Focus Points and Actual Focus

Nimai

This is killing me! I double, triple check my center focus point to make absolutely sure that I'm focused on the subjects, then... bleh~



My only defense against this is to re-take multiple shots every time and then pick the one that's in focus later. Am I doing something wrong?

kdog

That's weird. Are you holding the camera in some way that's causing you to bump the lens focus ring while you're shooting?

Also, the selected focus point can be misleading if you've focus/recomposed your shot. For example if you focused before everyone was completely ready then maybe there was a gap between the two center gals allowing the camera to lock onto the background. That would be more likely to happen if you use back-button focus. But since you say it happens frequently, I'm wondering if you might have an equipment problem. I would do a focus-consistency test.

Put your camera on a tripod and focus at a target and take a shot. Twist the focus ring on the lens to throw the camera out of focus and then grab autofocus on the target and take another shot. Turn the focus ring in the opposite direction as last time to throw the camera out of focus, then grab AF again and take the shot. Do this a half-dozen times or more and check all your shots. They should all be perfectly focused.

ziggy53

It would be nice to have an image with full EXIF intact. This PNG image has nothing to go on.

What AF mode?
What lens and camera?
What lighting? (Any flicker possible?)
As KDOG requested, what AF methodology?
Does the lens/camera ever get it right?
Are other lens/body combinations more successful?
Have you done any microfocus adjustments against this lens?

For the AF target in kdog's suggested test, I strongly suggest using a flat and simple paper target with a simple and bold "+" sign in the middle and no other markings around it to distract. You want something parallel to the image plane and simple enough that the AF sensor latches strongly and decisively on it.

For the AF test you should use One-Shot mode (Canon) or AF-S mode (Nikon). I strongly suggest using a tripod and turning off any shake reduction technology. Lighting should be typical for the scenario where you experience AF problems.

Teetime

One other point - most lens' autofocus have to be calibrated to the camera. There are products available to help with this, but if your camera has live view you can try the Dot-Tune Autofocus calibration technique. If that doesn't work you should have your camera and lens checked for back focus.