Tips On Using Apertures Creatively For Portraiture

The aperture has a hugely important creative role in that it controls the amount of depth-of-field in an image. For those new to photography, depth-of-field is the amount of front-to-back sharpness within a picture.

Depth-Of-Field

When your camera focuses on the subject it will come out sharp. But there is also some sharpness in front of and as well as behind where the camera is focused and it is called depth-of-field. Most cameras have something called a depth-of-field preview button that lets you see how much depth-of-field you have before taking the shot.  However, with the instant feedback of digital it is just as easy to take a test shot and check it out before taking the 'real' pictures.

The amount of depth-of-field within an image depends on several factors:

• The distance between the camera and the subject. The closer the subject the more shallow the depth-of-field. With distant scenes, therefore, there is plenty of depth-of-field.
• Choice of lens aperture. The wider the lens aperture (ie /2.8, f/4) the shallower the depth-of-field, and the smaller the aperture (f/16, f/22) the greater the depth-of-field.
• Focal length. Contrary to popular belief a wide-angle lens does not give greater depth-of-field than a telephoto lens if the subject magnification is the same. You can test this for yourself. Take a frame-filling head shot with a wide-angle lens (you will have to get close to the subject, so warn them!) and then do the same frame-filling shot with a telephoto – this means backing away from the subject. Use the same aperture for both and you will see that the depth-of-field is the same.

The reason people suggest using wide-angle lenses for greater depth-of-field is the way that such optics are used. Generally, you are not trying to maintain the same image magnification, ie change shooting distance, when changing lenses so a wide-angle lens will give greater depth-of-field at identical aperture than a telephoto from the same spot.

Photographing People

In terms of portraits, especially outdoors, wider lens apertures are often best because they throw the background nicely out of focus. How effective this is depends on the scene and focal length as well as aperture choice. If your subject is standing quite close to a distracting background even shooting at f/2.8 or f/4 will not throw the background out of focus. But bring the subject forward a couple of metres should work nicely.

Bokeh Backgrounds

How the background is thrown out of focus depends on the lens. Bokeh is the term used to describe the pictorial quality of the out of focus blur. Lens design and aperture shape play a large part in how effective its bokeh is so do try it with your own optics. A good test is shooting a close-up portrait outside against a background with some bright pinpoints of light, ie sun glinting off water, car lights, streetlamps etc.

Of course, you might prefer greater sharpness in your backgrounds and that is when small apertures are used. The important thing is to keep your eye on the background and if it looks messy or cluttered use wide apertures rather than small ones.

Sharp Eyes

If you do use wide aperture for your portraits, do make doubly sure that the subject's eyes are in focus. With the shallow depth-of-field created by wide apertures, even a small error can mean unsharp eyes and you do not want that in your portraits.

Fore more creative bokeh tips, have a look at our Christmas Light Portrait tutorial.

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