TheSkySearchers

Mirror vs. Dielectric vs. Prism Diagonal Comparison
by WilliamPaolini

Back Row ( 2" ) Baader Zeiss Prism, Takahashi Aluminum Mirror, Astro-Tech Dielectric, Baader Dielectric, Astro-Physics MaxBright Dielectric Center Row ( 1.25" ) Baader T2 Zeiss Prism, VERNONscope Enhanced Silver Mirror, Takahashi Prism, Tele Vue Everbrite Dielectric Front Row ( 1.25" ) Vixen Prism,...
Read more...

Thanks for reposting Bill! For those who did not see it on Cloudy Nights, this is a must read for any frac/CAT owner. People who are using premium EPs behind stock diagonals are kidding themselves.

Bigzmey wrote: ↑Wed Jun 30, 2021 6:59 pm Thanks for reposting Bill! For those who did not see it on Cloudy Nights, this is a must read for any frac/CAT owner. People who are using premium EPs behind stock diagonals are kidding themselves.

Fully agreed!

Thanks for the info Bill, that is quite the write-up! You've taken your experience and put a lot of time and effort into that and shared it with everyone. Much appreciated

I don't have a lot of extra coin for my favourite hobby, but I do the best with what I have. That being said, I have a total of two 1.25 diagonals. One came with the orange tube C80 I bought years ago, and the other, an iOptron, was bought for me as a gift.


I have to say in this case, the stock star diagonal is the hands-down winner. I'm assuming it's a prism, as when I took it apart and cleaned it with distilled water and the black felt, that's the shape the glass was...

The iOptron is good, but the Celestron diagonal has a blacker background, the stars and especially the Moon/Sun are more sharply defined, and it's sharp in the FOV right to the edge, whereas the iOptron shows a bit of distortion in that area.

I've never looked through anything else, so that's just what I know. I'm quite happy with the views through my C80 with it's star diagonal and some Fujiyama KK's

All the best,

Thanks for this Bill! It is quite a while since I originally read this, so it was a good exercise to do a re-read!

It would be interesting to see how the newer Chinese-made dielectric 2" diagonals stack up (like the GSO quartz). One of these days I would like to get a 2" Baader Zeiss prism, but for now my Tak 1 1/4 and TV 2" Everbrite will have to do.

I must admit, like you I was very surprised to see the plastic Tak when I got it (I picked up both of these on the Used market). Also, like you, I doubt that I will ever part with my TSA102!

All the best, and keep up the great work!

Dean

A excellent review Bill, ou of curiousity did you ever get to try the Vernonscope gold diagonal?
I was always interested in how well it actually performed.

Thanks! You should get paid for this. Have you thought of submitting it? There's half a dozen outlets for work of this quality.

Can one still get a new astronomy prism diagonals , I used to have a WO one , but was the correct image type ?

Thanks for this thorough and excellent article! Outstanding quality.
In the past I referred to it several times while advising people about what diagonal to buy. And I will continue to do so.

A great article Bill, a handy reference indeed.

Richard wrote: ↑Mon Jul 05, 2021 1:15 pm Can one still get a new astronomy prism diagonals , I used to have a WO one , but was the correct image type ?

Yes, the brand new prisms are still available from many brands (Baader, Celestron, Orion, WO, just to name a few).

Many manufacturers make prisms, there are only a few that make 2" versions though.

Richard wrote: ↑Mon Jul 05, 2021 1:15 pm Can one still get a new astronomy prism diagonals , I used to have a WO one , but was the correct image type ?

I just bought one also image-correcting from StellarVue and wrote it up here:
https://www.theskysearchers.com/viewtop ... 34&t=18441

Thanks all we have so little astro equipment for sale here in RSA and have not seen any for a few years now and now virtually impossible to order on line due to cost , years ago I did get one off ebay but was rubbish , it was all metal but badly made with lots of light scatter , I did open it and painted all black inside (was left shiny!) which helped a bit but was still terrible , probably an inferior prism
I quite liked the WO one where the actual prism was much larger but was no better than my normal celestron/Skywatcher ones , only advantage was correct image orientation which probably reduced its effectiveness for astro use ?

I am almost ashamed to say that I have a 2 inch astro tech dielectric on my AT102. They now come with twist lock and thumbscrew. I am probably not picky enough but i dont notice anything terrible in it. The frac is just a travel scope and now that i have it sorted it wont really see a lot of use and i guess i didnt feel like spending the money on a really good diagonal.

Mike Q wrote: ↑Mon Mar 11, 2024 11:42 pm I am almost ashamed to say that I have a 2 inch astro tech dielectric on my AT102. They now come with twist lock and thumbscrew. I am probably not picky enough but i dont notice anything terrible in it. The frac is just a travel scope and now that i have it sorted it wont really see a lot of use and i guess i didnt feel like spending the money on a really good diagonal.

Actually, the typical 2" dielectrics offered by many companies are pretty good, in particular for DSOs. I was happily observing with them for many years. But, premium diagonals are better. Like in any other hobby this is a game of performance vs price and everyone should look for their optimal ratio.

Bigzmey wrote: ↑Tue Mar 12, 2024 12:25 am

Mike Q wrote: ↑Mon Mar 11, 2024 11:42 pm I am almost ashamed to say that I have a 2 inch astro tech dielectric on my AT102. They now come with twist lock and thumbscrew. I am probably not picky enough but i dont notice anything terrible in it. The frac is just a travel scope and now that i have it sorted it wont really see a lot of use and i guess i didnt feel like spending the money on a really good diagonal.

Actually, the typical 2" dielectrics offered by many companies are pretty good, in particular for DSOs. I was happily observing with them for many years. But, premium diagonals are better. Like in any other hobby this is a game of performance vs price and everyone should look for their optimal ratio.

I am content with this one. Like i say the frac doesn't get a lot of use. I guess if i had a better one i would have sprung for a better diagonal, but what i have gets the job done well enough for us.

Mike Q wrote: ↑Mon Mar 11, 2024 11:42 pm I am almost ashamed to say that I have a 2 inch astro tech dielectric on my AT102.

I do not understand why you would be ashamed of this?
I have used 2" diagonals (aluminized and dielectric) with all my refractors 80 mm and larger.

Unless you are using your refractor at the limits of its optical capability you do not really require a top tier diagonal.
If you are just doing casual observing your AT diagonal will serve you just as well as a Vernonscope $1000 USD 2" diagonal.
The small percentage difference in the view is not really worth the cost.

Yeah with the 102 casual is the name of the game. We are far and away reflector people and definitely in the bigger is better group lol