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G9.25 2" diagonal questions

Started by rcordell, 07/08/2002 01:38PM
Posted 07/08/2002 01:38PM Opening Post

I have a G9.25 that I got about a month ago. I only have two eyepieces because I have been trying to decide if I needed to go to a 2" diagonal. I get the impression that on an SCT under 10" I will not gain much by going to the 2" diagonal. I do understand the difference when going from my Celstron 1.25" aluminum mirror to any dielectric. That isn't the question. Wouldn't a 1.25" dieletric diagonal give the same light to the eyepiece as a 2"? Comments?

If I do buy a 2" diagonal what are the tried and true solutions out there for SCT's? Do I go with screw on SCT style or get an adapter for a refractor style diagonal? I'm EQ, not fork, mounted so length isn't part of my equation. Comments?

Posted 07/11/2002 05:08AM #1
As far as light to the diagonal, you're right (I think). Certainly a 1.25" Eyepiece will not be any brighter with a 2" diagonal vs a 1.25" diagonal.

The only reason to get a 2" diagonal is access to excellent 2" eyepieces. The field stop of a 1.25" eyepiece is 26mm and that only allows 32mm eyepiece to be 50deg AFOV. A 2" diagonal however allows a 35mm Nagler to get 88deg AFOV. That allows 4 times the amount of sky to be seen with approximately the same magnification.