Modern digital cameras have marvelous autofocus systems. So good, in fact, that most of the time the autofocus mode is more accurate and certainly faster than manual focusing. Some cameras detect faces, even eyes, to focus on and can almost out-think the camera user.
There are circumstances, however, when the autofocus system can’t tell what you want to focus on. 
Subjects behind windows or fences are classic examples, although many cameras have even mastered those situations. Here is an example of a photo that had to be manually focused. The deer is among shrubbery with leaves in front of and behind the deer. Autofocus simply could not select the the intended subject.
The camera is likely to select the closest item in the focus area. This can result in missed focus even when the subject is not obscured.
My second example shows such a situation. There is no way for the camera to know if I want the pretty flower or the butterfly.The flower was closer to the camera and that is what the autofocus system selected (this photo is cropped, both subjects were much closer to the frame center in the original).
Most cameras have a “close up” mode which causes the focus system to use just a small area in the center. For this photo that would have worked. OK, I intentionally set the wrong mode to get this illustration.
Autofocus works so well that many users don’t even know how to focus manually. Some cameras do not even allow manual focus. Learn how your system works, know where the switch is located to select autofocus or manual focus. So when that unusual situation presents itself, click to “M”, focus and get the shot. Don’t forget to reset the switch to autofocus so the camera is ready for the next photo.
.:.
© 2011 Ludwig Keck
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