No matter how amazing the composition, how gorgeous the light, or how perfect the subject — if your photo is out of focus, the image is ruined, and there’s no way to save it in post-processing.
That’s why it’s so important to fully understand your camera’s built-in autofocus (AF) system and the different autofocus modes. While modern cameras make it easy to autofocus, there’s so much more to it than pressing the shutter halfway and waiting to hear the beep, hoping your camera will focus in the right spot.
If you want to take control of your images, learn how to use autofocus and how each AF mode works. This guide will teach you the different AF modes and when to use them, what affects autofocus, and offer tips to improve your camera’s autofocus performance.
What is Autofocus?
Autofocus (AF), basically, is a system that will allow your camera to automatically focus your lens. In order to use autofocus, you need to have a lens that is equipped with it. A camera will not be able to autofocus if you’re using a manual focus (MF) lens.
However, you can turn off AF and manually focus with an autofocus lens.
How Autofocus Works
There are many sophisticated and complex algorithms that go into modern lenses that allow them to autofocus. They can do amazing things like detecting human faces, animal eyeballs, track moving objects, and more.
At the root of autofocus, there are certain things that have a huge impact on the way it performs:
In order for autofocus systems to function, they must have contrast. If you’ve ever tried to focus on a plain wall or into a dark room, you probably found your camera struggling to find focus. That’s because there was no area of contrast or edge detail for the lens to focus on.
Autofocus points are the little dots or squares you see when you look through your viewfinder. Entry-level cameras will have just a few, while pro-level cameras may have upwards of 60 or 80 of them.
These autofocus points allow you to specify which point (or group of points) you want the camera to focus on. Check your manual to see how to change your camera’s autofocus point. By default, it’s usually set to the center point.
Other things that impact AF
Contrast and autofocus points greatly affect autofocus, but there are a few other factors that can impact AF performance, too:
- Your camera’s focus detection range;
- The maximum aperture of your lens. Lenses with a wider aperture tend to focus faster and perform better in lower light situations;
- The speed of the focus motor. Older lenses have older technology and tend to be slower to focus;
- Your firmware. AF systems are constantly being updated by manufacturers, so be sure to consistently update your firmware to take advantage of upgrades.
In addition to selecting an autofocus point that tells your camera where you want it to focus, you should also select an autofocus mode. AF Modes tell your camera what to do when it’s looking for focus.
Let’s explore the three most common AF Modes: Single-Point, Continuous, and Hybrid.
Single-Point AF, known as One-Shot AF on Canon and AF-S on Nikon cameras, is pretty straightforward. You simply select one focus point and the camera will look for focus in that one single point. So, even if you’re shooting a landscape and a bird flies into the scene, it won’t change what the camera is focused on.
Continuous AF is known as AI Servo on Canon cameras and AF-C on Nikon. This mode is best when you’re shooting something in constant motion — kids, animals, sports, and wildlife photography, for example.
Continuous AF works by tracking your subject as it moves through the frame. Avoid using it on something that isn’t moving as your camera will constantly try to refocus when it doesn’t need to.
AI Focus (Canon) and AF-A (Nikon) is the mode that combines the best of both Single-point and Continuous AF Modes. By default, many entry-level cameras are set to this mode. It’s a safe bet to use if you’re not sure which AF mode to use.
The way hybrid AF works is that is will lock focus on one point if your subject isn’t moving but it will refocus if the subject moves. Hybrid AF is not included in most high-end and pro-level cameras, as it’s designed for beginners, taking the control away from the photographer.
How to change the focus mode
Every camera is different, so you’ll need to refer to your manual for instructions on exactly how to change the focus mode. For example, on a Canon 6D, it can be done by pressing the AF button on the back of the camera and then turning the top dial to rotate through the different options.
Tips to improve autofocus
As we mentioned above, autofocus relies heavily on contrast and sharp edges. That said, there are times you will be shooting in low light and will find your camera struggling to find focus. Here are some things you can do to improve your camera’s ability to focus:
- Use the center focus point — it’s the most sensitive;
- If your camera has it, use the AF Assist feature;
- Look for contrast and edges, focus on that and then recompose your shot;
- Increase the light;
- Make sure it’s not camera shake that’s causing your images to look soft — check your shutter speed;
- If you don’t have AF Assist, use a bright flashlight to focus on, then turn off the flashlight before you press the shutter (this might require a helper!);
- When all else fails, switch to manual focus.
If nailing sharp focus is important to you — and it should be — then understanding the different autofocus modes and when to use each one will go a long way toward helping you get tack sharp photos every time.
Before you know it, technical things like AF will become second nature and you’ll be able to focus more on the art of photography.