TS (GSO) 1.25" Diagonal

[fozzybear]

Hi

Currently have a Celestron 45 degree image erect diagonal model #94112-A would I benefit from the TS equiv albeit 90 Degree and Reflectivity: dielectric 99% coating for bright images.

Any help would be appreciated.

this would be attached to my old C5 for better viewing. or stick with old 45 degree

 

Many thanks

 

Andy

[fozzybear]

forgot to add the TS equiv would be the TSZS1D spec as below

-- Field illumination: full 1.25" without vignetting
-- Reflectivity: dielectric 99% coating for bright images
-- Optical surface quality: 1/12 Lambda
-- Mirror substrate: BK7 optical glass
-- Body: completely CNC machined
-- Telescope side connection: 1.25" barrel with filter thread for 1.25" filters
-- Eyepiece side connection: 1.25" barrel with locking screw and compression ring
-- Effective optical Length: 85mm

 

 

sorry

[John]

Hi Andy,

You should see improved performance for astro viewing purposes. The standard 45 degree prisms create spurious reflections and light scatter when used for astronomy. They are fine to terrestiral use though.

The mirror diagonal will give you an upright image but left and right would be reversed. This is the same with all astro mirror diagonals. The TS / GSO one seems to have a good specification

 

[fozzybear]

John,

Thankyou I know about the inverse left right ok with that, just wanted to clarify a better image quality visual e.g sharpness of image as the old c5 with original diag has been somewhat frustratingand disappointing for astro use.

 

regards

Andy

[Dave In Vermont]

I have a GSO dielectric 99% 90° diagonal in my collection. And these are excellent diagonals! TS, or many other outfits, sells these re-branded with the company-name. But they is what they is - GSO - and they work beautifully.

You'll be a happy-camper,

Dave

[fozzybear]

Just now, Dave In Vermont said:

I have a GSO dielectric 99% 90° diagonal in my collection. And these are excellent diagonals! TS, or many other outfits, sells these re-branded with the company-name. But they is what they is - GSO - and they work beautifully.

You'll be a happy-camper,

Dave

Dave as per johns reply you have given me confidence thankyou greatly appreciated.  this site is a wealth of information better than a search engine. once again thankyou for the responce

[Timebandit]

Hello fozzybear and welcome to SGL. The stats of dielectric 99%reflec diagonal at 1/12 seem good, so should be a nice little diagonal 

I have a TS Binoviewers, and these are very well made and produce a nice clean image , so my experience of the TS items to date has been positive 

I hope the above helps☺

[fozzybear]

Timebandit

Thankyou so a good replacement to my aging old diagonal.

Andy

[Alan64]

The Celestron C5 Schmidt-Cassegrain, with its f/10 focal-ratio, is considered a slow telescope.  Therefore, a prism diagonal is preferred and recommended.  Celestron's larger Schmidts come with this 90° prism star-diagonal as standard equipment...

http://www.teleskop-express.de/shop/product_info.php/info/p2484_Celestron-1-25--90--diagonal-prism-for-refractors-and-cassegrains.html

You would experience less light-scattering with the prism; and don't let the low price fool you, as it's very good.  I have one myself for my slower telescopes...

Prisms are superior to mirrors, and would be used in faster telescopes if it were not for the alleged increase in chromatic aberration.

Light-scattering manifests itself as a hazy halo that surrounds brighter objects, so you want to keep that to a minimum.  If you feel that you'd want a prism that costs more...

http://www.teleskop-express.de/shop/product_info.php/info/p604_T2-diagonal-prism-90----T2---1-25--connection-on-both-sides.html

A Schmidt-Cassegrain already contains two mirrors that introduce light-scattering of their own.  There's no need to handicap the optical system further by using a mirrored diagonal.

[Dave In Vermont]

My experience is quite the opposite. I have a 12" Meade LX90. And I do use my William Optics dielectric mirror at 2" in it, and it's also an F/10 SCT. On the occasions I need to use a 1.25" diagonal, I use my GSO dielectric-mirror in it also. I've used the prism-diagonals in these as well - as did a friend of mine with his 12" LX200 SCT F/10 - and he recently got a dielectric. He reported a brighter and clearer view from these.

But this subject has been debated for years. Best that we can figure is the prisms can come in different grades. Some are extremely well figured, 1/12th-wave, etal. And these sell for high prices. From reports - these match the dielectric, and may even be better - as you indicated. But the bulk of prisms don't have these highly well-figured prisms. One's such as the inexpensive Orion-USA and the Meade #918A's. Likely the debate will continue. But I've rarely been told by people that the dielectric-mirrors are worse than the prisms.

Best wishes -

Dave

[Waldemar]

The best i.m.o.: http://www.teleskop-express.de/shop/product_info.php/info/p7950_Baader-T2-BBHS-Sitall-Zenitspiegel-mit-1-10-lambda-Oberflaeche.html

A chain is as strong as the weakest link... goes for optics as well!

Waldemar

 

[John]

I've used a few of the Celestron 1.25" prism diagonals in C5 and C8 SCT's. They used to be "stock issue" from Celestron. My experience was that they are quite good but a good dielectric mirror (such as the GSO / TS one that is under discussion) produces brighter and slightly sharper images.

A really good prism such as the Baader T2 Zeiss on that I use with my Takahashi 4" refractor are a slight step up from the dielectric mirror types for light scatter when viewing planets but these cost more than a pre-owned Celestron C5 is worth !

I agree that a weak link in the optical chain needs to be avoided for best performance but I don't think that the TS / GSO 1.25" dielectric prism would be that weak link.

 

[Alan64]

If there is doubt about the quality of the Celestron prism, then the second-tier Baader prism indicated may be had for little more than the TSZS1D.

Integrating a third mirror within an optical train is always a bad idea.  The model, the Newtonian, only has two.

"... but these cost more than a pre-owned Celestron C5 is worth !"

As though the diagonal could not be used with other telescopes in future; but then the Zeiss  was never mentioned.

Diagonals have always been primarily associated with refractors, and in the not-so-recent years the faster refractors have eclipsed the slower ones -- in manufacturing, preference, sales and acquisitions -- and with mirrored diagonals recommended for them.  That's all fine, well and good.  Could it be then that a bad habit has developed as a result, and in the recommendations of mirrored diagonals across the board?

I think so.