Last updated on April 14th, 2022
Camera systems have at least two autofocus modes, regardless of the brand. These manufacturers have given different names to these modes. Canon has at least three main autofocus modes: AI Servo, AI Focus, and One-Shot.
At first look, their differences may not make sense, making it important to dive into the topic. Before distinguishing one from the other, let’s first discuss the difference between manual focus and autofocus.
What is AF (autofocus), as opposed to Manual Focus?
Manual focus and autofocus do the same thing. Both adjust the camera lens’ focus on a subject. The difference lies in how the camera focuses on the subject. The photographer only needs to point the camera and shoot in autofocus mode. On the other hand, the photographer will have to adjust the focus by hand in manual mode.
Each mode has its advantages and disadvantages. In the below sections, we will discuss each.
Advantages and Disadvantages of Autofocus
In terms of speed, autofocus mode is typically more convenient and faster than manual. You can quickly lock onto fast-moving subjects, such as animals, babies, and speeding cars. If you are into street photography, autofocus mode lets you capture your object in a matter of milliseconds.
Manual focus does not offer the same speed and efficiency. By the time you focus, you will lose the perfect time to take the photo. However, it does not mean you can’t or shouldn’t manually focus on fast-moving subjects. You can pre-focus your camera on the location where your subject will move and take the photo as it passes through.
Camera manufacturers have a few autofocus modes available. Some of the available choices are:
- Auto-Servo (AF-A) – Let the camera system decide which of the several autofocus modes is most appropriate. The camera bases the decision on several factors, such as subject, lighting condition, etc.
- Single-Servo (AF-S) – This is great for still/motionless subjects. The focus locks into place as soon as the photographer presses halfway through the shutter.
- Continuous-Servo (AF-C) – This is excellent for moving subjects. The autofocus would continually track and focus on the subject, even while pressing the shutter halfway through.
You may encounter problems with autofocus working correctly when the background and subject have similar properties, such as having identical colors, partly in direct sun and partly in shadows, and when there is an object between the camera and the main subject. Should you come across any of these situations, we recommend manual focus.
Some lenses, especially zoom ones, have a toggle between autofocus and manual focus. It typically has a label A for auto and M for manual. There are also lenses with a M/A mode, autofocus with an option for manual focus override.
The autofocus system determines the shutter lag your camera would see. Pre-focus your camera on the scene by pressing the shutter halfway to avoid shutter lag. Then press the shutter all the way to take the photo.
- Faster, more efficient than manual focus
- Best for capturing moving objects
- Recommended for beginners
- It is automatic
- Prone to shutter lag if you do not pre-focus
- Not all camera systems have a 100% precise autofocus system
- May focus on the incorrect part of the subject
Advantages and Disadvantages of Manual Focus
Several professional photographers prefer shooting in manual mode over AF because it enables more flexibility and control. Generally, manual focus is great for still subjects, such as portrait, low-light, and macro photography. Auto mode sometimes focuses on the wrong subject (or wrong area of the subject), ruining what could have been a perfect shot.
Photographers would typically use their left hand’s palm to cup the lens, then their two left fingers to rotate the focus ring until they get a sharp focus. Having a proper grip on the camera is key when focusing manually. Otherwise, you may not provide enough support and get a sharp focus.
- Best with portrait and macro shots
- Best for low-light photography
- Lets the photographer have greater control over focusing, which results in more precision
- Sports photography may be quite a challenge
- Slower than auto mode
Using the viewfinder instead of the LCD screen is better when shooting in manual focus.
Which mode to choose?
If you recently started with photography, it would help to get familiar with autofocus mode. At the same time, learn the basics of your camera and improve your lighting and composition. Knowing the ins and outs of your system will aid you in becoming better at photography.
What is One-Shot AF?
Camera manufacturers have their way of labeling focus modes, as mentioned in the previous section. AI Servo, One Shot, and AI Focus are Canon’s main autofocus modes across its camera lineup.
The equivalent of One-Shot AF is Single Servo (AF-S) in other camera brands. If your subject is motionless or not moving, use One-Shot to capture the moment.
How to use One-Shot AF?
Using One Shot is straightforward once you get the hang of it. Here are the steps to follow:
- Press the shutter button halfway down
- The camera system will detect and focus on the subject
- The camera will lock on the subject
- Your camera will stay locked on until you fully press the shutter button
What is AI Servo?
Artificial Intelligence Servo Automatic Focusing, otherwise AI Servo AF, is equivalent to Continuous Servo (AF-C). As the name would suggest, it is ideal for fast-moving subjects, such as animals and cars. It is not always perfect, but it would be the best mode for moving subjects.
How to use AI Servo?
Like Continuous Servo (AF-C), the AI Servo mode will continuously track the subject even while the shutter button is halfway down. It stays focused on the subject’s movement, ensuring it is sharp. Canon’s camera system can move the focus point around the viewfinder to track a moving subject.
Here are the steps to follow when using AI Servo:
- Press the shutter halfway down
- The camera system will detect and focus on the subject and continue detecting and adjusting
- Press all the way to capture an image
What is AI Focus?
In the previous sections, we have covered One Shot and AI Servo. The former is for still subjects, while the latter is for moving subjects. So you might think we have covered everything? Not quite! AI Focus fills the gap between AI Servo and One-Shot.
So how does AI Focus work? Remember that One-Shot works best on still subjects as it focuses only once after pressing halfway through the shutter. On the other hand, AI Servo does continuous focusing as long as the shutter is halfway down. AI Focus automatically switches between One-Shot and AI Servo, basing its decision on several parameters defined by the camera system. In other words, if the system thinks the subject is moving, it switches to AI Servo. If the subject is motionless or still, it uses One-Shot.
Nikon has its version called Auto AF, and other manufacturers also have this sort of hybrid autofocus mode.
How to use AI Focus?
Using AI Focus is similar to One Shot and AI Servo. These are the steps to follow:
- Press the camera’s shutter button halfway through
- The camera system will analyze the subject
- If the subject is still/motionless, it will switch to One-Shot
- if the subject is moving, it will switch to AI Servo
- Press the button all the way to capture an image
One-Shot vs. AI Focus vs. AI Servo
We have already defined these three types in the above sections. We have also provided a high-level overview of how each one works, and we will determine which one is best.
There is no one answer to which one is best to use in the situation. Sometimes, manual focus is a better option than any autofocus mode. But for the sake of this comparison, we will provide examples and situations for when it’s best to use each type.
Use One-Shot when you are capturing still objects or subjects. The best situation would be during portrait, wedding, or landscape photography, where subjects have little to no motion. What about macro photography? We don’t suggest using any autofocus mode as it may not focus 100% precisely.
Use AI Servo when capturing moving subjects or objects, such as vehicles and walking people. It is best to use AI Servo on sports, action, and wildlife photography.
With animal photography, you can either use One-Shot or AI Servo. If your subject animal does not move a lot or is still, you can use One-Shot. Otherwise, AI Servo would be a better choice.
Use AI Focus if you are still learning the different autofocus modes. The AI Focus automatically determines which autofocus mode to use – One-Shot or AI Servo.
However, all of these are not hard rules. You can switch to AI Servo from One-Shot if you feel it is more appropriate to use it.
Although Canon calls these different autofocus modes differently, they still function similarly with other manufacturers, such as Nikon and Sony. When it comes to photography, there is no hard rule in everything. Sometimes, you need to adjust depending on the situation.
In conclusion, Single-Servo (AF-S) is the equivalent of One Shot, Continuos-Servo (AF-C) is the equivalent of AI Servo, and Auto-Servo (AF-A) is the equivalent of AI Focus.