35 Ultron 1.7 focusing problem

[aaron.tam]

Hi all, I just purchased a 35 Ultron 1.7 from ebay, lens looks beautiful, glass is clean, but one niggle -- the rf patch doesn't overlap properly at infinity.

This led me to test the Ultron on my Leica M2 with different adapters (these are third party made in China adapters) that have worked flawlessly with my Jupiter 3 lens, where it overlaps perfectly when the lens is in the infinity position. The problem prevailed, so I tried it on my Bessa R with its LTM mount, still the same problem. The second image in the rf patch shifts juuuust slightly to the left when the Ultron is focused at infinity on a subject that is far, far away.

This led me to continue testing the lens on the M2, on a tripod this time, and I found where the J3 said the object in focus was at 1 m, the Ultron would say 1.03 to 1.05m approximately for the same object, so it is a very small difference, but a difference nonetheless when shooting wide open!

The seller said the problem will probably go away if used with a "thinner adapter" and that he had no problem when focusing to infinity with a Leica iiic.

Any thoughts on what is causing this problem? I don't think it's the rf calibration on either my M2 or the Bessa R since I've had sharp photo from them with my J3 in the past. I think something doesn't add up with this lens. Would this be an easy fix, would one think?

Thanks and cheers.

 

[ferider]

This is typical of CV lenses, and if you want perfect, I recommend to buy a CV type II or original Leica adapter. They are very slightly thicker than most Chinese adapters. When the lens overshoots at infinity, your adapter needs to be thicker.

You can also use some teflon tape to slightly increase lens from body distance to achieve the same thing.

That being said, at minimum distance of 0.9m and f1.7, your Ultron has a max. DOF of 6.42cm, so your current setup isn't too far off the optimum. Also, I would trust the Ultron focusing scale more than the Jupiter's.

As a last note, the seller is likely telling the truth: such small difference is much easier detected on an M2 than on a IIIc.

Roland.

 

[aaron.tam]

Thanks for your suggestions Roland, I will definitely give that a try. But how would one explain the Ultron overshooting infinity on the Bessa R? I was under the impression the lens would be built for that mount. Thanks again.

 

[ferider]

Hi Aaron,

the Bessas that I had (R, R2, R3) were much less accurate than my M bodies (due to EBL, backlash, etc.). For example, when repeating your tripod experiment several times, focusing accuracy was never better than 5cm or so, while it's easily within 1cm accuracy with my M2 (and other M bodies for that matter). So, IMO, a Bessa R is not useful to reproducibly measure such a small focus error.

Roland.

 

[aaron.tam]

Thanks again Roland. Following your suggestion on a thicker adapter I noticed that the RF patch on the Leica M2 would overlap correctly at infinity, while focused on a far away object, when I unscrewed the lens out just a bit, thus replicating a thicker adapter. Would this test be a cogent one to replicate a thicker adapter? Cheers