Canon lens with a catch
A freind showed me a Canon Japan 16-35 L USM lens today. He said there was a problem in manual focus. I spent about a half hour with the lens, and it seemed to work fine in AF, but it would not manually focus at all. It seemed to be solidly locked, both in AF and MF if I tried to manually turn the ring. Under the rubber focusing ring, right at the bottom, I felt a bump that seemed to move slightly as I worked the tiny amount of free play trying to focus. It felt like it had one shotgun pellet under the rubber.
Is this something that could be an easy fix, or where should I have him send it?
It most likely being dropped or bumped really hard. The MF metal ring might be deformed and bound with the lens barrel.
Here's the rule on how much I pay for those kind of lens: If anything is faulty, it is worth only half of the good price.
Well, I found out what the small bump was. By picking up the edge of the rubber focusing ring with a fingernail, and using a toothpick to roll it off about its own width sideways, I discovered that there are several small screws under the plastic ring that the rubber seats on. They are accessed through one hole in the plastic ring, and they seem to fasten the piece immediately below the ring to the piece below that. Two (of three) had come loose, and one had become cocked in the access hole, keeping the ring from turning at all. I got all three pieces lined up and started and tightened the screw, and thought I had it fixed. There was another screw loose, and since the ring was now free to rotate, when it went past the next loose screw, the same thing happened again. I lined it up and tightened it, and everything seems to work normally.
I can't wait to play with it...
Well, the fix worked, for a while. I liked the lens so well that I bought it. And I still like it. About a week ago, the same thing happened again.
All the tools that I have for tiny screws and fittings are cheap junk. I am going to look at Snap-On, Starrett, and General for better quality small screwdrivers. I am also inclined to put a trace of blue Loc-Tite on the screws the next time they come loose. They are not stripped, but I am also really aware that I could strip them if I get carried away.
Should I look to something other that Loc-Tite?
One thing you could try after putting the screws tight again is to put a dap of nail varnish over the head with just enough to go on to the part the head sits into. Hopefully that will have enough resistance to stop the heads from coming loose again, but not so much of a lock than if you used loc-tight on the actual screw threads. Which might be problem if the lens needed to be opened up for cleaning or service in the future.