Digital Rebel/Tamron 28-75mm focus problem

It's not my camera, but I am trying to help a friend with his problem and he is not a member of this board.

With his brand new Tamron 28-75mm f/2.8 XR Di, he is having focusing problems indoors with enough lighting that you would think wouldn't be a problem. It was in our office that has tons of fluorescent lights, and we were trying objects that seemed to have enough contrast that focus should not be an issue. We were trying a basketweave material on the cubical walls from about 4-5 feet away, even the line in between the cubicles that has a black strip going down the center, and the logo on a printer that was about 10 feet away. It wouldn't focus on any of them, but my 20D has no problem on these same objects.

He tried to go back to the store where he bought the camera and the new lens, and they said it was normal but we're not buying it. Has anyone else experienced this problem with the same combination, and is the auto-focus that much worse on the digital rebel compared to the 20d?

I never had any problems at all with sharp and quick focus aquisition on the 300D. I also did not notice any difference in that respect when upgrading to the 20D.

Was he shooting with a small aperture or something different on the camera?

Sorry, I should have specified, we were shooting in Av mode wide open at f/2.8 when we were having the focusing problem, and then tried program mode as well.

I haven't encountered any focusing problems with my setup either.

Does the focus problem pop up at certain focal lengths?

I have seen something similar happen to a Canon Elan 7 before at work. What it turned out to be was a small speck of dust on the focusing sensor! I used one of those "Speck Grabbers" to get the dust off, and then the camera focused like new again.

You may want to check that on your friend's Rebel.

Shooting in a small aperture wouldn't cause the camera to not focus, since the aperture is always wide open while looking through the lens. It only closes down to the set aperture when the shutter is tripped.

Right... sorry scratch that!

Oh yeah.

We actually did play with the DOF preview button too to make sure the aperture was operating correctly, so you'd think I'd remember that.

We tried zooming in and out quite a bit, and I even had it at one point where it was going from black to tan right in the middle of the center focus point and still nothing. That's when we were convinced he had a problem.

I'll look into the focus sensor thing. Thanks. That actually does sound possible since we were all commenting on how casual he was about leaving his body and lenses uncovered, while we all treat this stuff like we are in an operating room. He pulled a 50mm f/1.8 out of his bag that had no caps on it at all and we all gasped.