Question about Canon EF 75-300mm Lens

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Fungus (oil spray/mist?) on inner lens surfaces - how to disassemble and clean a Canon 75-300mm EF AF lens? A skeleton picture would also be helpful. Thanks, Tom.

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  • kakima Nov 13, 2010

    Before you disassemble the lens, consider this. Do you have a lens collimator and other equipment necessary to ensure proper alignment when you reassemble the lens? If you don't, you may as well disassemble the lens with a sledgehammer: pictures you take afterward will be just as good.

  • tom_mille871 Nov 13, 2010

    I guess that is a pointer in the right direction. I take it from your comment, the guides and threads are not static and the groups may misalign. I got the lens in this condition for a song (5% of its new value) as a learning (to fix it) aid. Either I get it to work or I just have fun trying. Either way, I will have the knowledge to pass on or use, a pile of junk or a usable lens.

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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

  • tom_mille871 Nov 14, 2010

    I am using a Promaster 75-300 lens. Saw this one and just want to play. If it works, I'll have an all Canon badged kit. Thanks for the info, I'll hunt the book down and see where it takes me. Main barriers so far are the AF connections won't let me remove the mount, and the front lens seems glued with its inner screws rotating and not comming out. Anyhow, got to go for now Cheers.

  • tom_mille871 Nov 14, 2010

    I have mined into the centre of the lens, and found the "Fungus" is on the third lens from the front and its coating. This lens' mounting also carries the iris. Moisture from my breath and a lens cloth removed the mark and I am now putting the parts back together! Thanks for your help k_akima,

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