One Shot vs AI Focus vs AI Servo: Which Autofocus Mode Is Best?

Understanding the autofocus modes on your Canon camera is crucial to capturing the perfect shot. With different autofocus (AF) modes available and options for each mode, it can be a bit overwhelming, especially for beginners. 

In the world of photography, achieving sharp focus is essential. To assist photographers in this endeavor, Canon cameras offer three autofocus modes—One Shot, AI Focus, and AI Servo. Understanding these modes, customizing them, and knowing when to use each one enhances your photography skills.

In this article, I take a deep dive into Canon autofocus modes. With an appreciation of the powerful features available, you gain the confidence to choose the right autofocus mode for any photography scenario. By the end, you’ll have a clear understanding of Canon’s autofocusing modes and know when to use them to achieve precise focus in your photography.

An Overview of Canon Autofocus Modes

Before getting into the specifics of each autofocus mode, let’s differentiate between manual focus (MF) and autofocus. While the manual mode of focus requires photographers to physically adjust the focus ring on the lens, autofocus utilizes the camera’s internal electronics and the electro-mechanical functions of the lens to bring the subject into sharp focus at the press of a button.

Many Canon lenses have an AF/MF toggle. For autofocus, select AF.

Let’s explore the three AF modes offered by Canon cameras: One-Shot AF, AI Focus AF, and AI Servo AF. Note that the AI in these modes designates Artificial Intelligence.

If you own a Canon camera, you probably know how to select the AF mode. If you need to review, Canon offers a step-by-step guide to AF modes.

One-Shot AF

One-Shot AF mode is intended for still or stationary subjects. This is particularly effective in situations where you have time to carefully compose and focus your shot. Pressing the shutter button halfway locks focus on the subject, ensuring sharpness and clarity. It maintains lock focus until the shutter button is fully pressed and the image is captured.

One Shot Autofocus is ideal for landscape photography, portraits, product photography, or any scenario where the subject isn’t moving.

AI Servo AF

Artificial Intelligence Servo Autofocus mode is specifically designed for capturing moving objects. It continuously adjusts the focus to keep that moving subject sharp, tracking it as it moves within the frame. This continuous servo mode is particularly effective for wildlife photography, sports photography, or any scenario where the subject is in motion.

AI Servo Autofocus offers advanced configurations that allow you to fine-tune the tracking sensitivity, acceleration/deceleration tracking, and autofocus point switching to optimize focus accuracy.

How to Configure AI Servo AF Mode

Canon has robust options to fine tune AI Servo AF mode. You can adjust tracking sensitivity to control how the camera focuses and responds to subject movement. Fine-tuning acceleration/deceleration tracking and autofocus point switching further enhances AF performance in dynamic scenarios.

1. Tracking Sensitivity – This sets the AF system for subjects that are in motion. A minus setting makes the main subject the priority. That maintains focus on the primary subject even when something moves in front of and partially blocks that subject. A plus setting tells the camera to focus on anything that comes into the foreground.
2. Tracking Acceleration and Deceleration – The responsiveness of the camera changes according to the speed of moving subjects. For something moving at a steady rate of speed, set this to zero. For subjects that start and stop, move erratically, or change speed, dial up the tracking sensitivity accordingly.
3. Auto Focus Point Switching – In One Shot AF mode, this is off. Enable this setting any time you are using multiple focus points. This sets the speed of the change from one autofocus point to other points. When subjects move quickly and unpredictably, it increases the sensitivity of this setting.

AI Focus AF

This is a hybrid Canon autofocus mode. The camera automatically switches between One-Shot AF mode and AI Servo AF mode. It’s based on the movement of the subject. The camera begins with One-Shot AF and then switches to AI Servo AF when and if the camera detects motion. This mode is suited for situations where the subject is unpredictable or when you want the camera to assist in determining the appropriate focus mode. That is, you trust the camera to adapt to still subjects or to those that are in motion and maintain sharp focus in either situation.

AI Focus AF mode is often used in street photography, documentary photography, or any scenario where the subject’s movement is intermittent and unpredictable. A disadvantage of this mode is a slight delay when the camera switches from one mode to the other. You may miss a shot during that delay.

Set Your Camera for Back Button Focus

A good technique to use is Back Button Focus. This control, the AF-ON button, is located on the back of the camera in easy reach of your right thumb. This configures the camera so that you use the back button to focus, and then press the shutter button to capture the image. I wrote an article on back button focus that goes into detail on the how and why of this technique.

To set up the back button focusing on your Canon camera, follow these steps:

1. Access the camera’s custom function settings.
2. Assign the autofocus function to the custom button on the back of the camera.
3. Disable autofocus activation from the shutter button.

By utilizing the back button focusing, you’ll have greater flexibility and control over your focusing process. Also, it helps to prevent losing focus once it is achieved. My own experience with Back Button Focusing is that I became comfortable with it fairly quickly.

Common Issues with Autofocus

While autofocus modes are powerful tools, there can be challenges in using them effectively. Let’s address some common issues and difficulties photographers encounter:

1. Difficulty Tracking Moving Subjects: Moving subjects can challenge autofocus systems. Understanding the limitations of each mode and employing techniques like continuous AF point selection can help improve tracking accuracy.
2. Camera Focusing on the Wrong Subject: In complex scenes, your camera may focus on objects other than your intended subject. Utilizing single-point AF or manually selecting the focus point can ensure precise focus where you want it.
3. Inconsistent Focus in Low Light Conditions: Poor lighting makes it challenging for autofocus systems to achieve accurate focus. Using a lens with a wider aperture or assisting autofocus with the camera’s built-in focus assist lamp can help in low-light situations.

Customizing AF Options

AF1

This is the default setting and includes six options or Cases. These Cases allow you to select presets for tracking sensitivity, subject motion, and AF point automatic switching.

The Canon autofocus system includes case descriptions for autofocus presets, which allow you to customize the autofocus behavior based on specific shooting conditions.

• Case 1: The default setting for tracking this is designed for subjects moving at a consistent speed. A band marching in a parade is a good example. It’s a balance between staying focused on the original subject and refocusing if a new subject moves in front of it.
• Case 2: This case tracks focus on the original subject, even if another object blocks it. This works well for sporting events when you want to maintain focus on a specific player.
• Case 3: The priority is on immediate refocusing on an object when the active autofocus points detect a sudden distance change in the subject.
• Case 4: This is an optimization for changes in speed or direction, specifically movement away from or toward the camera. It is useful for sports photography.
• Case 5: This Case enhances the speed of autofocus points that automatically switch as the subject moves laterally within the frame. An example would be a volleyball game when the AF area mode is set for more than one AF point.
• Case 6: An optimization for erratic movement, side-to-side, abrupt changes in speed or direction. A small, quick animal such as a squirrel is a prime example.

AF2

First or second image priority in AI Servo: an option for the fastest shutter firing or to assure focus lock for the sharpest focus. This may mean a slight delay in shutter firing. Other menu options set this for the initial shot in a sequence or the subsequent shots.

AF3

One Shot Autofocus release priority: sets the camera for fastest shutter release or sharpest focus when shooting stationary or moving objects together. Sub-settings control the electronic M-focus feature on lenses and enable or disable the continuous autofocus-assist beam.

AF4

Autofocus Point Selection: an option to select autofocus points, how those points are selected, and whether the lens will continue to find focus.

AF5

Autofocus Point Display: A control to select how the viewfinder displays all the AF points together.

If you’re new at this, it gets confusing; Canon cameras feature robust autofocus options. The best approach is to start with one-shot focus and the simple options and learn as you go. You don’t have to fully understand everything today.

Selecting Autofocus Area Modes

Canon cameras offer a range of autofocus area modes to cater to different shooting scenarios and preferences. Single Point AF, also known as One-Point AF, allows the photographer to manually select a single focus point within the frame, giving them precise control over where they want the camera to focus. Another option is Spot AF, which further narrows the focus point to a smaller area, ideal for capturing subjects with intricate details.

In addition, AF Point Expansion and Zone AF modes allow for a wider coverage area by utilizing multiple focus points. Large Zone AF mode covers a larger portion of the frame for situations where quick and accurate focusing across a broader area is required. Further options include Large Zone AF: Vertical and Large Zone AF: Horizontal, useful for wildlife and erratic motion. Some cameras have Whole area AF, which uses auto-selection AF in the entire frame.

Let’s Review

Selecting the appropriate autofocus mode depends on the specific requirements of your photography scenario. For wildlife photography and sports photography, where the subjects are often fast-moving, AI Servo Autofocus mode is recommended. It provides continuous focus tracking to keep up with the action. On the other hand, for landscape and portrait photography, where the subjects are typically stationary, One Shot AF mode is more suitable. AI Focus Autofocus mode serves as a versatile option for situations where the subject’s movement is intermittent or unpredictable.

Understanding the strengths and weaknesses of each mode will enable you to select the most suitable autofocus mode for your specific shooting situation.

Conclusion

Mastering autofocus modes on your Canon camera is essential for achieving pinpoint focus in your photography. A thorough understanding of the three modes empowers photographers to keep focus, continuously track, and capture consistently sharp and well-focused images.

Get to know and work with the different focus modes. Address common challenges and know when to use each mode. You can capture stunning images in any situation. Remember to configure your autofocus settings correctly and experiment with different techniques to find what works best for you. Adapt to various photography scenarios, consider the specific requirements of each situation, and select the mode accordingly. With practice and experimentation, you will refine your skills and achieve outstanding results in your photography.

I hope this article helps you get the most out of your Canon camera. If you have any questions or comments, please submit them in the space below.

Take Away

With three autofocus modes – One Shot, AI Focus, and AI Servo – Canon cameras are designed to adapt to the photographer’s needs. Each mode can be customized for sports, landscapes, portraits, wildlife, street photography and other genres. Advance your skills by learning and working with the various AF modes.