# Problem with Canon EF 75-300 USM lens



## adamwsh (Jul 20, 2006)

[FONT=Geneva, Verdana, Arial, Helvetica, sans-serif]I just got a Canon EF 75-300mm 1:4-5.6 III USM lens for my Digital Rebel XT.

When in AF mode, the lens seems like it tries to focus (moves back and forth, makes noise, etc) but it never "locks" on a subject. Also, the red-dot indicators in the viewfinder never light up at all.

Is this lens defective or is there a setting I need to change on the camera (or lens)?

I tried both distant subjects and close subjects. I tried both outdoors in the sun and indoors with incandecent lighting.

The same happens whether it is in AI or One Shot mode.

The lens that came with the camera works perfectly.

Any help would be most appreciated! Thank you!

(P.S. I called Canon customer service, and all they told me I should try is to clean the contacts on the lens and camera body. I'm not home right now, so I can't try that... but somehow I don't think that is going to fix it.)[/FONT]


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## bethany138 (Jul 20, 2006)

Hmm.. I have one that is doing the same.  I just shipped it to Canon for a repair estimate.  I'll let you know what they say.


b


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## Big Mike (Jul 20, 2006)

Welcome to the forum.

I would also suggest cleaning the contacts, just to be sure.  Something definitely sounds messed up.  If the red indicators don't light up, something is not right.

Try taking the lens on and off a few times...just to make sure it's seated correctly.

Can you tell if the aperture blades open all the way?  When the AF is 'hunting' like this, it can mean that there is not enough light...or that the lens just isn't letting in enough light.  If, for example, the aperture blades were not opening all the way, the AF would not have enough light to focus.


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