Thanks for posting the examples...
I suspect it's as Wadizzle suggested, that the focus ended up on her elbow, instead of her face. (Are you entirely certain you don't accidentally have one of the Expansion or Zone focus patterns selected? Either of those could definitely explain this problem. I looked at the image EXIF data, but can't tell what focus pattern was set.)
Spot Focus might have worked better than Single Point, in this case. The AF point used in Spot Focus is much smaller than in Single Point.
This is a good example of very shallow depth of field. The 50mm lens at f/2.0 and, I'm guessing, about 6 foot working distance, will render roughly 4 inches deep sharp plane of focus. Anything closer than 5.84 feet or farther away than 6.17 feet will drop off dramatically in sharpness. Even slight focus errors will be very noticeable, with those settings and that lens at that distance.
The second shot, of the statue and wall, appears even closer, which would make for even shallower depth-of-field. It too might have been mis-focused because of the size of the AF point... or because the lens is not calibrated properly to the camera. Just be sure to read and follow the procedures carefully, if you decide to make Micro Focus Adjustments.
FYI: there are online depth-of-field calculators. I can't post a link here (forum won't allow it), but you can find them with a search. The one I used is called DOFMaster.
It may be that your lens needs Micro Focus calibration on that camera or that using Focus Assist (from either the onboard flash or an accessory flash) would have helped, as was suggested.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
FLICKR & EXPOSUREMANAGER
