Odd Canon 100mm f3.5 LTM issue

[jgoody]

I just picked a Canon 100mm f3.5 LTM lens. Here's what's weird -- on my Canon P it seems to focus correctly with the rangefinder, distant objects are focussing at infinity and an object at 10 feet focusses with the mark on the lens at that distance. But on my Canon 7 the lens will not show accurate distance when focussed with the rangefinder -- at infinity the rangefinder patch will not line up and focussing with the rangefinder patch at close distances the camera to subject distance does match the scale. And more weirdly both a 50mm Canon f1.8 and a Nikon 50mm f2 focus fine in both cameras! I haven't gotten any film processed yet but obviously something in my Canon 7 and this lens are not getting along. Anyone have any ideas? Is this lens just not Canon 7 compatible?

 

[02Pilot]

The 100/3.5 has a thin helicoid compared with the other lenses you mention. The only thing I can think off - and it's highly unlikely - is that the RF arm on the 7 is slightly bent and the 100 is not engaging it on the roller but on the arm itself, producing an incorrect measurement.

 

[jgoody]

I asked Don Goldberg and his thought was that the RF was off a little in the Canon 7 and "the longer the lens the more critical the focus is. For example, look at your 50mm lens scale. The amount of travel from 50 feet to infinity is quite small. Now look at your Canon 100mm lens and take a look at the distance from 50 feet on the focus dial scale to infinity." So I guess the consensus is that it's the Canon 7 not the lens. But what is odd is that I just remembered that two years ago I tried a Voigtlander 90mm f 3.5 and the rangefinder worked fine....

 

[jgoody]

The 100/3.5 has a thin helicoid compared with the other lenses you mention. The only thing I can think off - and it's highly unlikely - is that the RF arm on the 7 is slightly bent and the 100 is not engaging it on the roller but on the arm itself, producing an incorrect measurement.

The answer seems to be that on my Canon 7 the roller on the rangefinder arm is toward the left of the cutout and the small flat portion on the 100mm lens is a bit off to the right and they don't mate correctly, roller barely passing the end of the flat, causing misfocus; the roller on the P is a bit more in the center and works fine. Don Goldberg says the roller position is not really adjustable on the camera and he doubtful of correcting the flat's position on the lens. On the 50mm lenses I have the roller can hit anywhere as there is no "hump" and there are no issues. Does anyone have any idea if the part of the lens with the flat can be rotated without problem. Attached is a picture of the problem...

 

[Mackinaw]

Yes it can be rotated. I've never taken apart a Canon 100/3.5 lens, but I've taken apart other Canon rangefinder lenses and the internals can be rotated.

Jim B.

 

[jgoody]

Thanks!