Is it normal for a 70-300 lens IS USM to do this?

I have a Canon 30D with a 70-300 IS USM lens. while trying to focus using auto focus in Program mode, the lens will suddenly go bananas by going out and back in again ending up completely out of focus. When it does this, it behaves like it's locked out of focus and the camera is useless. Is this normal behavior?

maybe it cant lock focus. What are you trying to focus on?

Shane
When this has happened, I was usually trying to focus on a bird or some small animal.

does this lens freeze up when it can't lock in focus?

Is image out of focus when you take a picture? If it is not, then it might just be the diopter might not be set for you eye. It might also be dirt or something on the cmos AF sensor. Have you tried different auto focus points?

Sounds like the camera is searching for focus and not finding it. It needs some contrast to achieve focus. If you are a bit off the bird or animal you could be trying to focus on a low/no contrast background. Use the center point only and see if that helps.

Not to sure what you mean "camera useless", does it mean that even if you try to re-focus the lens still stay locked in one position?
All the obvious solutions/problems have been covered by previous replies to your thread.
Low light, low contrast, dirty lens contacts all can cause a lens to not work properly.
But if your lens lock after failing to focus and do not want to re-focus afterwards even if you point it somewhere else then it might need a service. I do not know this lens but know that some IS lenses needs the IS to be switched off when mounted on a tripod. So maybe try your lens with the IS switched off and see how it behaves.(even if not tripod mounted, as your IS might be playing up)

From your gear list it seems to be your only lens, but is there any way you can try the body with another lens?

Mine does this now and then on my 350D, mainly when there is lack of contrast or low light. All i do is aim off and try again ... usaually successfuly. I don't look at it as a problem ..... just something to get used to with this lens, seems to need a lot of light to get the best from it.

Not sure what you mean by the camera is useless tho?

thanks everyone for your input. By the camera becoming 'useless', I meant that I couldn't get it to focus again after it locked up in a blurry out of focus condition. Kind of like a gun that jams and won't fire.

I am hoping that the 'IS' on this lens is not defective.

I don't think IS has anything to do with AF, two different mechanisms. Body controls AF and tells IS to kick in, then moves AF back and forth.

Simwells
I have another Canon lens, a 28-135 mm 3.5-5.6 IS USM but I haven't been using it to try to capture pics of birds because it doesn't have the reach of the 70-300.

I need a lot of reach unless I dress like Rambo and camo myself.

i've seen this on my 28-300 a few times. i've always found that the problem is that i have the 0.7m-00 vs 2.5m-00 switch in the wrong position. switch that and it's all good. does your lens have that option?

bmx43
My 70-300 lens has an Image Stabilizer Mode No. 1 and 2 switch. I have kept it on the No 1 position and never switched to IS No. 2.

Guess I need to play around with the No 2 mode just to see what happens.

yea, i have those switches as well, but also the 0.7m-oo or 2.5m-oo switch. sounds like you might not have that switch on that lens.

unless your taking panning shots, like turning from left to right while taking a pic of a moving car turning it to setting 2 is not going to help you in any regard whatsoever its only designed for that

what AF mode are you using? was it dark outside? how close were you? sounds to me like its either to close or it cant focus because of low light

I never had these problems with the lens when I had it