10D Servo AF

[MarcS]

I've been experimenting with the CF4-1 setting to use the * button for AF and so far I like the results. As part of the testing I also switched to using servo AF so that I could press the * button once to get simulate the one-shot AF or hold down the * button to get servo AF. I've set the camera to only use the center AF point.

The problem I found was that in servo AF I wasn't getting a good focus when attempting a one-shot focus. Even when the subject wasn't moving the camera was continuously tweaking the focus and usually when I released the * button the focus wasn't right. If I use one-shot AF the focus seems to lock in fine.

The scenario was my 6 year old's little league baseball game. I was situated down the first base line. I wanted to one-shot focus on him when he was at the plate so I could shoot bursts of his swings with the focus already locked. Then when got a hit (yeah!) could hold down the * button for servo focus as he ran to first base.

It turned out that I had to zoom in tight on his face at the plate and hit the * button several times to get a clean focus and then zoom out and frame the shot.

Is this just the nature of the beast or is there something I can do to get better servo AF results?

[scottbergerphoto]

Canon's AF system is a passive AF system and is dependent on contrast. The only things that will help are pre focusing, more contrast in the subject or a lens with a larger maximum aperture.

[MarcS]

I thought it odd that with the same subject, same lighting, same lens and zoom that the one shot AF would lock into proper focus with a single press of the focus button the the servo AF would oscillate back and forth and very seldom find the proper focus. I'll just have to keep experimenting with it.