Radu Vadan , May 09, 2008; 03:37 a.m.
There have been numerous topics around here about this Canon lens failing after
a slight bang on the noggin. Many opinions have been posted, but the main idea
that everyone seems to agree on is that the USM's FTM "clutch" tends to break.
Well, mine just happened to get hit by this problem on Monday, and, since I
don't have any warranty anymore, I decided to take a screwdriver and take it apart.
My conclusions were mixed (i.e. I'm very disappointed by the build quality of
the inner parts of the lens), but the main idea is that it's not the USM
coupling that breaks. Actually, nothing really breaks, but rather, the focusing
helicoid, which is made of really cheap plastic, bends out of shape by maybe
half a millimeter, and blocks against the main assembly. For me it was a very
easy 15 minute fix, and now it works perfectly. If anyone is curious I can do a
short tutorial with pictures and all, if you want to attempt a DIY job.
Please be warned, UNSCREWING EVEN ONE SCREW ON THE LENS VOIDS YOUR WARRANTY!
William W 
, May 09, 2008; 04:07 a.m.
Well you`ve got my initial interest:
Do you have any idea as to why this bending happened?
Did your lens suffer a bump or a drop?
Do you use FTMF a lot (ie when the AF is engaged)?
WW
Mike Dixon 
, May 09, 2008; 04:23 a.m.
I'm interested in seeing what you did. After a more-than-slight whack, my 50/1.4 won't focus closer than 1.5 meters. It would be useful to see what's in there before I start tearing it apart.
Manfred Feuser 
, May 09, 2008; 05:21 a.m.
Hi Radu thank you this is a worthwile post if have taken a few shots please post those too.My 50 f1.4 is new and works very well but you never know.
Cheers Manfred
Radu Vadan , May 09, 2008; 05:26 a.m.
William, I'm pretty sure it happened because i kept it in a lens pouch together with another lens, and they hit each other face to face by accident. The other lens was a 24 f/2.8, which wasn't affected in any way. Also, the bump was definitely a minor one because I have no idea when it happened.
I will follow up tonight with a link to the pictures and explanation.
Mike, that's exactly how mine was behaving. I'm sure you have the same problem.
Erick Kyogoku , May 09, 2008; 08:43 a.m.
Interesting thread Radu, I too would be interested in your DIY disassembly photos.
I dropped my lens from over one meter in height onto a hard floor, and it seemed to
have become misthreaded. Basically I was getting uneven focus as, I believe, the
lens plane was uneven. I would not expect such a fall to go without damage, but
insurance covered it and it was repaired to perfect working order by Canon. I imagine
they just reassembled it properly.
Anders Carlsson , May 09, 2008; 09:50 a.m.
Many thanks for posting this, Radu. Extremely valuable and useful information. My copy is a rather bad one mechanically -- not optically -- with a somewhat loose focus switch and uneven friction as I turn the focus ring. When you were in there tinkering, did you see anything that might explain the latter? In any case, please do post some pictures of your operation. Again, thanks.
Samuel Parker , May 09, 2008; 10:34 a.m.
Please do post a tutorial. This happened to my 50 f/1.4 a while ago. It would focus ok if it started from infinity and moved closer, but not at all the other way. I took it the Canon FSC in Irvine, CA. They fixed it for free - a "complimentary repair," not warranty. I was very glad, too, because it's about a $100 repair otherwise. Among other things - adjustments, cleaning, and such - the repair slip said they replaced the "mechanical chassis" which sounds like what you are talking about.
Radu Vadan , May 09, 2008; 12:30 p.m.
OK, all done. Please note that the pictures were not taken during the original repair. I took it apart again to take them this afternoon. Please leave your comments and remarks.
http://www.fotomozaic.ro/artikel.php?idstory=225&s=1
I say again, Please be warned, UNSCREWING EVEN ONE SCREW ON THE LENS VOIDS YOUR WARRANTY!
If you ruin your lens, I'm NOT taking the blame.
Radu Vadan , May 09, 2008; 12:32 p.m.
The "English text in black: " thing is bogus. I wanted to write Romanian & English, but gave up on the idea, and forgot to delete this afterwards.
