What is focus lock?
Before we start figuring out how to use focus lock, it’s probably a good idea to explain what focus lock is. It sounds quite dramatic, but actually it’s just a way to focus on a subject and keep the focus on that subject, even if you move or your subject moves.
How do you lock focus with autofocus?
There are three ways to use focus lock. They are:
- Single servo – AF-S (Nikon) or One Shot (Canon)
- Continuous servo – AF-C servo (Nikon) or AI Servo (Canon)
- Back button focusing with isolated shutter release
The names are way more complicated sounding than it really is. Let’s look at each of these methods in greater detail. I’ll also explain when and why to use each one.
Further reading on autofocus: Nail your autofocus, get the shot
Single servo
When using single servo focusing the camera will focus on your subject when you part depress the shutter button. As long as you keep the shutter button depressed, the focus won’t change.
This is usually the first method of locking focus that photographers use when starting out.
When to use single servo focus lock?
This is ideal if you want to “focus and recompose”. You may have heard of that term. So, for example, you want to place your subject off centre in the frame. Such as when composing an image using the rule of thirds technique.
How to use single servo focus lock?
Part depress the shutter button to focus on your subject, then without changing the distance between the camera and your subject, move the camera to recompose the shot as you would like. When the image is composed in the frame to your liking, fully depress the shutter button to take the shot.
Drawback of single servo focus lock?
If either you or your subject move closer or further away before you fully depress the shutter button, they will no longer be in focus.
Continuous servo
It’s probably a bit obvious now what this is, but I’ll say it anyway. When your focus is set to continuous servo, the whole time you part depress the shutter button to focus on your subject, it will lock on and track the subject to ensure that the focus is correct.
When to use continuous servo focus lock?
An essential time for continuous focus lock is when your subject is moving, such as in sport photography or when photographing children (they’re never still) or your subject is walking towards you (confetti shot at a wedding).
Another time is when you are moving – maybe you’re photographing a stationary subject from a car or a boat.
How to use continuous servo focus locking?
As with single servo focus lock, part depress the shutter button to focus on your subject. Keep the button depressed and ensure that the focus stays on your subject, until you’re ready to take the shot. Then depress the button fully.
With this method you will hear the focus shifting as either you or your subject move.
Drawback of continuous servo focus lock?
You can’t “focus and recompose” the shot as the moment you move your focus point away from your subject the focus will shift to whatever is in front of the focus point. You therefore need to decide on your composition ahead of taking the shot, position the focal point over your subject and then depress the shutter button to focus etc.
Alternatively, you would need to be good at moving the focus point around with the subject while part depressing the shutter button to maintain focus lock.
Further reading on using continuous servo: How to focus on fast moving subjects
Back button focus with shutter button isolated for shutter release only
You can set the back button focus button as an additional focusing button so that you have an option between the standard method of using the shutter release button or the back button focus button to focus.
You can use back button focus with single servo focus or continuous servo focus.
I’ve used this method a lot, especially when photographing children.
Alternatively you can isolate the focusing ability of your camera to just the back button focus button so that the shutter button’s sole function is the take the shot, with no focusing ability.
I also use it to photograph still life. It’s ideal for sport photography too.
When to use back button focus lock?
Basically, I find it best at least 100% of the time.
It is particularly ideal when photographing still items when the camera is on a tripod. In this instance you need only focus once using back button focus. Then, as long as the focal distance between camera and subject doesn’t change, you can then just push the shutter button to take the shot each time. You won’t need to look through the viewfinder and focus each time.
The best example of this is photographing flat lays with the camera mounted on a tripod over products with the camera pointing down. I can change the arrangement of the objects as much as I like and simply depress the shutter button with each new arrangement, without having to even look in the viewfinder. It saves me a lot of time, and energy climbing up and down my little steps with each new arrangement.
Another use is with macro photography, as any small change in the focusing distance will impact on the sharpness of the focus. If you use back button focusing with continuous servo, the subject will constantly be tracked until you’re ready to depress the shutter button to take the shot.
Drawback of using back button focus lock?
The only difficulty is if you want to move the focus point while tracking your subject, without using 3D tracking (Nikon). On my camera both functions require my thumb. It is, however, really quick to move between the two functions, so with practice can be done without much interruption.
More on back button focusing: Why back button focus is your BFF, and how to use it
My preferred method of locking focus?
You’ve guessed it – continuous servo, with focusing isolated to back button focus so that the shutter button’s sole function is to activate the shutter to take the shot.
Why not just part depress the shutter button to track the focus and not worry about back button focus? Well, with back button focusing the camera continues to focus, even when the shot is being taken. If you part depress the shutter button to focus, then take a shot, the camera will need to refocus before being able to take another shot. You could lose the moment.
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Interresting article. But as the percentage of Sony users is increasing, is it possible to also include the Sony equivalent together with the Canon and Nikon?