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by evan-pak

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I bought a used Canon 17-40mm F4L a while ago, and I just noticed it had the Zoom Ring kind of loose and also a lot of my pictures that were taken at the widest were 19mm instead of 17mm

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So even if you turn it as far as you could, you couldn't get to 17mm? – Gapton Oct 5 '13 at 3:52
Exactly, on the ring itself it looked like I was at 17mm but looking at the EXIF picture data most of the time they were at 19mm – xblitz Oct 5 '13 at 4:44
up vote 3 down vote accepted

I am answering my own question since I managed to fix it myself, but wanted to share it with other people who might have the same problem!

It is actually quite easy, all you need to do is to pull/slide on the rubber of the focus ring (it's not clued) to reveal what is under it and you will find 2 screws which might be unscrewed... just screw them back and should fix your problem! no need to send it to Canon and will not void any warranty.

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Try stripping one of those screws and see what Canon says about warranty when you send it in. – Michael Clark Oct 7 '13 at 6:13
Or, to put Michael Clark's comment less snarkily: Be careful not to strip the screws, because that probably will void your warranty. – mattdm Aug 23 '15 at 18:46

Unless you've ever been inside a lens and know what you are doing you are much better off sending it to a Canon Service Center for diagnosis and repair. IF you take it apart first and can't get it back together it will cost even more to have them fix it because:

1) You'll probably wind up damaging something else that wasn't broken taking it apart.
2) They charge a "tamper fee" if they'll even attempt to repair an already disassembled lens, and often they won't even attempt to fix it at any price.

For a more complete warning list of why you shouldn't work on lenses yourself, see Roger Cicala's blog entry about cleaning dust from the front and rear elements of some of the easiest lenses to service. Getting down into the helical zoom collars is several levels deeper than the front and rear optical elements on most lenses.

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did you read my answer? there is no disassembly or opening of any kind required. it's just a matter of rescrewing the screws that are hidden by the rubber sitting on the zoom ring – xblitz Oct 7 '13 at 2:43
OK, So the screws were working out behind the rubber cover and you tightened them. But that might not be the case with the next person who comes here looking for how to fix their lens. And for someone whose lens is still under warranty, even tool marks on the screws you tightened might be enough for Canon to decline warranty coverage if something later goes wring inside the lens. When I wrote my answer there were none posted. It apparently took a while to post for some odd reason, and you posted yours in the interim. – Michael Clark Oct 7 '13 at 6:12

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