A pair of sonnars in post war ltm custom mounts

[S.H.]

Here is a pair of lenses I acquired a decade ago, I never was quite satisfied with them. Focus is slightly off on my m8... I suspect they need some shimming.

I am thinking of trying to adjust them but both are mounted in barrels I never saw elsewhere : no screw anywhere. Also the helicoid is apparent at the back. I suspect the ring must be unscrewed from the back but I don't want to mess anything up.







I'd be happy to get some pointers on how to adjust those two: it feels wrong to forget them in a closet.

 

[Sonnar Brian]

Hard to tell from the pictures: is the 39mm thread mount a separate piece from the DOF ring? Is it two peices that has been fastened?

Looks like a custom job done by a machinist. Lens on the right is a transition lens. One of the left- a post-war 5cm F2. Both look custom adapted to LTM.

 

[dexdog]

Both lenses appear in Thiele's book, the 305 series from 1947 and the 270 series from 1942. Both are listed in Contax mount. Those are very unusual, never seen anything similar.

 

[Sonnar Brian]

Second uestion: How far off is the focus? Do they back-focus? Front focus? Take a measurement at 1m, wide-open and report how far off the actual focus is to the RF.

For back-focus, you can built up the cam. I use 3M copped tape. Usually one or two layers corrects most problems.

 

[S.H.]

The DOF is engraved on the ltm mount : the rear is a one piece block with the ltm screw machined.

I have the Thiele book and both appear as Contax mount. However one is wartime, one is postwar so they could be zeiss irregular production or custom jobs from regular lenses. Both were separate eBay buys.

Edit : I'll take some test pictures tomorrow after work.

 

[raid]

Cool! I love seeing such finds. Thanks.

 

[TenEleven]

As others have already pointed out these are custom jobs. I guess what I can add is that is that "original" (well as far as that can be confirmed anyway) CZJ post-war LTM lenses all have a hourglass shape with a slim outline.

The construction of these is very basic with a single helical driving both the lens and rangefinder arm of the camera. The lenses are made to be 51.6mm exactly. They are however not my favorite to work on because the optical cells are mounted into the focusing part, i.e. the optical cell plus aperture does no longer come out in one piece making these hard to work on and adjust. Interestingly enough they kept the design of the LTM Biogons intact though, just like how the Contax mount post-war (but still Jena) Biogon is the closest to the pre-war lenses in mechanical contruction. (The Sonnars are very different.)

I cant find the picture of my f2 Sonnar but rest assurd the construction is virtually identical. My assumption is that once the dies for the more complex construction (collapsible, multiple helicals) got carted off to Russia CZJ had to re-design these mounts from scratch.

EDIT: Found it! That's the 1.5 and the 2.0 side by side. Both post war. I have seen at least 10 in total so this was more than a one-off for sure.

 

[S.H.]

Second uestion: How far off is the focus? Do they back-focus? Front focus? Take a measurement at 1m, wide-open and report how far off the actual focus is to the RF.

For back-focus, you can built up the cam. I use 3M copped tape. Usually one or two layers corrects most problems.

Here are some tests, fully open, minimal distance, focus on the red 20 mark. I'm on linux these days, and dng support on Gimp is not stellar. I mostly use film.

1.5 (it can focus down to 0.8m)




2.0

 

[Sonnar Brian]

Based on the above: the F1.5 Sonnar has a slight front-focus at F1.5. It might be optimized for F2.8, would be interesting to see. Front focusing means the optics need to be moved closer to the image plane. You could try unscrewing the rear triplet about 1/4 turn to see if the focus improves. If it does- I use some teflon tape or copped wire for a shim. I'd do with teflon tape, like what you use for plumbing.

The F2.0 lens- slight back-focus. Check the focus at infinity and F2. If it is good there- you could build up part of the Cam. As it rotates, you can use a Stepped cam. If focus is off at all distances, build up all of the cam. I use these techniques for lenses that refuse to be disassembled.

 

[S.H.]

Thanks a lot! I did a quick check with the 1.5 at other apertures, nothing obvious. I will redo some tests with a tripod to be sure.

I noticed that the aperture of the f2 lens is very hard after f4: I will concentrate on the bigger 1.5 for now. I will see what spanner I have, or make one to tweak the rear group.

Can I just unscrew the external ring?

 

[Sonnar Brian]

Thanks a lot! I did a quick check with the 1.5 at other apertures, nothing obvious. I will redo some tests with a tripod to be sure.

I noticed that the aperture of the f2 lens is very hard after f4: I will concentrate on the bigger 1.5 for now. I will see what spanner I have, or make one to tweak the rear group.

Can I just unscrew the external ring?

View attachment 4823651

Missed this! Been crazy busy.
The rear fixture should just unscrew, using the outermost spanner slots.