I just got a 50mm f/1.2 to go along with my T2i, but many of my photos are out of focus because the AF catches my subject's knee instead of her eyes, despite focusing on her eyes and recomposing. What can I do to achieve a more precise/consistent autofocus, particularly in low-light situations?
Selecting the autofocus point is covered on page 68 of the manual1:
Selecting the AF point
- Press the [AF point selection] button
- Select the AF point
Press the [4 way controller] to select the AF point
While looking in the viewfinder, you can select the AF point by turning the [main command dial] until the desired AF point lights in red.
The "AF point selection" button is the one at the top-right of the back plate of the camera, which you also use to zoom in during image replay.