Re: [APML]: Shortage of Guide Stars

[Chuck Vaughn <aa6g@aa6g.org>]

Philip,

>For me, discovery of the GEG has been a milestone event, which is why I was
>interested in understanding why you and Chris V have had (almost uniquely?)
>bad experiences with the GEG.  Perhaps we shall never know the answer, but
>one thing that I wanted to be clear about, especially for the benefit of
>new users, is that the ST-4 guides well on off axis images produced by the
>GEG - at least on an f/10 LX200.

One thing I forgot to mention was that I operated the GEG in the f/7 
position so that the pick-off prism was in front of the lens. The seagull
star images were produced by the C14 and had nothing to do with the GEG.

I pulled out "Telescopes Optics" by Rutten and van Venrooij and I see that
the spot diagrams for an SCT can vary greatly with slight over or under
correction. Maybe I had one that fell into this category. It's not clear
in the book what happens to the off axis images when you move the primary
far from its optimum position which happens when you add a focal reducing
lens.

Chuck  <aa6g@aa6g.org>