Need Help Understanding Auto Focus Modes? We Can Help!
One of the questions that I get asked the most is how can I get sharper photos? It’s a tough question to give a specific answer for because there can be lots of reasons why your photos aren’t sharp. But sometimes, it’s simply a result of not understanding autofocus modes and using them correctly.
Understanding the differences between several autofocus area modes might not be at the top of your list when you first get your camera. But understanding what the different area modes are and more importantly – when to use and how to control the different AF modes, are critical for long-term photography success.
So let’s get you right up to speed so you can have the confidence of choosing and using the correct autofocus mode.
What Are Autofocus Modes?
On most modern digital cameras, you can choose where and when to focus. This is known as manual focus, focusing like this gives you more control and freedom in creating artistic effects. With manual focus, you must have an internal sense of sharpness to ensure the camera is focusing on the object.
You can let the camera choose where and how to focus (with a little guidance for you). That’s what we call autofocusing or the built-in focusing system that determines the sharpness between the object and the camera.
Most cameras have two different kinds of focusing mode, single-mode focusing and continuous focusing mode. The terminology varies by cameras manufacturer, but the concepts in terms of focusing are the same.
The Basics of Camera Autofocus
Active vs Passive Autofocus
Active AF works by shooting a red beam on the subject, then bouncing that light back to the camera to identify the distance between the subject and the device. The camera will then instruct the lens to control focus based on this information.
While Active AF is ideal for poorly-lit scenarios, you can only use it for stationary subjects. If you have a Canon or Nikon Speedlight that has an AF Assist function, it will use an Active AF system.
Meanwhile, passive AF deals with special sensors within the camera to detect contrast from the light that enters the lens. It may also use the camera sensor for sharpness in a particular portion of one shot. Thus, passive AF requires you to have sufficient contrast in your frame for it to achieve proper focusing.
Focus Points
Focus points are the little empty dots or squares you see when you look through the viewfinder. While the focus points are deliberately laid out in particular parts of the frame, the layout depends on the brand and camera model.
Entry-level cameras typically have simple AF systems with a few focus points for basic focusing. In contrast, pro-level cameras have complex, highly configurable AF systems with plenty of focus points.
Types of AF Points
Vertical sensors are one dimensional and can only spot contrast on a vertical line. Cross-type sensors are two dimensional and can catch contrast both on horizontal and vertical lines, making this more accurate than vertical sensors.
The type of AF points sensor is also essential in getting accurate results. For example, Nikon brags of a 51 single point AF system with 15 cross-type sensors within the frame. This 51 single point AF system means there are 51 focus points, 15 of which are more accurate, cross-type sensors.
Factors Affecting AF Performance
- Quality and amount of light: While camera AF works great when shooting in daylight, you might encounter some challenges when moving indoors because it’s harder for cameras to detect contrast in low-light conditions. Poor lighting can affect passive AF since it relies on the light that passes through the lens.
- Lens condition: If your lens has some kind of physical problems such as dirt, dust, or mold, the quality and aperture performance may impact the autofocus mode.
- Camera quality and robustness: Canon and Nikon offer the most advanced AF systems that work well in various shooting conditions.
Changing Focus Modes
If you don’t know or can’t see how to change the autofocus mode on your camera, it’s advisable to consult the user manual because managing modes varies from model to model. For example, Canon has an AF Point Selection button that directs you to the modes.
With entry-level Nikon DSLRs, you need to go into the camera’s “Info” screen to change the autofocus modes. Meanwhile, higher-end ones feature a dedicated switch in front of the camera to change the autofocus mode, so that you can toggle between various focus modes.
Single vs Continuous Autofocus
Single AF Area Modes
In single AF area, (AF-S in Nikon Cameras or One Shot AF in Canonc Cameras) once you lock focus on your subject the camera will not retain focus if your subject suddenly moves. That means if you compose your image, press the button halfway down and gain focus, your focal points will stay in that position in the frame until you press the button halfway again EVEN if your subject moves.
This autofocus tecnique is good for taking images of stationary objects in the frame, or in low-light conditions, or if you use the focus and recompose technique. It also uses less battery because the camera isn’t constantly making micro adjustments to the focus.
This autofocus mode works great for portraits of adults or teens, still lifes or product photography work. If your subject is on the go, however, you’ll want to use continuous AF-C.
Continuous Autofocus modes (Nikon: Continuous AF-C / Canon: AI Servo)
In continuous AF (Ai Servo AF for Canon), once you lock focus on a stationary subject the camera will do its best to follow your subject keeping them in focus. The camera detects the movement of your subject and refocuses constantly to keep it in focus as long as you are pressing the shutter halfway.
This is great for capturing subjects in movement like sports, animals or pets on the go, or even people. We generally recommend using AF-C when shooting families with wiggly toddlers!
The drawback of continuous focus is it uses more battery and the camera doesn’t always predict the movement of your subject correctly. And how fast and accurately your camera grabs focus on the subject is influenced by the lens. So you might still get some blur. But your chances of nailing focus on moving subjects is better with AF-C.
Automatic autofocus modes (Nikon: AF-A / Canon: AI Focus AF)
In this mode, the camera decides if the subject is moving or not and will alternate between single focus and continuous focus. The AI Focus AF or AF-A for Nikon mode often works well, but letting the camera control the focus might not yield the results YOU were looking for!
While this one gives you more control by letting the camera change from Single to Continuous AF, depending on the movement of the subject, it will be harder to lock the focus and track the subject.
What is focus tracking with lock-on?
One additional feature your camera might offer is focus tracking with lock-on. This feature tells your camera how to handle adjusting focus if something comes between the camera and the subject where you’ve got your focus point.
For example, if you’re shooting a basketball game and are focusing on a player but the ref runs between you and the player. How would your camera handle keeping or changing focus? Focus tracking with lock-on lets you select the length of time that your camera will ignore an intruding object that blocks your subject.
This is a good feature to experiment with if you shoot a lot of moving subjects. If you find it makes your camera feel sluggish grabbing new focus points, you can always turn it off entirely. You can be the judge of how useful this technology is and at what threshold it best serves you.
How the Photographer/Camera Chooses Autofocus Points
Autofocus points are different from auto-focus modes. These are the points in your composition where the camera will try to grab focus. When you are looking through your viewfinder or Live View and press the shutter halfway, you’ll see a little small black or red square (in some cameras it may be a dot) floating in your image. That’s the focal point and that’s where your camera will focus for the image.
Your camera has different autofocus point modes. You can use a single point, a group of points or you can let the camera choose a point for you.
Single Point Area AF Mode
In single point AF area mode, you pick one autofocus point to focus on your subject with. The camera only uses 1 focus point in this mode. This mode is good for portraits, macro images, or other stationary objects and gives you the most control over your AF area point. You can use the area AF-S mode with both single area AF and continuous focus modes.
To select different focal points, use the round toggle switch on the back of your camera to move through the different focal points. This technique can take some practice. You need to build up muscle memory to do it quickly, but with time and repetition, the motion will feel like second nature to you.
Dynamic AF
With dynamic AF area mode, you are still able to be in control and choose the focus point. However, the camera uses a larger AF area to retain focus if your subject moves. This mode only works in AF-C.
The Dynamic AF-area mode works great for fast-moving subjects like flying animals. It involves panning the camera along with the subject, ensuring that the subject stays close to the selected focus points.
High-end cameras can control the number of surrounding focus points to obtain Dynamic AF. For instance, Nikon lets you choose one focus point while the camera locks on a specific focus point. Once it gets the necessary focusing, the camera will use the surrounding focus points to track the moving subject.
Auto Area Auto Focus
When using this AF mode, the camera is analyzing the scene and choosing which subject to focus on. It can be helpful because you aren’t having to manually select a specific focal point in one shot. But the camera can choose the wrong subject or wrong part of the subject to focus on.
The only time it makes sense to use this mode is if you can’t look through the viewfinder or Live View to accurately pick the focus point or if you just want to be able to point and shoot. Some cameras auto area AF modes are better than others. Sony camera lovers rave about the Sony autofocus system, for example, because it does an excellent job of locking on eyes in an image.
Since the camera decides what focus points to use, Auto AF will also pick the subject in the image according to contrast differences. This feature maintains and controls focus even as you change subjects or the subject moves. If you like having more control over what to focus on, this mode isn’t suitable for you.
Group Area AF
This one activates several focus points and evaluates the information from that cluster of points. If you are tracking a subject, Group AF mode will strive to follow the subject.
A lot of cameras now use this mode to recognize a face and lock onto the nearest eye, tracking the subject as it moves. When dealing with subjects that move erratically, Group AF may even provide more accurate results than Dynamic AF.
Auto Area Autofocus was used on this photo since we were holding the camera out aimed back at us for a quick self portrait and couldn’t look through the viewfinder.
Autofocus Point Configurations
If you’ve ever shopped for a camera, one of the specifications commonly listed is autofocus points. Different cameras offer different numbers of AF points and different configurations of autofocus points. You can choose a configuration that fits your shooting style and preferences.
Fewer autofocus points in a configuration means fewer options for composition but it also means you can toggle to your intended focal point more quickly. More AF points give you more control options but can slow you down finding the focus point you really want.
Autofocus Scenarios and Examples
Continuous Servo AF (Nikon, AF-C) or AI Servo (Canon) for Moving Objects
AF-C is particularly useful when the subject moves around during the shoot. If you are into event, wildlife, and sports photography, Servo AF helps you control the tracking of subjects and refocusing accordingly. However, this AF system won’t let you lock the focus point by half-pressing the shutter release, which means you also can’t reframe.
Single-Servo AF (Nikon, AF-S) or One Shot AF (Canon) for Still and Static Subjects
It would be best to use AF-S in this case so that you can control a single focus point while gaining the freedom of choosing the focus point. It also enables you to lock the focus by half-pressing the shutter release.
With One-Shot AF, you can press the shutter release halfway, and the camera focuses on the subject once. There will be no continuous adjustment once you press the shutter release.
If the subjects aren’t moving, like in landscape photography, or moving just a little, like in portrait shots, AF-S is handy when you want to reframe the shot without losing the focus point.
AF Modes in Low Light Situations
Your lens will find it hard to focus during low light situations. AF-Assist built-in light can be helpful in such cases. Once you turn it on, the camera will send out a red-orange light that will point to your subject and help the lens focus.
Although it focuses on using the central focus point, AF-Assist has a limited range, so you’ll need to get relatively close to the subject.
Why is it Necessary to Manually Choose the AF Point?
Today’s cameras are pretty “smart” but they still are unable to know exactly where you want to focus. Autofocus modules today use contrast or phase detection to guess where to focus and when you have numerous objects in the frame, there is a good chance that your camera will by mistake, choose to focus on something other than your intended subject.
If you are using fast prime lenses and shooting at wide apertures like f/1.8 any missed focus of the camera will be easily to see and the shot will be unusable. The key is simply to always choose the autofocus point and take control and tell the camera exactly what you want in focus. If you are taking a portrait – focus on the eyes.
Top Photo: This is NOT the autofocus mode you’d want to use for a portrait – the camera can focus on the shirt, a hand, the chin, anywhere it chooses, unless you specifically want to focus on the eye as shown in the bottom photo.
Does Back Button Focus Affect What Autofocus Mode I Need?
Back button focus, or assigning a button the back of your camera to act as the shutter, is a good option that lots of photographers swear by. Click here for our explanation of BBF and why you use it.
Everything we’ve discussed today regarding AF modes and autofocus system points is true, whether you use back button focus OR a traditional shutter.
Can I Use AF in Manual Mode?
Manual focus and manual mode are two different concepts. It can be tricky to separate them in your mind, though.
Yes, you can use AF in manual mode. In manual mode, you are telling the camera what shutter speed, aperture and ISO to use. It has nothing to do with focus. You can use any autofocus mode you’d like in manual mode: manual focus, single AF, continuous AF or Auto Area AF.
If you are shooting the camera in automatic mode, the camera takes control of the mode, focus points AND shutter speed, aperture and ISO. The camera is making all the decisions.
Key Takeaway – Autofocus Mode
It is always a best practice to take control of your camera and always use Single-Point or Dynamic AF Area mode and use the thumb pad to manually select which specific autofocus point to use to ensure properly focused photos. Use Single-Area for portraits and still objects and use Continuous AF for moving objects. Only use auto area focus in very specific exceptions that require it.
As always, I hope this quick read has been helpful to you! If you want more photography technical tips, head over to the “behind the lens” section right here.
Chat soon!
Cole
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