I’ve written about this before, and I’ll write about it again. Ask almost any photographer, and they will tell you the same- Focus on the eyes when taking pictures. It doesn’t matter whether you are photographing people or animals, birds or bobcats, this is advice to shoot by.
The windows are, as they say, the windows to the soul, and when we truly capture them in a photograph, they can draw us in and let us feel a powerful connection to the subject. Eyes that are out of focus will not do this. Our own eyes will automatically be drawn to the parts of the image that are in focus, and it seems a little harder to establish a rapport with someone’s nose.
It’s more than just drawing the audience in. It is also hedging our bets on making sure that more of the important details are in focus. The eyes are sort of mid way (distance wise) between the tip of the nose and the ears. Go ahead, imagine there is a camera right in front of you, staring back at you. Touch your nose, then your eyes, then your ears. Your eyes are right in the middle. This means that if you focus on the eyes, you are more likely to have the entire face in focus. If you aim for the nose, the ears have more chance of being out of focus, and vice versa. This can be minimized to some degree by adjusting your aperture so that you have a larger depth of field (although when shooting in low light this is not always possible.)
When shooting profiles, the difference in focal planes is usually minimized. Think about how far a beak or a nose can stick out, when facing toward the camera. Rotate that same face sideways, and many of the facial features will be in a single plane that runs parallel, or nearly parallel to the camera’s focal plane. This makes it easier, but it is still a good idea to pay attention to the eyes and try to focus on them.
Another advantage to focusing on the eyes, is that you can notice when there is sunlight or another light source sparking or glinting in the eye. That glint can add a lot of life to the photograph. I know of several professional photographers that will add that light afterwards in post production, or will use a flash, just so that it will light up there eyes with that spark. I myself don’t really see the need for that, since, with a little attention, you can get that light there naturally, just by paying attention and timing it right. Also, if you are shooting wildlife, that flash can be rather disturbing and can scare them off, ruining your chances for more photographs.)
There are however times, when it is best not to just watch the eyes. Safer.