If you are just starting in photography you must have come across the term focus or focusing quite a few times. Focusing is the process of bringing the subject of the photo to its maximum possible sharpness onto the image plane. The image plane is the sensor (or the film) at the back of the camera.
There is more than one type of focusing mode. Let’s learn about them in detail.
Types of Focusing Modes
Regardless of the camera make or version you are using there are broadly five different types of focusing modes. These are –
- Continuous, or AF-C or Ai Servo
- Single, or AF-S or Single Servo
- Automatic, or AF-A or AI Focus AF
- AF-F or Full-time Servo
- Manual Focusing
Continuous mode is the easiest and the most common of all focusing modes on your camera. In this mode, the camera keeps the subject in focus for as long as you have the focus button pressed down.
Nikon calls this mode AF-C and Canon refers to it as AI Servo.
Usually the shutter release button (another technique involves assigning a button on the back of your camera to work as your focus button. This technique is known as back-button focusing. We will try and discuss this in a future article) on your camera doubles up as the focusing button when you half-depress it. Meaning, when you are ready to take a picture, you have to half-depress the shutter button and that triggers the focusing mechanism inside your camera for locking focus.
When you fully depress the shutter release button, the shutter curtains inside the camera move along with a bunch of other things, allowing light to enter the camera via the lens, and strike the sensor (or the film as the case may be) to expose it. Et voila! Your image is created.
Continuous focusing is useful when shooting sports and action photos. It is also useful when shooting birds and wildlife. This process allows the camera to keep focus locked on the subject continuously even when it is moving around.
Single autofocusing, as the name suggests, is when the camera captures focus once when you half-depress the shutter button. However, focus remains locked on that precise point and the camera does not attempt to refocus if the subject moves. That means if your subject moves to another part of the frame, it will be out of focus.
This technique is useful only when you are shooting stationary subjects. As you can imagine this technique will not be useful for shooting anything moving.
Nikon refers to this autofocusing mode as AF-S and Canon refer to it as Single Servo.
This technique is widely used with the Focus and Recompose technique. The way it is done is this – photographer chooses the Single AF mode (discussed below). S/he locks focus by using a single AF point. Afterward, s/he would alter the frame by changing the composition before fully depressing the shutter release button and taking the picture.
Why would someone do this? To create off-center compositions of faces, flowers, and random items with lots of negative space. One can also use this technique for shooting landscape photography, especially when trying to shoot at the hyperfocal distance.
Automatic Focusing or Hybrid Autofocusing Mode
Automatic focusing is a technique where the camera decides whether to switch to AF-C or AF-S mode. This option is chosen when you are unsure about the autofocusing mode you should choose. It is also applicable when the subject is moving unpredictably, stopping and moving again.
Nikon refers to this autofocusing mode as AF-A and Canon refer to it as AI Focus AF.
Full-time Servo AF or AF-F
This particular model is available when shooting in movie mode. The camera will track moving subjects but it will only do so when you are shooting in live view.
Manual vs. Autofocus
The first four are examples of autofocusing, where the camera locks focus on its own with little or no input from the photographer.
The fifth type is as the name suggests, Manual focusing. In this mode, the photographer has to manually adjust the focusing ring to achieve focus.
The camera does precious little in manual focusing mode. Some cameras come with a manual focus assist option. The camera will highlight the areas where the focus is the sharpest by changing the color of those areas. This is handy when manually adjusting focus.
It may become necessary to shoot in manual mode when your camera is unable to or find it difficult to focus. This can happen when you are shooting something with very little contrast or texture, or when you are shooting something in very low light. Autofocusing sensors may be unable to nail focus in these circumstances.
Autofocus Area Modes
Autofocus area modes determine the number of AF points that are involved in the process of focusing as well as how they behave in relation to each other. Modern cameras come with several autofocus area modes. These are –
Single point AF mode as the name tends to suggest is about choosing a single AF point to do the focusing job. Usually, this is done for two reasons. One when your intended subject is very small and or occupies a small part of the frame. The other is when you are focusing on something very precise, like the eye of a model closest to your camera or a particular flower in a bed of flowers.
Dynamic Autofocus Area Mode
Dynamic autofocus area mode denotes that you select a group of AF points to work in tandem. Let’s take a Nikon example to explain how the Area AF mode works.
Nikon allows up to 153-point dynamic-area AF. When focus is locked initially, the AF point selected is the one that locks focus. As soon as the subject starts moving and the selected AF point no longer has the subject in focus the surrounding AF points will become active. The camera will be able to lock focus based on the information passed on by the surrounding points.
The number of points in the Dynamic Autofocus Area mode will depend on the total number of AF points available in your camera and how many you have chosen to activate in the area mode.
Starting from a basic 9-point area mode you can select 25, or 72, or even 153-points depending on the subject that you are trying to photograph. We recommend that you choose an area mode depending on the space occupied by the subject in the photograph.
3D tracking is somewhat the same as the Dynamic Area AF mode except in this case all the available AF points are activated when necessary. You start the same way by locking focus with one AF point and then as the subject moves within the frame the AF point that is closest will get activated.
Sometimes the dynamic area AF mode gets the focus wrong and in this situation, the 3D tracking is a better choice.
Eye Autofocus (popular in new mirrorless cameras)
Modern cameras use advanced subject tracking to assist the autofocusing process. This includes advanced face and Eye-tracking. These technologies use advanced algorithms to detect a subject’s face and eye to lock focus accurately. For example, the latest Sony Alpha 1 has the best-ever face and Eye-tracking mechanism. It can accurately detect not only a human eye but also an animal’s eye and that too in poor lighting.
So advanced are these tracking features that wildlife photographers like Dhritiman Mukherjee have been able to capture sharp photos of reptilian eyes underwater in murky conditions without an issue.