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Equipment Discussions >> Eyepieces

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george tatsis
professor emeritus
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Reged: 11/20/08

Loc: Flushing, NY - Europe
Re: Eyepiece Performance using a Prism Diagonal new [Re: urassner]
      #6226278 - 12/01/13 01:30 AM

Quote:

I do not have experience with either diagonal. Could the observed difference be just the higher optical quality of the Tak diagonal compared to the Astrotech diagonal. Would you still see an improvement if it was compared to an AP, TV or Baader dielectric diagonal? I would assume that a Zeiss prism diagonal should be of similarly high quality as a Tak Diagonal and would also show a similar improvement as a Tak.




PJ's reference to his excellent Zeiss prism diagonal corroborates Bill's report.

It's only logical to assume that quality and execution of design are of the utmost importance, because both samples come from reputable companies (Tak,Zeiss).

George


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Roy McCoy
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Reged: 10/13/05

Loc: Glendale, AZ
Re: Eyepiece Performance using a Prism Diagonal new [Re: urassner]
      #6226287 - 12/01/13 01:40 AM

I now use a Baader T2 with the Zeiss prism in an Orion 80 ED f7.5 and a 2” Zeiss prism in an 86’ AP 6" f8.

Incidentally, I feel the T2 Baader Zeiss prism outperforms the 2” Zeiss prism. Maybe the shorter path? But I use 2 inch ep’s in the 6” so I’ll keep it.

As Bill said “a definite notch better”. There were several of us testing the diagonals and all involved agreed the difference was not subtle. To me the difference is as pronounced as the difference between an achro and apo.

Dust lanes and mottling pop so much more with the prism in my longer focal length scopes.

I found that the Baader 2”mirror is the better performer in the AT106 f6.5.


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urassner
sage
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Reged: 07/08/12

Re: Eyepiece Performance using a Prism Diagonal new [Re: Roy McCoy]
      #6226302 - 12/01/13 01:50 AM

Thank you for the information. I am using an older AP refractor as well. I should think about a prism diagonal.

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Ernest_SPB
sage


Reged: 11/13/10

Loc: St.-Petersburg, Russia
Re: Eyepiece Performance using a Prism Diagonal [Re: urassner]
      #6226331 - 12/01/13 02:36 AM

I have 2" Amichi prizm from baader.

It is nice to see objects in right orientation. But so thick piece of glass introduces noticeable chromatic aberrations into image of my 80 mm F7.5 ED-apochromat. Then roof edge makes some artifacts: two strong rays into opposite sides of bright objects (like Jupiter, Venus) and distort a bit fine features in high magnification image (like astigmatism or doubling).

I think 2" prisms should not be used if you want to get image with high resolution/contrast.


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ivan86
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Reged: 05/08/09

Re: Eyepiece Performance using a Prism Diagonal new [Re: urassner]
      #6226424 - 12/01/13 05:26 AM

I have a Carl Zeiss 2" prism diagonal and i have used it with a Skywatcher 100 ED and now with my new Meade ACF 12 " SC.

This diagonal when compared to standard dieletric mirror 99% diagonal such WO / TS show better definition on planets and better contrast agaist background on deepsky objects.

The difference is more noticeable when i look at low contrast structure inside nebula.

Ill use in the future only prism diagonal and ill keep my Carl Zeiss (350 euro) forever.

Ivan


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Heavens Above
sage


Reged: 01/25/09

Loc: Bristol, UK
Re: Eyepiece Performance using a Prism Diagonal new [Re: ivan86]
      #6226633 - 12/01/13 10:11 AM

I compared a Baader Zeiss prism diagonal (1.25) against a Astro Physics Maxbright, which must be the best mirror diagonal made and decided to keep the prism. On planets I found it had less scatter and greater clarity. These results were the same on an TMB 115 Apo and a Tak Mewlon 210.

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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: BillB9430]
      #6226696 - 12/01/13 10:40 AM

Quote:

+1 on Chuck's reply, David. Amici prisms (90 degree) and Schmidt prisms (45 degree) both have a "roof" with an edge in the center of the field. This roof portion of the prism reverses right and left to give a fully corrected image. Diffraction of light hitting the "roofline" creates a horizontal spike visible both directions from every bright object. Better quality correct image prisms have a finer edge and so a fainter spike, but all have it. Regular right angle prism astronomical diagonals show an erect image but it is reversed right and left - no roof in these, hence there should be no spike. - Bill




IME, Amici prisms are fine for low power use. I have one in my 70mm finder scope on my 10" Dob. I prefer the natural orientation when star hopping. (Why wouldn't I?) But for higher magnification, the diagonal or prism which gives a reversed image also gives a sharper image.

Mike


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Philip Levine
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Reged: 03/22/07

Loc: near Boston, MA
Re: Eyepiece Performance using a Prism Diagonal new [Re: BillP]
      #6226698 - 12/01/13 10:41 AM

thanks Bill,
Very informative post. I'm always looking for ways to improve visual observing detail, the prism diagonal info is most welcome.
Phil


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: george tatsis]
      #6226705 - 12/01/13 10:44 AM

Quote:

Just wondering how many CNers have been Googling "1.25 prism diagonal reviews" since Bill started this subject.

I know I have.

George




I still have many of these threads in my favorites here on CN.


Mike


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ibase
Vendor Affiliate
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Reged: 03/20/08

Loc: Manila, Philippines 121*E 14*N
Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226715 - 12/01/13 10:49 AM

If one is going prism on the diagonal, don't cheap out - got a low-cost prism diagonal and its performance is less than desirable compared to the mirror diagonals.

Best,


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226716 - 12/01/13 10:50 AM

If you're going to use the prism diagonal mostly for moderate to higher power work, would it be worthwhile to buy a 2"? Why not go with a 1.25" prism diagonal?

A 2" dielectric mirror diagonal should be good enough for low-power wide-field. And a 1.25" Amici would be best for a natural orientation finder scope.

Mike


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BillP
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Reged: 11/26/06

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Re: Eyepiece Performance using a Prism Diagonal new [Re: urassner]
      #6226721 - 12/01/13 10:51 AM

Quote:

Bill, in some older CN threads it was mentioned that Prism diagonals are not suitable for shorter focal length telescopes (f10 and faster) due to refraction effects when light enters at an angle creating chromatic aberration. I noticed that you used a f8 refractor and it did not seem to be an issue. Might it be more of an issue with 2 inch diagonals and lower magnification? I would appreciate your insight.

Thank you, Ulrich




Yes. Tammy mentioned this to me as well. I do have an 80mm f/6.25 APo so will plan to give the 2 diagonals a compare on that scope as well. I will also do some low magnification testimng as well on bright objects.

btw, has anyone compiled a list of current production prism diagonals (not the amici types)? I was Googling for a full 2" one that would accomodate a full 46mm clear light path so could use max TFOV 2" EPs. Came up with nothing so far.

Edited by BillP (12/01/13 10:58 AM)


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: BillP]
      #6226738 - 12/01/13 10:56 AM

Here's an old CN thread on prism diagonals:

Prism vs. Mirror

Mike


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226744 - 12/01/13 10:58 AM

Here's another:

Prism Diagonal

Mike


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226763 - 12/01/13 11:10 AM

If I upgrade to a better prism diagonal I will use it mostly in my f/10+ SCT's and Maks for moderate to high magnification. IMO, it would make more sense to get a 1.25" diagonal.

Which is the best 1.25" prism diagonal? Which ones are almost as good?

Mike


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Roy McCoy
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Reged: 10/13/05

Loc: Glendale, AZ
Re: Eyepiece Performance using a Prism Diagonal new [Re: BillP]
      #6226786 - 12/01/13 11:24 AM

Hi Bill,

AlpineAstro has the 2" Zeiss, it is listed on the price page as PRISM-2.


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urassner
sage
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Reged: 07/08/12

Re: Eyepiece Performance using a Prism Diagonal new [Re: BillP]
      #6226799 - 12/01/13 11:29 AM

Bill, I spent some time yesterday after I read your report and could only find one 2 inch version: The Baader 2 inch with a Zeiss prism, available directly from Baader or from Agena astro.

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george tatsis
professor emeritus
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Reged: 11/20/08

Loc: Flushing, NY - Europe
Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226809 - 12/01/13 11:33 AM

Quote:

If I upgrade to a better prism diagonal I will use it mostly in my f/10+ SCT's and Maks for moderate to high magnification. IMO, it would make more sense to get a 1.25" diagonal.

Which is the best 1.25" prism diagonal? Which ones are almost as good?

Mike




Apparently not many 1.25" options are currently available.

The Tak Bill tested is supposed to be the best one on the market.

https://www.astronomics.com/takahashi-1-25-inch-prism-diagonal_p3349.aspx

Baader T-2 is another option of course!

http://www.alpineastro.com/Star_Diagonals/Star_Diagonals.htm

Last but not least, we have the Vixen!

http://www.astroshop.eu/vixen-diagonal-prism-90d-1-25-/p,5833

TS

http://www.teleskop-express.de/shop/product_info.php/info/p604_T2-diagonal-pr...

El cheapos are not included here!

Take a pick Mike!

George

Edited by george tatsis (12/01/13 11:51 AM)


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Hesiod
sage


Reged: 01/13/13

Re: Eyepiece Performance using a Prism Diagonal new [Re: Roy McCoy]
      #6226833 - 12/01/13 11:39 AM

I have the Baader-Zeiss 1.25" and I feel that it is better than any other prism I have ever tried, but the "standard" Baader prism follows him quite closely.
Anyway I have not ever tried the Takahashi (which at 90€ could be a real bargain) and I use the prism mainly behind my 8" SCT which somebody could judge a rather junkish telescope compared to a TSA.


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: urassner]
      #6226837 - 12/01/13 11:41 AM

I'm looking at the T-2 Prism Star 1.25" Diagonal. That is supposed to incorporate a Zeiss prism with Baader coatings. How does this prism diagonal compare with others?

Mike


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