em-5 auto focus and face recognition question

so the camera or photographer must choose which eye to focus upon.

If depth of field is shallow, both eyes can not be in focus at the same time, so the camera offers the option of choosing which eye to focus upon. The closer eye almost always the preferred eye to the viewer.

If you're coming from a small sensor camera background, you may not have encountered shallow depth of field issues like this. In the larger sensor/film format worlds, it's not uncommon to shoot head shot portraits with the leading eye in focus and the further eye out of focus, lending a sense of depth to the image.

Nikon D700, 105mm f/2 DC: