Strange artefact - help needed!

[Rowland]

If you haven't done so, weeding out the subs might improve things. I think Che is correct. Looks like a bump or some other mechanical interference.

[almcl]

It was guided but unfortunately there were problems with the DEC axis that night (since resolved) and those are actually the better subs. The bad ones were awful:

double stars.jpg (230.99 KiB) Viewed 2831 times

Ursa Major is getting a bit low, so next spring before I can get some more data