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Contax_crisis
Tinkerer
Username: Contax_crisis
Post Number: 18
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 12, 2009 - 11:22 am: | 
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Despite trying to live with a Leica M6TTL, I just can't get along with its weight and bulk. Looking back, I've been putting up with it just to use some of the Zeiss lenses (Sonnar-C 50mm f1.5 T* ZM mount and the Biogon 21mm f2.8).
The IIIf has always been my preferred 35mm camera, and I wonder if anyone has tried to modify the ZM/Leica bayonet mounts to a LTM screw mount.
Checking the rear elements with a set of calipers, the rear element has sufficient clearance to the film plane. The ZM mounts would need to be shimmed by 1mm, reducing the flange thickness. Would this affect mounting stability....or is there a way around this problem?
Neither lenses block the rangefinder patch either, so both can still be rangefinder coupled, if the shimming of the flange mount and machining of a screwmount meets the correct tolerance.
I wonder if anyone has done this before, or had any experience outsourcing this kind of work to a technician? I guess it wouldn't be cheap, however I'm hoping the M6TTL body would pay for the conversions.
Thanks for any thoughts. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 980
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 12, 2009 - 03:03 pm: |
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It sounds like an awful thing to do to the lens. Wouldn't it be as easy and more economic to sell the M mount lens and buy an LTM equivalent? |
Glenn
Tinkerer
Username: Glenn
Post Number: 662
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 12, 2009 - 05:33 pm: |
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The throat dimension of the M mount is 44mm and the LTM is 39mm - So unless the male bayonet is easily removed from the lenses in question and the diameter of the rear barrel is less than 33mm, forget the idea.
The reasoning behind the M bayonet dimensions was to allow the LTM lenses to be used on the new M Series models, not vice-versa! |
Contax_crisis
Tinkerer
Username: Contax_crisis
Post Number: 24
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 13, 2009 - 11:41 am: |
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Rick & Glenn - thanks for the thoughts.
It is a terrible (?) thing to do to a great lens. I wish there were modern LTM equivalents; the 35mm Summicron Asph f2.0 works well with the IIIf, but nothing I've found is quite as impressive as the modern Sonnar-C lens. The M6TTL requires a separate 21mm viewfinder in any case, and the pure mechanical size and shape of the IIIf is such a delightful little rangefinder camera to use. I guess the M6TTL is too modern for my taste 
One alternative for the 50mm Sonnar-C I can think of, is to use a Contax-LTM adapter for the older original Sonnar 5cm f1.5 if diassembling and remounting the Sonnar C into another barrel proves too fraught with engineering challenges. I've seen a few optical specialists who will do laser (multi-coatings) too. In any case, the technical skill is way beyond me so I've asked someone who knows what he's doing to have a look at which option would be more workable. I think he'll say what Glenn says about the throat issue, however re-machining the rear throat dimensions down to LTM dimensions won't necessarily lead to the loss of rangefinder coupling, will it?
PS - Rick: this is a question you might know the answer to. Was the Zeiss Sonnar C 50mm f1.5 T* lens, reissued in a limited series, for the original Zeiss Contax I/II/III series/Nikon rangefinder camera? If it was, then maybe the alternative, is to source one of these lenses, and use a Contax-LTM adapter, instead of wrecking terror on the lens... |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 981
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 13, 2009 - 02:25 pm: |
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I don't know if the reissued Sonnar is the same or not; but my own experience with an original 50/1.5 Zeiss-Opton Sonnar has been very good, for whatever that's worth.
As for modifying the M mount lenses, they're your property to do with as you like. You might want to consider the possible cost involved in chucking them into the trash bin, though, as one slip or miscalculation on the lathe will spell the end of the lens both as a usable and as a saleable item. Usually, when people do this sort of thing for a living, they have a few practice pieces along the way, a luxury that you don't have.
I agree 100% on the LTM vs M series designs, by the way: Leica used to scoff at the bulk of the Contax in the prewar years .... after the war, the Contax became as small as a Leica IIIC, and the Leica M3 weighed more than a prewar Contax III (meter and all). Not my cup of tea, for all the excellent quality and performance. |
Glenn
Tinkerer
Username: Glenn
Post Number: 663
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 13, 2009 - 04:01 pm: |
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"This standard focal length offers special qualities which make it wellsuited for portraiture. The ‘C’ designation in the C Sonnar T* 1,5/50 ZM name means ‘classic’. The lens design and aperture geometry reflect its predecessor from the 1930s, the Sonnar 1,5/50, which was the fastest standard lens of its time. The excellent flare control inherent of the Sonnar lens design is further optimized with the ZEISS T* anti-reflection coating. This new lens stays true to its heritage, physically resembling the objectives of by gone days. With its fast aperture, taking photographs with a beautiful ‘bokeh’ that reflect the ambiance of the golden age of rangefinder photography is as simple as pressing a button."
As the above factory info indicates, the Sonnar 1.5 C is designed specifically to give one a chance to reproduce those classic portraits of the 30s/40s. This optical designs accounts for the shift in ' plane of critical focus" that this modern lens exhibits when the lens is stopped down from maximum.
Unless you are actually reproducing the classic images of yesterday, why not look at the Voigtlander 1.5 Nokton in LTM. I have both the Sonnar 1.5 C and the 1.5/50 Nokton, along with various other Voigtlander LTM optics which I use on my 111f, 111g and M series (with suitable adapter for LTM on M). My example of the Nokton is a superb lens, giving results that are nearly equal to the Sonnar for 'modern day' images. Obviously it does not give that 'classic look' to portraits, but I did not buy it for that end and one must remember that there is a vast difference on the effect it has on one's wallet. |
Contax_crisis
Tinkerer
Username: Contax_crisis
Post Number: 27
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 14, 2009 - 12:21 pm: |
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Rick - used side by side, the modern Sonnar-C 50mm f1.5 T* lens resolves more detail than the 5cm f1.6 Zeiss Opton which I use on a Contax III which I repaired, through the help of your detailed diagrams and instructions.
I presume the optical glass in the modern Sonnar has been optimised; it isn't a function of higher contrast rendition alone either; both lenses are fantastic.
Glenn - thanks again for your input. I'm not a huge 35mm user at all; these days, I only use a 35mm camera for pleasure. I lived with a Nokton 50mm f1.5 for six months before parting with it. It is a fine lens indeed. Perhaps I'm too clear in my own mind, that I'd rather stay with the Zeiss Sonnar look.
In any case, I've asked a technician to look at removing the M mount and remounting the Sonnar. The rear element is in fact, small enough to enter the 39mm diameter. The shim/LTM adapter coupling is more a challenge so it might take a few weeks to clarify if it's a workable solution.
Thanks. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 982
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 14, 2009 - 02:45 pm: |
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Good luck! If nicely done, they'll certainly be unique lenses when they're finished. The RF coupling should work - the biggest challenge there is probably to make sure that the lens comes out right side up when fully threaded on. That's easy enough on a production basis, but maybe not so much when cutting a thread on a single piece. |
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