Discovering when to use manual focus and when to use auto-focus is a photography technique that will serve you well in getting sharp photos every time. In most situations your autofocus camera will do a good job for you, but there are several situations when you will get better digital pictures when you focus manually.
This first situation when this occurs becomes obvious when it happens, but if you are prepared ahead of time, you'll be ready. You won't miss your photo because the focus was wrong. It occurs when there is a fence or glass you have to shoot through at your subject.
Have you ever been to the zoo, or a museum or perhaps your car and you tried to photograph something through the glass or with an object between you and your subject.
Your camera focus will automatically be on the closest object to the lens. The fence or glass or object in the foreground will be sharp and your subject will be out of focus. Manually focusing on your subject will overcome this situation.
The second situation on when to use manual focus can occur when you are in a low light situation. Auto-focus lenses work in most situations, but often fail when it's dark or your subject has very little contrast for the camera lens to analyze.
I did this family portrait pose at sunset. It was extremely bright backlighting. My camera focusing mechanism was trying but couldn't find sharpness when I composed my photo. I switched to manual focus and was able to photograph this wonderful family.
Night photography situations, such as pictures of fireworks or strong back lighting situations will cause your lens to continuously search for sharpness and will delay the shutter or won't allow the picture to be taken at all.
Here is a little photography assignment you can try on your own and learn how your camera behaves. Look for these situations right now in your environment. Try taking a picture through a window. Place your subject with a large bright window behind them.
Try this with them wearing a dark solid shirt. The try it with a bright shirt or a shirt with stripes or a pattern. Your results will depend on how much Fill Light is present.
You may want to put emphasis on something within your photograph with selective focus. You can do so by having it sharply focused and other parts of the photo intentionally blurred.
The auto-focus system of your camera may not know which part of the photo you want to emphasize. Manual focus combined with a shallow depth of field will give you more control of your intended the center of interest in your image.
If your camera does not have manual focus your only option is to center on an object and focus on it first. Squeeze the shutter button half way to lock the focus distance, then aim your camera to compose your photo and gently squeeze the shutter button the rest of the way down.
I used manual focus to shoot the image at the beginning of this article.
Most cameras have auto-focus capabilities when shooting macro photography and with SOME cameras auto-focus can do an adequate job. The challenges come into play when you are extremely close to your subject and your depth of field is so limited.
Focusing accuracy and precise control is better handled manually, particularly in lower light situations when a larger aperture is needed for a good exposure. Point and shoot cameras definitely will fall short if you are photographing a moving target like an insect.
Shoot more photos. Watch less TV.
Some high level DSLR cameras have fast focus tracking and are able to follow fast moving objects and keep them in focus. Some situations and many cameras won't perform this well. That's when you need to focus manually on a pre-selected spot where your subject is going to be at the exact instant you take your photo.
Auto-focusing is particularly difficult when the subject is moving rapidly toward or away from you. The point of sharp focus is changing very rapidly as opposed to a situation where the subject is traveling across your field of vision.