Tuesday, February 17, 2009

Background blur and depth of field


In my post for the February Monthly Special, Ilan commented that a blurry background is one of the first styles of background most people use. That got me thinking that I should do a short post about depth of field, blur, and "bokeh."

I will make this short and sweet because I really hate getting mired in technical details, but I will give you a great link at the end of the post for more detail.

Depth of field and blur
Take a look at the photo above of two brothers. The younger brother in front is in focus and the older brother behind him has some (in my opinion, pleasing) blur. I hate turning photography into math homework, but I need to give a few numbers to illustrate a very simple point:

The wider the aperture, the more shallow the depth of field.

"Aperture" describes the opening through which light passes to hit your camera's sensor or film. The lens of your camera will indicate the possible values of aperture in "f-stops." I used a canon 24-70mm L lens for the above shot at an f-stop of 2.8 (its widest aperture) with a shutter speed of 1/50 sec and an ISO of 100. Aperture, shutter speed, and ISO pretty much cover the technical aspect of a photo, and if you already shoot with manual settings my guess is you are already more than familiar with how the settings work.

But if you usually just let your camera make all of the choices and maybe you are not always happy with the result, you may want to experiment with the aperture settings (provided that your camera allows it). Most SLR cameras (cameras that have interchangeable lenses), for example, have an "aperture priority" mode which gives you the freedom to choose the aperture but to let the camera worry about the shutter speed. If you set the f-stop at a relatively low number, you are more likely to get background blur than if you leave the decision up to the camera.

But I just have a little point-and-shoot digital camera, you say.
Even in that case, you still have control. Look at those little icons on your camera dial or menu. Here's a shot of some standard icons:

Let's look at three of the five icons above (yours may vary slightly):
  • The flower is "macro" mode. It has the most shallow depth of field (i.e. most blurred background). The f-stop is probably 2.8 or slightly higher.
  • The profile of a portrait is "portrait" mode. The f-stop is a little bit higher—probably 5.6 or 8. This should mean less blur than macro.
  • The icon of a mountain is "landscape" mode. Now the f-stop is at its highest—maybe 11 or 16. In this mode, pretty much everything will be in focus.
My point is that you don't need to be taking pictures of flowers for "macro" mode or of mountains for "landscape" mode. Instead, think about depth of field when choosing a setting.

And now, for your word of the day: Bokeh.
Bokeh is an anglicized version of a Japanese word for blur. People use it to describe the quality of blur, especially in relation to different lenses. Higher quality lenses will usually produce better bokeh than low quality lenses. How does this help you? Not much. But it's good to know what it means when you hear it.

Want to know more?

A thorough technical explanation of bokeh and blur.

1 comments:

monkey mania said...

Just wanted to say that this post has definitely been most helpful to a person who knows next to nothing about photography. Thanks again!