Understanding focus is key to getting a good photograph as it’s critical that you get a part of your image in focus. This may sound simple — the camera does it all for you, doesn’t it? That’s often the case with modern DSLR cameras (when using film cameras often the only option was to focus manually), but in order to get the best image it’s still important to understand how focus works.
When taking a photo, light is directed through the lens before reaching the recording medium. The lens, regardless of whether it’s built into your camera or interchangeable, is made up of elements and these elements together are what focus the light. This can be done automatically, or you can focus the lens manually.
Manual focus vs autofocus
Whether you’re just starting out or already have some level of experience, chances are the terms manual focus and autofocus will be familiar. Lenses nowadays often feature both (when photography was still relatively new, this wasn’t the case) and you can set this on your lens (MF or AF).
Manual focus is when the photographer manually sets the focus by adjusting the focus ring of the camera. Less commonly used than autofocus, manual focus is still particularly useful when the camera has difficulty focusing or when taking a series of images where you don’t want the focus to change.
Autofocus refers to the mechanism that automatically moves the elements within the lens in order to achieve the best focus. This is done through a series of autofocus points that are visible through the viewfinder — the camera (or photographer) selects a particular focus point and this is used to achieve focus.
Above are two examples of what you can expect to see through your viewfinder. This not only shows how different cameras have different focus layouts, but how they also have a different amount of focus points, which you can use to select your exact focus position (it doesn't always have to be in the centre).
When it comes to your camera automatically selecting a focus point, this is done one of two ways: Phase detection or contrast detection.
Phase detection: This is the system most commonly found in DSLR cameras. The advantages of this system is that it is very fast and therefore great for tracking moving objects. Although the system doesn’t always get it right, this technology continues to improve.
Contrast detection: This system is commonly used in mirrorless cameras, point-and-shoot cameras, DSLRs in live view mode and smartphone cameras and is much simpler than phase detection. Although it is slower, it is much more accurate, which makes it far better suited to genres like product or landscape photography.
Depending on the model and make of the camera, different cameras have different focus systems, and different focus points. Depending on the focus mode you choose, you or the camera can choose the best point of focus. Some modern day cameras also feature eye detection, which can be very useful as this is often the best place to focus.
When using autofocus, there are a number of different modes to choose from, each of which are better suited to particular scenarios.
Single shot/Single-servo focus mode: Only one focus point is used to determine focus and this does not change until you re-focus. This is shown as ‘One-Shot’ on Canon / ‘AF-S’ on Nikon.
Continuous focusing/Continuous-servo: Once a focus point is set, the camera continuously tries to monitor the distance of the subject from the camera and readjust as necessary for as long as the focus button is held down. This is shown as ‘Al servo’ on Canon / ‘AF-C’ on Nikon.
Automatic autofocus mode: This is a cross between single shot and continuous focusing. The camera focuses on a single subject and only refocuses when the subject moves. Until that point, the mode behaves more like single shot than continuous focus.
Where to focus when taking a photo
Now that you understand how focus works and the different focus modes, the next thing you’re probably asking is “Where should I focus in an image?”.
This is a common question, especially for new photographers. Where you focus in an image depends on a few things: what you’re photographing and what result you want to achieve. From the example shown in the video, you’ll have seen how different focus points can have a big impact on an image.
When selecting your focus, it’s important to think about two specific things: your subject and depth of field. What do you want to be in focus, and how much of the subject do you want to be sharp?
Depth of field (which is controlled by adjusting the aperture) will increase or decrease the sharpness either side of your focus point. We’ll look at this in more detail in the next chapter.
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