Camera rotators for alt/az mounts

[Sammyb]

Hello - I saw one of these on the Modern Astronomy site and wondered if anyone had any thoughts on using them for correcting field rotation on long exposures with alt/az mounts?

Do they work? Would it be possible to get reasonable results?

Sam

[andrewluck]

Our society's 20" is on an Alt/Az mount and we also auto-guide it with an old STV. The issue you get is that once you turn on the auto-guider the centre of rotation switches from the centre of the main field to the guide star. This renders a field rotator useless unless you using a separate rotator on the guide camera or an OAG. OAGs are problematic on a newtonian scope as you've generally only got limited back focus available.

I've some pictures taken with it (most recent were NGC 6888 and M42) on my blog http://blog.andrewluck.me.uk and if you follow the link from there to 'Far away things' you'll find some more images taken with it.

[ollypenrice]

This is a professionals' arrangement and carefully thought through. Nobody that I've ever come across has used the system in amateur imaging. It's possible that one day it might become available in a coherent package but for now I'd stick to a GEM and autoguider. WIth direct drive, unguided, and a complex model of the sky then a field derotated alt az can work. When your multi-tonne pro scope is too big for a GEM and really cries out for alt az then it's worth it. My neighbour Marc has a derotated alt az in his observatory. Erm... six million euros. Lottery ticket, anyone?

Olly