‘How should I set up the autofocus on my camera?’ It’s one of the most common questions asked by our safari guests, a question we addressed recently in an article in Amateur Photographer magazine. If you missed that article, here’s a reprint of our ten tips.
Photographing wildlife is forever challenging, capturing great images of moving animals even more so – like the Kalahari lions above, they’re often fast, unpredictable and erratic. The ability to acquire and maintain focus on active subjects is an essential skill if you want to capture pin-sharp, dynamic shots – it’s one thing you can’t fix in Photoshop. Helpfully, the latest autofocus technology has dramatically improved our hit rate for wildlife action, but understanding the capabilities (and limitations) of your camera, and how to utilise its range of AF settings is vital.
Be ‘action aware’
By default we set our cameras to predictive autofocus (AI servo in Canon, AF-C for Nikon), which means we’re always ready to shoot wildlife action when it kicks off. The camera will continue to track a moving subject after locking on. We can easily shift to One-shot for static subjects, but moving subjects often don’t give us time to go the other way.
Use back button focus for ultimate control
Many DSLRs have an AF-ON button on the back of the camera, or an AE/AF button that can be customised for focusing. By using this, and disabling focusing on the shutter release button, it’s possible to use predictive autofocus all the time. Press the back button to continually focus on a moving subject, release when your subject stops moving and the focus is locked. That way if your subject starts moving again, you’re primed to follow focus immediately by pressing the back button again. No more switching between one-shot and continuous focus. Some DSLRs have ‘hybrid’ modes. AI Focus/Auto Select mode sounds great in theory, delegating focus responsibility to the camera, which automatically switches between one-shot or continuous focusing for still or moving subjects. But it can be unreliable, so we’d rather retain full focus control ourselves.
Stay single, stay simple
We both use a single, usually central, focus point for most of our shots. It’s a cross-type sensor, offering the most responsive AF performance for moving animals. For a static, off-centre subject that might not hang around long we can focus and recompose quickly, rather than waste precious time choosing off-centre points. A single point means we have absolute control over where we focus, vital for good wildlife images, where it’s crucial to ensure key elements like the eyes are sharp.
Go off-centre if time allows
If you use the ‘focus and recompose’ central point technique with a long lens and shallow depth of field, then the focal plane will change slightly, which can result in a defocused image. To avoid this, if we’re photographing a subject that is rooted to the spot (i.e. we’ve got time), and we want the point of critical focus to be off-centre, we’ll select a suitable off-centre focus point, rather than focus and recompose with the centre point.
For critical focusing on static subjects, we’ll also use Spot AF mode, which uses a smaller, more targeted area than the standard setting. Spot AF is also good when shooting through obstacles such as grass. It’s redundant for moving subjects, when it’s impossible to be so precise about where you aim.
Don’t be over-sensitive
Many DLSRs allow you to adjust how long the camera will wait before refocusing if you accidentally move the focus point off your subject, or something like a branch momentarily gets in the way (‘tracking sensitivity’ in Canon, ‘focus tracking with lock-on’ for Nikon). Intuitively you might think greater sensitivity was best for AF on moving subjects, but in truth this makes it harder to hold focus on an erratic subject. Shooting with long lenses, we dial down sensitivity by -1 for most situations, so the camera is slower to lose focus. When using shorter lenses, where it’s easier to keep the focus point over the subject, we’ll dial in +1, for greater sensitivity.
Tweak the parameters
As well as tracking sensitivity, our Canon cameras allow us to tweak ‘Accelerate/Decelerate Tracking’, controlling how the AF handles fast-moving subjects that change speed suddenly. Few of our subjects move at a steady speed, so we set this to +1. The higher setting of +2 is more responsive, but also less stable. We leave ‘AF point auto switching’ at 0, as we rarely use multiple focus points. ‘AI-servo image priority’ determines how much time is allowed for focus before the first and subsequent frames are taken. We set this to give maximum emphasis on focus rather than speed, for both first and second images in a burst. We want our images sharp, even at the expense of a fractionally slower AF.
If all these sound confusing, many DSLRs have a range of AF setting ‘recipes’ to choose from – called ‘cases’ on our Canons. These are geared up for sports photographers, but you’ll find suitable options for most wildlife action.
For tricky subjects, think expansively
With erratic and fast moving subjects, it’s often hard to keep a single focus point on the target, so we’ll set AF to use a nine point array, rather than single point (‘point expansion’ in Canon, ‘dynamic-area’ in Nikon). We rarely go bigger than nine points, because then there’s more chance the camera will lock onto the wrong bit of our subject (a flying bird’s wing-tip instead of its head, for example), or onto background/foreground clutter. We find point expansion works best when shooting moving subjects against a clean background like blue sky, rather than a ‘hectic’ background, such as woodland.
Use AF for macro ‘grabs’
Our macro work generally demands manual focus and a tripod, as AF is rarely precise enough. But AF predictive tracking can work with close-up ‘grab shots’ when we don’t have a tripod handy, and/or our subject is constantly moving, like a chameleon on a wind-blown reed or a butterfly on a leaf. It’s not an exact science, so take plenty of shots.
Give your AF a helping hand
AF can struggle in low light, or with low contrast subjects. Give it a bit of help by using a shorter, faster lens (say a 70-200mm f2.8 rather than a 100-400mm f4.5-5.6 – then crop in post-processing as necessary), avoid using a teleconverter (these reduce the light reaching the AF sensors), use a focus limiter switch to reduce the amount of hunting your lens needs to do when acquiring focus, and switch off image stabilization/vibration reduction (which slows focus acquisition and is in any case redundant at high shutter speeds). Don’t forget to use good fieldcraft, such as shooting birds flying into wind, shooting against clean backgrounds, and looking for backgrounds that contrast with your subject.