While the lens’s maximum effective aperture determines the total amount of AF points available, the AF Area Selection mode enables you to choose how the camera uses them.
On a beginner-level camera, you have two choices: either manually select a single AF point, or activate all the AF points and let the camera decide where to focus.
The higher-end DSLRs give you a wider range of area modes to choose from, with manual, automatic and semi-automatic (where you manually pick a zone of AF points and the camera automatically tracks) options available for tailoring the performance to the situation and your style of shooting.
Below, our friends at the Canon magazine PhotoPlus explain what you get in the EOS 7D Mark II, 5D Mark III, 5DS/R and 1D X…
Speeding up selection
In a compatible EOS camera’s AF menu, you can remove the AF Area Selection mode options that you rarely use. If I’m shooting with AI Servo, depending on the subject, I may remove the single-point spot, regular AF point expansion and auto selection options.
This makes it quicker to go from a tighter point of focus to a wider tracking zone, or go back through options!
Manual selection: Spot AF
This option offers a finer measurement of focus than the standard single point. While it’s good for picking out a stationary subject from a detailed background, it’s pretty poor for AI Servo AF. It may appear to track focus in a similar way to single-point AF, but the smaller area it covers makes it more prone to dropping focus more often.
Manual selection: 1 pt AF
Picking a single AF point that corresponds with the most important feature on a moving object – such as the head of a flying bird – gives you full control over focus tracking. The problem is that it can be deeply frustrating trying to keep that AF point positioned correctly, particularly with subjects that are close to the camera and moving erratically.
Expand AF area
A good compromise between precision and ease of tracking. The AF points directly above and below and to the left and right of the selected point will automatically assist the main AF point, continuing to track the subject should you fail to keep the main point centred on it. You do need to initially acquire focus with the main point though.
Expand AF area: Surround
Follows the same principle as Expand AF Area, but uses all eight neighbouring points surrounding the selected one to increase the chances of a smaller subject remaining in focus. In my experience, it’s more assured than the regular Expand AF Area setting, holding onto a subject more readily when the selected AF point drifts from the subject.
Manual selection: Zone AF
Zone AF sees the total number of AF points split into nine smaller groups (the EOS 7D Mark II also has Large Zone AF with three groups) each of which can be manually selected. But the camera automatically chooses which AF point(s) to use within a zone and prioritizes objects that are closer to the camera, making it harder to pick out a specific target.
Auto selection: 61/65-point AF
With all available AF points active, you’re leaving it to the camera to keep track of the subject. It’s not entirely pot luck – you select a single AF point which the camera then uses to initially set the point of focus – but areas of high contrast or features in the foreground can cause the camera to refocus and lose the subject.
The post How to choose AF points: pros and cons of single point vs area selection appeared first on Digital Camera World.