[Leica] Correct a front-focussing 90 Summicron (Leitz Canada)

[Frank Filippone]

Take some time to test it right....

First of all, you realize that the DOF for a 90mm lens at F2, at 5 feet
away, is roughly an inch?

Using the M9 in question, and a tripod, focus using the RF on the pencil.
Shoot,  Refocus and shoot again, several times.  Move the focus ring from
infinity to the correct focus,, and also from 3 feet to the correct focus
point.  Evaluate all the test shots on your computer in the center of the
image, at 1:1.  Try to mentally average the good ones.
 
If the shot is out of focus, you have 2 possible problems:  the lens or the
camera is wrong.

Beg, borrow, or steal (rent?) a M240.  Repeat as above.  In addition, use
Live View to check your result.
Live View represents the sensor.  Use a magnifying glass ( loupe is
preferred) to evaluate the LV output.  If the result using the M240 is
correctly focused, either in the Live View or the output file, the problem
is with the M9 body.

If it not correctly focused with the M240, and especially if the actually
focus point is the same between the 2 cameras files shows the same WRONG
focus plane for both bodies, then it probably is the lens.  It is unlikely
that 2 different camera bodies RF are both off.  And especially off by the
same amount.

Now the wild card... some lenses have focus shift with changing Fstops or
with distance.  Is the 90 Summicron one of them?????

DAG charged me $100 each or so to collimate a couple of lenses I had that
were funky  ( including a 75 f1.4, whose DOF is the same at 5 feet and F1.4)

Frank Filippone
Red735i at verizon.net

My 90 Summicron is front-focussing on my M9. A colleague recommended an
independent repair man proficient with Leica lenses (this is in Japan). The
repair man emailed me back to say the lens is fine and his machine says the
focus is fine too, so probably my camera is in error, perhaps the distance
meter, rangefinder or the mount.

Thing is, Leica replaced my sensor in July, and I haven't used it much in
the four months since. The camera seems to be fine. Last night I took some
focus test shots with my other lenses wide open and focusing on the 25cm
mark of the ruler where the pencil tip is pointing:

https://www.flickr.com/gp/geordiepete/5r3ce9

OK, I didn't use a tripod, and I could have made the test more rigorous, but
it's still clear that those lenses are spot on wide open. I couldn't test
the 90 Summicron at the same time, as it is in another city with the repair
man. However, I made many tests with it before I sent it off, both in
real-life situations, and with rulers. It wasn't the kind of error that only
shows up with rulers. I'm not into that kind of photo. The lens was clearly
front-focussing to a large degree, so that a portrait wide open would always
be unusably out of focus.

I'm thinking, the repair man must be wrong, so I'll ask him to send me the
lens back, and I'll ship it out to Leica. But they might say the same thing!
If my camera is at fault, it looks like Leica should repair it free, as they
recently replaced the sensor. But my other Leica lenses (plus the
35/1.2 Voigtlander) are all spot-on. I'm beginning to worry that to get my
90 Cron working properly on my camera might be very expensive indeed, as I
might have to send the camera and all lenses together to be examined.

Does anyone have any good advice?

Peter