View Full Version here: : Diagonal Dilemma

The Mekon
30-09-2017, 07:55 PM
Ok, I have just filled my cart at Teleskop Express with 500+ euros of goodies, but now am having second thoughts.
My problem is getting the absolute best diagonal (for the best price of course). I currently have a 2" Bintel 99% mirror diagonal and an old University Optics 2" prism. The difference in viewing at high magnification (120x +) is substantial. The UO prism is way ahead in every respect - no scatter, better resolution.....only problem is keeping the UO prism square in the visual back. The UO prism has the worst mechanics possible, the 2" nose piece is sloppy in the holder and will not hold square and the eyepiece holder is not much better.
Now I had thought to order a Baader T2 Ziess prism with clicklock and 2" nose piece (270 euro), but now am thinking perhaps spend a bit more and get the Baader 2" Sitall mirror (357euro) or max out on the Baader 2" Zeiss prism (378 euro).
I only want to do this once - I realise if I go for the T2 option I will have to keep my Bintel 2" mirror for wide field.
Any thoughts on the 2" Sitall Mirror Vs. the 2" Zeiss prism - as said earlier, my thoughts are that prisms are way better than mirrors.

30-09-2017, 08:26 PM
John, I have used both the 2" BBHS Sitall mirror ClickLock and the T2 Zeiss extensively and now also have a T2 Maxbright. The BBHS 2" is very very good, giving an excellent view that to me seems brighter than any other ones I have tried. Seems to be better on scatter control as well.

If you're not in a rush to spend your dollars I am happy to let you try mine to do a comparison. This diagonal also has external collimation via push/pull screws...

Were it not for the shorter light path needed for binoviewing I would just have the BBHS 2".

The Mekon
01-10-2017, 05:17 PM
Thanks Matt for the offer of a comparison with your diagonals, but I am not sure whether I can wait that long! I am particularly interested in the performance on uneven double stars.
Are your saying that the T2 Zeiss prism and the BBHS silver mirror are at the same level of performance?
My current equipment leads me to favour prisms, but that may be only because this Bintel 2" (GSO I believe) mirror, though nicely made is just not up to Baader standards, so setting me against mirrors.
I have read both of Bill P's articles on diagonals and he does give the BBHS 2" mirror a good review, but he still appears to give the prisms the nod when it comes to fine details.

01-10-2017, 06:12 PM
I have the Baader-Zeiss BBHS prism (T2) and it is exceptional. I only use 1.25" EP's so don't feel the need to get a 2" diagonal, though if I did it'd probably be the Tak 2" mirror or the Sitall.

I definitely can see more detail in the BBHS prism compared to a friend's Tak mirror, though I am sure his astigmatic eyes disagree :P

01-10-2017, 06:41 PM
I use a 2" BBHS and find it quite excellent. A really noticeable improvement, not yet mentioned here, is improvement in colour rendition.

01-10-2017, 08:13 PM
John, I use the T2 and the 2" BBHS mostly on different scopes and targets and rarely compare them directly. I recently switched my binoviewers onto a T2 Maxbright and have found that the view of Saturn is not as vivid as the Zeiss T2 or the BBHS Sitall.

The Zeiss T2 prisms have had the BBHS coating applied to the hypotenuse face since 2000. BBHS mirrors are a new product.

The Mekon
02-10-2017, 06:45 PM
Thanks Matt, Wren, Lewis.
I have just ordered the 2" BBHS silvered mirror diagonal. What made up my mind was: 1. Observing last night on a few uneven double stars, the difference between mirror and prism was not as great as I had imagined - more connected with the seeing than anything. 2. Calculated all up weights with T2 prism + extension + T2 holder etc, came to more than 2" diagonal.
My 132mm CFF is very close to requiring a 3rd cwt, and I don't want to add that!

03-10-2017, 06:21 AM
Hi Guys, I'll just add that I've found it useful when comparing diagonals to include the ultimate diagonal in terms of image quality (not ergonomics), which is no diagonal. Comparing various available units against this benchmark could add a welcome level of objectivity, especially when not all units are available for testing on the same night. I do appreciate it's not always practicable to view straight-through.