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Posted by Andy Kidd on August 17, 2002 03:33:58 UTC

i would probably allow for the 1" in and 1/2" out or split it 50/50 as you can always get [or make] a 2" extension tube if you run out of out travel?

If you're trying to get by w/ the smallest secondary you can my suggestion may not be applicable but i think a movement of 1/2" or so of where the focal plane sits would make less difference to the elliptical than the eyepiece [if, that is, you can't get your eyepiece in the right place. On the eyepieces i use it seems the difference between 'in-focus' and full O-O-F diffraction rings is only about 1 turn on my helical focuser or about 1/16" (going by the thread pitch) so if you can't get your eyepiece in (or out, for that matter) that last 1/16" you'll be S-O-O-L].

What you might want to try if you're concerned about exact placement for secondary 'efficiency' is make some kind of 'focuser board' assembly that wil allow you to 'tweak' the placement of your focuser during your final testing stages [provided your spider has some 'stick-out' range to it] so you can have the focuser placement 'optimized' for the eyepieces you'll be using with it. Just one of my hair-brained suggestions...

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