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Old 27-02-2008, 10:14 AM
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Garyh
Amongst the stars

Garyh is offline
 
Join Date: Jun 2006
Location: Glen Innes, N.S.W.
Posts: 2,847
Quote:
Originally Posted by ghsmith45 View Post
If you are imaging stars, focal ratio theoretically makes no difference and in practice makes hardly any difference, so for things like the jewel box, use any method you find good to increase the focal length. It is only for imaging extended objects--nebulae, galaxies, planets etc that you need to worry about focal ratio.
Geoff
Exactly right!
You will find little difference in the stars recorded even with a 2x extender but diffuse objects, the all important focal ratio makes a difference. The faster the better I reckon! Also remember the seeing and focus and guiding all have to be spot on to appreciate the extra scale.
If you are after a convertor go for a genuine canon one as the cheap ones arn`t very good showing coma and CA in the corners. Mine cost close to $200 and is rubbish for astro work.
cheers Gary
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