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Diagonals or prisms?


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14 minutes ago, davekelley said:

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.....

 

Yes, when I was observing Albireo the other day the double star was brighter and colours were deeper, more pronounced - and double stars are my main thing for visual. In my mind there is no doubt. This was BBHS mirror with Tak FS-60Q. I changed the diagonals back and forth and used the same eyepieces - Vixen SLV 6mm, Vixen SLV 9mm and Baader Zoom. I did this multiple times just to confirm.

Go for it. You will not be disappointed. Inquire at FLO ;) Steve just posted they can get them. Beware...I was patiently waiting exactly one month for all the pieces to arrive from RVO.  Hope FLO can get yours sooner :)

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In a fast optical system with steep angled rays then an simple 90 degree prism will introduce aberrations compared to a similar quality mirror. 

Ray tracing will easily show this. I suspect in slow visual instruments this will not generally be an issue as shown in the posts above.

Regards Andrew 

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Pity you can’t try a few prisims first to see what suits you best in your scope. No two people are the same and while one will say this one is better than anything else the next may say another is the best. Eyeballs differ. 🙂

Interesting discussion on the matter. There is someone who compared the Zeiss and non Zeiss on a small mak and couldn’t see any difference.

https://www.cloudynights.com/topic/480944-baader-t2-prism-vs-t2-zeiss-prism-on-planets/

Edited by johninderby
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I use the Baader Zeiss spec prisms for mono and bino viewing with the TEC 140.  To my eye they clearly outperform the AstroPhysics dielectric that I used previously - and the AP is supposed to be as good as it gets in terms of a mirror/dielectric.  There’s less scatter and better contrast and image brightness - I sold the AstroPhysics. 

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I have 2 Revelation 2” dielectric diagonals. One for use in Ireland and one for use in London, so I don’t have to worry about hoiking one back and forth and potentially forgetting one.

I accidentally took the London one on my latest trip to W Cork, and naturally I accidentally left it there. So I have both my diagonals in Ireland whilst I’m in London.

I do have a little WO 45 deg erecting prism here though, and it’s that I’ve been using with my 105 f/6.2 refractor lately. It works, but produces a sharp diffraction spike on bright things. Looking at the off-focus diffraction pattern of Vega, for example, it produces a beautiful vivid mesmerizing kaleidoscope of all the colours of the spectrum.

So, I’ve ordered a Baader-Zeiss 2” prism and am excitedly expecting it shortly.

When I get my dielectric mirror Revelation back to the UK, likely October, I’ll do a proper comparison between the three: the 45, the Zeiss and the Revelation mirror.

M

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2 hours ago, JTEC said:

I use the Baader Zeiss spec prisms for mono and bino viewing with the TEC 140.  To my eye they clearly outperform the AstroPhysics dielectric that I used previously - and the AP is supposed to be as good as it gets in terms of a mirror/dielectric.  There’s less scatter and better contrast and image brightness - I sold the AstroPhysics. 

You must have more acute vision than I do :smiley:

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Don’t know about that , John ... 🙂.   I do like the prisms though.  I read somewhere that they’re back coated with the BBHS silver.  Not sure whether that’s true.  When I bought my TEC more than 10 years ago I went for what I thought at the time would be the best diagonal, the 2” AP.  It was good, of course but I think the prisms give a more scatter free, brighter image. So much of visual astronomy is down to taste and impression though, so I wouldn’t want to claim any more than that. 

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19 hours ago, heliumstar said:

FLO doesn't seem to stock them :( ) :

Prism: 2456095

Mirror: 2456103

Nosepiece: 2458105

1.25" Clicklock: 2458100

 

18 hours ago, FLO said:

Sorry about that. It is a simple matter to add them to our website and to stock. I will do that when we reopen Monday 🙂

Steve 

They are now listed at our website. 

Star-Diagonals

Baader T-2 Prism Star-Diagonal

Baader T-2 BBHS Mirror Star-Diagonal

Nosepiece

Baader Nosepiece 1.25" - T2

Baader Nosepiece 2" - T-2

ClickLock Adapters

Baader ClickLock 1.25" Adapter with T-2 Thread

Baader ClickLock 2" Adapter with T-2 Thread

If there is anything Baader you want that is not already listed at our website please ask, it is highly likely we can source it 🙂 

HTH, 

Steve 

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I am after a diagonal for my Meade 127 achromatic refractor, I'm going to see what FLO have at SGL in my price range I would like to put a self centering adapter in so I don't have to fiddle with thumb screw's in the cold this thread has give me some ideas thanks.

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20 hours ago, johninderby said:

Pity you can’t try a few prisims first to see what suits you best in your scope. No two people are the same and while one will say this one is better than anything else the next may say another is the best. Eyeballs differ. 🙂

Interesting discussion on the matter. There is someone who compared the Zeiss and non Zeiss on a small mak and couldn’t see any difference.

https://www.cloudynights.com/topic/480944-baader-t2-prism-vs-t2-zeiss-prism-on-planets/

To be fair, there's not alot of point making judgements on these when the scope is likely to be the limiting factor with lower optical quality. Stick them in a decent apo under good conditions at higher powers and then the differences should start to show.

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The TSA 120/Baader Zeiss 2" prism is superb, no detectable scatter using top eyepieces and with razor sharpness. No loss of DSO contrast.

However....this is a very well matched system, a good triplet APO at f7.5 that likes the prism.

In my other refractors the prism seems to have one small issue or another- false color in the SW120ED on Jupiter for example (almost able to focus out) or a loss of DSO performance in the 90mm SV triplet APO.

To the OP, if it were me I would get a good, low scatter mirror diagonal as they are less fussy IMHO.

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8 minutes ago, Stu said:

To be fair, there's not alot of point making judgements on these when the scope is likely to be the limiting factor with lower optical quality. Stick them in a decent apo under good conditions at higher powers and then the differences should start to show.

I think that’s right.  I’m clear that the Baader Zeiss prisms give me the better results with my TEC140 - which is a very ‘decent apo’ - than the AP dielectric did.  Less scatter, purer and brighter. That goes for mono and bino viewing. If I plugged them into my dusty old, uncollimated Newtonian perhaps these differences might not be apparent.

There is something subjective about this though that isn’t easy to characterise. Can you ‘see more’ with the prism than a quality mirror? Perhaps not, unless scatter is an issue. Is the observing experience a little bit different? In my opinion, yes. But however hard I try to be objective about this, I’d have to agree that in the end it might boil down to preference and taste. 

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