After looking through some of my photos from that same shoot, it is clear to me that the size of thesubjectin frame andapertureselection make a huge difference in sharpness.





This shot is at f/2.8 and is a comparable subject framing as the shot you uploaded. As you can see at 100%, it isn't tack sharp, but when looked at medium or even large, it is quite acceptable. The same would go for your shot.


http://farm2.static.flickr.com/1339/4731047902_c3af123905_o.jpg


In this one, the subject's face is a very small portion of the frame, shot at f/5.6. As you can see, her face is not tack sharp at 100% (not even close), but when you click on medium or large, the shot is still in focus. So, even stopping down the aperture isn't the whole ball game, it would seem.



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http://farm2.static.flickr.com/1420/4730413933_e26f524250_o.jpg


Now, if you had filled the frame with your subject's face, and dialed down a few stops on the aperture, you should get some extremely sharp shoots, especially with that 85L of yours. Keith B had some amazingly sharp shots of one of his friends up not to long ago with his 85L, similar tight framing, and shot at about f/5.6. You could see the pours on his subject's face in perfect detail, and the eyes weremesmerizing.