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Autofocus vs manual: Take Control of Focus

Autofocus vs manual: how to take control of focus in problem foregrounds
Your camera is like a faithful and efficient assistant, but it’s not the brains of the outfit. Some scenes can fool your camera into thinking that something else is the more important subject. In these situations you might debate whether to use autofocus vs manual mode, but there’s no reason you can’t still use autofocus.

Your camera’s AF system usually gets it right, but you need to know when it won’t… and what you can do about it.

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Like your camera’s other automated functions, its autofocus is designed to work out what to do so that you don’t have to think about it. Most of the time it makes the right decisions and produces perfectly sharp pictures, but really it can only guess at your intentions.

If you’re in a hurry, and have no time to make manual adjustments to your camera settings, autofocus is the perfect solution.

But it’s important to know how it works and what it’s going to do, so that you can take charge of focusing in situations where the camera might make the wrong guess.

Taking control doesn’t mean you have to focus manually; Most autofocus systems are both faster and more accurate than trying to focus by eye. The trick is to set the camera up so that it does what you want in the way you expect.

The range of autofocus modes and options can look daunting, but they are quite simple when you break them down. In fact, there are just two things you need to know.

First, you need to know when the camera is going to focus. In continuous AF mode it keeps focusing all the time you keep the shutter button half-pressed.

That’s fine for action sequences, but unpredictable for regular photography – for this, you need the single-shot AF mode.

Second, you need to know what it’s going to focus on. In auto-area AF mode, the camera decides on your behalf. It’s quick and simple, but sometimes wrong. Single-point AF mode is simpler and cruder but it’s the one most experts prefer because you can make the camera focus exactly where you want.

Different DSLRs use different autofocus systems, and some look fearsomely complex, like the pro-spec 51-point system in the Nikon D300s we’re using for our outdoor photo shoot.

But the same principles apply, and in a matter of moments you can tame even this super-complex system to work simply and clearly.

Autofocus vs manual: why not focus manually?

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Could you save yourself time and trouble by focusing shots like this manually? Yes and no!

The problem is that your DSLR’s optical viewfinder is not large enough or crisp enough for the pinpoint focusing that high-resolution digital sensors need if they are to deliver their full potential.

But there is a quick, simple solution: use your autofocus system to set the distance, then push the autofocus switch on the lens barrel to the M position.

The focus distance will now stay locked until you change it.

 

How to take control of autofocus

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01 Let the camera choose
The auto-area AF mode on our Nikon D-SLR copes perfectly well with this shot, because Sarah is more or less in the middle of the frame and there’s nothing in the foreground to confuse the autofocus system. But if we get lower down to shoot, it’s another story…

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02 Problem foregrounds
Auto-area AF mode will automatically focus on objects nearest the camera, and here it’s picked out some blooms lower in the frame, leaving Sarah out of focus. That’s the problem with automatic focus point selection: it doesn’t always focus on what you want it to.

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03 Single-shot mode
There are two steps you need to take to gain control of your autofocus. First, set your camera to single-shot AF mode. This means it focuses once when you half-press the shutter button, and stays focused on that point until you press it the rest of the way to take the picture.

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04 Single-point AF
You now control when the camera focuses, and the next step is to take control of what it focuses on. For this you need to set it to single-point AF mode. The camera no longer chooses the AF point automatically. Instead, you’re forcing it to use the focus point you’ve selected.

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05 Focus lock
There are two ways to use single-point AF mode. The quick way is to stick to the centre AF point, place your subject in the centre, half-press the shutter release to lock the focus, then reframe the shot and press the shutter button the rest of the way to take the picture.

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06 Set your AF point
The other way is to compose your shot, then use the multi-selector on the back of the camera to position the focus point over the critical part. In this shot it’s our model’s eye – the most important thing in a portrait. This is the best method when you’re using a tripod.

 

Taking control of AF video tutorial

For a more in-depth look at how this is done, this video shows the step-by-step process as we worked around a tricky foreground to take control of our autofocus in a field of wildflowers.

Spot metering and AF

Spot metering is really useful for high-contrast lighting or other difficult shooting conditions, but the results can be unpredictable.

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On many DSLRs the spot reading is taken from the current AF point, so if you’re using Auto-area AF this means the exposure may change each time the camera swaps autofocus points – another good reason for using single-point autofocus!

Set spot mode
On our Nikon D300s, there’s a metering pattern dial on the back of the camera. Here, it’s set to Matrix mode – the spot mode setting is directly below.

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Spot metering point
Linking the spot area with the focus point works well here because we want Sarah’s face correctly exposed and in focus. We’d get a different exposure, though, if the AF point was over the background, or the bright white areas of her dress. This is why you need to use the spot metering mode with a good deal of care.

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