Canon 50mm f/1.5 ltm focusing alignment

[DSB]

I purchased a nice condition f/1.5 about a year ago, shot a few rolls, then sent it in for a CLA to remove a little haze. When I used it recently I noticed the focus patch was not aligned at infinity. I contacted the person who did the CLA is he said that some lenses have variation at infinity, this is not adjustable, lenses went off factory this way. I don't remember any issues when I used it previously to the CLA, but I may not have shot at infinity. I've shot a roll since and I'm not certain if the images are as in focus as they could be. I understand that sonnar types are not the sharpest lenses.
I have tried several different ltm to M adapters (some high quality and some cheap) and one (cheap) actually made the focus patch line up a little better. I've tried two different M cameras with the same results. Seems like the lens needs to screw into the adapters just a little bit further to get the focusing to align at infinity.
I was wondering if there is a simple solution. Maybe by modifying an adapter? I would feel a lot more confident knowing that the focusing is accurate because I usually shoot mid to close ups between f/1.5 and f/5.6.
Or, maybe it just doesn't matter. Any advice or suggestions would be appreciated.

Thanks,
David

 

[brbo]

Do you have some other lenses to establish whether it is the lens or the body? And I pretty much doubt that Canon 50/1.5 can't be adjusted to proper infinity focus.

Testing the focus accuracy of a sonnar lens is a bit tricky. First you need to be sure that your camera's rangefinder is properly adjusted and then establish at which aperture the focus of the lens is in agreement with the rangefinder. This might happen at wide open or closed down somewhat as the focus shifts with changing of the aperture. Depending on this you then adjust your focusing.

 

[mdarnton]

I think almost every Canon lens I've ever had has been a bit out, usually with the RF going past infinity by just a little, which means the lens is focused ahead of the subject just a bit. There is no easy adjustment for this in the lenses I've had.

When I first noticed this, 40 years ago, I wasn't aware of focus shift, and I was shooting sports with a 135mm lens wide open, where the problem of misfocus quickly became obvious. Now I wonder if it was an intentional Canon strategy to deal with that problem. Since the focus point of many fast lenses moves back with stopping down, this would put infinity right on with a stopped down lens, which is actually probably mostly the situation for near-infinity shooting. Shooting close up it would result in a bit of front focus until the lens was stopped down, but probably not enough for most people to notice.

Consequently, I have corrected long, fast lenses that I use close and wide open, but not slower and shorter ones. The correction is permanent, in one direction only, and not something I will describe.

 

[DSB]

Thank you both for your replies. I had a feeling that the sonnar focus shift was going to make this a little tricky to guage. I have also had another Canon lens that slightly went past infinity, but this lens doesn't reach infinity. Other than that lens, both of the M bodies viewfinders align very well with my other lenses.

It doesn't sound like this is going to be a twist a screw or shave down the adapter kind of solution. I think I'll grab the tripod and a tape measure and run a few test this weekend. Even with some mixed focusing results with the small sampling of rolls that I've shot I like the look I get with this lens. I'll try to adapt to it instead of the other way around.

Best,
David

 

[presspass]

Speaking of adapters, have you tried another one on the Canon to see if that could affect the focus?

 

[mdarnton]

If this lens were mine, the first thing I would do would be to run tests at about five feet and twenty feet, wide open and two stops down, to see if there is a focusing problem to worry about.

 

[Dante_Stella]

Get a thinner adapter. Usually the Chinese ones are short of 1.0mm. The cam rate and focus position on a 50mm lens move at the same rate. Done.