6 replies to this topic

[M11Mike]

Celestron Star Diagonal Model # 94115-A

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)

[barbarosa]

Prism.

 

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.

[zyzyz]

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.

[ChristianG]

Hi.

 

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.

 

--Christian

[Redbetter]

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.

[M11Mike]

Thanks guys - I thought is was a PRISM type but wasn't 100% sure. Now get this - with my new Celestron Sky Prodigy 6SCT 150mm F10 CAT it works BETTER than with a very popular Dielectric Mirror Star Diagonal!!! I spent last night observing and all I did was go back and forth between the 94115 and the dielectric mirror....in each and every case (mostly deep sky stuff like M13, M11, M81, M82, M57) and some relatively close double stars - it was either the same or better. And I used several different eyepieces and powers on each subject. I never was big on prism diagonals but recently read somewhere here on the net that Celestron DID choose properly between mirror and prism for many of their scopes. Note that this IS NOT the star diagonal that came with the scope - that had NO markings. I had this lying around from some old scope I bought back when - I can't remember what Celestron scope it came with. And yes - I DID notice the difference in prime focus distance - but it's well with the focus range of the Celestron 6" SCT. Thanks again guys for the info. Mike

[Sky Muse]

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.