Question about Canon 75-300mm f/4-5.6 III USM EF Lens
There's a screw located on the barrel of the lens. This may help tighten things up, but don't count on it. Don't try to take it apart unless you know what you're doing. There are a series of sleaves within the barrel which need to match up and you might have to fork out more than the lens is worth just to get it fixed
Posted on Nov 26, 2013
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Posted on Jan 02, 2017
Mine had the same problem. The electric flexible wire that links to the moving aperture motor in the center is most likely broken, causing the aperture to stop reopen after a shot. this could be proved if you feel something touching inside when zoom. (that is caused by the loose flexible wire, if so do not zoom anymore, you could further damage the wire) It need to be replaced and this requires the complete disassmebly of the lens. I repaired mine myself by adding a thin wire, took me more than 10 hours in total (first tear it apert, pin point the problem, then think of a solution because I did not have the parts for repair, then finally repaired it). If you have never done lens/electronic repair before, don't do that, too many tricks that could lead to further damage.
Posted on Jun 07, 2008
SOURCE: EF 24-70 lens droop...
The zoom creep is an easy fix for Canon. I really do not recommend trying to tighten it yourself, since that would void your warranty.
It is usually free to tighten the zoom ring.
Posted on Jan 19, 2009
SOURCE: Canon EF-S 17-85mm - Stuck Zoom
this lens has a design shortcoming in it's aperture's ribbon cable ,the cable will rupture after around 1 year using, this problem taken place in more than 60% of owners with this lens. Canon has no respons with it problem and ask you send to their quick fix store for repair.
Posted on Nov 26, 2009
I hate to re-invent the wheel (and I don't want to cut 'n paste someone else's hard work to present as my own) so please click here for a likely practical solution which usually works and for Canon's own suggestions on the error 99 fault.
If this has assisted you then please rate my answer; if not then add a comment to provide feedback and I'll attempt to provide an alternative solution.
Posted on Mar 02, 2010
Okay. I just wanted to scare you away from ruining a perfectly good (or nearly so) lens, but a learning project is a different matter. And a lens collimator is not that hard to build. One source is the book "Camera Maintenance & Repair" by Thomas Tomosy. I'm sure a quick Google search would show even more.
I did the same thing myself decades ago, taking apart a damaged zoom lens. Unfortunately, I never got it working properly again :-( But it was an educational experience, even though I didn't have a lens collimator...
Posted on Nov 13, 2010
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