Adjusting the Canon 100/3.5 lens

[outfitter]

My Canon 100/3.5 lens focuses about 1 meter behind (IOW an object at 2m shows almost 3m on the lens distance scale). Does anyone know how to adjust the lens (built in or shims for example). Has anyone posted detailed instructions?

Many thanks

Michael

 

[Xmas]

Is the image at the film plane similar?

Noel

 

[outfitter]

Is the image at the film plane similar?

Noel

I've focused the Canon on a groundglass at the film plane and read off the distance on the scale This was rough and quick but I already had similar data photographing a measuring scale and in actual photos. I'll do a precision job once a learn how to make the adjustment (unless I convince myself to send it out).

Michael

 

[John Shriver]

I presume you're talking about the black/silver one with 34mm filter threads.

The difference between 2 and 3 meters is about 2 mm in difference in lens extension. That's a huge error!

Could be a wrong start in the focusing helical. The lens should extend 70 mm from the lens mount plane when focused at infinity.

Like every LTM lens, the focusing cam should extend 7.5mm back from the lens mount plane when focused at infinity.

The collimation adjustment is probably inside the removable head of the lens. But this error is vastly beyond the range of any collimation shimming or adjustment!

 

[ferider]

Like John said, something else must be wrong.

- check the infinity RF alignment
- check the camera with another lens

If both is OK it's likely the lens.
Could be mis-aligned helical (you should see that on the scale at infinity),
or a loose element. Check if the front element is tight, for example.

Roland.

 

[outfitter]

I presume you're talking about the black/silver one with 34mm filter threads.

The difference between 2 and 3 meters is about 2 mm in difference in lens extension. That's a huge error!

Could be a wrong start in the focusing helical. The lens should extend 70 mm from the lens mount plane when focused at infinity.

Like every LTM lens, the focusing cam should extend 7.5mm back from the lens mount plane when focused at infinity.

The collimation adjustment is probably inside the removable head of the lens. But this error is vastly beyond the range of any collimation shimming or adjustment!

Yes the balck and silver one. The focusing cam appears to be 7.5mm but I'm having difficulty measuring the distance from the mount plate to the front element because of the bezel - when I guess it looks like 65mm.

A huge error make me suspicious of my technique. Obviously I must now set this up so as to take precise measurements of the focusing error and report back.

Thanks to everyone for all the valuable information.

 

[John Shriver]

Yeah, being too short would cause it to focus too far away.

Take a measure from the mounting plane to the front of the lens (front of the filter ring, not the glass), and then unscrew the lens head (just turn CCW), and measure to the front of the focusing mount, both at infinity. That lets us know if the focusing mount is too short (what we suspect), or the lens head is too short.

 

[outfitter]

I set a LTM test body up on a pro copy stand and squared everything off and measured and set film plane to baseboard at exactly 3.5'. Using an antique Contax ground glass insert for the film gate I carefully focused on a test target printed on a piece of letter paper. The distance scale on both the 100/3.5 and 50/1.8 showed exactly 3.5'. Assuming this technique is OK for confirming collimation it looks like everything is setup properly and my issues with the lens resulted from focusing error (i.e. it was me not the lens).

So much for quick and dirty checking when it comes to lenses.

Thanks to all

Michael

 

[ferider]

Now you confirmed the lens is OK. But, you still might have a problem with the RF
coupling and whatever body you used for the test photos.

Roland.

 

[outfitter]

Now you confirmed the lens is OK. But, you still might have a problem with the RF
coupling and whatever body you used for the test photos.

Roland.

Yes I know particularly as the body is an FSU camera. OTH the J-3 is a very sharp lens on my Canon 7. Only goes to show that there is no substitute for shooting up a lot of film before assessing whether or not there is a problem.

Michael

 

[photodog]

Sounds like the problem is the FSU camera. Russian tolerances have been known to be a bit lacking.

 

[John Shriver]

FSU cameras are calibrated for a different rate of change in focusing cam distance as you focus closer from infinity. They are calibrated for a 52.3mm lens, not a 51.6mm lens. So if it is right at infinity (which is always 7.5mm from the lens mount plane), it may not be right at closer differences.

To make a FSU camera focus accurately with non FSU lenses, you need to change the effective length of the rangefinder arm. I won't dare to try and figure out whether it is closer or nearer.

Easiest solution is to use FSU lenses on FSU cameras, and Leica, Canon, etc. lenses on Leica, Canon, etc., cameras.

 

[peterm1]

Many years ago, I had two Canon lenses that focussed wrongly with Leica cameras (an M3 with LTM to bayonet adapter to be precise) One was an 85mm f 1.8 on chrome and the other the little serenar 135mm f 4 in chrome. So the problem may be in the lens, not the camera body. I have also heard of others having similar problems when mounting Canon long lenses of this vintage. I spoke to a technician about it and he advised me to find a picket fence and set up a tripod at about a 45 degree angle, then pick and mark a specific picket at say 5-6 meters and focus on it by the rangefinder and take a shot. Then repeat the experiment by measuring the distance to the point of focus using a tape, followed by using scale focusing (ie use the lens distance scale set to the distance indicated by the tape.) Use widest aperture to minimise DOF in both cases. When the shots are developed that should then tell whether the lens is focussing wrongly by the rangefinder or by the scale and help isolate the problem. It should also confirm whether its focussing in front or behind and by how much. I never got around to it, but it might be worth trying if you are of a mind to. I gave up beccause the next step was outside of my knowledge - how to shim the lens correctly to get it focussing right.

 

[outfitter]

FSU cameras are calibrated for a different rate of change in focusing cam distance as you focus closer from infinity. They are calibrated for a 52.3mm lens, not a 51.6mm lens. So if it is right at infinity (which is always 7.5mm from the lens mount plane), it may not be right at closer differences.

To make a FSU camera focus accurately with non FSU lenses, you need to change the effective length of the rangefinder arm. I won't dare to try and figure out whether it is closer or nearer.

Easiest solution is to use FSU lenses on FSU cameras, and Leica, Canon, etc. lenses on Leica, Canon, etc., cameras.

I didn't use the FSU camera RF but focused on a ground glass. The registration (mount to film plane) can be off but the cam calibration did not come into play.

Michael

 

[outfitter]

You may have to use a depth gauge and measure the distance between your FSU camera lens mount platine and the film plane in several points.

You must find that the distance is 28.80mm +/- 0.01mm all over the film plane surface.

If not, you must re-shim your FSU camera lens mount platine.

You can use some aluminum foil (0.02mm to 0.10mm), bristol cardboard (0.40mm to 0.45mm) or A4 standard paper (0.18 to 0.20mm).

Thanks, I'll check it out as soon as my depth guage stops hiding from me.

Michael