Front Focus & Two 35mm Summicrons

[Jim Watts]

Hi All,
A little more about the front focus problem that some R-D1 users have been experiencing with some lenses.

The rangefinder on my R-D1 is perfectly aligned and I have tested the focusing accuracy with the following rangefinder coupled lenses: My 35mm f/2 Summicron, 50mm f/2 Summicron, 90 f/2.8 Tele-Elmarit. Plus a friends VC 28mm f/3.5, 40mm f/1.4 and 75mm f/2.5. The only lens that does not achieve accurate focus is my 35mm f/2 Summicron, Leitz Canada about 1975 vintage and owned from new. This at distance of about 5 feet and at full aperture shows a front focus of about 3 inches.

On Thurday I was with another friend who also has a 35mm Summicron f/2, again Leitz Canada but of a later vintage than mine, he thinks about 1985. I took the oportunity to try his lens on my R-D1 to see how the focusing compared.

Attached are 100% crops from both lenses shot at full aperture - f/2.0. Number 1 mine, Number 2 his. The point focused on (at a distance of about 5 feet) is marked FP. The point where I see best focus in these photos is marked SP (sharp point) and is very slightly different for both lenses. You will first notice that his lens seems quite a bit sharper and a little more contrasty, but BOTH seem to front focus by about the same amount, just over 3 inches.

This you will note was not a totally controlled test as both were not Raw but H jpegs straight from the camera. There was no further adjustments, iso was set at 400 and the camera was handheld - shutter speed was about 1/112 in both cases. I would think that it does at least represent some 'real world' conditions of use.

As the lenses achieve accurate focus both on my M4 and his M6, I can only assume that the issue comes down to incompatibility with the cams and the R-D1's focus wheel with certain vintages\factories. It would be interesting to know if other R-D1 owners who also have a 35mm f/2 Summicron have a problem with this lens.

[Ed Schwartzreic]

My 35/1.4 old style and my 75/1.4 have similar issues to the 2 35 Summicrons in your post. Both of my Summiluxes check out just fine on my M6. Since I just had my rangefinder adjusted by DAG, I'll report what he sais about this.

"Concerning your 2 lenses that are not focusing correctly, I'd say that they're
assembled correctly because if they weren't they'd be WAY off. I can check
them with my test equipment. I have a dial indicator that the focus cam
rides on when it's installed into this & what ever the lens is focused to
the dial indicator will indicate if it's accurate or not. Also, the optics
need to be checked at each setting. This can get complicated if the focus is
not evenly on, or off."

And--

"Even Leica Cameras have a problem with cams lining up. Some lens cams couple
to the top of following arm, some more in the middle & others couple to the
lower part of the cam, if the cam is slightly tilted then there's a problem.
If one keeps looking into the possible areas of problems like this one can
easily wonder how a camera can work correctly"

Ed

[Doug]

Interesting... And it reminds me of a focus error in my 35 Summicron that I purchased new in 1967. (Chrome, Canada.) While in for its first CLA a couple years ago the technician found it had been assembled incorrectly, with the focusing helix one thread off. He figured by f/2.8 or so the resulting focus error (at all distances) was covered by depth of field. I never had noticed the error myself because I never used it wider than f/2.8! FWIW, the Tele-Elmarit (1968, Canada) was right on.

[Jim Watts]

Ed: "Even Leica Cameras have a problem with cams lining up. Some lens cams couple to the top of following arm, some more in the middle & others couple to the lower part of the cam, if the cam is slightly tilted then there's a problem.
If one keeps looking into the possible areas of problems like this one can
easily wonder how a camera can work correctly"

This makes ense and would seem to be the root of the problem. I expect then that a good repairer, with the correct equipment like DAG, could adjust or regrind the cam so that it would be accurate for both cameras. I not sure how much this would cost but I guess it would be expensive so it might make better economic sense to trade up to a later version of the lens if I find it becomes too much of a problem. This would need to checked it was satisfactory before purchase of course.

Doug: "He figured by f/2.8 or so the resulting focus error (at all distances) was covered by depth of field. I never had noticed the error myself because I never used it wider than f/2.8!"

I find that with my Summicron that depth of field covers the problem at distances greater than 5 feet and/or apertures smaller than f/4. Close up at wide apertures (I tend to push the iso up rather than open beyond f/2.8 if possible) I have learnt to live with the problem by rear focusing a little e.g on an ear rather than an eye.