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Mirror vs. Dielectric vs. Prism Diagonal Compariso

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#1 Charlie Hein

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Posted 29 March 2014 - 06:32 AM

Mirror vs. Dielectric vs. Prism Diagonal Comparison

By William Paolini

#2 davidpitre

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Posted 29 March 2014 - 07:24 PM

The best comparison and review of diagonals I've ever read.

#3 Daniel Mounsey

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Posted 29 March 2014 - 08:34 PM

Bill, has helped make observers aware that prisms are unquestionably the best diagonal for planetary observation in scopes more dedicated for that application. This is why Thomas Back of TMB Optical preferred them. I use prisms for deep sky as well. Prisms and silver coated diagonals are my favorite diagonals hands down.

#4 Scott in NC

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Posted 29 March 2014 - 10:24 PM

The best comparison and review of diagonals I've ever read.


+1

Excellent job, Bill! :applause:

#5 roadi

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Posted 30 March 2014 - 07:09 AM

Very interesting reading! thanks Bill ;)
It also confirms my own experience with prism vs mirror diagonals.
My beloved 1.25" takahshi prism diagonal will never leave my home, It has proved its worth many times against some highend dielectric mirror diagonals :cool:

I do disagree a litle about the issues on the compression mechanics on the Takahashi 1.25" prism!! IMO and Experience the issues simply lies in the old fasioned and conservative undercut on many EP's and not on the compression mechanics on the Takahashi diagonal.
To name one, as much as I love TV products I find these undercuts on their Ep's and barlows realy annoying! fortunately the are "slowly" stearing away from it with their newer Ethos wich has tapered barrels like others! ;)

#6 BillP

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Posted 30 March 2014 - 08:28 AM

So true. If manufacturers didn't add the undercut, which was never needed or asked for, then we wouldn't have problems like this. It goes further too. If you examine it the undercuts and compression ring interactions often result in misalignment. Truly a BAD idea the undercut.

#7 roadi

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Posted 30 March 2014 - 08:35 AM

I fully agree ;)

#8 Roy McCoy

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Posted 30 March 2014 - 11:22 AM

Bill, has helped make observers aware that prisms are unquestionably the best diagonal for planetary observation in scopes more dedicated for that application.



+1

The best comparison and review of diagonals I've ever read.


+1

Excellent job, Bill! :applause:


Bill's reviews, as he might say about the gear itself, are "in a different league".

Thanks a lot Bill!

#9 Bill Steen

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Posted 30 March 2014 - 08:02 PM

Thank you for the very enlightening report! I have often wondered about what the real differences between the two types were. I have, however, been using Meade, Celestron, and Astro Visioneer prism diagonals. These lower levels did not seem to measure up as well. I did notice that the Celestron diagonal tested was 1980s vintage. I have noticed improvement in eyepieces over the years, or at least I think I have. I am wondering if there have been improvements in the mass produced prism diagonals as well. Naturally, I would like to think so.

Again, thanks for all of your hard work that you have graciously shared with us!

Bill Steen

#10 Ed D

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Posted 31 March 2014 - 08:10 AM

Excellent and detailed article. I really enjoyed reading it and found the information very useful.

Ed D

#11 Littlegreenman

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Posted 31 March 2014 - 09:25 PM

Excellent article! But I do have a complaint: now I have to upgrade my diagonal. :step:

My experience with a TV Everbright diagonal with a compression ring and a Panoptic 35, with an undercut, is a great example of how not to do things: it frequently required removing the diagonal from the tube and then some minor 'surgery' to extricate the eyepiece.

Of course, you can't expect every diagonal to be include. I've had a couple of Lumicon 1.25" Enhanced over the years. These are aluminum mirrored. Mine were set screw types. The ergonomics were a high point for me. They came with a larger than usual brass set screw.

Thanks again,
LGM

LGM

#12 davidpitre

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Posted 02 April 2014 - 06:13 PM

Anyone know much detail about the Stellarvue Diagonal? 2" Mirrored . I had one for years and felt it gave as good images as my Everbright.

#13 azure1961p

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Posted 05 April 2014 - 12:40 AM

An excellent article Bill that was technically well covered with very honest impressions conveyed. Superb.

Pete

#14 cjc

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Posted 07 April 2014 - 01:04 PM

A very clear very useful review!

I am particularly struck by the minimalist conclusion that: "In assessment of scatter around Jupiter and bright stars, straight-through observing without any diagonal was very clearly and distinctively better, perhaps showing only half as much scatter as the best diagonal."

#15 Ed D

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Posted 22 July 2014 - 10:55 PM

It was thanks to Bill's article that I recently made the decision to get the Baader/Zeiss prism diagonal for planetary observing. It really is the best choice for the dedicated planetary observer, and not super expensive. The fine focuser lets me rotate my binoviewer a bit to find the most comfortable position.

Thanks Bill,
Ed D

#16 ehallspqr

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Posted 23 July 2014 - 12:20 PM

It was thanks to Bill's article that I recently made the decision to get the Baader/Zeiss prism diagonal for planetary observing. It really is the best choice for the dedicated planetary observer, and not super expensive. The fine focuser lets me rotate my binoviewer a bit to find the most comfortable position.

Thanks Bill,
Ed D


Ditto. Great article and confirms what I have always thought. I'm on my 3rd Baader prism diagonal, the Zeiss version. Tried the latest greatest mirror prism's over the years but have always returned to the Baader Zeiss. There are a number of reasons why I prefer them. No doubt they are the best for planetary observing, at least to my eye's. There is a certain vibrancy and "pop" to the image. Hard to describe except to say I Like it! Not bad on deep sky either. Again great review thanks for posting.

#17 combatdad

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Posted 24 July 2014 - 07:08 AM

Very thorough and balanced assessment. Thanks for taking the time and for sharing.

Dave

#18 Daniel Mounsey

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Posted 26 July 2014 - 01:08 PM

Excellent article! But I do have a complaint: now I have to upgrade my diagonal. :step:


I like this :lol:

#19 Jon Isaacs

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Posted 13 September 2014 - 09:45 AM

I was rereading Bill's article in reference to a thread in the beginners forum.

 

Very well done.  

 

One thing that I found somewhat odd was that mention was made of light fall off with a couple of the mirror diagonals but none was mentioned regarding the prism diagonals.  I did not see a mention of the clear aperture of the various diagonals but when I have looked into this, the prism diagonals typically have a limited clear aperture.  For example, the Baader T-2 has a clear aperture of 34mm and since it is relatively close to the focal plane, one would expect vignetting, light fall off, with an eyepiece with a 46mm Field stop.  Did I miss something in the discussion?

 

Jon



#20 Don Allen

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Posted 17 September 2014 - 06:32 AM

Very good article. Thanks.



#21 Froggynews

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Posted 23 September 2014 - 01:46 PM

Excellent article! Thank you Bill. I wonder how a Baader 2456130 Amici diagonal would have performed if one were included in the comparison. Would have been interesting to see how the supposedly astro-grade Amici performs.

 

Froggynews

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#22 S Gazer

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Posted 28 September 2014 - 10:35 AM

Wow!

 

I didn't know half of the information that was presented in that article.

 

I think this saved me some serious $$$ on detecting marketing hype.

 

Very much appreciate this article.








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