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Old 20-08-2015, 02:59 PM
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rustigsmed (Russell)
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Location: Mornington Peninsula, Australia
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Originally Posted by glend View Post
Why not use the 2" GSO ED Barlow which is 2x but customised based on extension used. The Baader MPCC MkIi will fit inside the extension ahead of the barlow. Low cost option if you have the coma corrector which already has the right spacing for the Canon.
Originally Posted by Shiraz View Post
if you haven't already come across it, this gives a good summary of the various types of Barlows and some of the things that you could consider when using them.

re quality etc, the GSO 2" that Glen mentions is worth a look - mine is almost as good all round as the much more expensive TV Big Barlow.

Powermates are just another Barlow, but they have extra lenses to turn them in telecentric systems - for your application, that means no extra field curvature. That might be worth having if you can find a way to control coma.
thanks guys,

Ray, I guess good flats would take care of the curvature?
if I was going a low cost option then going a barlow with a cc could work. but would that be

Camera - OAG - MPCC - barlow


Camera - OAG - barlow - RCCi

not knowing the connections is makes it harder to visualise. Glen did you mean the GSO would connect after the coma corrector or before?

I would have thought it be better to 'correct' for some reason I would have thought the second option be more likely to deal with the coma correctly?

If it were in my f5 scope I don't think i'd worry too much f4 might require some fairly severe cropping.

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