Autofocus gives erratic results

If it is a dark scene and the camera cannot detected edges well the autofocus will either move around a lot or simply will not focus and thus wont expose. You will just have to manually focus or use the flash

I think you should use the manual focus for best results. the autofocus might not provide the best results at most times.

Hey mate,

I've been having the same problem. It annoyed me during a day out once.

Set the camera in one of the Creative Modes.
-> Then go to Menu (the button on the left of the screen)
-> Setup 2 (thats the furthest menu on the right)
-> Custom Functions (3rd option down)
-> Go to function 4 and change it to "0: AF/AE LOCK"

Hope that helps mate :)

Cheers
Baghdad_boy

Be sure that beep and AF assist beam is turned on. You can check this in camera menu first page and beam in custom functions under number 05.

I dropped my camera and thought the autofocus broke. It turn out that it swithed from autofocus to manual focus. There's a switch on the lens. Check if that's your problem too.

Hi everyone.

I had the same problem with my 400D. It refused to focus. On manual focus I could take pictures though, but not on Auto focus.
What happened was I cleaned the mirror with a piece of soft cloth, the spring hooked onto the cloth and came loose.

I took my lens off, checked the mirror, found that the little spring connecting the mirror and the little glass part above the mirror was loose. Took a lot of patience and hours to get it back in. I used a pair of tweezers 2 x toothpicks and a short piece of fishing line (thin line). Go have a look at another 400D how the spring should be clipped in. I used the fishing line to hook the " L " shape of the spring back in after I lined the back part of spring up, since there is no space next to the mirror and the body of the camera.

Like I said. This takes a lot of patience and be prepared to sit for 3 to 4 hours.

It worked though.

Hope this helps.

Where can I get a service manual for the 400D ?

in that case my tipp don't mess with it further, pack it in (the body ) and send it to canon for a repair see www.canon.com and cntact them about this isue ask what the cost will be and send the camera in by secured and insured parcel service like tnt (www.tnt.com) describe on paper what ypi have done so that a expensive technician knows where to look.

Backfocus problems will be magnified when using wide aperture lens with shallow depth of field, nice lens btw. Camera's adjustments for manual and autofocus are inside mirror cage behind mirror, and you dont want to risk getting dust on sensor or damaging sensor. Qualified camera repair shop or sending to canon for adjustment would be my suggestion.

(facing the LCD screen towards you, as if you're going to take a photo) there's a button in the upper right-hand corner that will allow
you to AF to a certain point (9-pts total) or the center, or all 9-points, maybe you have it set to one point and it's off center??
definitely sounds like a camera setting probelm
just a thought

AI should be focusing. You really can't change many settings when you are shooting in auto mode. Is the lens in AF mode?

I'm sure you have long since returned from vacation!

Hope this helps!