Diagonals or prisms?

[davekelley]

I have always believed that a mirror diagonal, especially a dielectric one, produces a brighter and sharper image than a prism.  I've never tested it out it's just something I read a long time ago and have always taken as fact.   Lately I have been reading that, on long focal length scopes, a prism will give noticeably better images, brighter, more contrast, no false colour etc. as well as the nice advantage of producing an erected image.  I have a 127 starmax and I want to upgrade the diagonal.  What's the best way to go?  I have a telrad because I find upside down back to front images in the finder just annoying and I think a combination of telrad + prism diagonal would suit me so well.  Having said that, my scope is goto so it shouldn't really be an issue, I just haven't quite got the goto to go to anything very well yet!  I like to keep things simple.  I was looking at a baader t2 90 deg prism.  

Any  thoughts or experienced user observations would be excellent thanks folks.

regards 

Dave

 

 

[johninderby]

I use the Baader T2 prism with the fine focuser top with my Bresser 127 Mak. Works OK although not a lot of difference to a decent dielectric mirror diagonal. The fine focuser is useful though.

Edited September 19, 2019 by johninderby

[Moonshane]

I have never noticed a difference and use the same prism as John in my 120mm Equinox and my 100mm pst mod. My main reason is not optical quality but the ability to shorten the light path for binoviewers and the pst mod. It always looks good in monocular vision too although there's a minor amount of vignetting with my 27mm Panoptic.

Buy quality either way and I don't think you can lose.

[davekelley]

This is all good news.  I had always thought that there was a big trade off in image quality if you wanted an erect image.  I shall make the Baader my next purchase

 

[johninderby]

24 minutes ago, davekelley said:

This is all good news.  I had always thought that there was a big trade off in image quality if you wanted an erect image.  I shall make the Baader my next purchase

 

With the Baader prism images will still be reveresed left to right as with a mirror diagonal.

Edited September 19, 2019 by johninderby

[xtreemchaos]

diagonal, im not a lover of prisms ive tryed a few over the years and some are quite good just not as good as my mirrored 99% diagonal. charl.

Edited September 19, 2019 by xtreemchaos

[davekelley]

27 minutes ago, johninderby said:

With the Baader prism images will still be reveresed left to right as with a mirror diagonal.

Oh!  Thanks for that, I assumed a prism produces a correct image?

[John]

3 minutes ago, davekelley said:

Oh!  Thanks for that, I assumed a prism produces a correct image?

The astro prisms discussed here deliver an image with the same orientation as a mirror diagonal.

There are prism diagonals that give "correct" image and the lower cost versions of those are not great for astro use. I believe that there are some higher end correct image diagonals available now though.

I use one of the Baader T2 Zeiss prisms with one of my refractors and its excellent.

 

[johninderby]

I use one of the Omegon errect image prisims with my Lumicon finder with Big Red my Carton 100 f/13. Very good prisim although not as good as the Baader in a scope. Miles better than the type of  diagonal usually used in a finder. 🙂

Works well with the 127 Mak for daytime terrestrial observing.

Edited September 19, 2019 by johninderby

[davekelley]

I really like a telrad zero magnification finder!  Once I'm looking through an optical finderscope, I get lost in all the stars, I find I have no idea what I'm looking at!  I like to use telrad/red dot/rigel, then widest tfov eyepiece I have, tolocate an object!  It's horses for courses I suppose!  

[Moonshane]

Yes sorry Dave I didn't think you meant erect image prisms. They are a bit more variable and (I believe) can sometimes result in star spikes at night. 

[davekelley]

12 minutes ago, Moonshane said:

Yes sorry Dave I didn't think you meant erect image prisms. They are a bit more variable and (I believe) can sometimes result in star spikes at night. 

I have heard about the spikes.  I think I'm confusing myself!  I'm not having spikes!  erect image prisms are just for terrestrial? I'll have to be careful choosing.

 

[heliumstar]

After trying many diagonals from Altair Astro, SkyWatcher, Baader 2" mirror (white one), Baader T-2 prism, BBHS mirror, Tak prism and all those that came with the scopes like Bresser, SW, Celestron I settled on Baader T-2 BBHS mirror and Takahashi Prism. Baader BBHS mirror is absolute best to my eyes and 1.25" clicklock is so effortless to use. You can clearly see how Baader is brighter than all the rest and colours of Albireo are deeper for example. It's even better than Tak prism. Baader's T-2 prism is on-par with Tak I might add.

Now, I only tested this on double stars, planets and Luna so not sure how it would work on deep-sky objects since I can't really see any from where I observe - I use camera for that (EAA).

[johninderby]

I’ve come to the conclusion after reading so many conflicting opinions re: mirror vs prisim that owing to differences in individuals eyesight that one may suit some more than the other. 🤔

[heliumstar]

In my opinion it's down to the the diagonal itself. I was comparing Celestron prism with Bresser mirror in Bresser 102XS and SW 127 Mak. We all know about the theory of f ratio (which honestly I don't completely understand) and use of either one but in both telescopes Celestron was clearly 'clearer'.

[omo]

As a result of this, and being a newbie plus not wanting to buy more than once i ended up with a Baader T2 zeiss prism:

https://www.cloudynights.com/articles/cat/articles/mirror-vs-dielectric-vs-prism-diagonal-comparison-r2877

The author has cost readers thousands, i believe BillP is on here too

[dweller25]

I have also found the Baader T2 Zeiss prism gives me the best views 👍

[John]

I have a Baader T2 Zeiss prism and it's a great performer but so are my Tele Vue and Astro Physics mirror diagonals

 

[davekelley]

On 19/09/2019 at 20:54, heliumstar said:

After trying many diagonals from Altair Astro, SkyWatcher, Baader 2" mirror (white one), Baader T-2 prism, BBHS mirror, Tak prism and all those that came with the scopes like Bresser, SW, Celestron I settled on Baader T-2 BBHS mirror and Takahashi Prism. Baader BBHS mirror is absolute best to my eyes and 1.25" clicklock is so effortless to use. You can clearly see how Baader is brighter than all the rest and colours of Albireo are deeper for example. It's even better than Tak prism. Baader's T-2 prism is on-par with Tak I might add.

Now, I only tested this on double stars, planets and Luna so not sure how it would work on deep-sky objects since I can't really see any from where I observe - I use camera for that (EAA).

That's interesting but the BBHS costs more than my OTA!  Quite a lot more.  I'm not sure I want to spend £400 on a diagonal.  Would a Baader T2 (not zeiss) be an improvement over the stock mirror diagonal that came with my scope?  (skymax 127).  I might even stretch to the zeiss at about £250 if that makes a lot of difference....I think £400 is just not on really.....

 

[johninderby]

On the mak doubtfull that you could tell the difference between the two different prisims. The T2 has a shorter light path which can help with a mak. 

[heliumstar]

3 minutes ago, davekelley said:

That's interesting but the BBHS costs more than my OTA!  Quite a lot more.  I'm not sure I want to spend £400 on a diagonal.  Would a Baader T2 (not zeiss) be an improvement over the stock mirror diagonal that came with my scope?  (skymax 127).  I might even stretch to the zeiss at about £250 if that makes a lot of difference....I think £400 is just not on really.....

 

True. It's expensive - not 400. I bought mine from RVO and it was 260 with nosepiece and 1.25" Clicklock. It's T-2 BBHS mirror - not 2". Still if you think about it it's the same price as SW 72ed! 🙄 I had T-2 non Zeiss Baader prism and it was very good as well. I settled on Tak prism due to being so lightweight and Baader BBHS mirror for to my eyes being the best. It only hurts once when you buy it and if you take care of them they will last decades I guess. With BBHS that is actually a promise from Baader.

If it helps. With my 127 Mak I always use Tak prism and Baader 8-24 zoom and I am very happy with that combination. In my opinion that is actually one of the finest combinations of portability, price and capability in the market. Put it on AZ GTi Wifi and you have a perfect scope for beginners and experienced observers.

[davekelley]

1 hour ago, heliumstar said:

True. It's expensive - not 400. I bought mine from RVO and it was 260 with nosepiece and 1.25" Clicklock. It's T-2 BBHS mirror - not 2". Still if you think about it it's the same price as SW 72ed! 🙄 I had T-2 non Zeiss Baader prism and it was very good as well. I settled on Tak prism due to being so lightweight and Baader BBHS mirror for to my eyes being the best. It only hurts once when you buy it and if you take care of them they will last decades I guess. With BBHS that is actually a promise from Baader.

If it helps. With my 127 Mak I always use Tak prism and Baader 8-24 zoom and I am very happy with that combination. In my opinion that is actually one of the finest combinations of portability, price and capability in the market. Put it on AZ GTi Wifi and you have a perfect scope for beginners and experienced observers.

I do have AZ GTI WIFI, I have only tried it a few times and found it not to be very accurate.  I'm not very good with the finder and have added a telrad, I think that will help with me setting it all up.  I would be prepared to buy a 1.25" Baader BBHS if the total came to £250 or so, all I can seem to find is the 4" and the 1.25" non zeiss or tax prism.  Is the BBHS worth the extra? I'd stretch to it if you think it's a lot better.  Thanks

 

[heliumstar]

I don't go along with magnified finders as well so I move Rigel from scope to scope. If you are set on a prism I would go either T-2 non Zeiss or Tak for your 127 mak. Both around 100. If you are set on either prism or mirror BBHS check these codes on RVO website ( enter codes into search - FLO doesn't seem to stock them ) :

Prism: 2456095

Mirror: 2456103

Nosepiece: 2458105

1.25" Clicklock: 2458100

T-2 non Zeiss prism : 2456005-K - similar price to Tak prism. I had it but didn't go along with eyepiece holder and three screws. ClickLock is much more comfortable in use.

 

Edited September 21, 2019 by heliumstar

[johninderby]

Or 365Astronomy. They carry all the Baader stuff.

https://www.365astronomy.com/search.php?mode=search&page=1&keep_https=yes

Edited September 21, 2019 by johninderby

[davekelley]

18 minutes ago, heliumstar said:

I don't go along with magnified finders as well so I move Rigel from scope to scope. If you are set on a prism I would go either T-2 non Zeiss or Tak for your 127 mak. Both around 100. If you are set on either prism or mirror BBHS check these codes on RVO website ( enter codes into search - FLO doesn't seem to stock them ) :

Prism: 2456095

Mirror: 2456103

Nosepiece: 2458105

1.25" Clicklock: 2458100

T-2 non Zeiss prism : 2456005-K - similar price to Tak prism. I had it but didn't go along with eyepiece holder and three screws. ClickLock is much more comfortable in use.

 

Thanks.  So the BBHSis noticeably better than those prisms?  I should go with that thank you.  Like you say it's a one off payment and you get a lifetimes use.  Also, I can sell a few bits I don't really need anymore.....put that towards it.....