Canon 75-300mm f/4-5.6 III USM EF Lens Logo

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Posted on Mar 17, 2008

Canon EF 75-300mm f/4-5.6 Repair Manual

The apeture is stuck closed. Maybe at f/22. How can I get into this lens to repair it? Is there a free online repair manual?

  • 3 more comments 
  • Anonymous Mar 31, 2008

    Iris or diaphram does not open

  • Anonymous May 06, 2008

    When trying to use lens on AF it will not focus correctly and when trying to focus manual it will not go back past 100mm

  • soony May 14, 2008

    Aperture is stuck on 80mm and can't be turn either way? How to i fix it??

  • photomom15 Jun 03, 2008

    Aperture is stuck (almost closed) on cancon 75-300 mm lens. How can I repair this? Mona

  • Anonymous Jun 07, 2008

    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.

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  • Posted on Jun 07, 2008
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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.

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