have the same effect as the gears binding - but I've had the mount for a year now and the gears haven't bound yet, it was a warm-ish night so I'm guessing (hoping, discounting entirely 'cause it's a Paramount MX and that would give me a lot of grief if they were binding
) that they didn't bind. I've used the scope since this and it still slews and tracks smoothly.
This was the last sub in the sequence, would have been around 3:00am-ish. The others are nice, clear, no star trails.
Correct, the field is not flat. I'm using a focal reducer to get a 'flatter' field than without, but it's a C9.25 SCT and those can be notorious for mirror flop and curved fields towards the outside of the picture. Normally I'll take some subs, process them and crop the outside because I prefer my eggs to be NOT on my deep space pictures.
