What is Focus?
Focus is an extremely important concept in photography. A photographer can use focus to highlight certain objects in an image, to create an air of mystery, or to invoke a dream-like nature. In this lesson the basic principles of focus will be explained, and we will begin to look at ways to manipulate focus using your camera.
Objects that are in focus will appear to be sharp and clear. Objects that are out of focus will appear to be blurred and difficult to see clearly. The two images below show the same scene with the camera focused on different objects. In the photo on the left the lantern is in focus while the gate is not. In the photo on the right the situation is reversed. Notice one of the key features of the images – the focus seems to depend on the distance from the camera. In the left photo only the objects very close to the camera are in focus, while in the right side photo only far away objects are focused.
This is not an accident – distance and focus are intimately related. We will not go into the mathematical properties, but we can think of focus as a kind of 2D window, which we can move closer or further away from the camera by adjusting the lens position. This window is called the “focal plane”, and any objects that fall on the focal plane will appear sharp and clear.
Take another look at the pictures above. In the second image we can see that not only the gate is in focus, but also the boat, and the buildings on the shore. Why is this, when they are not at all close together? In truth the focal plane is not simply a 2D window, it also has depth. This means that for some distance in front and behind the focal plane objects will appear to be in focus, before gradually getting more and more blurred. This concept is called “depth of field”.
How to Focus an Image
Almost every camera now has an option called auto-focus. This is a feature that will attempt to automatically focus the camera lens for you. When you use the auto-focus feature your camera gathers information from a number of points in the scene. If you look through your viewfinder you will probably see a pattern of rectangular boxes – these are the points the auto-focus is using. Press halfway down on the camera button and you should see the image come into focus. You can hold the focus, or adjust it as you need, before pushing the button all the way down to take a photo.
If you want to focus on a particular object try pointing your camera directly at the object so that the central focus point is covering the object when you look through the viewfinder. Press the button half way down to focus, and then adjust the view by moving the camera as you desire to compose your final photo. Keep the button half way down until you are ready, and then push all the way down to get the shot. What you’ve done here is to focus on an object, and then held the focus even through you moved the camera. This allows you to pick a focus and then arrange the photograph as you desire.
As well as auto-focus you also have an option to manually focus an image. This is usually done by turning a ring on the camera lens (you may have to flick a switch to turn off auto-focus mode). As you look through the viewfinder and adjust the ring position you’ll see different parts of the image come into and out of focus.
I recommend you experiment a bit with both auto-focus and manual focus. Try focusing on nearby objects and far away ones. Try focusing on an object using the auto-focus, holding that focus and then shifting your view before taking the photo.
When to Use Manual Focus
If a camera offers auto-focus then why would you ever want to manually focus an image? Well there are a few occasions when auto-focus fails. This can happen in low light conditions, as the auto-focus is not able to find enough light to focus the lens. You may also want to choose the focus for artistic reasons, as in the photos above (although auto-focus is often capable of achieving effects as in those photos). In some situations you may find the auto-focus is not choosing the right thing to focus on (for example, if you have a fast moving object in the image), and in this case your only choice is to use manual focus.
Alternatively, you may want to experiment before taking a photograph to see how different focus points look. In this case being able to manually shift the focus gives you an excellent way to quickly try different options.
Finally if you want to shoot multiple images in a very rapid sequence you will find the rate of taking photographs is much faster with manual focus. Why? Because in manual mode the camera is not trying to re-calculate and re-focus the lens before taking each photograph. This also applies in any situation where you need a fast response time between pressing the button and taking the photo. Auto-focus introduces a small amount of delay, and removing that may sometimes make the difference between capturing a great photo and missing the subject completely.
“Bokeh” is currently quite a popular concept in photography. Bokeh basically refers to the way out of focus parts of an image look. The easiest way to understand is by looking at the two examples below. Notice how the out of focus backgrounds to the photos have a pleasing appearance – they do not distract unpleasantly from the image, and even add to the quality of the photograph.
The way bokeh appears is determined by the physical properties of your camera lens. Older lenses often form hexagonal patterns in out of focus areas, while newer ones tend to form circular patterns. Some lenses have been deliberately designed to produce pleasant bokeh effects, and there is plenty of information available online if this is something you really want to get into.