Focussing

Needless to say, getting a picture in focus is very important!

You are going to learn:

How easy focus is
How to make your camera do the work
How to take control when you need to

Focussing is all about making sure you have your subject nice and sharp in the picture.

The human eye is really clever and shifts focus all the time. When we have a close up object and a distant one we can switch focus between them. It looks as though we are seeing detail in both at the same time. In reality, we only have one of them in focus at a time and our brain is putting the two together.

Your camera cannot do that. When you take a picture the whole scene is recorded at one time. Whatever is focussed on the digital sensor is sharp and crisp. Whatever is not in focus in will appear soft and blurred.

DSLR cameras are pretty good at getting things in focus very quickly. If you have used a compact camera or your Smartphone camera you will have noticed that it can take a while for them to focus before you can take a picture.

How Auto-Focus Works

Essentially your camera looks for points of contrast in a scene and uses that to get crisp focus with no blurring. Just like with exposure your camera has a library of scenes and can make intelligent decisions about what your subject is and focus accordingly.

When taking a photo of someone standing in front of a building the camera "knows" that the person is the important part and focuses on them, not the building.

Your camera can also track moving objects and anticipate where the focus needs to be when you press the shutter button.

Focal point (green square) is right on the subjects' eyes, not on the building.

Focussing Modes

These options are controlled by using "focussing modes". Here are the main standard modes.

Single Focus

Single focus: (also called AF-S, S-AF, One-shot or Single). The camera finds your subject and locks on focus. If you lightly press the shutter button the camera will set the focus and give you an indication of what it has focussed on. Then you can fully press the shutter button to get the picture.

But if your subject moves after the camera has focussed then they will go out of focus.

Continuous Focus

Continuous focus: (also called AF-C,C-AF,AI Servo, Monitoring or Tracking). This is best for moving subjects. Lightly press the shutter button and the camera finds a first focus point. But as the subject moves the camera will keep adjusting the focus. It predicts how the subject is moving and is ready for the actual shot. This works best with subjects moving towards or away from the camera. This mode is often used in sports photography.

Automatic Focus

Automatic focus: (also called AF-A, A-AF or AI Focus). A "best of both worlds", it starts assuming single focus mode, but if it detects a moving object switches to continuous mode.

Focus and Recompose

This is a very common trick to make sure your camera is focussing on the right thing. Point your camera directly at your subject and lightly press and hold the shutter button. The camera will focus. Now you can recompose your image by panning the camera away from the subject to include some background. Your subject will remain in focus even though they are not in the centre of the picture.

You must keep your finger lightly pressed all the time, otherwise the camera will re-focus.

The green rectangles indicate possible focus points.

The red rectangle shows the point actually used.

However, we have been let down here, because our required focus point is actually the face in the blue circle - which is not covered by any of the camera focal points.

Focussing Points

Your camera has a range of focussing points, some as few as 9, some as many as 50 or more. When the camera is focussing it can use all of these points or just a few to work out what to focus on. For general snaps use all of them. The camera uses its scene library to work out what you are taking a picture of and how to set the focus. In fact it may also set the aperture as well (because aperture has an effect on focus).

But you may want to pick an individual point of focus. This tells the camera to only use that point for focussing and ignore everything else. For example you might set your camera to only focus on the centre point, and then use the focus-recompose method we've just talked about.

Manually Focussing

Your lens probably gives you a means to focus manually. In some cases you have to turn auto-focus off by a switch on the lens. Some lenses let you override camera focus without this.

You rotate the focus ring to bring the scene into focus.

There is a certain "machismo" view that says you should always manually focus. In my experience manual focus is overrated and the camera will usually do the job faster and better than I can. That's not to say there aren't times when manual focus is a must.

Live View Focussing

Live view is where the camera can show you on the rear LCD screen the actual view of what your camera is seeing now. There is a magnify or focus option that will enlarge a small portion of the screen so you can see exactly where the focus is. This is particularly useful when manually focussing.

The advanced version of this is to attach your laptop for live view where you can see on the large screen how the image is focussed.

Trouble Shooting Focus

There are two main problems with auto-focus where it fails to find a focus point and it "hunts". Hunting is where the camera is continually trying to refocus but doesn't stop. Usually your camera will not let you take a picture in auto focus mode unless it has locked on focus.

Dark situations are difficult for auto-focus. Some cameras have an "auto focus assist" beam, sometimes visible, sometimes invisible infra-red. These shine a light out which the camera can use for focussing. While this is less common on cameras, most flash units have this function - since their main purpose is taking photographs in the dark.

Auto focus also needs contrast to focus on. So if you try to focus on a plain wall, or a white shirt, or bare skin, then the camera may not find anything to latch on to. Point the camera to an element of contrast (a window frame, tie on the shirt etc), then focus-recompose.

Video

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Exercise

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Assignment: Focus and Composition

In this assignment you will be taking photographs combining what you learnt in the first chapter about composition and what you have learnt in this chapter about focussing techniques.

Your best subject will probably be some kind of landscape. It does not need to be countryside, your local park would be sufficient.

Practice the techniques of combining composition and focussing together, so the correct focus point matches with your composition technique. For example if you are using the Rule of Thirds, then the subject on the third should be in focus, not the centre of the image.