Advice please: R/F accuracy, Elmar front-focusing

[KEH]

Friends,

I have done a bit more investigation of the 'softness' problem of my new Elmar 50/2.8 wide open on my R-D1. A lot of the problem is definitely a severe front-focus issue. A few questions to the experts here:

1. When mounted tightly on the Voitglander LTM to M adapter, the focus mark on the lens only comes to about 11 o'clock rather than the expected 12:00 (when viewing the camera with lens towards you). I presume this is indicative of the problem? Is this something that a competent technician can fix (we have some good folks at Prophoto here in DC), or do I need a Leica specialist? People refer to DAG, but I'm not sure who this is, how to reach them.

2. The other lens I tested for front-focus, my CV 35/3.5C, did show a small amount as well. However, I note that with all my lenses the rangefinder 'lines up' on very distant objects a little bit short of infinity on the lens (that is, I can turn the focus a little bit further to reach infinity). Is this a problem with rangefinder alignment? It certainly would lead to some front-focus, as far as I can see. Am I obsessing here, or is this a real problem which should be fixed? Again, suggestions for who can fix the problem on the R-D1 are appreciated.

Many many thanks for responses.

Cheers,
Kirk

 

[pfogle]

Kirk,

if the pitch of the LTM is 1mm, then the turning of the adapter by 1/12 turn would cause a front focus from infinity to 30m - which I would think would be within the depth of field at f2.8 - anyway, that's the distance you would expect to find.

edit - just did the calculation for 1m distance on scale and a 1/12 turn mount error - it comes out to a 2.92 cm front focus, which would be quite noticable.

If you like, I can send you the math...

I've had mounts that varied by 30deg either way, but they've worked ok. I've never used the elmar, but FWIW I use an old Summar (1936, uncoated) and it's a very fine portrait lens wide open - focus on my body seems spot on.

Sorry that's not much help for your problem 🙁

cheers
Phil

 

[KEH]

Thanks Phil - yes, ~3cm out of 1m would be noticeable. At any event I probably need to talk to a technician about getting the focus adjusted.

Cheers,
Kirk

 

[Peter Klein]

Kirk: The focus mark only reaching 11:00 when you mount the lens is no big deal. I had the same thing on some LTM lenses with adapters. So you may have a problem, but this is no indication of it. The issue is not where the focus mark falls, but whether the lens is the proper distance from the film plane.

A good way to test near focus is to put the camera on a tripod. Focus on a ruler or a printed book or document set at about a 45 degree angle to the lens axis. Take several pictures, refocusing the lens each time.

Distant objects are another issue. Infinity is actually farther away than you think. Use the moon, the planet Mars, or a TV tower a couple of miles away to check infinity. The telephone pole down the block isn't far away enough.

If you can *repeatably* get the same "wrong" result with focusing, then either the lens or the camera are off. If you can test the lens on another camera, then do so and compare the results. Also test the same camera with a couple of different lenses. This will give you an idea of which item is not working right.

Then send the offending item off to the repairperson of your choice. If the problem is the RD-1 RF, then DAG can adjust it for around $50.

And if you can't get consistent results no matter what you do, then maybe your focusing technique needs adjusting 🙂

--Peter

 

[KEH]

Thanks Peter, very helpful. I do get repeatable focus problems using a convenient hedge with a few Christmas tree lights along it. This shows front focus at all apertures, with the depth of field behaving as expected. Time for a CLA!

Kirk