Autofocus Mode AF-C (Continuous) or AI SERVO

Read also: Autofocus mode AF-S (singular) or ONE SHOT

Focus is the process of adjusting the lens to make your subject appear sharp in the photograph. If not done well, your images will appear blurry, spoiling an otherwise great shot.

There are two main types of focus: manual focus and autofocus. Trust me; you want to use autofocus whenever possible. There may be rare moments when manual focus is necessary or preferred; we will explore them later. But let us first dive deeper into autofocus, as it will likely be the standard option throughout your photography journey.

You can activate autofocus on your camera by pressing the shutter button halfway down. The camera uses built-in sensors to adjust the lens and automatically focuses on the subject. There are two settings concerning autofocus: focus modes and AF points (autofocus points). A thorough knowledge of these settings will allow you to acquire correct focus faster and more precisely.

The choice of autofocus mode determines how the autofocus on your camera will function.

There are several modes available on most cameras, including single autofocus (AF-S), continuous autofocus (AF-C), and automatic autofocus (AF-A). The equivalents for the Canon cameras are ONE SHOT, AI SERVO, and AI FOCUS.

Each mode is designed to work optimally in specific situations, depending on whether the subject is stationary or moving. Therefore, it’s important to select the appropriate focus mode for your shooting circumstances.

THE LOGIC BEHIND THE CHOICES

How to select an appropriate focus mode

The choice of focus mode is a subject-related decision. AF-S/ONE SHOT is the mode for stationary subjects. AF-C/AI SERVO mode has been developed to capture moving subjects. AF-A/AI FOCUS is the automatic mode that allows the camera to choose between AF-S/ONE SHOT and AF-C/AI SERVO modes.

AF-C/AI SERVO mode is designed for moving subjects. It is particularly beneficial when the motion is fast and unpredictable, like birds in flight or dynamic sports, where you need to track the subject’s movement while keeping it in focus. For slower-moving subjects, such as a pedestrian, you can successfully use the AF-S/ONE SHOT mode.

When using the AF-C/AI SERVO autofocus mode, the camera takes an entirely different approach compared to the AF-S/ONE SHOT mode. After half-pressing the shutter button to activate the autofocus, the camera continues to focus as long as the button is kept pressed. The focus is not locked onto a specific subject; instead, the camera tracks the movement and adjusts the focus continuously. You can take a shot when you deem your subject to be in sharp focus.

It is imperative to avoid using this autofocus mode to capture stationary subjects. Things will go wrong the moment you reframe. As soon as you turn the camera away from the subject, it will focus on something else since the focus cannot be locked.

The AF-C/AI SERVO mode is highly effective for capturing fast-moving subjects in challenging conditions. However, it is worth mentioning that the camera model significantly influences its capability. It is a demanding focus technique that functions well only on more powerful camera bodies. In this regard, I recommend using the AF-S/ONE SHOT mode for as long as possible. This mode operates adequately on every camera and has fewer issues, reducing the risk of missing a photo.

EXERCISE: Understand how AF-C/AI SERVO mode works

Select A/Av mode, f/5.6, and auto ISO (or an appropriate ISO value).

Select autofocus mode AF-C/AI SERVO.

Place an object on the table not too far from the camera. Check the lens for its minimum distance to the subject to avoid getting too close. Zoom in for a shallow depth of field to observe the effect better.

Point the camera at the subject and press the shutter button halfway down to get it in focus (Figure 1).

While keeping the shutter button pressed, reframe the photo by turning the camera toward the background (a background with a lot of details would be convenient). The camera will now focus on the background (Figure 2).

Turn the camera toward other objects around you. The camera keeps focusing on all of them.

Figure 1

Figure 2

Conclusion: The AF-C/AI SERVO mode allows the camera to continuously focus on all subjects in front of the lens and track moving subjects. You cannot lock focus on a subject and reframe for better composition as in AF-S or ONE SHOT autofocus mode.