Auto Focus not always correct

It seems that auto focus does not always perform up to my expectations when using large aperture lenses at or near wide open.

As I am shooting with a tripod and remote shutter release I would think any and/or all camera vibration would be mute and using center point focus should have the image spot on. Look at the two photos as an example; first was taken at the minimum focal limit wide open f/1.4 center point right eye.

The image is razor sharp.

Rocky Rhode wrote in post #12865518
Can someone please explain why this happens?

Could be a number of reasons, but a common one is that either the subject or the photographer moves slightly, between locking focus and taking the shot. At close range and big apertures it may only take an inch or two of movement for focus to be off, a very slight lean forwards or backwards by either person and you get a result similar to the posted shot of the girl.

Alternately, if you focus / recompose the geometry means that focus can again be thrown out a couple of inches. I suspect from the position of the girl in the frame though, that you didn't recompose so that isn't the problem here

Using the Online DOF Calculator, it shows that at 50mm FL using f/1.8 on a 60D (all from the second photo's EXIF information), it would yield a total DOF of about 11 cm at 2 meters distance. As sandpiper said, a very slight movement could throw you out of that acceptable DOF. Movement doesn't seem to be an issue on your part since you said you're using a tripod and remote release, but if the girl leaned back slightly between the time you focused and the time you took the photo, that could be enough to do it.

If it's not as describe by the two previous replies it could be the lens might need AF Micro-Adjustment.
Before you attempt that make sure it is the problem.
http://www.canonrumors​.com …-is-soft-and-other-myths/
http://www.northlight-images.co.uk …s3_af_micoadjus​tment.html

At f/1.8 I too suspect it's the DOF and a possible shift in position. Or if you're using the shutter button to activate AF you will have a hard time maintaining consistent focus from one shot to the next. If you're not already switch to Back Button AF and AI Servo, especially if you're not using a tripod.

tkerr wrote in post #12866539
.....if you're using the shutter button to activate AF you will have a hard time maintaining consistent focus from one shot to the next. If you're not already switch to Back Button AF and AI Servo, especially if you're not using a tripod.

To me this sounds the most likely. If you are using one shot AF it will focus once when you half press the button but will not readjust if the subject moves. Therefore the subject moves yet your focal plane does not. Try using AI Servo and see what happens.

Dont half press and then screw around if you are using shutter button focus. Get it done fast. If you are using back button then use servo, IMO. I tend to keep af on the shutter on the 5d and usually use back button servo on the 7d.