135 does not focus at infinity

[back alley]

so my mint 135/3.5 canon lens does not focus all the way to infinity.

i took it out for a spin today and it was the first time to play outdoors with it.
when trying to focus at infinity i discovered the barrel would not turn all the way and the image would not completely coincide.

will this likely mean that it will front or back focus also?

and the big question...how do i fix it?

joe

 

[schmoozit]

My guess is that someone took the lens apart and put it back together improperly. Although, Dante Stella noted that this was a problem with some of these lenses, so maybe that's not it.

If it is focusing properly otherwise, which I guess you'd say if it weren't, then I'm not too sure. Is it simply stuck and needing a re-lube? Luckily, you've just practiced that!

 

[back alley]

i have yet to develop any film from it. i did take some shots today and when i see the results i'll know better about it's focusing.
the lens does not look like it was worked on but who knows for sure?

no need for a re lube, it is smooth to turn.
the infinity mark lines up with the focusing mark perfectly.

joe

 

[schmoozit]

Well, the negs will hold the secrets. However, you can do a mirror test. The point of the test is to check the rangefinder, but it should tell you if you are getting a funky reading from the lens' scale, as long as you know the distance to the mirror.

 

[John Shriver]

I presume that the focusing scale goes to infinity.

Set the lens at infinity. Measure how far the focusing tab projects "back" from the lens mount flat plane. It should be 7.5mm. You can measure it with some sort of micrometer, or just put one of your 50mm lenses (at infinity) back to back with the 135, and see that the cam sticks out the same on both lenses.

If it doesn't stick out 7.5mm when focused at infinity, some fool started the helical at the wrong start.

Another check is that the roller on the RF push rod is about 1/4" from the end of the sloped cam inside the lens when at infinity.

Oh, if you're saying the focusing scale doesn't go to infinity, see where that sloped cam is when your lens is focused as distant as it can go. If this is the case, I bet that the roller on the push-rod is banging up against the large vertical discontinuity in the cam.

Sorry, I have no idea how to take this lens apart. Mine is so clean and smooth there's been no reason to. I can only guess that you start with the two large screws that hold the push-rod, and them remove the three small set-screws.

Hmm, I does look like there's a slotted ring in the rear, on the outside of the rear element, that probably is what holds the lens block in the focusing mount.

Looks like the helical "only" has 12 starts. Eleven wrong ways to put it together, one right.

 

[peterc]

However, you can do a mirror test.

Cool test! All four of my RF cameras passed with flying colours.

Peter