From: R. A. Greiner (ragreiner1_at_antispamdomain.not)
Date: Wed Nov 26 2003 - 19:40:00 EST
The eyepiece requires a full illumination of its field stop to be effective. Thus though the image is in focus at the field stop, the cone of illumination has to be the same size as the field stop in the eyepiece.
The small opening in the back of a C-5 will definitely not support a 2" eyepiece of longer focal length because the filed stop in the 2" eyepiece is very much too large.
I have a C-5 that I use as a guide scope. While you can get an adapter ring to fit the C-5 to convert it to a standard Schimdt thread, it does little good because of the vignetting. Stick to 1 1/4 inch eyepieces for this scope.
Doc G
----- Original Message -----
From: bretm151
To: digital_astro_.at._yahoogroups.com
Sent: Wednesday, November 26, 2003 6:03 PM
Subject: [digital_astro] 1.25" visual back to 2" visual back
Greetings:
I have a Celestron 5" SCT with a 1.25" visual back. If I take it
off, the tube that goes forward isn't much more than 1.25"s.
I would like to use one of the 2" "digital camera" eyepieces
(Williams, Scopetronics) with my CP 5700 but to do that I would need
to get a 2" visual back. Unfortunatly, I'm doubting that they will
do me any good since the entry to the eyepiece isn't 2".
But...
I have a picture in my head (and there lies the danger :-) that the
light is focused into the eyepiece and it might not need to be full
width in front of the eyepice.
If someone who knows more about telescopes than I do could comment I
would really appreciate it...
Bret
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