And suddenly, my 50 1.4 isn't working!

[Takkun]

I was shooting an event last night when I realized something was up with my Canon 50 1.4. Nothing was really in focus. I've never noticed this to be a problem before.
At first I suspected it might be the adapter ring. Nope, same problem on a Voigltander or no-name adapter. Then I shot side-by-side with the 50 1.8 I didn't get around to selling.

Please excuse the bad photography and taped-up posters on my wall. All were shot at f/1.4 on an M8.


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And by comparison, with the 1.8:



Click through for full resolution.

So what's going on here? the glass is clean, and the lens hasn't taken any knocks.

 

[KoNickon]

Have you ever shot the lens at 1.4 before? It may not be that good at max. aperture. And what shutter speed did you use on the indoor shot (of the poster)? Maybe a little shake?

 

[Takkun]

Thought of that--Shot the event last night at f/4, still blurry. And the indoor shots were at 1/125s.

 

[Mackinaw]

Actually the Canon 50/1.4 is quite sharp wide-open. Maybe it needs to be shimmed? Mine is quite the stellar performer, at all apertures.

Jim B.

 

[Brian Legge]

You may also want to check for haze. Shine a flashlight through the lens to see if it is significantly more hazy than the 1.8

 

[nhchen]

Could it be possible that the rear retaining ring has come loose?

nathan

 

[raid]

I once had such a case with a Canon 50/1.2. DAG took the lens apart, and he found that one of the lns elements has moved.

 

[maddoc]

Most probably a lens element that shifted ...

 

[Takkun]

I once had such a case with a Canon 50/1.2. DAG took the lens apart, and he found that one of the lns elements has moved.

Judging by the lack of contrast (no haze!) that was my guess. I just wasn't aware that was possible. I have a lens with DAG right now, but it's been there almost a year, so I may send it in if I ever get ahold of him.

 

[raid]

Another repairman can do same repair.

 

[Scrambler]

I was reading a blog where someone complained that their lens was not in focus at any distance - which isn't possible. And in your case it isn't happening either. Look at the photos and you will see that the lens is focusing well in front of the intended subject. e.g. the power lines.

As the 1.8 is focusing correctly we can disregard the possibility that the camera is out of allignment. Now the possibilities are that the lens's RF cam is out of whack, or that the lens elements are not properly mounted, or that something has shifted within the lens. If you haven't taken the lens apart we can disregard the first possibility as highly improbable. I can't make my example move in its mount so I can't comment on the second, and the third will require professional assessment.

As focus has moved toward the camera, the (nodal point of the) lens has moved AWAY from the film, or the focal length has suddenly reduced. It's hard to see how this could involve just a rear element, so possibly the front element has moved forward? Can you check to see if it has been screwed in tight? Otherwise it's off to the repair shop.

 

[Takkun]

Scrambler--that's a great observation. I checked all the obvious signs of RF alignment with other lenses and adapters, and you proved my guess right that someone might spot a pattern in my test shots that I didn't catch.

I suppose I meant to say when I said lens shifting wasn't possible (of course it is) was more that I didn't think it was possible without obvious signs, such as damage, rattling/play, etc. I took it apart, made sure the rear group was on tight and the retaining collar was locked down.

I think the front may be the culprit. I hate to turn it into one of *those* sorts of threads, but does anyone have a favorite repairperson who works on Canon? In Seattle, we have one place in particular that does SLRs and video lenses, but isn't too hot on RFs.

 

[Takkun]

Update, after taking it to CameraTechs, who tightened up the front element and checked it on a ground glass with an M6:


Focus was on the "R," in "LENS CLEANER" but the price tag was what was in focus, so it still looks like it's front focusing a bit.
the lens tech wasn't in when I stopped by, but it was relayed to me that it looked fine on their body, with my adapter. I had my body's RF checked, and my other lenses appeared to confirm this. They're not experts with DRFs but couldn't really pinpoint the problem without tearing the whole thing apart at possible great cost.

Unlike the Zeiss Sonnar formulae, I haven't heard anything about the Canons having focus shift/curvature of field problems (it's a Planar-type lens), but I could be wrong. Anyone shooting digital have any problems like this, or is it as good as it gets wide open? I hate to sink more money into an unfixable problem. Normally I wouldn't bother too much, but this lens is my go-to for low-light people pictures, so acceptable results wide open are fairly critical. The issue at hand isn't sharpness (it's plenty sharp and these were shot at 1/125 or faster), but focus being off.

If not, there is a nice Voigtlander Nokton in the classifieds...

 

[Balto]

I haven't heard of focus shift problems with the 1.4, I would agree with others that an element must have moved. If you are wanting to get it repaired I would probably suggest avoiding cameratechs, their prices have always seemed high compared to the competition, though they are local which is a plus. Alternatively, I have a black 50 nokton (new version) for sale local in Seattle if you decide you want a new lens.

 

[Brian Legge]

I can't tell you why you just started having problems - the construction is fairly simple and I can't think of much that come loose. These lenses are relatively simple to disassemble. I suppose its possible for the rear group to have unscrewed slightly but that doesn't seem likely.

If its off throughout the range (and if you hadn't had it work in the past) I would assume it was mis-shimmed for the body you are using. I've seen a slight bit of variation in focus with film bodies. The results are usually find but digital is much less forgiving. If its focusing too close you'd need a thinner shim. The Canons I've seen have only had a single shim (not a stack of them) so thinning it down may be a headache. You could try checking with Dag or someone else who does reshimming regularly as they may have parts on hand. Or they'd perhaps they'd just tighten the rear group and call it good.

 

[Takkun]

I can't tell you why you just started having problems - the construction is fairly simple and I can't think of much that come loose. These lenses are relatively simple to disassemble. I suppose its possible for the rear group to have unscrewed slightly but that doesn't seem likely.

Does it focus correctly at infinity or is it off throughout the range?

I can't tell what caused it either--It was just fine on my film body, and I looked at a few snaps I took at a cat show (go ahead and laugh!) and everything was fine. At infinity after the first round of repairs, it was still front focusing. So I'm guessing the shims might be the case.
I'm going in to meet with the technician this week with the digital body and see what he thinks. As it stands, the cost is $40 but they said could go up to $200 or so.

Balto--what're you offering that lens for? After poking around online, its looking like a viable option should this not get resolved.

 

[Takkun]

And an update (I seem to be going through my old question threads and posting the outcome for the sake of completeness):

Took it in with the M8 to CameraTechs and they were able to sort it out, no problem--re-shimmed it and re-greased the helicoids. Same-day repair, too.

Ironically, over a year ago, they had me send a Leica lens to DAG, but they were able to fix this one up quite well despite having never seen a Canon LTM lens before. Apparently, according to the tech, they're pretty similar to the FL-mount lenses.

 

[kuuan]

good to know that you got it sorted out!

taking apart this lens is very streight forwards, for anyone interested there is an instruction on youtube. The video is badly focused, but one can see that e.g. there is a washer that's there to adjusts the focusing: https://www.youtube.com/watch?v=qMRnqIysGAk