slow auto focus?

[mickello]

hi all. I think I have a problem with my AF, but I'm not sure if it is the camera or the lens? could it be either? I have a canon 550d, (6 mths old) with a canon 28-135 IS USM lens(2 yrs old). In bright light it seems to be ok, but in only marginally less light I have to manually focus first, then its happy to auto focus. otherwise it doesnt hunt for focus, it just blinks and goes nowhere. its like if it has to refocus a long way it just couldnt be bothered. Is there such a thing as a lazy lens? I did have this same lens on a 450d and dont remember it being an issue, so maybe it could be the camera? any ideas? cheers

[DelCan]

I have a 7D and I use mainly "L" lenses. I can have the same problem in low light conditions. I'm not familiar with that camera, but my wife has a T1i and it won't let her take a picture like that in some modes. Most likely it will have been too dark to get a decent photo anyway. Just my 2 cents!

[OsmosisStudios]

Likely too dark, but also likely an issue with maximum aperture. your 28-135 isn't exactly a fast aperture lens.

[oldwolf]

It's too dark. Any camera that can't see what it needs to focus on will have this problem.

I carry a flashlight in my camera bag for instances like that. I shine the light on where I want to focus, acquire the focus, turn off the flashlight then take the picture.

[mickello]

hi thanks for the replies. that is what I thought originally too,( that is that its just too dark.) but as time goes on I'm questioning that. for 2 years I never once used manual focus, now I'm using it a lot.(actually, if I didn't HAVE to use it, I sometimes quite like it) its not so much the level of light, but the distance out of focus, if I manually focus till its just off focus, the auto focus is happy to kick in and finish it off. in the same light, if its way out of focus, it wont even try. I only have the one lens, so I'm thinking I should borrow another and see if there is any difference. just trying to work out if its the lens or camera.cheers

[inkista]

That is really weird behavior. Typical low-light behavior is more hunting, and failing to lock, not a refusal to hunt at all. If you were shooting with an XXD camera, I'd suspect you messed with the custom function that tells a camera not to bother autofocusing if it can't lock immediately (on my 50D, it's C.Fn III-1: "Lens drive when AF impossible" can be set to 0: Focus search on, or 1: Focus search off)--I turned it off once, and saw behavior exactly like what you're getting, but the 550D doesn't even have this setting. And it's not like the 28-135 has a focus limit switch.

I'd say it may be time for Canon Service.

[crockny]

Ah inkista - I think that was very helpful to me -- I did get the 7D and went out for the first time with my 400mm 5.6 lens and had a terrible time with autofocus - I just read your post and changed that setting -- hopefully it will help next time I can go out (big blizzard here and stuck at work - drat - would rather be taking pictures in the park) ....