One of the first steps toward taking more creative photos is learning how to control how much of your picture is in focus. In this quick depth of field tutorial Marcus Hawkins shows you how to check and affect sharpness, as well as answers some of your burning questions.
What exactly is depth of field?
The lens on your camera can only be focused at one distance at a time. But there’s an area that extends outwards from the point of focus, both towards the background and towards the camera, in which objects still look relatively sharp. This is referred to as the depth of field.
How big is it?
Depth of field is a movable feast. Sometimes it’s shallow, with a wafer-thin section of the scene appearing to be focused; at other times it can be much larger.
There’s no abrupt end to the depth of field, rather a gradual transition from sharpness to blur.
You can manipulate the depth of field for a creative effect. For instance, you can’t focus on both a flower close to the camera and a mountain on the horizon – only one or the other.
However, you can get both to appear sharp by increasing the depth of field.
The opposite is preferable in a portrait, where a shallow depth of field helps to separate the subject from the background.
How do I change the depth of field?
There are several factors that affect the depth of field. The size of the sensor in the camera plays a part: larger sensors make it easier to achieve shallow depth-of-field effects, while smaller sensors make it easier to make more of a scene appear sharp.
However, most of us don’t have the luxury of swapping camera bodies to exploit the different benefits each offers for depth of field!
But you can directly the affect the depth of field by your choice of aperture and the distance at which you focus.
How does the aperture change the depth of field?
Larger apertures, represented on the camera by low f-stops like f/1.4 and f/2.8, let in more light, while smaller apertures like f/16 and f/22 let in less light.
The choice of aperture has much more impact on the look and feel of an image than brightness alone.
Although small apertures let in less light, they offer a wider depth of field.
Landscape and macro photographers routinely use small apertures to get more of the picture to appear as sharp.
Large apertures produce a narrower depth of field, letting you sandwich a sharp subject between a blurred foreground and background.
The closer you are to the foreground, and the more distance there is between the subject and the background, the more pronounced the effect.
How does the focus distance affect the depth of field?
The closer you are to a subject and the closer you focus, the shallower the depth of field becomes. The effect is particularly obvious when you use a macro lens.
Focus on a flower just in front of the camera, and the depth of field will be very narrow, even with a small aperture of f/16 selected.
Move away from the flower and focus on it again, and the depth of field will be noticeably more extensive.
Doesn’t a wide-angle lens give a greater depth of field than a telephoto one too?
Internet forum debates about depth of field quickly descend into arguments about the effect of focal length.
On the surface, it does seem that you can get more of a scene to appear sharp with a wide-angle lens.
However, as long as the subject remains the same size in the frame, the depth of field will be essentially the same for a given aperture, whether you’re shooting with wide 14mm lens or a long 400mm one.
The reason that depth of field is perceived as being shallower with a telephoto lens is down to the angle of view.
Longer lenses compress a scene and show substantially less of the background, so any blurred features will appear larger in the picture.
To maximise the effect, get close to the subject, ensure the background is a good distance away and choose a large aperture.
With a shallow depth of field, you’ll need to be bang-on with the focusing, so select an AF point in the viewfinder that lines up with the focal point of the picture – such as the eyes in a portrait.
And how do I maximise the depth of field instead?
To get as much of a scene as you can to appear sharp, use small apertures and wide lenses, and focus on subjects that aren’t close to the lens.
Landscape photographers often use hyperfocal focusing to increase the depth of field.
This involves manually focusing at a distance approximately one third of the way into the scene, making nearly everything look sharp.
Because the hyperfocal distance changes according to the camera, lens and aperture you’re using, you’ll get the best results by using a depth-of-field calculator to give you the precise distance at which to focus.
There are many free ones available both online and as photo apps for your smartphone.
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