Focusing Issues - need some help

[specialshadow]

Hello everyone,
I am a wedding and studio photographer and own a Canon xti and 7D. My lenses include Canon 50mm 1.8 and 28-135mm 3.5-5.6. Sigma 17-70mm 2.8-4. and a Tamron 70-200mm 2.8.
I have been having issues focusing on my subject, but have realized that the camera is grabbing the most detailed object and focusing on it, even if I do a focus lock and recompose.
I shoot in one-shot mode with single point focus and normally use center-weighted metering mode at around f4-f8 depending on the situation, but have used different combinations which result in the same problem. An example is when I have 2 people in frame I do a focus lock on them, recompose, take the shot and the trees are in focus behind them, whether the trees are 2 feet away or 20 feet away.
I have explored the back focus problems with my camera, but have decided that back focus could not be the issue simply because I realized that it was the detail of the tree (in my example) that grabbed my focus. This problem has followed me from my xti to my 7D, has anyone else had this issue and is there a way to fix the problem? I have looked for months for a solution and have decided to ask for help.

Thank you in advance,
Ed Hughes

[inkista]

How are you focus locking?

Have you considered using back-button autofocus and reversing the half-press behavior? (i.e., using half press to start autofocus, rather than stop it?)

[specialshadow]

I am doing the old half-shutter press to lock focus. I will give the back-button autofocus a shot. At this point I am willing to try just about anything.

[inkista]

Weird. I mean, the 7D has some known autofocus issues, but you say this followed you from one camera to the other, so I'm more inclined to think this might be a user issue, but it also sounds like you're doing everything right.

What happens if you use an AF point other than the center one? (i.e., you don't recompose, but you just use the point that's actually on your subject). And does this happen with all your lenses? Or does it tend to happen with one specific lens? Also, have you compared what the AF does, vs. manual focus with liveview and 10x magnification?

[Vagebond]

Asking te experts, could this be a combination of depth of field and turning the focal plane of the camera while recomposing?

[specialshadow]

It doesn't matter what AF point I use, it would still focus on the detail in the back ground. If there is something plain in the background I do not have an issue, but if it is a stained glass window I have a heck of a time. Last time I did a focus lock on their feet and then recomposed for the shot because if i would have focused on the subject or their flowers the stained glass window would have grabbed the focus. I would like to stay away from manual focus with weddings, I feel it would take to long to focus and shoot. I will give that a try and see how it works.

[specialshadow]

Vagebond,
I have shot at f11 to broaden the dof and used the joystick on my 7D so I would not have to recompose the shots thinking that would help, but I get the same results.
One of my shooting buddies said he did not think I was waiting till my camera was focused completely, but after turning on the beep sound to make sure I still had the same issue.

[inkista]

And what autofocus mode are you using? Try "One Shot" mode, vs. the auto/servo modes. Particularly the auto modes.

[sk66]

I'm not a Canon user, but on my Nikon there is a setting for "focus tracking"....this setting defines how long before the autofocus refocuses (on whatever it determines best). I f I use single servo (single shot?) The camera only focuses once, then it is a matter of choosing focus mode.
I suspect it's "focus tracking" setting...whatever that is in Canon....

[specialshadow]

Originally Posted by inkista

And what autofocus mode are you using? Try "One Shot" mode, vs. the auto/servo modes. Particularly the auto modes.

I use the "One Shot" mode for my line of work.