Celestron Star Diagonal Model # 94115-A Question
Posted 01 June 2016 - 10:55 AM
Question: Is this a prism diagonal (or a mirror diagonal)??? Not sure, so I thought I'd ask all you experts.
Thanks - Mike P (Ballston Lake, NY)
Posted 01 June 2016 - 11:12 AM
I have two of these and they get regular use with c mount cameras and 1.25" EPs I have a much more expensive TV 2" mirror diagonal. I think I can see a difference, at least sometimes.
Posted 01 June 2016 - 11:17 AM
It's a prism diagonal supplied with most entry level Celestron scopes. I have an old diagonal that's unmarked and didn't know if it was a mirror or prism. Rather than take it apart or find a Q-tip to probe it, I blew some air though it. If you can't get air to pass through, it's a prism. Don't eat Cheetos first.
By the way, welcome to the forums.
Edited by zyzyz, 01 June 2016 - 11:20 AM.
Posted 01 June 2016 - 05:36 PM
It is the diagonal usually included with Celestron SCTs. Being a prism, it has the shorter optical path required to allow the instrument to operate at the design focal length. It is cheap but surprisingly good in a slow instrument f/10 and above. I use one with my 8SE OTA and see no need to 'upgrade' it apart for the the two little screw holding the eyepiece. But a third screw can be added to make it more symmetrical if wanted.
Posted 01 June 2016 - 07:57 PM
It is a surprisingly good diagonal, same one that came with my SCT 20 years ago and much better than the same vintage Meade equivalent. The Meade 1.25" prism I have came with the finder I put on the SCT the same year. The Meade diagonal was always used at low power and seemed to be okay...until I tried using it in a 70mm refractor I was working on. While the images looked okay initially, I was in a for a surprise when I turned the little refractor toward a bright star and conducted a high power star test: the star became a small cross at highest power. Putting back in the other diagonal restored the star images to normal.
Posted 01 June 2016 - 09:21 PM
Posted 10 June 2016 - 06:36 PM
I placed an order for the 94115-A last night. However, depending on the age of the telescope that included your diagonal, it might've been made in Japan.