Last month I wrote about light metering modes. This month is about focus modes. There is one point or one area where the plane or distance from the lens is where the subject will be in focus. The goal is to get the focus point where you want it, and with an acceptable Depth of Field (DOF). It is frustrating to have the focus in the wrong place. Example: if you shoot thru a fence and the camera focuses on the fence instead of the subject beyond the fence. There are a few general focusing modes, such as continuous, single, and manual.
Of course, with autofocus, the camera will try to focus on faces, eyes and other features. With all the types of focusing choices available, today’s cameras should be very accurate and give you the shot you want. You should learn the strengths and weaknesses of each type of focus mode to get the best shot possible.
Continuous Focusing Mode
Each manufacturer calls it different things, like AI Servo AF (Canon) or AF-C (Nikon) for Continuous Focus. This focus mode is useful for tracking moving objects and keeping them focused as you track or pan with the camera. Set the Focus mode by selecting it in a menu item or a level/button (see below, C is continuous, S for Single, and M for Manual) on your camera. The setting is unique for many cameras so refer to the manual for how to set it. Focus on most cameras is done by pressing the shutter button down halfway to start the focusing. The camera senses the moving object and continually refocuses to keep it in the focal plane. This mode is battery hungry, so make sure you have extra batteries if you shoot in this mode all day. Also, with a lot of motion, set the proper shutter speed and aperture as required for the shot.
Single Focusing Mode
One-Shot AF (Canon) or AF-S (Nikon) sets the focus to one single focus point. When you press the shutter down halfway, it focuses on the subject once, and with your finger on the shutter button, the focus will stay on that spot. You can either take the image, or you can recompose the image and then press down the shutter to take the shot. This mode may have a single point or an array of points to help you pick a subject to focus on.
A Nikon viewfinder is shown below and has an array of points with the one highlighted in red chosen to be the focus point. I can choose a different focus point by using the arrows on the back of the camera body (the same arrows used to scroll through images).
This is what a Canon viewfinder might look like.
Automatic Autofocus Mode
Autofocus mode is AI Focus AF (Canon) or AF-A (Nikon), which stands for Automatic Autofocus. In this focus mode, the camera is using both the AF-C and AF-S (Nikon) or One Shot AF and AI Servo AF (Canon) as needed. The camera is sensing if the subject is moving or static by how you move the camera and will change as needed. It is the default setting by most camera manufacturers.
Nikon choices might look like the following.
The White Rectangle (above) lets the camera choose the AF points itself.
The middle Crosshair lets you choose the sensor, and then the camera moves it around to track action as selected by you. The image shows a single sensor but you can move it by tapping the selector wheel on the back of the camera.
The bottom position selects only one fixed sensor at a time.
Manual focus is just as it sounds. You’ll need to use your fingers to turn the focus ring (not the f-stop ring) on the lens to measured distances. Since most lenses have a motor to focus the lens, you may need to set the lens switch on manual to shoot in manual focusing mode. It usually has both imperial and metric measurements. Often older lens will have an acceptable depth of field (DOF) scale as well. DOF is greater at f/22 than at f/4, so you know what will be an acceptable focus. With cameras being so good at focusing why use manual? It is the most accurate. Measuring the distance and setting the lens, is very accurate. I just purchased a manual focus ultra wide lens. My reasoning was that at most F-stops, the focus ring moves very little. I could set it myself and leave it alone for images where the foreground, midground, and background are my subject areas. Following my example before, about shooting thru a fence… if the subject is 12 feet from me, I can set the focus to 12 feet. The fence in the foreground will be out of focus, and my subject will be in focus, and the background can be out of focus, thereby framing my subject.
Today’s lenses allow you to turn off and on auto-focus. Most camera bodies allow you to choose the focus mode, either continuous or single (single zone or multiple zones). Knowing when to shoot in single or continuous mode is important. If you learn how to select your preferred focus point(s), and to learn how to quickly move them, your success rate of having the important part of the image be in sharp focus will increase.