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Zeiss 50/540

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#1 Astrojensen

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Posted 10 September 2018 - 01:21 PM

I was attending this years star party in Kompedal, Jutland, where one of the regular vendors offered me a brand new C 50/540 Zeiss objective for just $62.  I wouldn't say I had wanted one BADLY for a long time, because if I had, I'd bought one many years ago, but now that I have one, I obviously am going to build a scope around it. It has the potential to become a very nice traveling scope.

 

gallery_55742_4772_218902.jpg

 

I'm sorry for the very poor image quality; the one in my cellphone isn't very good at all, but it was what I had on hand.

 

Naturally, I'm now thinking a lot about what kind of tube I should build around it. I might of course just slap a crude one together from various parts from my boxes with miscellaneous junk bits and pieces, so I can actually use it, while trying to build something better. Ultimately, I'd really like something that looks like a mini version of a Zeiss AS100/1000 or one of the APQs or something. That'd be both fun and cool, I think. smile.gif  Maybe something very compact, where everything, including the mount and tripod, fits into a single, not too large box. I already have a small, surprisingly stable, black wooden tripod, which might be suitable. I just need a tube and a mount.  

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 10 September 2018 - 01:22 PM.

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#2 Chuck Hards

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Posted 10 September 2018 - 01:38 PM

I bought one of these a few years ago, still have it.  The DPAC tests were disappointing, especially for CZJ.  I decided to not build a scope around it because I had mass-produced Japanese lenses that are better.  Have you tested yours, Thomas?

 

Curious as to whether I just lost the "luck of the draw" yet again.



#3 Astrojensen

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Posted 10 September 2018 - 01:45 PM

I've not tested mine yet and yours is the first bad one I've ever heard about. Are you sure the lens isn't flipped in the cell? That would be easy to do accidentally, as they're cemented and a little hard to tell which is front and which is back. Properly installed, the front end is the one with the retaining ring, but if it has been taken apart, for cleaning, for example, any bets are off and it might have been installed backwards. 

 

Since the lens diameter is 52mm, which is the same as many Japanese cemented achromats, and the retaining ring has quite a bit of room for adjustment, there's also a real risk that it has been replaced with a cheap 50/500mm achromat... I hope this isn't the case. Mine has the telltale pale brownish Zeiss T* coatings, so I know it's the real deal. 

 

 

Clear skies!
Thomas, Denmark


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#4 Chuck Hards

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Posted 10 September 2018 - 02:03 PM

Tested both ways, it's not backwards.  Just not a very good lens.  Came in factory wrappings so I hope I wasn't scammed.  I'm at work now, my pics are on my home computer, and I"ll check the cell for signs of tampering.

 

I have heard grumblings of others with less-than-perfect examples of this lens.



#5 Astrojensen

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Posted 10 September 2018 - 02:06 PM

I am very surprised to hear that there should be a number of these in circulation with less than good optics. All reports I've read so far only mentions very fine images. 

 

BTW, I've found some parts with which I can make a workable telescope.

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 10 September 2018 - 02:07 PM.

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#6 Chuck Hards

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Posted 10 September 2018 - 02:15 PM

Surprised the heck out of me, too.  Zeiss was my last hold-out for "perfect optics, every time" and I now know that there is no such manufacturer on earth.  Never has been, probably won't be, in my lifetime.



#7 Piggyback

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Posted 10 September 2018 - 03:34 PM

Never before heard of a bad 50/540mm lens on this side of the pond. 


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#8 memento

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Posted 10 September 2018 - 06:45 PM

There are some stories of sub-par Zeiss Jena optics yes. Often this is in regard to SLR camera lenses (that Zeiss Jena also produced during all those decades) but also in regard to telescope optics. The saying is that they made sure that all first-rate stuff got shipped to the Western countries, as former East Germany was always in an urgent need of foreign currency. While some of the less perfect products were sold within the own country (former GDR).

 

But is it true? After so many years, if an individual lens is faulty, that can have a lot of reasons that don't have anything to do with how it was originally delivered ...

 

Regarding your idea of building a nice little scope around it. It reminds me of the Kosmos LW50. It's just the coolest little telescope I've ever seen :) Something like this but looking like a mini Zeiss AS 100 surely would be awesome!

 

16-0.jpg


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#9 Steve Allison

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Posted 10 September 2018 - 08:37 PM

My Zeiss "Teleminor" 50mm telescope was apparently sold originally as a kit. It uses a readily available and fairly inexpensive helical focuser. You can find pictures on the internet if you want some ideas.

 

Like most of these small achromats, mine is a cemented doublet. While cemented lenses have good contrast and light transmission, I understand that coma and astigmatism go along with this, hence the use of air spacing with larger lenses.

 

My own little Zeiss has a beautiful star test and punches above its weight when observing.


Edited by Steve Allison, 11 September 2018 - 04:36 AM.

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#10 Chuck Hards

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Posted 10 September 2018 - 09:04 PM

I remembered that I got mine from a gentleman in Europe, Germany, if my memory is still good.   

 

I was much too hard on it earlier in this thread. 

 

I dug-out the Ronchigram.  This was a poor photographic setup but it tells the tale.  It shows a very good lens, just a touch of SA and perhaps a smidgeon of turned edge.  It's actually a terrific lens and the small issues cannot be discerned by the eye in either imagery or star testing, I'm betting.

 

I probably got soured on it because I tested it immediately after a Royal Astro or Swift objective.  Most of those that I've tested have been at least as good as this and better.  Essentially beyond my ability to be critical of (and that is saying something!)  I do remember having a hard time wrapping my mind around what I was seeing, Japanese lenses testing better than Zeiss.  Still hard to swallow, even though the difference is very, very small.

 

For a cemented lens especially, this one is good.  I suspect one real advantage Zeiss has is that their polish is better. 

 

I may have to finish my build, as well.  

 

CZJ 50mm.jpg

 

 


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#11 starman876

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Posted 10 September 2018 - 09:13 PM

I still have one of those lenses also.  Has been laying in the drawer for years. I should test it.  You are welcome to it Chuck if it tests ok.  


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#12 Chuck Hards

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Posted 10 September 2018 - 09:19 PM

Might make a really good binocular.  We'll talk, thanks Johann.


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#13 Chuck Hards

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Posted 11 September 2018 - 07:11 AM

Thomas, are you going to use a 1.25" focuser, or .965" on your build?



#14 AllanDystrup

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Posted 11 September 2018 - 08:44 AM

    Thomas,

 

     Congrats with your new toy, -- I'm sure you'll have fun configuring and using it.

 

      I have a Zeiss Teleminor OTA with 1.25" focuser, and I have the cemented as well as the air spaced version of the objective, so I can "plug in" my lens of choice as I desire.;Not a big difference in performance between the two versions tho'.

 

     I've done a DPAC of the CZJ cemented C50/540 objective, and it tested pretty darn good (but I have also come across tests that were not so favorable) : https://www.cloudyni...ting/?p=8304964.

 

     For practical observing I do prefer my Vixen FL55S/440mm due to its smaller size, better focuser, sharper image and better color correction. (I also use this one with a T2 backend and up to 2" eyepieces…). Interesting the DPAC of the Vixen was close to (~1/8 wave) - but not quite - as perfect as for the Zeiss...

 

-- Allan


Edited by AllanDystrup, 11 September 2018 - 10:32 AM.

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#15 bremms

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Posted 11 September 2018 - 09:09 AM

Surprised the heck out of me, too.  Zeiss was my last hold-out for "perfect optics, every time" and I now know that there is no such manufacturer on earth.  Never has been, probably won't be, in my lifetime.

Zambuto is no slouch... Although that's not production stuff.



#16 bremms

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Posted 11 September 2018 - 09:18 AM

I have two 50mm f10 ish lenses. One has no cell. Coatings look brownish if I remember correctly FL is closer to 540mm.  I'll check when i get home. The other is mounted, air spaced with about a 1.5-2mm air space. It was part of some optical bench equipment. Quick DPAC showed it to be close to perfect as I could see. I'm not really into small scopes, but I do like my Asahi Jupiter 50mm 600. Crisp little thing.


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#17 memento

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Posted 11 September 2018 - 09:20 AM

For practical observing I do prefer my Vixen FL55S/440mm due to its smaller size, better focuser, sharper image and better color correction. (I also use this one with a T2 backend and up to 2" eyepieces…). Interesting the DPAC of the Vixen was close to (~1/8 wave) - but not quite - as perfect as the Zeiss...

So the Vixen produces a sharper image, yet still when testing the Zeiss is better?



#18 AllanDystrup

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Posted 11 September 2018 - 09:44 AM

Memento,

     Yes, the DPAC I did was monochromatic in green. The Vixen is a fluorite APO with shorter secondary spectrum (better polychromatic correction), the Zeiss is a traditional Crown/Flint Achro.


Edited by AllanDystrup, 11 September 2018 - 10:31 AM.

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#19 terraclarke

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Posted 11 September 2018 - 10:20 AM

I have always heard good things about the little Zeiss ‘Teleminors’ and was often tempted to buy one until I finally decided that for me anyway, it was just about as easy to set up one of my ~60mm scopes. For a travel scope, my diminutive 70mm and 80mm ATM shorttube RFTs or one of my pairs of binoculars suit my needs better. When I travel, I am always more intersted in expansive views of of starfields, asterisms, open clusters, and DSOs that darker skies and wider fields provide. Solar system objects and double stars are just fine at home with my >50mm scopes, and if I really want a fine view and do want to take a 60mm longer scope (like with the Great American Total Solar Eclipse last year), my 60mm Mayflower on the Paragon XHD tripod and Unistar Dwarf is almost as small. On the other hand, the Teleminor would be far smaller and much quicker and easier to take out than my Telementor.

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Edited by terraclarke, 11 September 2018 - 10:40 AM.

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#20 Sasa

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Posted 11 September 2018 - 11:40 AM

Congratulations, I built around my E50/540 lens this

E50a.jpg

I have not finished it. I realized the same as Terra and the project is sleeping. I still need to add bafles and painting. Telementor requires same hasle and it provides significantly more power. Still, I saw through it 8 Gly distant blazar...
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#21 Sasa

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Posted 11 September 2018 - 12:34 PM

This is how I solved the attachment of the cell:

https://www.fzu.cz/~...E50/E50_002.jpg

https://www.fzu.cz/~...E50/E50_001.jpg

I wanted that tube would be also dew shield so the lens is hidden quite inside. I also wanted to use vintage Zeiss focuser. This backfired a little bit. The center of mass is quite off and I can't balance the telescope on Zeiss Telementor mount.

Edited by Sasa, 11 September 2018 - 01:14 PM.

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#22 Astrojensen

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Posted 11 September 2018 - 01:20 PM

 

Telementor requires same hasle and it provides significantly more power.

What I'm currently envisioning is something much smaller than my Telemator, more like the Kosmos LW 50 Memento posted a picture of. The Sterne und Weltraum review of the LW 50 in 1977 is one of my all-time favorite small-scope reviews, so a scope like it around the 50/540 objective was instantly what I imagined. It'll have a tripod, rather than a table-top pier, though. What would be nice would be something dual-purpose, IE a scope that could be used on a very small and lightweight mount for travelling and also on a more substantial mount, like the Zeiss TM, when I want to use the scope at home for quick H-alpha solar viewing in the winter, for example. Even if the scope isn't all that much lighter, it would be much more compact, which allows for easier setup and take down, simply because it's less bulky. 

 

 

Still, I saw through it 8 Gly distant blazar...

I missed that event, due to clouds. That has got to be the most distant object ever seen through a 50mm telescope. 

 

 

Clear skies!
Thomas, Denmark


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#23 Bomber Bob

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Posted 11 September 2018 - 02:17 PM

a scope that could be used on a very small and lightweight mount for travelling and also on a more substantial mount, like the Zeiss TM, when I want to use the scope at home for quick H-alpha solar viewing in the winter, for example.

 

Maybe something like this...

 

Swift 838 S10.jpg

 

50x700...  virtually CA-free...  with a Lunt Wedge, it's now my g&g solar scope.  (Though the night time views are very good, too!)


Edited by Bomber Bob, 11 September 2018 - 02:20 PM.

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#24 Astrojensen

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Posted 11 September 2018 - 02:43 PM

Yes, something like that. Zeiss also had a ultra-simplistic, yet solid mount like the little Swift. It was made from machined steel, so it was probably a fair bit heavier, though. It was designed for the AS63/840 mid-60'ies version with the long drawtube and held that scope quite well. An even smaller version would be sufficient for the 50/540.

 

http://www.astrotref...CZJ-E50-540.jpg

 

The scope in the picture is a E50/540 in a homemade tube with a Zeiss M44 helical focuser from a Telementor 1. 

 

 

Clear skies!
Thomas, Denmark


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#25 Astrojensen

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Posted 11 September 2018 - 03:33 PM

This is how I solved the attachment of the cell:

https://www.fzu.cz/~...E50/E50_002.jpg

https://www.fzu.cz/~...E50/E50_001.jpg

I wanted that tube would be also dew shield so the lens is hidden quite inside. I also wanted to use vintage Zeiss focuser. This backfired a little bit. The center of mass is quite off and I can't balance the telescope on Zeiss Telementor mount.

The focuser is also what gives me headaches right now. I have a tube with a lightweight 1.25" R&P focuser for testing purposes more or less ready, but if the objective turns out to be really good (what I hope, of course) I'd like to build a tube with a more substantial focuser, so I can use modern, heavier accesories without problems. 

 

I did some calculations and interestingly enough, you actually need a 2" focuser on it (or at least a M44), if you want the maximum exit pupil with moderately wide-field eyepieces. This is logical, of course, since the f/ratio is 10.4, but it seems counterintuitive, because the scope is so physically small. If you want an AFOV of ~68°, the lowest magnification is 22.5x and the TFOV is 3° with a 2.22mm exit pupil. This is actually WORSE than what the 63/840 can do with a 2" 40mm 68° eyepiece that will yield 21x, 3.24° and a 3mm exit pupil! So if you decide to stay with a 1.25" focuser, you're not getting a wider field than the 63mm and the view is going to be considerably fainter, too. You can brighten the field (enlarging the exit pupil) by using longer focal length eyepieces, for example a 40mm for 13.5x and a 3.7mm exit pupil, but the TFOV is still just 3°. A 2" is going to widen that to 5° at the same power with a 40mm ES68, for example.  

 

Now, the obvious question is of course whether you NEED that extra field. 3° is nothing to sneeze at and hauling the big eyepieces around on a vacation, where you have to travel light, is of course not going to work well - or at all. From home, things might look different, however, especially on deep-sky. On most occasions, 1.25" might be preferable, though, simply because of the weight issues with such a tiny scope. 

 

But finding a quality focuser for a decent price is actually MUCH, MUCH easier if you choose a 2"! I had a very hard time finding a good quality 1.25" focuser. The obvious problem is of course that a 2" crayford or R&P is BIG. I've found a 2" helical focuser that is not much bigger than the M44 helical focuser, but it only has 30mm's of travel, which is short for a refractor and may necessitate an additional drawtube. 

 

https://www.astrosho...ab_bar_0_select

 

Nothing's decided, of course.

 

And then there's the question of finderscope or not, to further complicate things. Before you say "it's too short to need one", I've actually often found myself wanting one on scopes with even shorter focal length. I'm thinking something like a 4x25 with RACI diagonal. This is because if the scope is used on a low tripod, getting low enough to aim along the scope or use a red dot finder (which I despise, BTW) or a straight through finder can get very awkward or downright impossible. 

 

All of this is merely dreaming and future planning, of course. I do have a more important project right now, which is to get my 125mm f/14 Lichtenknecker up and running. 

 

 

Clear skies!

Thomas, Denmark


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