LTM lens mounting question???

[jolefler]

I'm having trouble with why this situation happens...David or anyone, can you explain what's going on?

I have two bodies, a II and a III. The II came with a 50/3.5 Elmar. I later purchased a J3 and use it regularly with good results on the II body.

I later purchased a III body, then added a 90/4 Elmar which gives great results, but the distance scale does mount slightly past 12:00 toward the windows. The 50 Elmar gives good results when used on this body, but again the DOF/distance scale rotates slightly past straight up.

When I mount the J3 on the III, the distance scale goes around the mount almost to the baseplate....AND the rangefinder is WAY off in all directions???

Why does the J3 work on one body but not the other? Why do the two Leitz lenses work on both, but rotate slightly past straight up on the III?

Thanks, Jo

 

[David H. Bebbington]

Quite a few "Davids" here - don't know if you mean me, perhaps the others will chip in too.

I presume J3 means Jupiter 3 - I have no experience of this lens, but a guy here:
http://pentax-manuals.com/repairs/j3service.pdf
seems to have found build standards to be highly variable!

If a lens focuses accurately on an LTM body, I personally would not worry whether the focus witness mark is exactly at 12 o'clock. As Leica II and III are virtually identical apart from slow speeds on III only, I am at a loss to suggest why a lens should work on one body but not the other - do both bodies have the correct round Leitz rangefinder cam, and is the cam in good condition in both cases and not worn?

Regards,

David

 

[jolefler]

Yep, I meant you, David!

You've been able to answer my Barnack questions in the past...thank you!

Yes, both are cammed correctly and in nice shape. Both will host either Elmar without issue. The III does rotate the focus witness mark (thanks for the term) slightly past 12:00, but focusses either perfectly.

Yes, it's a Jupiter 3 that fits and performs well on the II, but won't seem to even mount correctly on the III. Hmmm...thanks for the reply. A mystery.

Jo

 

[lens_hacker]

About the only reason I can think of that the focus is off on the III, where it comes to rest at a different spot, is that the RF Cam of the J-3 is at an angle. I've had this happen before when the helicals have a lot of slop on them, and require heavy grease to fill them in. The helical with the RF cam can move at a slight angle, messing things up. OR- the threads for the helical to screw into the lens mount (portion with the 39mm threads) is at a slight angle. 0.1mm will mess things up quite a bit.

I am "the guy Here" that wrote the J-3 article on Kim's web site. I've worked on at least 30 of them, and YES quality control on the machining is all over the place. But a good J-3, shimmed for the Leica, can be the equal of a Nikkor 5cm F1.4 or Zeiss 50mm F1.5:

Dead Link Removed

 

[jolefler]

Thanks, Lens hacker! the helical on the J3 really needs a CLA....it's sloppy and erratic in focusing. More later, gotta run.

 

[jolefler]

Great Article!

Looks to be exactly what I should do. After chewing on your response overnight, that whole gummed-up/bad alignment thing HAS to be the problem. Assuming I can disassemble/clean/reassemble properly, will the focus be the same as it is now? I ask because with either body I have no way of checking focus at the film plane....another reason film doors are handy! Thanks for the response!

Jo

 

[matti]

[...] I ask because with either body I have no way of checking focus at the film plane....

Hi,
Well, it is a good idea to actually run some film through the camera and check out the results

Actually. With range finders and TLR:s I put some pens, coins or something on a surface with a structure and make a picture on the middle one wide open. That is the only way you can know for sure.

/matti

 

[lens_hacker]

The focus "should" be the same, and the way to tell if it is shimmed the same as before is if the F-Stop lines up. The optics module just screws in. When you change the shim, you have to tap out new holes and re-align the F-Stop ring. SO, if you want it to be the same- screw it back together so it lines up to where it is now. I also scribe the filter rim just to make sure.

Make sure you note the position of the helicals. And set the focus to infinity when taking apart, and note the position of everything that can move.

 

[jolefler]

Thanks!

I'm going to give it a shot. I'll check in with results.

Jo

 

[jolefler]

Done Deal

Thanks to Lens Hacker I've been able to rid the J3 of the "notchy focus". A clean/re-lube of the helix fixed that. Thanks for the webpage!

I actually DID run some film as a focal point check when that was done. I set up 3 targets about 1/3 meter apart and focused on the middle taget from 1, 2 3, 4, and 7 meters away. The focus favors the further of the 3 targets at 1 meter. From the rest of the distances the OOF targets diminish according to distance from target.

From this, I assume I could use anothr shim in the focussing mount. I believe I'll just give the focus ring an extra small turn toward closer when shooting at close distances . Unless, of course you can tell me the thickness of a shim required to shorten the focus by 6" @ 1 meter