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View Full Version : Canon USM 100-300 no longer auto focuses

mcneguy
8th of March 2004 (Mon), 21:02
Anybody have any ideas besides take it to a repair shop?

Thanks
G3
8th of March 2004 (Mon), 21:56
You haven't accidentally set the switch to manual, have you?
mcneguy
8th of March 2004 (Mon), 22:16
Nope...and my 28-105 usm does focus, I have cleaned the contacts on the lens as well.
tganz
8th of March 2004 (Mon), 22:52
Check the three pins in the camera body that contact the lens. They should move freely when pressed and they should have an even height. One of them got stuck in my camera and it affected some lenses but not others, depending on how deep the lens contacts were. Good luck!
G3
9th of March 2004 (Tue), 06:38
If the contacts on the lens are OK and the contacts on the body are OK, and other lenses work with that body, then you have either a bad manual/auto switch on the lens or the focusing motor in the lens is bad, or there's some sort of a mechanical bind in the focusing element and it's mechanical parts. If there is a bind, or if it is an external focusing lens and you have a habit of holding on to the focusing ring while it's focusing, the motor will fail pretty quickly.
Jim_T
9th of March 2004 (Tue), 07:18
How does the AF/MF switch feel ? Does it make a positive click when you move it, or is it mushy.. I just tried my 100-300 and the switch is very crisp..

The reason I ask is that the AF/MF switch on my 50mm f/1.8 lens is getting a bit sloppy.. There is no click when I move it back and forth. Sometimes it doesn't make contact and the AF doesn't work.. I have to run it back and forth a couple of times..

I'm thinking it is your AF/MF switch.. Usually (but not always) a major flaw in the lens AF system will generate an error.. Either an Err 01 or Err 99
G3
9th of March 2004 (Tue), 07:22
How does the AF/MF switch feel ? Does it make a positive click when you move it, or is it mushy.. I just tried my 100-300 and the switch is very crisp..

The reason I ask is that the AF/MF switch on my 50mm f/1.8 lens is getting a bit sloppy.. There is no click when I move it back and forth. Sometimes it doesn't make contact and the AF doesn't work.. I have to run it back and forth a couple of times..

I'm thinking it is your AF/MF switch.. Usually (but not always) a major flaw in the lens AF system will generate an error.. Either an Err 01 or Err 99

That's true, but if that switch goes bad, the camera simply thinks you want to manually focus.