Some questions on focus

hockdub · Sep 7, 2010

Hey all I have a few questions for all the pro's out there. I am no pro photographer and love getting out to shoot the things I get involved with very much. I have asked in the past in other places about focusing under low lighting with off camera flashes, etc and learned a bit, but Id like to be solid at learning how to focus shots perfectly.

I am mainly self taught and learning along the way.

I have started toying with different focus settings on the camera, ie - one shot, ai servo, ai focus. Some questions I have are what the best focus settings for the camera should be? I realize this can change in different shots - fast pace vs slow pace, long range vs close range. But how can I prepare and be able to fire off a shot at the right time and keep the subject in full focus?

I feel that some of my shots come into perfect focus while other great shots are missed because of blur or not being able to setup in time. It can be frustrating to miss a sweet shot.

Below are a couple of shots that I have gotten in the past that came into focus, while others were just missed because the background was "pre-focused" to be ready for the shot.

Any tips or pointers would be greatly appreciated!

I remember specifically in this shot I had pre-focused on the end of the barrel... a longer DOF could keep this in focus though right?

out of focus:

background in focus, subject blurry.

pre-focused, guess i wasn't looking but it was on the trees in the background.
Would AI servo be good for a shot like this?

thanks for your time

Big Mike · Sep 7, 2010

One thing you might try is to move the AF away from the shutter release button. (custom function #4)
I have the AF set to the * button on the back. That way, I can turn AF on or off by pressing or releasing the * button with my thumb...and I can hold or press the shutter release button without changing the focus at all.

Also, keep in mind that AF speed is a result of the camera's ability to process what it sees and the lenses ability to physically move parts of the lens that need to be moved.
So for example, a 7D or 1D will likely focus a lot faster than your 20D. A lens that is smaller and/or has USM focus, will faster than a heavy lens or one that doesn't have a USM focus motor.

hockdub · Sep 7, 2010

hey thank you for the pointers... i was not aware that you could change the function for af like this. kind of helps eliminate the need to pre-focus and hang onto the shutter button while you wait for the subject right?

im actually selling the 20d as well to move into a 7d so I can shoot the things I enjoy with less frustration as well. I have missed a few sweet shots and sequence opportunities in the past. It would be fun to have a quick camera!