Depth of Field – How to Control It

by Christopher B. Derrick

There are several crucial means by which a photographer controls “the look” of his photos. Composition is the most obvious, but camera focus and depth of field run a close second. You may want everything sharp in the photo, or only what you want to draw the viewer’s eye to a specific subject… that pretty girl reading on the grass, for example.

You achieve this quality by controlling the depth of field, which is the front-to-back zone in the frame in which objects appear sharp. When little else but the main subject appears sharp, that’s known as “shallow” depth of field. When the image is sharp from front-to-back, that’s known as “deep” depth of field.

Three factors affect depth of field – lens aperture, distance from camera to subject and lens focal length. Aperture is most often used to control depth of field. To make as much of the scene as sharp as possible, set as small an aperture (f-stop) as the lighting will allow. To single out a subject, set as wide as aperture as possible; you’ll have to change the shutter speed to compensate in both instances.

Photo by Diego Sevilla Ruiz

The aperture ranges from f/1.4 (a super-fast lens) to f/22, with increments in between (f/2, f2.8, f/4, f/5.6, f/8, f/11 and f/16). Each f/number up or down represents one “stop” of light, such that when you move from f/4 to f/5.6 you’re letting ½ as much light, and if you move from f/16 to f/11 you letting in twice as much light. This number ratio is the same across all lenses, regardless of focal length… making it really easy to understand the concept across lenses. By understanding how the aperture works, you can utilize the hyperfocal distance for each lens for maximum effect. The hyperfocal distance is basically a point in which you focus and everything from that point to infinity will be sharp. When you want your landscapes to blow everyone’s mind, you have to master hyperfocal distance. How else do you think guys like Ansel Adams expanded the complexity and beauty of their work?

Another way to affect depth of field is to change the distance of the camera to the subject. To increase depth of field, move back; to reduce it, move closer. Think about how your eye works, the closer you are to an object the less you can see around you that’s in focus, but the further away you are, the more you can that is in focus. Of course changing your distance changes your composition, yet you could change lens or zoom the focal length to maintain the composition you want at the new distance. Now this negates any change in the depth field. Why is this?

Photo by mr.kitux

At a given distance, at a given aperture, the longer the focal length of the lens, the shallower the depth of field is (the reverse is also true). The depth of field you get for a specific f-stop varies with distance, such that a small f-stop (like f/11) on a 35-70mm zoom set to 35mm gives a deep depth of field (from six to 20 feet with the lens focused at 9 feet), but you’ll have a relatively shallow depth of field with the lens zoomed out to 70mm (from 8 to 11 feet with the lens focused at 9 feet).

Just like with changing the distance from the camera to the subject, adjusting the focal to control depth of field is extremely difficult, too, because you won’t be able to maintain the composition that you wanted.

It is ideal to use the f-stop to control depth of field and shoot at your preferred distance with the focal length you want, because you can always alter the shutter speed (be sure to use a tripod and a cable release) to compensate for large f-stops, if you’re looking to obtain deep depth of field.

Featured top photo by Blake Danger Bentley

Chris Derrick is a writer, photographer, screenwriter and director living and working in Los Angeles. He studied film production and screenwriting at the University of Southern California, and continued to expand his photographic knowledge through classes at the Art Center College of Design.

Website: shadowboxercinema.com

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6 Comments

Black
October 10th
Amazing, thanks !
Stevens
October 12th
Thanks for the DOF tips. This helps clear up some of my confusion!
Christopher Derrick
October 12th
Black and Stevens,

Glad to help clarify a topic that does leave people scratching their heads (I know I was at first).

Thanks,
Chris
Bonita
October 13th
great article! I’m really glad to have come across this site.. bookmarked for future reads! :D
Robert
November 18th
Very good article, and a good starting point in addressing the subject.

However, you are mistaken about one point. Ansel Adams didn’t use hyperfocal techniques to control depth of field. He did it by changing the relationship between the lens and film planes; a fourth way of controlling depth of field that you didn’t address. It is called the Scheimflug principle.

With a large format camera, like Ansel Adams used, you do this by tilting either the lens or film planes of the camera, thereby altering the way the light strikes the film plane. This is a technique that you can’t do on a traditional SLR or DSLR without a specialized lens.
Bill Jones
November 18th
@ Robert

Thank you so much for pointing this out and explaining the Scheimflug principle.