Canon 350D Autofocus - low light?

[pirate_ewan]

Having just made the jump to DLSR with a 350D, I have what is probably a really stupid problem.
Basically, the auto-focus on my 350D seems to be a bit touchy - i.e. it refuses to confirm a focus in almost any conditions and gives me a blinking light to tell me that I can't take a photo.
The only way that it will confirm a focus and allow me to take a picture is pointing directly at a light bulb so I am assuming that it is a low-light sensitivity problem.
Now, as I can switch to manual focus and take a good photo without any adjustments, I am assuming that there is a setting somewhere that has made the auto-focus extremely sensitive but I can't work out what this is.
Can anyone point out the probably very simple mistake I've made before I go back to the shop and make a prat of myself?
Thanks

[Bursar]

As far as I know, there are no settings for the sensitivity of the autofocus.

What lens are you using? If it has a small aperture (large number) then autofocus could hunt around a bit in dim/dark conditions. If you pop the flash so the camera can use that as an autofocus assist, does it help?

[Brammers]

A few things come to mind.

The centre autofocus point is by far the most sensitive on consumer cameras, it's sensitive to both vertical and horizontal contrast changes. Try forcing the camera to use this point only.

Is continuous autofocus on? Try turning it to single shot mode.

Are there any filters on your lens? A polarising filter will easily suck 3 stops of light - with f5.6 on the long end of a kit lens that will make it very, very hard for the autofocus. A linear polariser probably (although I've managed it :E) won't let you autofocus at all.

What conditions are you shooting in? Autofocus works on detecting contrast, bright sunlight creates the most contrast, dark interiors the least.

Which end of which lens are you using? Cheap zooms decrease their maximum aperture as they zoom in - they let less light in and that makes it harder for the autofocus. Try using the wide end - if it's a kit lens that's f3.5 and that's reasonably bright. f5.6 on the long end is quite dim, especially indoors!

Try popping up the flash to let autofocus assist work. If you have an external flash, stick that on, the autofocus assist lamp will work wonders.

Having said all that, it's weird that you can't get any shots other than on bright lights. Does sound faulty... Let us know how you get on with those suggestions 350D autofocus isn't spectacular, and certainly not with the kit lens (autofocus is largely dependent on the lens), but it shouldn't miss everything.

[pirate_ewan]

Thanks very much guys - really appreciate the help.
I'm using the kit lens and the in-built flash - having popped the flash, it fires the initial beams but doesn't seem able to lock the autofocus even with these.
I've tried changing the autofocus point to just the central one with no effect (although perhaps not in combination with firing the flash)

To be honest I've only had it a few days and most shots have been indoors due to work and weather but with a load of spotlights on I would have thought the light should be OK. Added to that is the fact that it does focus correctly - when I switch to manual focus the pictures are fine without changing anything - it's just not recognising that it is focused!

I'll give it another play tonight with your suggestions but unless something leaps out, it's going back to Jessops to let them have a look at it.

Cheers again

[pirate_ewan]

Having played about further, took it back to Jessops today who happened to have the guys from Canon in.
20 minutes later and having tried a new lens, the conclusion was a dead camera and i'll pick a new one up on Saturday.
Annoyed in the malfunction but also a little pleased that I hadn't done anything stupid.
Thanks for the help anyway.

[jamesbryan17]

The problem can actually be solved by switching the camera off removing the CF card, battery and lens. Then put them all back in/on and switch it back on, should be fine.

[pirate_ewan]

Thanks James; tried that a few times but no luck and the canon engineer seemed to agree that it was beyond that method.