Canon 50/3.5 Collapsible

[kermaier]

I received my Canon 50/3.5. It's a very late example -- probably from the last year of production, 1955 -- in nice condition. It's a beautifully machined, very compact lens which, by the way, collapses very nicely on my R-D1 (as opposed to the various Elmar 50/3.5 versions which, I understand, do not).

Now I'm going about experimenting with the lens to see how it draws and at which apertures and distances it's good. Alas, it appears to focus somewhat behind where the rangefinder indicates. For example, using the oblique bookshelf testing method, if I'm focused at 4 feet, the actual sharpest focus is about 5-6 feet. (I haven't tried at farther focus distances yet.)

Is this the sort of thing that can be readily corrected by a good service shop?

::Ari

 

[John Shriver]

What's wrong with the focus? Does the scale read 5-6 feet when the object in the rangefinder is 4 feet away? Or is the actual focus at 5-6 feet when the object in the rangefinder is 4 feet away?

If it's the former, either the focusing helical is started on the wrong start (tab should go up against mount at infinity), or someone has been filing at the rangefinder cam (ugh!).

If it's the latter, there's a shim missing inside the lens barrel that some nincompoop lost in an inept servicing attempt. (Or, you didn't properly bayonet in the lens tube after extending, although I suspect that would lead to much worse errors.)

 

[kermaier]

It's the latter <sigh>. Are shims parts that need to be matched to a specific lens, or are they fairly generic LTM lens parts that repair shops would have around?

 

[Sonnar Brian]

You need to increase the thickness of the shim. You can make them out of aluminum foil.

RF and Distance scale indicate 4ft, actual focus at 5.5ft: the optics are too close to the film, and it is back focussing. Move the optics out. Look at the movement of the lens as you change the focus from 4ft to 5.5ft. That is how much you need to increase the shim.

 

[kermaier]

Thanks, Brian and John! I'm not a confident lens surgeon, so I guess it'll be making a trip to the repair shop.

 

[kermaier]

DAG tells me this may be difficult, as the 50/3.5 collapsible was not designed for focus adjustment. But presumably the lens once focused correctly, so maybe there's something else amiss that can be corrected.