Yes you may have acquired one of the adapters made from Nikon S helical from @jonmanjiro ?
Coldkennels
Barnack-toting Brit.
I've just received the LTM/Contax adapter I ordered from this latest batch. I had a play with it last night; it mounts a range of 50mm lenses fine as expected (pre-war and post-war 50/1.5 Sonnars, a Jupiter 8M, and a Helios 103), but there's a fair amount of variance in how easy they are to mount, with the J8M in particular being incredibly tight to fit. The Jupiter 11 mounts fine, but my Jupiter 9 will not - I suspect that's down to the lens and not the adapter though, as that's always been difficult to mount on any camera, whether Kiev or Contax.His current adapter design is entirely Amedeo's own proprietory creation, with it's own helical and lens release design. I'm unsure if there are physical differences between older adapters and his current adapters with regards to lens compatibility.
Compatibility of Nikon S / Contax RF lenses on Leica M with Amedeo Adapter
Disclaimer: I thought about starting this thread in the Nikon forum, but decided to start it in this forum so it can be a combined resource for both Nikon and Contax mount lenses. Background: Lately, there's a lot of interest in Amedeo type adapters for mounting Nikon S-mount lenses and old...rangefinderforum.com
I did have a play with a Jupiter 12, and it's not the easiest thing to put on the adapter, but it will mount if you're patient. The problem is there's not a lot to hold on the adapter if you're trying to fit the adapter to the lens first, and fitting the lens to the adapter while it's on a camera inevitably unscrews the adapter from the camera if the fit is quite tight. Nevertheless, with a bit of trial-and-error, I got the Jupiter 12 and Amedeo combo mounted on a Leica Ic (I went with that first as there's no RF cam for it to interfere with), then (gingerly!) mounted it to a IIIg. Sure enough, it mounted fine - and even had full RF coupling. I'm not sure I'd do it again (the Jupiter 12 isn't good enough to be worth the hassle!), but it's good to know it works. Presumably this means some of the Zeiss lenses may work now, too.
Now I just wish I could figure out what makes my Jupiter 9 so difficult to mount...
das
Well-known
Thanks for the report! That's pretty good to know that the Jupiter 12 can mount with some practice. That may mean that many more lenses with large rear blocks that did not work with the M adapter may work with the LTM one, maybe?
This is a 35/2.5 S-mount Nikkor mounted on the Amedeo LTM adapter, the gap between the rear lens retainer on the lens (black) and the brass determines how large a rear element can fit into the adapter. I measure 1.333 inches or 33.86mm for the throat diameter of the adapter. The diameter of the rear lens assembly needs to be smaller than this.
This photo shows the RF cam after the adapter is mounted. The cam rides on the brass helical of the adapter
maddoc
... likes film again.
I think that I got it from Robert Jagitsch here at RFF. However, there was so much trading of gear at that time that I lost track.
Oh well then you got the adapter from me! 
I got the helical from @jonmanjiro, as there were some of the Nikon reissues that were having problems with the reissue helicals. So Nikon would swap out the helical with a replacement. He somehow got them to return the old helical as well, along with the repaired camera! The helical then went to Amedeo which he built into an adapter. The adapters with the black focusing scale were *so* nice looking, compared to the Kiev helicals he had been using...
I got the helical from @jonmanjiro, as there were some of the Nikon reissues that were having problems with the reissue helicals. So Nikon would swap out the helical with a replacement. He somehow got them to return the old helical as well, along with the repaired camera! The helical then went to Amedeo which he built into an adapter. The adapters with the black focusing scale were *so* nice looking, compared to the Kiev helicals he had been using...
maddoc
... likes film again.
I learned something new! Very interesting.Oh well then you got the adapter from me!
das
Well-known
I had a question if anyone knew offhand. I want to mount a 21mm 4.5 Biogon with the LTM adapter. But I really want to get the Nikon version as I don't have any other Contax lenses. Do you think the Nikon adapter would be "close enough" if used with the Biogon? Or would it be better to just get the Contax version?
dexdog
Veteran
The depth of field on a 21mm lens is pretty wide. Given that the 21mm Biogon is max aperture f4.5, you should be OK with using the Nikon version adapter, ie., the depth of field will overcome the focusing differences between the Nikon and Contax helicals. Link to DOF Master, using a Leica M9 as an example. You may of course use any camera on the list
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I have two Zeiss lenses which @Sonnar Brian adjusted for use on Nikon S-mount, both 50mm. I doubt the 21 needs any adjusting as explained by @dexdog
So now with one adapter (Amedeo Nikon S to LTM) I can use all my S-mount Nikkors as well as my Contax RF mount lenses on Leica bodies.
And all these lenses also work on my Nikon RF bodies.
So now with one adapter (Amedeo Nikon S to LTM) I can use all my S-mount Nikkors as well as my Contax RF mount lenses on Leica bodies.
And all these lenses also work on my Nikon RF bodies.
dexdog
Veteran
The zeiss 21/f4.5 for contax is one of my favorite lenses. I have posted this pic before. Otovalo market in Ecuador, Contax IIa
das
Well-known
The Biogon is certainly great. I would enjoy being able to use it on a metered M body, a Bessa R4, or even on a Canon RF. Nikon RF bodies have never done it for me.
A blast from the pastOh well then you got the adapter from me!
I got three replaced reissue focus helicals back from Nikon before they stopped returning the replaced parts to me. I gave one to Tom A who said he planned to make an S-mount Leica M2 with it (don't think that ended up happening though), I sent another one to a guy in SG, and I still have the 3rd one converted to an M-mount to S-mount adapter by Amedeo.
It was a loong time ago, so my memory is rusty, but I think your helical actually came from a donor S or S2? I do remember that Amedeo had my helical and your helical at the same time, so was able to measure and compare, and iirc he started making his own excellent S-mount adapters from scratch shortly after.
Richard G
Veteran
Awesome depth of adapter lore in this thread.
Bingley
Veteran
I was lucky enough to pick up the Amedeo Contax to LTM adapter while they were available. I have used my W-Nikkor C 35mm f2.5 lens with this adapter with great results; however, it will not mount the vintage Contax Biogon 35mm f2.8. I don't use 21mm lenses, but I'm glad to see that the Amedeo adapter has opened up the use of these lenses on Leica cameras.