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Question of size

Wed Jul 28, 2010 8:53 pm

Most or some magazine articles say that a 6" scope or larger will show a particular deep sky object well.

The problem however is this... is that 6" Refractor or 6" Reflector?
Is there a conversion to step down or up for Refractors as most articles seem to be based on reflector size. Or is it best to take as written the size regardless of telescope type?

Thank you

RE: Question of size

Wed Jul 28, 2010 9:26 pm

Best to take them as equal.
A 6 inch reflector will have the secondary in the way and that will take out 10-14% of the light so it could act more like a 5.5 - 5.6 inch.

However some state 6 inch effective diameter so that makes me think they may be a little over 6 inch to compensate for the secondary.

Equally I have read of refractors stopped down internally using the internal baffles to improve the aberations and these then act as smaller then the lens diameter.

RE: Question of size

Fri Aug 06, 2010 10:06 pm

Yes, I think that generally they are talking about catadioptrics or reflectors that have a secondary obstruction, although as uea74 says, the difference it makes is limited.

Bear in mind that refractors of 6" or over are fairly rare among amateurs, as they are mahooosive!
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