taffy
Well-known
Hi I was able to buy a nice and clean copy of the Canon 50 1.8 LTM - nice cosmetically and the glass is clean. However testing it on my M8 and my M10 it back focuses about 2 inches or 5cm at 1-2 meters distance at f/1.8 to 8.0 (didn't test for smaller apertures).
Right now I'm trying to compensate for it by trying to focus closer than than the focus point and use live view but that's not ideal. Testing it on my Barnack now if it does the same.
Is there a DIY fix to this? Would appreciate any tips on how to fix or manage?
Thanks!
Right now I'm trying to compensate for it by trying to focus closer than than the focus point and use live view but that's not ideal. Testing it on my Barnack now if it does the same.
Is there a DIY fix to this? Would appreciate any tips on how to fix or manage?
Thanks!
retinax
Well-known
The helical must be assembled wrong. This is possible to diy if you have some experience and understand how focusing helicals work, but as you had to ask, it will be difficult for you...
lukx
Well-known
Does the rangefinder align at infinity? If not I'd agree with the notion of a falsely assembled helicoid (if you are certain that the RF is calibrated correctly). If it does align it might be an issue with the lens block, or how the block sits in the helicoid. A possible reason might be missing shims. Usually you'll have shims at the surface where the lens block sits in the helicoid. Other possible location for shims might be between parts of the lens block itself.
If you search for repair or images for this lens, you'll probably get an idea on how the inside of the lens should look. But all that means you'd have to disassemble it...
General question: have you researched whether this might be normal behavior of this lens? Some lenses just have focus shift.
If you search for repair or images for this lens, you'll probably get an idea on how the inside of the lens should look. But all that means you'd have to disassemble it...
General question: have you researched whether this might be normal behavior of this lens? Some lenses just have focus shift.
Chriscrawfordphoto
Real Men Shoot Film.
This lens doesn't have focus shift. It should be accurate at all apertures. I've used one for awhile now and it is flawless. It needs to be sent in and adjusted by a technician. Youxin Ye or Don Goldberg can do it. Will cost about $100 but is worth it.
peterm1
Veteran
You may be able to shim the lens. Not checked my 50mm f1.8 but other Canons of the era have thin donut shaped brass shims to correctly position the elements so focusing is correct. I recently had a technician fix my 50mm f1.2 which was front focusing by thinning down the shim. This sat behind the optical block to position all optical elements correctly vis a vis the helicoid. A new shim can be cut using scissors etc in aluminium. Aluminium salvaged from a soft drink can could work though the exact thickness required involves trial and error. This variety of lens is easy to open up to do this. If you are not sure a technician will do it for a price. For some reason my tech did not think the problem lay in the helicoid assembly though I thought this the most logical issue as others suggested here. I forget his reasoning.
xayraa33
rangefinder user and fancier
Luckily you own digital Leicas that make shim adjusting and testing this lens much easier and faster. Just loosen the back ring collar a bit that hold the lens block in and pull on the lens block and make focus test photos to see if you nailed the focus at close distance at f1.8
If you luck out and get the focus 100% right on it will tell you a good estimation on how much to shim the lens block. You can make ring shims out of aluminum as Peter suggested or of stiff paper or even wraps of dental floss or teflon pipe tape . Trial and error is the way to go to get the shim just right.
If you luck out and get the focus 100% right on it will tell you a good estimation on how much to shim the lens block. You can make ring shims out of aluminum as Peter suggested or of stiff paper or even wraps of dental floss or teflon pipe tape . Trial and error is the way to go to get the shim just right.
davhill
Canon P
Agreed, a Sonnar may backfocus slightly but the Canon 1.8 isn’t a Sonnar and should be dead on at all distances. You may want to argue to get part of the CLA cost from your seller rather than returning it—since it’s a clean copy its worth getting sorted out. Last I knew Don Goldberg (DAG) was limiting himself to Leica gear, but Youxin Ye specializes in Canon RF.
zenza
Well-known
Just want to say the Canon 50/1.8 I owned was bang-on accurate on my Canon P. I even find the 50/1.5 bang-on, despite being a sonnar that many claim has backfocus issues.
Ko.Fe.
Lenses 35/21 Gears 46/20
I'm with second copy of this lens. This one is gift from HH.
First and this one are with focus shift.
Just as any RF lens this one has shim. Shim is made for calibration of focus.
Canon lenses LTM are much better lenses for DIY servicing comparing to Leitz made. Disassembly of this nifty fifty is simple and getting it back is easy as well.
I forgot what was focus shift on first 50 1.8 I had. I solved by adding shim to back element, which is screw in ring with lens.
While dissembled you could also apply watch lube into focus thread (no disassembly needed). I did it after seeing it in video from known repair person in Finland. My lens is smooth to focus like new Leica made ones.
You could also change position of focus tab to have it at 1 meter and infinity in much better positions on M mount cameras.
First and this one are with focus shift.
Just as any RF lens this one has shim. Shim is made for calibration of focus.
Canon lenses LTM are much better lenses for DIY servicing comparing to Leitz made. Disassembly of this nifty fifty is simple and getting it back is easy as well.
I forgot what was focus shift on first 50 1.8 I had. I solved by adding shim to back element, which is screw in ring with lens.
While dissembled you could also apply watch lube into focus thread (no disassembly needed). I did it after seeing it in video from known repair person in Finland. My lens is smooth to focus like new Leica made ones.
You could also change position of focus tab to have it at 1 meter and infinity in much better positions on M mount cameras.
pyeh
Member of good standing
Ko.Fe you're back! Hallelujah.
peterm1
Veteran
I am assuming the one you have is the later black and chrome version and the following is based upon that. The earlier chrome one is similar but no doubt has differences. I have not had to open that one up so you may need others guidance though I am sure it is simple as is this one.
As I mentioned and others have too this lens is very easy to open up (and more importantly put back together - that's the bit that foils most "lens technician" beginners but here it is simple as long as you are systematic and make sure you note which way lens elements face as they are removed.)
Although this video focuses on cleaning lens elements, it effectively shows you how and what tools you need to open the lens and get to the bits you need to access. A lens spanner is not strictly necessary I suppose but is highly, highly advisable. They are cheap on eBay and worth their weight in gold as trying to loosen a tight retaining ring without one can result in a scratched lens element, especially if you are as clumsy as I am. You will also need small jeweler's screwdrivers - available cheaply just about everywhere.
https://www.youtube.com/watch?v=HX93S2iuG5E
Open it up just as he shows you then right about 3.00 minutes in, you will see him unscrew a retaining ring at the rear of the camera allowing the optical block to drop out at the front of the lens - place a hand at the front to catch it. At 3.15 as he removes the block you can see the bronze coloured shim around the neck of the rear portion of it. That's what you need to adjust by inserting an additional thin shim to supplement the one that is there. Small increments are the way to go. Of course if you have metal working / machinist skills you could machine a new one up and substitute that for the existing one. My 50mm f1.2 was so far out (front focusing) that I cannot imagine how it got that way if it were not a poorly done helical reassembly. But my camera guy assured me it was not. In which case I cannot imagine how it ever left the factory in that condition - did a company like Canon really have a quality assurance issue back then??????? Someone else may have a theory or better still information.
After reassembly it is a matter of testing the lens on your camera to see if it's now focusing correctly or needs further adjustment . Some trial and error supplemented by patience is required but as others have said this is infinitely more simple on a digital camera as you can check outcomes so easily compared with a film one.
I used the following process to check the rangefinder on my M8 when it went out of "whack". The same can be used to check your lens. To check its focus point , I used a black marking pen to mark out a piece of board about a meter long (but length is not important) with a clearly marked central focusing point and marks at 2 centimeter increments ahead of and behind that (no need to go the full length of the board). I numbered each of these so I had a clear estimate of how far off the lens is from the central aiming point. I laid this on the floor and set my camera on a tripod exactly 3 meters from the focusing point (you could use another distance but I always choose one which is also marked on the lens distance scale. That way I can focus in two ways - by the rangefinder and by the distance scale - this is essential only if you are checking rangefinder accuracy. But its useful as if actual focus point coincides with the distance at which you are shooting as indicated by the lens then its and extra indication that everything is now kosher) . I don't think the sensor plane is actually marked on the body of the M8 but had to estimate this. The camera points at about 45 degrees give or take. Not sure if with this angle the distances marked ahead and behind the focus point are still accurate due to parallax, but it was good enough to estimate what changes were needed. Try focusing wide open then stopped down to a moderate working aperture so you also know if there is focus shift between these. Though I would probably suggest adjusting the lens to its widest aperture in practice. It is just useful to know the extent to which this changes as you stop down when out in the field so you can manually adjust your point of focus accordingly.
As I mentioned and others have too this lens is very easy to open up (and more importantly put back together - that's the bit that foils most "lens technician" beginners but here it is simple as long as you are systematic and make sure you note which way lens elements face as they are removed.)
Although this video focuses on cleaning lens elements, it effectively shows you how and what tools you need to open the lens and get to the bits you need to access. A lens spanner is not strictly necessary I suppose but is highly, highly advisable. They are cheap on eBay and worth their weight in gold as trying to loosen a tight retaining ring without one can result in a scratched lens element, especially if you are as clumsy as I am. You will also need small jeweler's screwdrivers - available cheaply just about everywhere.
https://www.youtube.com/watch?v=HX93S2iuG5E
Open it up just as he shows you then right about 3.00 minutes in, you will see him unscrew a retaining ring at the rear of the camera allowing the optical block to drop out at the front of the lens - place a hand at the front to catch it. At 3.15 as he removes the block you can see the bronze coloured shim around the neck of the rear portion of it. That's what you need to adjust by inserting an additional thin shim to supplement the one that is there. Small increments are the way to go. Of course if you have metal working / machinist skills you could machine a new one up and substitute that for the existing one. My 50mm f1.2 was so far out (front focusing) that I cannot imagine how it got that way if it were not a poorly done helical reassembly. But my camera guy assured me it was not. In which case I cannot imagine how it ever left the factory in that condition - did a company like Canon really have a quality assurance issue back then??????? Someone else may have a theory or better still information.
After reassembly it is a matter of testing the lens on your camera to see if it's now focusing correctly or needs further adjustment . Some trial and error supplemented by patience is required but as others have said this is infinitely more simple on a digital camera as you can check outcomes so easily compared with a film one.
I used the following process to check the rangefinder on my M8 when it went out of "whack". The same can be used to check your lens. To check its focus point , I used a black marking pen to mark out a piece of board about a meter long (but length is not important) with a clearly marked central focusing point and marks at 2 centimeter increments ahead of and behind that (no need to go the full length of the board). I numbered each of these so I had a clear estimate of how far off the lens is from the central aiming point. I laid this on the floor and set my camera on a tripod exactly 3 meters from the focusing point (you could use another distance but I always choose one which is also marked on the lens distance scale. That way I can focus in two ways - by the rangefinder and by the distance scale - this is essential only if you are checking rangefinder accuracy. But its useful as if actual focus point coincides with the distance at which you are shooting as indicated by the lens then its and extra indication that everything is now kosher) . I don't think the sensor plane is actually marked on the body of the M8 but had to estimate this. The camera points at about 45 degrees give or take. Not sure if with this angle the distances marked ahead and behind the focus point are still accurate due to parallax, but it was good enough to estimate what changes were needed. Try focusing wide open then stopped down to a moderate working aperture so you also know if there is focus shift between these. Though I would probably suggest adjusting the lens to its widest aperture in practice. It is just useful to know the extent to which this changes as you stop down when out in the field so you can manually adjust your point of focus accordingly.
taffy
Well-known
Hi everyone! Sorry for the late reply -- work has been hectic. Thanks for all the knowledge. It looks like the lens needs to go in for some adjustment -- I'm not confident enough to do it myself but I will see if I can pick out the points here when I take this to the repair man.
I thought I got a good deal on this lens because cosmetically it looks great and the glass is clean and I got it for $110. I suspect this may have been serviced before and they didn't put it back together properly.
I thought I got a good deal on this lens because cosmetically it looks great and the glass is clean and I got it for $110. I suspect this may have been serviced before and they didn't put it back together properly.