Simultaneous Auto and Manual focus

[Fernando Cerra]

Some times when I am photographing small birds and using autofocus the image comes out
out of focus and something near the bird is in perfect focus, is there a way to use autofocus
and switch to manual focus without having to move the switch on the lens, I mean to do the
initial focus using auto and then fine tune with manual but without having to take the eye off
the subject ?
I am using Canon 40D and 400mm f5.6 Canon lens.

Thanks for your help.

[Roger Clark]

Fernando,

Not that I know of. Are you using a single AF point? Also, an image stabilized lens might improve your AF performance as the AF point will be more stable so could stay on the subject better. With multiple AF points, the camera will often choose the brightest high contrast signal. So if you have a bright background, for example, the camera will tend to lock onto that bright background. A single AF point on the subject will work best. And note that the AF sensitive area is larger than the AF rectangle in the viewfinder and has a fuzzy edge. So the AF rectangle must be surrounded by the subject and if even a little bright high contrast background is close to the AF rectangle, the camera could lock onto that background.

Roger

[Daniel Cadieux]

Fernando, USM lenses feature full time manual focus...just grab the focussing ring and fine-tune to content without moving the switch, even when in auto focus. It can be convenient when trying to focus on a still subject hidden in grass or other small twigs and such.

[John Chardine]

Fernando, I further thing you will have to do is change one of the AF custom functions (not sure what it is on the 40D) so that AF is on the AF-On button and off the shutter release. If you leave it on the shutter release then AF will be activated when you eventually take the picture. With AF on the AF-ON button, press that one to AF, then stop pressing it and manually focus, then take the picture.

[Fernando Cerra]

Thanks a lot ! these answers bring a smile to my face, I am sure it will help others like me !

[Chris Ober]

It's always been custom function 4 to switch the auto focus button with the bodies I've had.