Using autofocus correctly can solve a great number of the common photography problems you face on a daily basis. But easier said than done, right? Behold the bible on AF points!
In this tutorial we’ll show you everything you need to know to take control of your AF points and nail focus every time you shoot.
Focusing has never been so simple. Use any of the Basic Zone shooting modes – Full Auto, Portrait or Landscape – and your camera does all the work for you. It’s almost too easy.
A light press on the shutter button is all you need and, 99 times out of a 100, the camera will focus in a split-second and you’re ready to fire.
So why is it that many shots simply aren’t sharp in the places that matter, such as the eyes in a portrait or the rolling hills of a landscape? The answer lies in the way that the autofocus system actually works.
Left to its own devices, a typical mid-range DSLR uses all of its nine autofocus sensors, which are spread out in a wide array around the image frame.
There’s one AF point at the centre, one both above and below it, another two to the left and right, and a final pair positioned towards the extreme left and right sides of the frame.
More advanced cameras feature an additional six ‘AF Assist’ points, although these, unlike the first nine, can’t be selected manually.
It works out the distance of each part of the scene from the camera, chooses the closest object that coincides with an AF point and locks the autofocus at that setting.
This is fine if you want to focus on the nearest object in a scene, but often that’s not the case.
If you’re shooting a sweeping landscape, for example, you don’t want to focus on the grass in the foreground.
In these cases it’s better to select a Manual AF point. And in close-up or
telephoto photography, especially with a large, wide aperture that reduces the depth of field, pinpoint accuracy becomes even more critical.
Making the most of your range of AF points
Auto select
By default, your DSLR uses every AF point in each shooting mode but often you can choose AF points manually. Press the AF Point Selection button at the top-right of the rear of the camera (this will differ by brand and model) and the display will confirm that multi-point Auto Select AF is in use.
Manual select
To switch from AF Auto Select to Manual Select mode, press the AF Point Selection button as in the previous step, but then press the Set button. The camera will now switch from multi-point selection to using only the central AF point for autofocus. Press the Set button again to revert to multi-point Auto Select.
Change the AF point
You’re not limited to using the central AF point in Manual Select mode. After switching to single-point AF, you can use the arrow keys to switch to any of the other eight AF points. To return to the central AF point, press the Set button again.
AF modes
Manual AF point selection works in any of the various AF modes, so you can couple use of selective AF points with One Shot AF for stationary subjects, AI Focus AF for erratic subjects, or AI Servo AF for tracking moving subjects. Select the most appropriate AF mode by pressing the AF arrow key.
When to use your different AF points
Auto Select
When you generally want to focus on the closest object in a scene and you need to react quickly to what’s going on around you, Auto Select is a good option. It saves potentially missing a shot because you’re too busy adjusting AF point selection, and is also good for tracking action.
Central AF point
The central AF point is the most sensitive and accurate of all, so it’s great for use in very dull or extremely bright lighting conditions, when other AF points can struggle to achieve autofocus. It’s also perfect for when the main object of interest is at the centre of the frame.
Upper AF point
When you’re taking a landscape shot and your emphasis is on distant scenery rather than the foreground, select the upper AF point. This stops the camera focusing on spurious foreground objects or areas that happen to coincide with a lower AF point.
Diagonal AF point
Portraits usually work best when the subject is slightly off-centre in the frame. Shooting in landscape or portrait orientation, choose the appropriate diagonal AF point and focus on one of the subject’s eyes. If the face is at an angle to you, focus on the eye that’s closest.
Edge AF point
The AF points positioned at the far left- and right-hand sides of the image frame are very handy when you want to throw foreground areas into soft focus, concentrating on a more distant subject that’s positioned on one side of the frame.
How to choose the best AF point
While for most of us, nine selectable AF points are more than enough, top-end professional cameras, like the Canon EOS-1D X, can have an incredible 61 to choose from. You can even choose multiple AF points in small groups.
Whichever camera you’ve got, knowing which AF point to select can, understandably, be a challenge.
Often it seems easiest is to stick with the central AF point, position it over the object you want to focus on, then lightly press the shutter button to achieve AF.
You can lock the AF setting by holding the shutter button, recompose the shot, then fully press the shutter to take the shot. This often works, but it’s easy to come unstuck.
The main problem with only using the central AF point is that a light reading is also taken, and the exposure value locked, at the same time. If, for example, you focus on an object that’s in shadow, then recompose to include brighter areas, your image will be over-exposed.
Get the point
One answer is to press the AE Lock button after recomposing the image, thereby taking a new light reading, while still holding the shutter button to keep autofocus locked.
But it’s usually easier to pick the AF point that’s closest to the point you want to focus on,
so any subsequent camera movement will be minimal.
Selecting the most appropriate AF point not only ensures more accurate light metering, but focusing as well, because there’s less camera movement after AF has been locked. Plus, AF point placement is based on the rule of thirds, aiding
photo composition.
How to fool your autofocus – and why you should do it
Unlike One Shot AF mode, which locks the focus setting as soon as autofocus is achieved, AI Servo AF mode automatically tracks moving targets, from kids and pets at play to racing cars or roaming wildlife, adjusting the focus as necessary up to and including the moment when the shot is taken.
It’s tempting to manually select a single AF point that corresponds to the position of the moving target within the frame, but this often demands an incredibly steady pair of hands and an almost superhuman panning technique.
Switch to the Auto Select AF Point (multi-point) setting when using Canon’s AI Servo AF or AF-C on Nikon and Pentax cameras, and the camera will initially focus and track moving subjects using only the central AF point.
If
the target strays from the centre of the frame, alternative AF points will be automatically used as necessary, so the camera can continue to track its movement.
