Leica LTM canon 135mm lens focus calibration

[sanmich]

Hi all

a while ago I bought a chrome canon 135mm mainly because it was so cheap (about 50$).

A few test after, it seems to be a very decent lens, and now that my M3 is operational, I thougth to start using it.
Only problem is that focus is off by a fair amount: At 5 feet, the lens focuses just between 5 and 6 feet. enough shift to ruin these portraits I want to do.
Soooo, me thinks, let's adjust the lady. I thought I spotted an excentric roller that follows the helicoid inside the lens, and sits on the small brass trapez that pushes the camera roller.
Well, so far it didn't work. I'm not even sure that IT IS an excentric. opening the screw that maintains it simply frees it completey what makes any adjustment a completely random process.

Any suggestion?

Thanks!!

 

[John Shriver]

It could have been assembled on the wrong start of the helical focusing threads.

There's basically two calibrations you need to achieve. The first is collimation. When the lens is focused at infinity, a distant (more than a quarter mile) object must focus accurately on the film. Mount a ground glass at the film plane to check this. Canon did this adjustment with a spacing ring of selected length inside the lens.

The second is to adjust the rangefinder cam. It should project from the lens flange exactly 7.5mm (6.5mm with the M adapter on) when the lens is focused at infinity.

Just looking at my chrome 135/3.5, I don't see how one could adjust the length of the RF cam. No idea if the follower is eccentric or not. Since mine focuses accurately, I'm not messing with it.

 

[ferider]

Like John said, first make sure the lens is correctly assembled. I.e. infinity is infinity, both optically, as well as on the focus scale of the lens.

Second, these long throw lenses are dependent on a good adapter. A Voigtlander or generic adapter might throw you slightly off at infinity. Get an original Leica adapter.

Third, if you are still a little off, what has likely happened is that the RF tongue of the lens has been hit by a previous owner and that the roller that follows the helical is slightly bent. The roller is not excentric. But, you can take the tongue out, take a set of pliers, and carefully bend the roller axis a bit in the right direction (hope the explanation makes sense). I just had to do this on an 85/1.9.

Best,

Roland.

 

[sanmich]

John, Roland,

Thanks for your answers.

The right thread: I did open the helicoids to clean and re-lube them. My guess though is that the lens is correctly assembled since the shift is quite limited (about 30 degrees). Although it is a multi helicoid mount, my guess is that there are not a thread start every 30 degrees.

About the adapter: I gave this issue a thought a while ago (and I hope I'm right about this):
lets assume the adapter is too thick. Then the whole lens will stand too far from the flange The optical block AND the lens cam will be too far from film plane resulting in the right focus...
The only thing is thst you may experience a shift in the focus limits (above 0.7m or not reaching infinity).

That leaves us with the follower bending. I'll try first to add some masking tape to that tongue that pushes the camera RF roller and see what happens..

Cheers