[ATM] Field derotator or equatorial?

["Paul Bradley" <paul@paul-bradley.com>]

Hi all,

I know this might be a bit of a contentious question but can a field derotator really be made to work well
in the context of long exposure, prime focus photography with guiding?

I've been doing a lot of searching the net and reading on field derotators, and I can envisage a system using
either a single field derotator and an off-axis guider, or a separate guidescope and 2 derotators with a software
fix to allow inputting the alt/az offset of the guidescope to allow it's field to be properly derotated. 

I can see the first option being a bit tricky in terms of finding good guidestars in the field, does anyone here
who uses an off-axis guider find it a major problem, or am I worrying over nothing?

In the second case (2 field derotators) I can envisage problems in the sheer complexity of the system causing
guiding errors, with small errors in the offset measurement being blown up to unacceptable proportions in the
imaging scope. Has anyone tried this before?

I'd be most interested if anyone has any links to sites with work from people using field derotators as I've had a 
lot of trouble finding this on the web, and would like to get a better idea of the sort of results I could expect.

Thanks.

Paul
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