When we’re out and shooting it’s all too easy to become wrapped up in our shutter speeds, apertures and even our ISO’s, but we rarely give much thought to our focal settings.
Many photographers will and almost definitely shoot using autofocus in this day and age, and for a good reason! Modern DSLR camera’s and lenses are incredibly quick and can pick up and focus on subjects, sometimes before we even have the chance to, making them incredibly useful when shooting things like street photography, public events or candid, reportage and documentary.
But how many of us have ever considered the various modes of focus and how best to utilise them? In this article, we’ll be taking a look at these autofocus modes, as well as all-out-manual focus, and shedding some light on when best to make those changes on shoots.
The basics of Auto-Focus
Autofocus (AF) is a key feature of modern digital cameras, and it works by detecting various contrasts in tone and exposure within a scene. These contrasts can be caused by differences in proximity, texture, and lighting conditions, and the more pronounced and contrasting the elements in an image, the easier it is for the AF system to select and bring into focus these differences quickly.
Despite the advancements in digital photography, AF can still occasionally get it wrong. This is because fundamental variables can prevent it from working to its full effect. For example, it could be that an item is lost within a scene of similar exposure and colour, such as a muddy dog on a muddy field, making it difficult for the AF system to identify and focus on the subject.
Additionally, movement can also pose a challenge for AF systems. If the subject is moving quickly or erratically, it may be difficult for the AF system to keep up and maintain focus. Similarly, if the photographer is moving, such as panning to capture a shot of a cyclist or trying to take a quick shot while on a moving train, keeping the subject in focus can be challenging.
To address these challenges, cameras offer various modes and sub-modes of AF. These modes allow photographers to adjust the settings and parameters of the AF system to best suit their needs and the specific shooting conditions. For example, some cameras offer tracking AF modes that are designed to follow moving subjects, while others offer single-shot AF modes that are better suited to stationary subjects.
While AF systems have come a long way, challenges can still prevent them from working optimally. Understanding the different AF modes and sub-modes available on your camera can help you overcome these challenges and capture the perfect shot.
DSLR Focus Modes
Most DSLRs will have various focus modes for specific situations. When photographing still subjects, you acquire focus once and take a picture. If the subject moves, you reacquire focus again and take another picture. But if you have a subject that is continuously moving, you need your camera to readjust focus automatically as you take pictures.
Single Area Focus Mode
The “Single Area AF”, also known as “AF-S” in the Nikon world or “One Shot AF” in the Canon world, is a pretty straightforward way to acquire focus. You pick one focus point, and your camera will look for contrast in that single focus point.
When you half-press the shutter or press a dedicated AF button (if you have one), the camera will snap into focus once, and if your subject moves, it won’t reacquire focus even if you continue half-pressing the button. Hence, the focus remains “locked”.
The Single Area AF mode often requires the camera to lock focus before allowing you to take a picture, so if the focus is not acquired or your subject moves, pressing the shutter will do nothing (due to focus error).
A couple of things to note about the AF-S mode – if you mount an external speed light that has an “AF-Assist” red beam, you will need to be in AF-S mode for it to work. The same applies to the “AF-Assist” lamp in front of your camera; it will only function in AF-S mode.
Continuous/AI Servo Focus Mode
Another focus mode that is available on all modern DSLRs is called “Continuous/AF-C” (Nikon) or “AI Servo” (Canon). This mode is used for tracking moving subjects and is the go-to mode for shooting sports wildlife and action in general. The way this mode works is it analyses the subject movement and predicts where the subject will be, placing the focus at the predicted point.
The nice thing about the Continuous mode is that it will automatically readjust focus if you or the subject move. All you need to do is continue half-pressing the shutter button or holding your camera’s dedicated AF button (if you have one). The autofocus system will automatically track any movement.
Compared to Single Area AF, the Continuous mode is highly configurable – particularly on high-end DSLR cameras – and can do multiple tasks, such as tracking subjects with single or multiple focus points.
It’s important to note that single or multiple focus points are part of the focal area, not the AF Modes. These are the dots or squares that you usually see light up in your viewfinder when using your focus. The number of focal points you have can be changed within your camera’s settings. Should you use this mode, you can also usually choose where your single point focus is in the frame.
Single/Continuous Hybrid Mode
Some cameras also have another mode called “AF-A” (Nikon) or “AI Focus AF” (Canon), which is a hybrid mode that automatically switches between Single/One-Shot and Continuous/AI Servo modes. The way this works is the camera detects if the subject is stationary, in which case it automatically switches to Single focus. In contrast, if the subject moves, it will switch to Continuous focus.
The default method on lower-end Nikon DSLRs is AF-A, which works quite well for most situations. Many of the higher-end/professional DSLRs do not have this mode since it is designed for beginners.
So there you have the true basics of autofocus and it’s various modes!
It’s always useful to know what each of these modes can accomplish so that you can switch between the two when necessary. For example, you may want to continually shoot Continuous AF at a wedding, as there’s a lot of movement and unpredictability amongst guests.
But when the light fades, or you get rapid, changing light for the evening party, it may be that Single Point suits you better. This way, you can simply point and shoot. Single-point AF makes for a much quicker shooting process and gives you a definitive focal point, so it’s all about your preferences as the photographer.
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