canon 100 F2.8 focusing problem?

I've noticed that the focusing ring as seen through the clear window moves really slowly indoors and is pretty fast outdoors. Is this because of the low light condition or did I get a faulty lens? My Canon 28-105 f 3.5-4.5 focuses really fast both indoors and outdoors and they are both supposed to have the same type ring USM motor. thanks in advance.

Are you saying in a roundabout way that that lens focuses more slowly inside?

yes. if I point the lens at something bright you can see the focusing ring inside the window move really fast and when I point it at something dim it moves significantly slower. It focuses really fast outdoors. Like I said, my 28-105 focuses at the same speed both indoors and outdoors.

Strange. I don't think it's a lens problem, I think it's the camera having trouble in lower light. Strange that the other lens works fine and it's F3.5+

well it's not the camera.. I just tried the 100mm Macro on my old EOS Elan 7e (EOS 33). Same thing with that one. With the lens cap on the the focusing ring travels back and forth slowly... I take the lens cap off and point the camera outside the window and it focuses really fast.. Maybe that's normal. I'll keep reading this thread to see what others have to say.

Is mine the only lens that does this ? Someone please respond.

Mine sometimes 'searches' a bit for focus but not to the point of annoyance. I just tried it indoors with my 1D and mine doesn't move any slower than normal (whatever normal is......) Could be your lens.

Thanks guys. If anyone else has any feedback please post up. Its begining to sound like I'm going to have to send it back for an exchange.

Compare the turns necessary to move your 28-105 from close focus to infinity to the turns necessary to move the macro the same distance. I think that will answer your question.

the 28-105 turns about 100 degrees and the 100 Macro turns a little under 180 degrees. I understand that one travels more than the other,,, what I don't understand is why the 100 macro travesl significantly slower in low light conditions and super fast in bright environments. Its not a problem with searching, its a problem with the speed at which the focusing mechanism travels as seen through the distance scale window.