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Old 12-01-2010, 01:33 PM
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Garyh
Amongst the stars

Garyh is offline
 
Join Date: Jun 2006
Location: Glen Innes, N.S.W.
Posts: 2,839
Hi and welcome to IIS. Moving the primary doesn`t change focal length but brings the focal point further out of the OTA so your DSLR can achieve focus. I would forget eyepiece projection, barlows etc for Deepsky imaging, just use prime focus for this and if you want to, get a Baader MPCC, Your f/5 primary will show coma in the corners and the coma corrector will give you fairly round stars to the corners. The only thing with moving the primsry is that you shall have a slightly smaller field of illumination (vignetting like) but taking flats will fix this.
Hope that helps.
Gary
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