Let's focus on the realities - The Autofocus Modes
Let's focus on the realities - The Autofocus
Let's focus on the realities - The Autofocus Modes
15 July 2008
There is nothing worse than a picture where everything is just a blur. Anyone who wears glasses (or contacts) will understand how annoying it is to not see things sharply and clearly. Autofocus is fantastic at making sure the image is sharp and clear, but cameras do sometimes get it wrong and focus on the wrong subject, and there are situations where focusing is a lot harder. So it's good to understand to focus manually and the various parameters.
Most of the time you can let your camera focus for you, and to make this easier cameras often offer three primary focus modes.
AF-C
Continuous focus as it's called is useful for moving objects. When the shutter is half pressed, the camera begins to focus but in this mode, it detects movements and will refocus accordingly to keep the subject sharply in focus. The drawback to this mode, besides it using a lot of battery power to focus and refocus, is that if the autofocus mechanism is slower than the moving subject the photo may still come out a blur. Of course it may be better to get a slightly blurry shot of an important subject then no shot at all. But that's up to the photographer to decide.
AF-S
Single focus is just that, when you press the shutter down halfway, the camera will focus on the subject once and then stop. It saves energy to not have to focus constantly over and over. While it's perfect for something that won't be moving, it won't be entirely useful for shooting pictures of things that are changing their positions. Most photographic subjects don't tend to move all that much unless you are shooting sports or wildlife so single focus is often the one that's most used.
AF-A
Automatic autofocus is a feature that's still relatively new but very useful. It alternates between AF-C and AF-S depending on the situation. It's generally the default mode because it's very useful. Photography is an art where you can never be sure what will happen and having the camera make the decisions between the modes can save a lot of time and hassle. If your subject decides to move unexpectedly it's not a problem at all for the camera to refocus on it.
Manual Focus
An essentially forgotten skill, for some DSLR users this might be a useful one to rediscover. DSLRs all tend to come with the option to turn off autofocus. You then fiddle around with the rings on the lens itself to get the image in focus. It's time consuming and not at all easy since the human brain doesn't quite always have a good memory when it comes to sharpness which means jiggling the focus back and forth till you get it right. There are situations where manual focus can do what autofocus can't. If you're photographing fast action and you know where the subject will be ahead of time, you can focus ahead and snap the photo when the subject reaches that point. Also autofocus is often confused if there is a wire fence or glass in front of the subject. The camera may focus on the glass rather than the real target.
