Re: [ATM] Field derotator or equatorial?

[Dale Eason <atmpob@yahoo.com>]

http://www.ghg.net/cshaw/14newt.htm


--- Paul Bradley <paul@paul-bradley.com> wrote:

> 
> 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
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


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