peterm1
Veteran
Bit of a long story so please bear with me.
For quite a while I have owned a Canon 50mm f1.2 in LTM but only ever tried it on my M8 once or twice. I expected to have problems with rangefinder calibration and/or focusing generally when shot wide open on a rangefinder camera so I was not in the least bit surprised when I did. The last time I tried this was a few months back and I just put it out of my mind as this really was never its intended use.
Instead I intended to mainly use it on one or another mirrorless camera where I would be shooting at portrait distances where, with focus peaking and image enlargement to assist accurate focusing this never really presented a problem.
Previously I only ever shot at closer portrait distances. Today for the first time I was fooling about and for probably the first time mounted the lens on a Sony NEX and tried focusing full open at f1.2 at infinity only to find that it just would not focus at infinity when shot wide open.
I had expected it to be a little off - as usually lenses are stopped down when shot at infinity and stopping down will often move the focus point backwards due to focus shift. In fact though, it is substantially off - subjects considerably closer than infinity are out of focus too. So for more abundant caution, I swapped out the adapter (I happen to have a couple of L39 - NEX adapters) and found much the same with the second adapter. I then decided to test my Canon 50mm f1.4 in LTM and found that it did not seem to have anywhere near the same problem on either adapter (it just reaches infinity and when stopped down a tad will work fine). Just to be sure, I repeated the test with both lenses with another NEX body as well - and got same result with both lenses. So the problem is not the adapter nor the camera, it is the f1.2 lens only. OK I recognize this is still a bit artificial as one does not normally shoot a fast lens wide open at infinity but remember this was a test.
Having decided that this lens is definitely front focusing at infinity I then decided to see how it performed at more normal portrait distances (where I would be shooting wide open or near wide open more regularly) by comparing the f1.2 with the f1.4 on the same adapter and camera body. I picked a target at about 3 meters (by eyeballing it - I did not measure it) only to find that when focus peaking lights up on the camera the f1.4 lens shows about 2.6 meters on the lens' distance scale for that subject while the f1.2 shows about 3.1 meters. In other words the f1.2 lens is front focusing by 0.6 meters or about 2 feet at that range compared with the f1.4 lens. Thats huge - no wonder the M8 was unable to focus this lens accurately
I will repeat the tests tomorrow with a target at a measured 3 meters and compare results in order to get a more accurate and repeatable result. I know that I should be able to fix this - the 50mm f1.2 is an easy lens to open up and the brass shim inside the lens is easy to remove and in theory easy to make thinner - I just need a flat diamond sharpening stone (I have one) and a bit of time and patience. Great - if all works as it should, with an hour or so of patient work I then I should be able to also use this lens on my M8 as well as on sundry mirrorless cameras as I presently do. It is worth the time, I judge.
My point, I suppose is how the hell does a Canon lens get this far out of calibration? I did some research on the internet and it seems this is not that uncommon for that era of Canon lenses. Other people in other threads reported essentially the same problem. I find it hard to imagine how a manufacturer of Canons standard could have let a lens leave the factory that far off. Or do the Canon bodies of that era have a different spec to Leica bodies and regularly require recalibration? There is nothing about the lens that would suggest its been hacked by a subsequent owner. I have opened it up before to clean the fog off the elements and recall removing then reinstalling the shim (which is presumably the factory installed one) as you would expect. (In fact what this problem suggests is that the shim is too thick not too thin or missing so of course it is still there!)
Anyone else had to deal with this?
For quite a while I have owned a Canon 50mm f1.2 in LTM but only ever tried it on my M8 once or twice. I expected to have problems with rangefinder calibration and/or focusing generally when shot wide open on a rangefinder camera so I was not in the least bit surprised when I did. The last time I tried this was a few months back and I just put it out of my mind as this really was never its intended use.
Instead I intended to mainly use it on one or another mirrorless camera where I would be shooting at portrait distances where, with focus peaking and image enlargement to assist accurate focusing this never really presented a problem.
Previously I only ever shot at closer portrait distances. Today for the first time I was fooling about and for probably the first time mounted the lens on a Sony NEX and tried focusing full open at f1.2 at infinity only to find that it just would not focus at infinity when shot wide open.
I had expected it to be a little off - as usually lenses are stopped down when shot at infinity and stopping down will often move the focus point backwards due to focus shift. In fact though, it is substantially off - subjects considerably closer than infinity are out of focus too. So for more abundant caution, I swapped out the adapter (I happen to have a couple of L39 - NEX adapters) and found much the same with the second adapter. I then decided to test my Canon 50mm f1.4 in LTM and found that it did not seem to have anywhere near the same problem on either adapter (it just reaches infinity and when stopped down a tad will work fine). Just to be sure, I repeated the test with both lenses with another NEX body as well - and got same result with both lenses. So the problem is not the adapter nor the camera, it is the f1.2 lens only. OK I recognize this is still a bit artificial as one does not normally shoot a fast lens wide open at infinity but remember this was a test.
Having decided that this lens is definitely front focusing at infinity I then decided to see how it performed at more normal portrait distances (where I would be shooting wide open or near wide open more regularly) by comparing the f1.2 with the f1.4 on the same adapter and camera body. I picked a target at about 3 meters (by eyeballing it - I did not measure it) only to find that when focus peaking lights up on the camera the f1.4 lens shows about 2.6 meters on the lens' distance scale for that subject while the f1.2 shows about 3.1 meters. In other words the f1.2 lens is front focusing by 0.6 meters or about 2 feet at that range compared with the f1.4 lens. Thats huge - no wonder the M8 was unable to focus this lens accurately
I will repeat the tests tomorrow with a target at a measured 3 meters and compare results in order to get a more accurate and repeatable result. I know that I should be able to fix this - the 50mm f1.2 is an easy lens to open up and the brass shim inside the lens is easy to remove and in theory easy to make thinner - I just need a flat diamond sharpening stone (I have one) and a bit of time and patience. Great - if all works as it should, with an hour or so of patient work I then I should be able to also use this lens on my M8 as well as on sundry mirrorless cameras as I presently do. It is worth the time, I judge.
My point, I suppose is how the hell does a Canon lens get this far out of calibration? I did some research on the internet and it seems this is not that uncommon for that era of Canon lenses. Other people in other threads reported essentially the same problem. I find it hard to imagine how a manufacturer of Canons standard could have let a lens leave the factory that far off. Or do the Canon bodies of that era have a different spec to Leica bodies and regularly require recalibration? There is nothing about the lens that would suggest its been hacked by a subsequent owner. I have opened it up before to clean the fog off the elements and recall removing then reinstalling the shim (which is presumably the factory installed one) as you would expect. (In fact what this problem suggests is that the shim is too thick not too thin or missing so of course it is still there!)
Anyone else had to deal with this?