Screw mount focussing mark question

[lutz]

Trying to narrow down focussing issues... Where would the focus mark

typically sit with screw mount lenses mounted to an M body with the

help of an adapter? Right on top, 12 o'clock position? Or could that

vary with the type of lens? What about the Canons? I have two where

the focus mark would sit elevenish (viewed from the camera's back,

i.e. "beyond infinity"...) with the lens screwed in tightly. Could

that mean that the flange is mispositioned, that, in short, I would

have to fit a shim in between the lens and the adapter, as to make the

mark stop sharp at 12 o'clock? Thanks for your insights...

[furcafe]

Not to worry. It's not unusual @ all the have LTM lenses that seat off of 12 o'clock & it does not mean that there's anything wrong w/them. IIRC, some lenses (e.g., many if not all those for the Canon RF) were made that way intentionally so that the photographer could read the DoF scales through the VF.

[mark-j]

Lutz: I had a 50 LTM collapsible Summicron that I mounted via a LEITZ adapter. The infinity point was about the 11:00 range as you reference it. I also have a 35 Canon, 135 Canon, 135 Hektor and a CV 21 that all reference about the 11:00 position. All lenses are mounted using differenct LEITZ adapters, not the same one.

 

Mark J.

[james mitchell dc]

Most of my LTM lenses with adapters line up at the 1:00 position (facing the camera from the front). I like that, as I prefer to use my right eye in the finder and can see the focus and depth of field marks easier (by peeking around the side, of course). The CV lenses tend to center at 12:00 more than the others--Canon, Nikon, etc.

[james mitchell dc]

Chris, reading these markings through the VF is a bit of a stretch, I think. I just tried this with the 35/1.8 and the 135/3.5, and neither is very viewable in this way. But a quick look aroung the left side of the camera puts all of this in plain view.

[james mitchell dc]

And Chris, for reference, I was looking through a Leica M2--not a Canon RF camera.

[peter_n1664876959]

I've read that the line-up at 1 o'clock or so was to help with viewing the scales on lenses that use a separate viewfinder.

[james mitchell dc]

That makes even more sense, Peter.

[mark-j]

I just checked and the 21CV lines up at 12:00. I was going from memory which is prone to err.

 

Mark J.

[ronald_moravec1]

Leica lenses end up at 11:00 on screw bodies too. Use as they come out. Measre the adapter thickness and be sure it is 1 mm, My original Leica ones and new CV are all exactly 1 mm.

 

CV lenses end up at 12:00. Don`t rmrmber about Nikors and neve had a Canon.

[al_kaplan1]

It's normal. My 85/2 Nikkor is on an old "no-name" Japanese M adapter and it's about an hour off, but the focus is perfect.

[huw_finney]

Hi Lutz,

 

The thread wears on LTM lenses and moves the 'zero point', no problem though as it is the face of the mount is what matters.

[lutz]

Thanks, everybody. That has been very informative and helps me narrow issues down.

[pensacolaphoto]

I sold a beautiful collapsible Summicron to a man in thi Forum, but he returned it to me twice because the focus mark was not at the 12 o'clock position, insisting that it was repairable.

[ronald_moravec1]

Seems he missed out on a nice lens.

[ben z]

"Could that mean that the flange is mispositioned, that, in short, I would have to fit a shim in between the lens and the adapter, as to make the mark stop sharp at 12 o'clock?"

 

The stop position of the threaded lens is determined by where they started the threads when they cut them. You'd think they'd all be the same, but they're not. Provided the adaptor mics out to the proper thickness, shimming would mess you up in a big way.

[owen w.]

I go with "its a feature, not a bug." The original viewfinders stuck out and you could not read the details on the lens at 12:00. I have several screw mounts, and have looked at a few more. Particularly those that had external viewfinders associated with them seem to be at that very convenient 11:00 position. Owen

[dan flanders]

If your adaptor is the correct thickness (1mm) there should be no problem unless the lens you are using has a sloped cam surface. I have never encountered a sloped cam on any Leitz, Nikkor, or Cannon lens though I have been told that some are so adjusted. A sloped cam requires that the lens comes exactly to the mark when tightened to battery. I have a couple of Leica(?) Sonnars that have sloped cams which requires that the threads begin at exactly the correct point. If the threads do not start precisely at the correct point on the flange circumference the cam will be rotated past the infinity point and the follower will then move with the sloped cam giving a false reading.

[lutz]

As a side effect of my recent testing on Hexar RF vs. Leica M rangefinder coupling I have found that it can make a *substantial* difference which exact LTM to M mount adapter you are using with a given lens on a given body. This is especially critical with fast lenses such as the Canons 50/1.2 or 50/1.5 wide open. I have experienced differences in focussing of several centimeters at 1.5 meters subject distance. In practical terms that means *on* or *off* for any available light portrait.<p>Conclusion: If you have a tested adapter which assures critical focussing with a given lens on a given body *never* split that precise combo!