Re: [ATM] Banishing the diagonal

["Bob May" <bobmay@nethere.com>]

One of the things that you have to remember is that once you get below a
certain point (usually about 15% by diameter) the effects of the secondary
become rather irrelevant to the image quality at all.  This may mean that
you also accept a slight dimming of the image in wide field views as there
will be some vignetting of the image by the diagonal size but that is part
of the tradeoff that needs to be done with any scope.
Putting a barlow lens before the secondary will also limit the FOV of the
scope as the scope will immediately be one of a much longer FL and that
means that larger EPs are needed to obtain the same FOV as the original
scope would need.
The whole design of a scope is a weighing of the needs and desires and
accepting the limitations that such desires produce in the end.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net


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