Auto-focusing (AF mode) is one of the fundamental functions on a modern digital camera. However, it was not always the case. Cameras did not always have the functionality of auto-focusing built-in. That said, it is now an integral part of any camera system. Today, we shall learn about 7 essential aspects that you need to keep in mind when working with the AF mode.
# 1 – Types of AF Modes
There are three AF modes that can be selected on most interchangeable lens cameras. These are:
Continuous AF, also known as AF-C,
Single-shot auto-focusing, also known as AF-S; and,
Automatic auto-focusing mode, also known as AF-A.
There is a fourth focusing mode available on interchangeable lens systems but that does not come under the definition of auto-focusing. We are referring to manual focusing.
# 2 – Selecting the Right AF Mode
The first thing that you need to know when working with AF modes is to select the right mode for the scene in question. If the subject is stationary the right AF mode is either AF-S or AF-A. In the first mode the camera uses a single AF point which you can move around on the AF point selector. It allows you to lock the AF point on the precise spot where you want to focus on before firing the shutter release.
In the second mode the camera switches between AF-S and AF-C focusing modes (in this case it is likely going to select AF-S mode) automatically based on its analysis of the scene.
If the subject is moving about, then selecting the AF-C mode makes more sense. This AF system is assisted by subject tracking. The camera automatically corrects focus by selecting the nearest AF point when the subject moves around. Alternatively, you could select AF-A mode.
# 3 – More the Better
By now you know that the AF points are imperative when it comes to auto-focusing. The more AF points your camera has the better it is in terms of locking focus. Because the more AF points there are the more is the likelihood of these points to be spread across the viewfinder. The more there are the wider they would be spread out allowing you to even focus on subjects that are at the corners of the frame.
Looking through the viewfinder will reveal how many of these your camera has and how they are spread across the viewfinder. Every time you half press the shutter button the focusing points will light up before one or a small cluster remain activated.
# 4 – Never Trust the Viewfinder Blindly
The viewfinder of your camera is tiny and often very dark. As weird as it may sound it is not the ideal tool for judging whether your images are in focus. How many times you have captured a ‘perfectly focused’ image only to find later that the image is not focused where it is supposed to be?
# 5 – Use the Magnify Button to Lock Focus
This technique will work for stationary subjects and only when you are setup on a tripod. Use the magnify button combinations at the back of the camera to zoom in while in live-view mode. Lock focus by moving the focus square around and then press and hold the focusing button (shutter button / back-button) until you have focus. Zoom out and capture the image.
# 6 – Use the Focus Delimiter Button
Some telephoto lenses have a focus delimiter button on them. This is a physical button present on the lens barrel. This allow you to limit the focusing distance range within which the lens hunts for focus. This is a useful way to limit the amount of time the camera spends rocking back and forth the lens’ focusing elements to lock focus. If you don’t use this function every time the shutter button is pressed half-way the lens is going to hunt for focus across the entire focusing range. This technique is used mainly by sports photographers. They know the maximum focusing distance they need the lens to rock back and forth.
# 7 – Back-Button Focusing
Another useful tip to speed up the whole process of image making is to use the technique of back button focusing. Back button focusing is basically about assigning any button at the back of the camera to control the process of focusing. Therefore, this technique splits the two processes of focusing and image making while assigning two different buttons to take care of each of them.