28-105 mm doesn't have Autofocus?!

Discussion in 'Canon EOS' started by c_jin, Aug 8, 2009.

  1. So I just opened up the lens I got in the mail. Nothing else looks questionable, but the autofocus does not work. I'm starting to think I made a very elementary mistake or did something otherwise stupid.
    I'm pressing the shutter button halfway down with the AF switched on, but there's no noise or any kind of movement. There are two focusing "barrels" I guess, both of which need to be turned manually to get the image into focus. When switched into manual mode, I have to do the same thing to get a sharp image, so I see no change.
    The electrical contacts look clean, and I'm pretty sure I'm snapping the lens into place correctly. I really don't know what's going on, so some help would be appreciated.
    Thanks a lot!
  2. Okay, I'm updating this. Somehow I guess I didn't put it in right. I reinstalled the lens several more times later on (got frustrated) and it now magically works.
  3. You may need to clean the contacts on both the lens and the camera.
  4. Could your camera have been set to back button focus some how?
  5. A question that I've often thought about, does taking lenses on and off self clean the contacts? I can understand that if the contact surfaces are not wiped for sometime a thin oxide film may form preventing good electrical contact.
  6. Probably not oxide, given that the contacts are gold plated for that very reason. However, it is perfectly feasible that something, probably grease and dust etc, gets on the contacts, and they do indeed "self clean" as you say.

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