Focus Problem with 400D

[Byrhtnoth]

Hi,
Think I may have a focus problem with my Canon 400D when in AI Servo mode.
Out shooting sports the weekend and found camera not confirming that the subject was in focus either by beeping or the focus light in the veiwfinder.

Camera seems fine when One Shot or AI Focus are selected and focus points are all ok and are all selectable.

However when AI Servo is selected (M,Tv,Av,P or auto sports), none of the auto focus points light up and theres no confirmation focus light in the veiwfinder when half pressing the shutter button.
When I manually select the centre focus point and half press the shutter button the centre focus light comes on but still no confirmation focus light in the veiwfinder.

Took 300 shots using the AI Servo and centre focus point.
While some were in focus, theres also a load where the main subject is blurred and the background sharp, or the whole shot is out of focus.
Now this might just be my poor photography skills,
but Im having trouble focusing a fast and close subject with no confirmation from the camera that the moving subject is in focus.
Im using f2.8 lens with high shutter speeds and in some cases external flash.

Is this normal for AI Servo :shrug:
Shouldnt the camera confirm that the subject is in focus
Red the manual but not much help there

Any advice please before I contact Canon?

 

[Canon Bob]

.....Im having trouble focusing a fast and close subject with no confirmation from the camera that the moving subject is in focus.
Im using f2.8 lens with high shutter speeds and in some cases external flash.

The situation you're describing sounds like......

Fast shutter speed....hence large aperture.
Subject is close....high'ish native magnification from the lens.
Subject is moving fast....through the focal plane quite quickly at a guess.

The DOF for the setup you have will be quite small....large aperture and close (high mag) gives small DOF. I'll take a guess at a 70-200/2.8 type lens....maybe wrong.

My impression is that the 400D/lens combo simply can't keep pace in this type of situation and the subject either moves through the focal plane too quickly or the correct focus is never achieved because the feedback arrives too late.

Someone else is sure to have a better take on this....?

Bob

 

[Byrhtnoth]

I'll take a guess at a 70-200/2.8 type lens....maybe wrong.

Lens was the Sigma 24-70mm f2.8 (2.8 throughout the range)

The light was bad so I tried shooting large aperture (av) also high shutter speeds (tv) and even plonker mode (p) but still not focusing properly and lens hunting.

Tried kit lens at home but still no focus confirmation in AI Servo

 

[mole2k]

One shot and AI Focus confirms with a bleep and a flash of the focus point, AI Servo doesnt because the selected point should always be in focus.

A fast close subject means that you are either struggling to keep the focus point actually on the subject (if you flick off to the background it will then move to focus on the background, as its f2.8 its quite heavy bits of glass that have to be moved and they have to be moved further when at close focus. Also it might be as canon bob suggested that the 400d focus just cant keep up with the subject.

EDIT: just seen your reply, in low light the focus will hunt, especially on a 400d.

 

[Byrhtnoth]

One shot and AI Focus confirms with a bleep and a flash of the focus point, AI Servo doesnt because the selected point should always be in focus.

Thanks thought the camera was at fault.
Why doesnt it tell you that in the manual :bang:



So, it looks like the problem could be my skill in using the camera or im using the wrong type of gear for the situation I want to photograph :shrug:

 

[CT]

As said above there is no focus confirmation in Servo Mode, but your best guide is that the image is visibly sharp in the viewfinder when you've achieved focus, but quickly goes so far oof it's obvious, once the lens loses focus and starts to hunt.

 

[Canon Bob]

Simon...I think you've just discovered why the 1D series bodies cost a little more...

Bob

 

[Byrhtnoth]

Simon...I think you've just discovered why the 1D series bodies cost a little more...

Bob

just a little more
Also could do with more than 3 frames per minute.
And a weatherproof casing

Would the 40D be a good candidate for this as although the same pixel it has a better processor and a faster frames per min. :shrug:
Or can i find a secondhand 1D for less than a grand