Bokeh. Yup, it’s time to continue my discussion on that screwy term and talk about what goes into creamy out-of-focus backgrounds. So, before we dive into today’s topic, let’s mention what we’ve learned so far:

1. Bokeh comes from the Japanese, and roughly means to be out of focus. It describes the aesthetic quality of a shot’s out of focus area.
2. It is a complex thing influenced by many variables.
3. One of these variables is aperture, and wide (low number) apertures are better because they have shallower DOF.

So, next up is the variable of focal length. Focal length, you’re likely aware, is how long the lens’ front element is from the sensor and it affects how your camera “sees” the world. The human eye has roughly a 45 degree field of view. A telephoto lens might only have, say, a 25 degree field of view. That means it’s seeing less of a scene than your eyes, but since it’s putting it on the same size sensor your final shot will make it seem like the lens made an area “bigger”. It’s the other way around for wide angles, and they’ll shove much more of a scene than you can see onto that same size sensor, making everything look smaller.

These behaviors, due to some pretty crazy math that I’ve seen but won’t inflict upon you, also affect the depth-of-field a given aperture will have. Put simply, telephoto lenses have much narrower depth of field bands than wide angles do. Wide angles, in turn, naturally have more in focus that standard lenses or primes, even at the same apertures.

I know, I know, this goes against what I talked about last time. Here I am, telling you that f/3.5 on a real wide angle lens (like a 24mm equivalent) will have less out of focus area than f/5.6 on something like a 400mm equiv. But, last time, we hadn’t touched focal lengths. Now that we have, let me amend things to this: for the same focal length, a wider aperture will give more out of focus area. However, the wider the lens, the less out of focus it will have across the board, and more telephoto the lens the more out of focus it will have across the board.

For proof, here are some shots I took downstairs. I grabbed my trusty Olympus digital camera and some lenses, got me a subject (it’s a sales floor, what did you expect?) and set up a tripod. The focal length (in equivalents, something I’ll touch on soon when I talk about crop factors) and apertures are listed on them. They’re also shot from the same distance (the topic of yet another future post on this beast called bokeh). I have two sets of shots. First off is the whole frame just scaled down, so you can see the total effect of zoom on bokeh.

Now, these shots are crops to focus on my focal point (the Bogen Manfrotto tripods video head there.) If you couldn’t see the effect of bokeh in the shots above (and I wouldn’t blame you if you couldn’t), then I want to draw your attention to the pan handle on this head (in the bottom left corner.) Watch how it gets fuzzier and fuzzier as you approach 400mm. You can also pay attention to the back wall. And I promise, just like they say they were all shot at f3.5.

So, the lesson for this post? Wider aperture is better, but if you want even more bokeh, grab a telephoto and leave the wide-angle.