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Which Future-Proof Baader Diagonal?!

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#1 oliveraplin


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Posted 06 August 2020 - 04:05 AM

Hi all,


Hoping you can help.


I am pretty much sold after reading many in-depth reviews and recommendations of the various Baader diagonals to get one of the BBHS coated diagonals, however, due to their steep price and my current entry level equipment which i'll be looking to upgrade in the future (but probably not for a few years), I'm a little stuck on which to pull the trigger on - the T2 zeiss prism (the 36mm one, not the smaller one), the 2" mirror or the 2" zeiss prism.


I currently have (don't laugh) a Celestron Astro Fi 6" SCT and 1.25" eyepieces only due to the narrow baffle tube diameter.  Down the line I'll look to upgrade this to either the C9.25 or Edge 8 as an absolute aperture minimum but hopefully bigger - sticking with an SCT I am reasonably sure of i.e. likely f/10 minimum too.  This is making me think I should get one of the 2" options to give me the best flexibility in the future if I do use 2" eyepieces with no vignetting.  I am aware using 2" eyepieces is useless now due to my current baffle tube restrictions but I do have the clicklock 2" SCT visual back and a 1.25" clicklock adapter for a more secure connection of accessories.


I'm also keen to use a binoviewer ideally before I upgrade my OTA (and mount) with a set of Hyperion Zooms which is making me lean towards the T2 prism with its great flexibility of adapters and the need for a shorter optical path with binos.  The ideal back focus on my SCT is 127mm.  It is worth noting, and I have checked with Baader, that I cannot connect a 2" diagonal directly to the SCT thread on a 6" using their locking ring as the locking ring diameter is too large and will not fit due to the distance to the focus wheel.


I basically want to buy one best-in-class diagonal which will cover all use cases with any size SCT which is probably not possible and I should just suck it up and accept i realistically need a T2 set up should I choose to use binos at any point and a 2" when I upgrade, but if anyone has any advice on what I should do, please let me know!



#2 db2005



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Posted 06 August 2020 - 05:00 AM

You could consider getting a f/6.3 reducer/corrector to use with the 1.25 diagonal instead. Using the reducer means you can utilize the maximum field of view the C6 (or a standard C8, not the Edge) can provide and the reducer provides a better corrected field.

#3 havasman


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Posted 06 August 2020 - 05:20 AM

As the speed of change continues to accelerate, future proof becomes even more mythological.

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#4 sanbai


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Posted 06 August 2020 - 07:01 AM

From your list I would pick the 2" BBHS mirror. There you can use the maximum field stop of a 2" eyepiece. It's a bit lighter and there is no chromatic aberration possible in any type of scope.

What I like from the Baader options is the clicklock. Otherwise a AP Maxbright is cheaper and practically or equally as good, as per CNrs opinions.

But as a note to future-proof equipment: the future is not proven yet. What if your next scope is a dobson? The diagonal would be useless.

Other CNrs should confirm at what point they see vignetting. Assuming the baffling is strong in the 6" SCT, either the T2 or a good 1.25" would do a good job at lower expense.

Edited by sanbai, 06 August 2020 - 07:02 AM.

#5 Eddgie



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Posted 06 August 2020 - 08:07 AM

For the C6, there is only one configuration that will work at full aperture with binoviewers without using a GPC or amplifier and that is pretty much the 1.25" prism diagonals, and even then, you need to use a short visual back. It is pretty easy to turn a C6 into a C4.7" at f/15, with a 40% obstruction Now that only matters if it matters to you, but C6 has a design that is intolerant of much flange to focal plane displacement.  


If you want to go 2" then to use the binoviewer in the 2" diagonal, a Televue Bino Vue 2x or 2x Barlow becomes important, again, to prevent aperture loss.  Now the C8 will be better than the C6, but depending on the model, you still only have a couple of hundred millimeters to pay with and the 2" and BV is going to add 350mm of focal length and potentially 1/6th wave of spherical aberration. 


My own advice then would be to buy the less expensive T2 diagonal for the binoviewer and whatever 2" diagonal you prefer later on.  I would not give too much credence to the many reports that suggest that this or that diagonal will make a big difference.  Mostly the difference are too small to see or so subtle that it is difficult to see.  All good quality diagonals will perform well. 


But the C6 is going to loose aperture with anything but the T2 diagonals and a T2 binoviewer attached to it.  I recommend getting the standard T2 prism (it has the same specs as the former Zeiss prisms and you don't need the extra aperture for BVs and 1.25" eyepieces). IF you get the larger scope later, you can swap in the standard T2 for planetary work or barlow up.


Also, be aware that the C9.25 is also a design that is not super tolerant of large flange to focal plane distance.  The 8" EdgeHD is unknown.  I measured aperture loss at 170mm, but someone else measured it at 200mm, so clearly more measurements would be needed to really form a concensus. The C8 should be good for 200 to 220mm.

Edited by Eddgie, 06 August 2020 - 08:15 AM.

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#6 SonnyE



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Posted 06 August 2020 - 10:17 AM

Using a 2" would be my preference.

There are numerous reasons, bigger sweet spot being one that comes to mind.

My diagonal is a Photographic Quality. Because I do imaging, but also consider, is there such a thing as too good?

No matter what your currant telescope, one day you may get a better one.

Wouldn't it be nice to have a diagonal that can give you the better view? Rather than buying a newer telescope AND a better diagonal?

Better viewing through better use of intelligence.

#7 Hesiod



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Posted 06 August 2020 - 10:43 AM

IME the "Zeiss" and "BBHS" are needlessly expensive if not paired with top-tier telescopes, especially in the case there are mirrors somewhere in the design as those mirrors will be the main source of scattering.

In such case the standard Baader T2 prism is already more than enough, with the added benefit of a somewhat shorter light path which may be of interest if want to use a binoviewer (by the way, I have the original Maxbright and judge very fool to use it with the Zeiss or BBHS diagonal because the optical issues of the Maxbright are several magnitudes larger than the difference between such diagonal and the "basic" Baader prism).


If want to use a 2" diagonal I would suggest a dielectric mirror of decent quality, such as the GSO unit (or its rebranded sibling): its mirror is very likely smoother than those installed in typical SCTs/MCTs and indeed smooth enough to make an acceptable compromise even with very good telescopes with excellent optics

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#8 Spikey131


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Posted 06 August 2020 - 09:00 PM

Do what Eddgie says.  A T2 prism will serve you well, whatever you do in the future.

#9 Bean614



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Posted 07 August 2020 - 08:28 PM

Nothing is "future proof", period. Nothing. Zero. Zilch. Nada. NOTHING. 

#10 oliveraplin


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Posted 08 August 2020 - 12:20 AM

Thank you all for your comments and great detailed advice!


Even my brief time on the forums here on CN has taught me that Eddgie’s advice really ought to be followed!  I can’t bear the thought of losing aperture so will be going for a T2 with shortest optical path possible.  I’ve just found out yesterday I’m having twins so I think the second scope will be a longer way off now, I guess that does mean more time to save though...


Cheers all and clear skies!

#11 Supernova74


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Posted 08 August 2020 - 02:58 AM

Well when it comes furture proofing personally I thing there is no such thing to be honest as manufactures and brands are always trying to push the boundaries of technology.even tho the trade off is considerable more money for small increments of optical performance.and as a general whole soon as a new product that comes out on the open market curiosity kills the cat and we must puchase one that’s just the nature of the hobby I guess and we all can get dragged into the sugar coated tech jargon.so is the baader BBHS diagonal worth the premium price tag yes for myself personally as I’ve just recently puchased one after lengthy decision making and the appropriate feed back I’ve received from forum members who have actually used them on a regular basis.i intend to take reviews by a narrow pinch of salt initially as reading one thread is not adequate for parting with my cash especially at that price point as I want a sound product that it claims it can achieve even the small increments of optical performance as I stated my only be marginal.however I truly believe that a diagonal does play a major role in the optical chain as it’s a optical device that presents to you the final image to the eyepiece.


You are correct thinking that the BBHS diagonal T-2 equivalent introduces vignetting on some 2” eyepieces especially on the Exsplore scientific 40mm 68 degree EP that I own.this is due to how the feild stop is situated.however on the Televue 27mm panoptic this didn’t seem the case and I got away with it.personaly I truly feel that baader should taken this major detail into consideration when thay was writing the script so to speak in the spec sheet. So in a nutshell I returned it.the T-2 prism and diagonal is only suited for imaging purposes 1.25”EP,s and binoveiwers and has a stated clear aperture or mirror opening to the eyepiece of 31mm compared to 47+ mm for there oversized 2” mirror diagonal so this would be a more wiser choice for furture proofing as you stated in your post.


you also may of heard that some of the models in the range may be collomatable which I’m very sceptical about on those claims as most are set in 45 degrees angles in the housing and seems a tad shady at best in fidderling around with screws which could cause mis-alignment altogether so I would leave well along as I’m finding it hard to believe this would play any effect for visual purposes.


performance wise it has silver coated mirrors then is diectic coated for added protection and gives you maximum image brightness in the substrate possible and only one other diagonal on the market could better that which is an vernonscope diagonal at a colossal $800 or so.and the coatings will remain that way over time without tarnishing

also the colours will be more evenally distributed over the physical spetrum and this will enhance views while observing colours in stars,more better colour  saturation on the planets and when I observed the M13 in Hercules I noticed a more like 3D exsperiance on the globular cluster.you should also be able to detect ever so slightly lower magnitude stars in the background.


regards sean

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