Focus is off too often

moshepupkin · Jun 22, 2013

Any idea how my Pentax k-x with Sigma f2.8 17-50mm lens managed to get focus wrong on one of the following pictures taken from the same spot with about 1 second difference? In general, I find that focus is wrong too often, this is just a good pair of pictures to demonstrate it.

samm · Jun 22, 2013

Check for your back & forward focus ,against a focus chart.Just a thought.I had the same problem till i adjusted my focus in the camera .
My Nikon is the AF fine tune adjustment

Derrel · Jun 22, 2013

Holding a piece of paper up to the screen and checking the diagonals by making a "X" on the frame, it seems that the center AF spot might have missed the child's chin and wrist, and been aimed precisely at the distant lawn and trees. This is called back-focus; the focus point is well in back of the desired target. It could also be an issue with the Sigma lens; I have a Siggy that just loves to back-focus, for no apparent reason...

480sparky · Jun 22, 2013

Your Focus Mode setting may need to change.

SCraig · Jun 22, 2013

First one is focused on the child, the second is focused on the asphalt in the background. For whatever reason you or your camera picked a different focus point for the second shot.

tirediron · Jun 23, 2013

Change to a single focusing point and make sure you place that over the point of critical focus (in portraiture/people photography, that's normally the near eye).

moshepupkin · Jun 23, 2013

It was in single focusing point. I was starting to think that this was the problem (single point is easy to miss), but now that last comment confused me again...

paigew · Jun 23, 2013

he probably moved just a little and the fp hit the asphalt behind him (user error).

emdiemci · Jun 25, 2013

How do you figure out where the person focused? Software or just by eye?

Big Mike · Jun 25, 2013

What focus mode are you using? You may be inadvertently locking the focus and then changing the camera to subject distance.

gsgary · Jun 25, 2013

you were shooting the lens wide open so your focus has to be spot on, not the cameras fault

SCraig · Jun 25, 2013

emdiemci said:
How do you figure out where the person focused? Software or just by eye?

Sometimes software, sometimes eye. Nikon RAW files (perhaps Canon as well) record the focus position in the RAW data and their software can display where it was. Other times one can draw diagonal lines from corner to corner, and if the focus point was in the center where they cross will show it. Other times it's just a function of looking for what has the best focus.