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Re: 2" visual back for C8

Started by gjcarter, 09/23/2010 05:17AM
Posted 09/23/2010 05:17AM | Edited 09/23/2010 05:20AM Opening Post
There are two reasons to do this. The first is to allow the use of 2" diagonals and 2" eyepieces that will allow you to enjoy the wider AFOV available in the "wide field" class oculars. The second, and more important, is to securely hold these heavier eyepieces whilst permitting you to reposition them as you swing your mount into position.

There are several designs on the market. Some 2" diagonals will have the visual back integrated into the eyepiece. Parks makes one of these. It is a convenient method, however, the one I have does not include a compression ring to prevent marring of the eyepiece so I do not use it. It is the most convenient design - I just prefer a compression ring.

I've used Lumicon, Televue, and Astro Physics visual backs. Televue and Astro Physics are the better designs. The Astro Physics features a second screw (and a third screw on 11" and 14" models) to hold the diagonal firmly preventing rotation when the diagonal is positioned such that the weight of the heavier eyepiece it parallel to the ground (and thus, the force of gravity). I've had some close calls when the diagonal has rotated upside down when using my 20mm T2 or 31mm T5 when using single-screw and non-clamp ring visual backs. Steer clear of these designs altogether!

-Gary
    There is only one constant in our infinite universe; it is change.
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