Photography Tip: Depth-of-Field

Have you seen photos where a subject is in focus, but the rest of the image is not? When done with the camera, that effect is due to altering the depth-of-field. This can create “bokeh”, the blurred background. Here’s an example image, taken from Pondtopia, the pond in our backyard:

Depth-of-Field Explained

The aperture setting on the camera controls the depth-of-field, thus affecting what areas of the image are in focus. Aperture refers to how wide open your lens is, which affects how much light is entering your camera and hitting the sensor. It is designated by a ratio of something called the “f-number”. The larger the number (and thus the smaller the ratio), the more closed your lens is. I’ll write a more in-depth post on aperture in a later post, but for now I encourage you to play around with the f-number on your camera to get a feel for it.

The following image shows how the aperture affects depth-of-field. I like to think about depth-of-field as the area in focus between two parallel plates. When the two plates are close together, much less of the scene is in focus. As the plates move further apart, more of the scene gets into focus.

To illustrate this, I went outside to Pondtopia and set up a tripod aimed at some of the cacti surrounding the pond. Think of the following image as the previous image, just turned horizontally by 90-degrees. I took the same image using different apertures. Hopefully you can see more and more of the scene getting into focus as the aperture gets smaller and the f-number gets bigger.

Depth-of-Field in the Camera

Some cameras allow you to preview your depth of field before taking a photograph. If you can map this feature to one of your function buttons, it really helps a lot. Just look for this symbol:

Depth-of-Field Examples

Using a shallower depth-of-field can be useful to help viewers focus on a particular spot in a photograph. Take the following two side-by-side images. On the left, the depth-of-field is wide, while on the right the depth-of-field is small. If I wanted the viewer to focus on the flower, which shot serves that purpose better? The one on the right blurs the background and leaves only the plane containing the flower in focus. This draws the viewer’s attention straight to the flower.

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The next example is from my post on the Cholla Cactus Garden at Joshua Tree:

And here’s one from a flower field at Lake Kaweah:

Depth-of-Field and Portrait Photography

Portrait photographers take full advantage of depth-of-field sometimes when taking certain shots. I’m no portrait photographer, but Minhan asked me to take some maternity shots of her. When we arrived on location, she wanted to get a shot with a lot of greenery. I choose this particular spot because of the orange flowers in the background giving a little bit of contrast to the green.

One thing to keep in mind when trying to get that bokeh effect is the distance between your camera and the subject as well as the focal length of your lens. To illustrate this, take a look at the following two images. The one one the left is shot at f/11, and the one on the right is shot at f/2.8. In both images, I focused on Minhan using a 12mm focal length. Theoretically, the one on the right should have the background blurred, right? Not necessarily. As the distance between you and the subject increases, or as the focal length decreases, the effects of aperture on depth-of-field is decreased. This is due to something called the hyperfocal distance, a topic for another post.

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To get the background sufficiently blurred, I zoomed in to 31mm. Here is my favorite shot:

I hope this guide was helpful! As always, comments, questions, and feedback can be left in the section below.

One more month to go before baby is here!