What is depth of field?

Depth of field (DOF) quite simply defines the area of a photograph that is in focus. It can also be thought of as depth of focus or field of focus. It is important in photography for several reasons. First and foremost, it helps isolate your subject and guides the viewer's eye in your image. If I try to take your picture with a busy or disturbing background and it's all in focus, you (my subject) gets lost in the background. Photographers help to guide their viewers eye in the finished image by putting the main subject in focus and creating blur (bokeh) in the background and foreground. Here are some examples

This photo was taken on aperture priority  (AV on Canons and A on Nikons and Sonys) stopped down all the way to f25 (very small aperture). The corresponding shutter speed was 1/8th of a second.  The settings are on the image. As you might notice, both this beautiful creature and the background are in focus (at least more so than the photo below).

The blurriness that is obtained  from a shallow focus is called Bokeh (bowkah or bowkay), a Japanese word which means hazy or blurry. When we first look at a photograph, the human eye tends to go to what's in focus, what is brightest and what is familiar. So, if we are able to put our subjects in focus and blur other areas, it can make for a more dynamic or appealing photograph. 

Depth of field effects both the background and the foreground. As I narrow my depth of field (make fewer things in focus) I blur items both in front of my subject and behind it. If I deepen or broaden my depth of field, it makes things both in front and behind my subject more in focus.

This photo was also taken on  aperture priority opened up all the way to f2.8. The corresponding shutter speed was 1/800th of a second.  Many people find the blurred background more appealing. However, if I were shooting for a nature magazine for example, I may want the viewer to see some of the trees and jungle in the background to set the environment for the image. Depth of field is an artistic decision.

The way I control depth of field is with my aperture setting. The larger the aperture (smaller number-for example f2.8 or f3.5) the narrower my depth of field will be. I create more bokeh. If I “stop down” my lens (make my aperture smaller-for example f11 – f32) I will deepen or broaden my depth of field and things both in the foreground and the background will be more in focus along with my subject.

One other consideration is the distance to my subject. If I stand back and take a picture of something my background and foreground will be more in focus and if I got closer (using the same lens) and took the same picture.
There is also something called lens compression. Distance from the subject compresses information. What that means is if I'm very far away from my subject and I use a telephoto lens I still get bokeh, but the depth of field is much broader.

n this picture I'm using a 200 mm lens with a 2x extender. As you can see the middle of the photograph is in focus and the foreground and the background fall in out of focus. However the depth of focus (probably about 30 yards from the balloons in the center to the four globe light on the right) is much greater because I am so far away.

Get out and try this. Put your camera on a tripod and put it on aperture priority using your mode dial (AV or A). It is probably best if you do this in daylight to begin. Find a subject and focus on it. Lock your camera down so that it doesn't move and turn your auto focus off momentarily. Adjust your camera so that you have a wide aperture (small number). Take the picture. Now adjust your camera so that you have a narrow aperture (larger number) and take the same picture. If you are in aperture priority your camera should adjust for differing shutter speeds. Look at the difference in the depth of focus. Get the idea? Keep practicing.

Depth of field is an artistic decision. Having the ability to adjust the shallowness or the broadness of your focus is an important aspect of photography.

Keep Hitting That Shutter Button!
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For information on other Tampa photography classes, digital photography classes, and Tampa photography workshops feel free to call me or look under the Tampa Photography Classes section. I also give private individual lessons on camera operation and making better photographs and would love to work with you one on one to make you a better photographer. Photography instruction gift certificates are also available. They make great gifts for the photo enthusiast in your life. Let's talk about what you need! 813-786-7780. See you in class!

Chip Weiner is an award winning photojournalist and food photographer in Tampa. He has been a photography instructor for 10 years.

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