Quote:
Originally Posted by Stardrifter_WA
Good question Glen.
I too am confused by this offset on fast newts, which is probably why I have so much trouble collimating my 16" f/5.
How is this offset determined and why?
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Peter ,
The offset is really there on fast scopes to keep the illumination field nicely centered on the axis with a minimum size diagonal . If you have a large enough secondary you do not need to offset but you may waste a bit of light through having a slightly larger than necessary secondary.
At the end of the day if you have adequate size secondary and the secondary is catching all the on - axis light ( ie your extra focal star image is looking round inside focus and not clipped , having offset or not will not effect your ability to collimate .
This article will tell you everything you ever wanted to know !
http://web.telia.com/~u41105032/kolli/kolli.html