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Baader prism diagonals and f7 scopes

Moonshane

By Moonshane
in Discussions - Eyepieces

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Moonshane

Moonshane

Posted
Posted

hi all,

I have been thinking about getting one of these for a while. Preferring 1.25" eyepieces in my refractors, I sold my 2" diagonal (a Baader Clicklock) and now want a 1.25" replacement of equal or better quality.

I have a Revelation dielectic diagonal that I use in my PST mod which seems pretty good but it's a faff to keep taking it apart to use it for night time observing.

In a way I have an itch to scratch I suppose hence the wanted ad for a Baader prism diagonal which seems a good buy at £100 or so new.

My question is really two fold:

  1. Should I buy a Baader T2 prism diagonal now or wait a couple of months or so to buy one of the Zeiss versions. Are they really that different? I am mainly assuming that observing planets (obviously this can wait a few months now) and double stars will benefit from the decreased scatter of the Zeiss but would the T2 be far behind? In a way I think I have answered my own question. I think I should wait - anyone disagree?
  2. I read slightly conflicting views about the sort of focal ratio that prisms start to show aberration - presumably CA. I am quite sensitive to CA. Would my 120ED at f7.5 and my (yet to be paid for / collected) Astro-Tech 102mm f7 be suitable scopes for either of the prisms? Should I forget the idea and buy a 1.25" Televue Everbrite?

Finally, anyone know if the eyepiece holder usually sold as a package (the one with the fine focus) have an eyepiece stop? Or is it not possible to hit the prism with eyepieces that have a long nose like my Nagler zoom.  I suspect the male t2 mounting ring might stop the eyepiece?

Thanks for any guidance. Shane 

 

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DRT

DRT

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Shane,

I bought a brand new 1.25" TV Everbrite three weeks ago for my TV 60mm. You are welcome to borrow it at SGL XII to give it a go. Hopefully someone else will have a Baader Prism that you can use as a direct comparison.

Derek

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DRT

DRT

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7 minutes ago, Moonshane said:

cheers Mark that's kind of you.

I definitely want to stick with 1.25" though so maybe best to stick with Derek's equally kind offer.

Best wishes

Shane

I also have a 2" TV Everbrite (or perhaps it's three :rolleyes: ) and a TV 2" Enhanced Aluminium so you can knock yourself out with comparisons :wink:

 

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Highburymark

Highburymark

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Shane, you are probably aware that there are conflicting views on the various merits of the Baader T2 prisms, but the majority view, as far as I can see, is that scatter is better controlled through the Zeiss, although the cheaper T2 diagonal is still an excellent performer. As I spend so much time observing the moon and planets I thought the extra investment was worth it - I haven't yet tried my new Zeiss prism out. I'm hoping it will also deliver in my F6.25 refractor - I'd be very surprised if there are any aberrations in your 120ed.

It's a really good point you raise about the danger of EP noses potentially coming into contact with the prism surface. I bought a relatively low profile telescop service T2-1.25" EP holder and my Delos EPs are no more than a mm above the prism. No chance of using a Nagler zoom or Pentax XF zoom with their long noses - so the spacer would be a good idea

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Stu

Stu

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Shane, like all these things the improvements are marginal, but at high powers for critical planetary observing I do think the Zeiss is worthwhile.

To my eye it holds the image quality to higher powers than standard diagonals, and I find that the scatter is very well controlled. This is all gut feel rather than scientific, but I have always found myself using it over other options.

Quite right to worry about hitting the prism surface, I did damage one in just the way you describe; a painful and expensive mistake!

I find that the prism is fine in my f7.4 Tak, I'm sure the 120ED would be fine. Note that they do need a little cool down time to perform at their best, particularly if brought from a warm house. The T2 much less than the full 2" though.

One other option to try is the Tak 1.25" prism. It gets great reviews and is very good value. I've not used one but believe MikeDnight does, and he knows a thing or two about planetary observing :) 

 

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Moonshane

Moonshane

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Cheers Stu

That's good enough for me mate. I thought about the Tak but didn't like the sound of having to do lots of turns on the compression fitting with barrel undercut eyepieces. Would soon get boring. What you describe is exactly why i want one.

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DRT

DRT

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9 minutes ago, Stu said:

One other option to try is the Tak 1.25" prism. It gets great reviews and is very good value.

I had a Tak prism with the Skylight 60mm F16 I sold recently and it was excellent. The only thing I didn't like about it was the twist-lock as it was a bit of a faff with some styles of EP and almost impossible to use with the 1.25" Ethos EPs with 2" skirts.

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jetstream

jetstream

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The 2" Baader/Zeiss prism is extremely sensitive to focus in my SW120ED on the planets, Jupiter in particular, one side of focus gives one hue the other side another. In focus it is simply amazing. This prism offers very low scatter and is great on doubles. On DSO is seems to give less transmission ( or something) that can make really faint objects hard or impossible to see, I use a VG copy of SW's diagonal for this use. The Moonlight CFL on my 120ED really made a difference with this prism diag and it does excel on planetary/lunar. I've heard the T2 version offers even less scatter than the 2", which would be amazing.

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iPeace

iPeace

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newarrival.jpg

I have a 2" Baader/Zeiss with ClickLock (so no danger of eyepiece hitting prism) which I have used with a TV85 (f/7) and a SW ED120 (f/7.5) with total satisfaction. I do not know how sensitive I am to CA but I do recognize it when I see it and I have seen none whatsoever. To me the views are marginally better than with a TV dielectric, and I do recommend it highly but it is quite the premium item and I can't help but feel that for many it may not be worth the outlay. The versions without the ClickLock eyepiece holder are less expensive and may be better value - though I wouldn't want to do without.

:happy11:

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Moonshane

Moonshane

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Cheers guys. I'll be using it on my 120ed with dual speed moonlite and a 100mm f7 with dual speed feathertouch.

I think I need to scratch the itch but will try and find a used one.

Another area this might benefit me is that I am considering binoviewers in the future and I think these prisms allow for a reduction in light path vs standard diagonals.

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iPeace

iPeace

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2 hours ago, Moonshane said:

Cheers guys. I'll be using it on my 120ed with dual speed moonlite and a 100mm f7 with dual speed feathertouch.

I think I need to scratch the itch but will try and find a used one.

Another area this might benefit me is that I am considering binoviewers in the future and I think these prisms allow for a reduction in light path vs standard diagonals.

For what it's worth, my f/7 also has a dual speed FeatherTouch and my f/7.5 (also an ed120) also has a dual speed Moonlite.

:happy11:

I feel quite confident you will not regret carrying out this plan.

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Knighty2112

Knighty2112

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On 9 September 2016 at 22:28, Knighty2112 said:

No, there is no stop in the diagonal. You have to be careful with any longer EP's or other equipment that you put into it. Wish there was one. 

Actually, scrub what I said there. On closer inspection there is a stop, however it will only stop items inserted into the diagonal as long as they are larger than 30.47mm diameter (typically EP barrels). I have a Celestron 2x Barlow lens where the lower  lens part (which can be unscrewed from the barlow) is less than this measurement at just over 29mm. However the prism itself when the focusing eyepiece holder is wound fully up to its maximum height has a distance of 43.1mm from the top before any object would hit the prism, so you must check carefully all items that you might insert this diagonal.

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