Autofocus is a feature that many of us take for granted. Today’s cameras can capture the action and focus even on moving objects extremely well. I cut my photographic teeth back in the old film days when autofocus wasn’t even available. I was thrilled when it first came out and I am an even bigger fan of it now with the current digital cameras. My Nikon D300, for example, has fantastic autofocus accuracy.
Some photographers look at a photograph and wonder why their main subject or the subject they were trying to focus on is not in focus. Several contributing factors could be the culprit in this situation. One possibility is that the camera’s autofocus may have tracked on to a different subject in the frame. One of the problems I used to see happen frequently was in composing a photograph. The photographer focuses on a subject but then wants to re-position the frame for a more pleasing composition. If the shutter release is not kept pressed down halfway, the camera may re-focus on a different subject.
This is why I like to use separate buttons for focusing and exposure instead of having the shutter release do both. A simple change in the camera’s menu can set this up properly. On my D300 I use one of the buttons on the back of the camera as the focusing button. The shutter release still sets the exposure. I like this because I can focus in on a subject by pressing the back button. When I release this button the focus stays locked on that subject. I can then re-position the frame to get the composition I want. Of course I only release the back button if the subject remains still. If not, I can keep the button pressed, track the subject, and keep it in focus.
Separating the focus and exposure by using two different buttons can take some time to get used to. I recommend trying this on a free day when you do not have an important photography shoot planned. Just experiment with it but stick with it at least for one full day. Eventually you will get the hang of it and the technique will become second nature.