Depth of Field, Demystified

Depth of field (DOF), simply put, is the portion of your photo that is perfectly in focus. Due to the nature of camera components and the way they interact with light, every photo you take (with some random exceptions we won’t get into) will be impacted by your focal length, the distance to your subject (the object or person you are photographing) and your aperture. There are several mathematical calculations involved in determining exactly what depth of field you can expect, but as my goal is to make this subject a simple and easy to remember as possible, I’m going to forgo those explanations for today. If you have some free time and want to explore this in more depth, I’d recommend checking out an online depth of field calculator.

Today, though, we’re keeping things simple and to the point. To break this somewhat complex interplay between your camera and light down into simpler concepts, remember:

Focal length: Greater focal length = shorter DOF.
Distance to subject: Greater distance to subject = longer DOF.\
Aperture width: Wider aperture (smaller f number) = shorter DOF.

So, with that in mind and without further ado, let’s take a look at some photos!

How Aperture affects Depth Of Field

A large, bright lens aperture lets a lot of light into the camera and onto the image sensor, however such a big aperture also results in a very thin plane of focus, and a lot of foreground and/or background blur.

A small, tight, dark lens aperture lets less light into the camera, but because it is smaller, it focuses the light very sharply for a greater depth that extends in front of and behind the actual focus distance.

How sensor size affects Depth of Field

The size of an image sensor, whether digital or film, affects depth of field in a similar way to a lens aperture. This is because depth of field is a product of both the lens aperture and focal length, plus the sensor size relative to that aperture and focal length.

Courtesy of I Chabacano

Examples of Depth of Field

Here are some real world examples of varying depths of field along with an explanation of how it was achieved.

Here you can see the dragonfly is in focus, but the grass behind is completely out of focus and blurry. I was close when I snapped this photo and was using my telephoto lens to allow me to get really focused in on my subject. This combination of closeness to the subject and use of a zoom lens enabled this level of background separation even though my aperture was at a mid-range setting.

Here is an example of blurred background using my prime lens. Utilizing a lower aperture and getting close to my subject helped keep the face, snow, and ice sharp, but blurred out the background details that may have distracted from the shot.

Not only is this an example of “the decisive moment,” it is an example of a larger depth of field. This is achieved by being a bit further from the subject in the photo and by having a smaller aperture opening.

(Remember! Smaller aperture = larger f stop and vice versa.)

In order to see where depth of field begins to blur the background, look toward the upper right of the photo. There we begin to see the legs and feet of people walking past start to go out of focus. I would have preferred a smaller depth of field but this was a “let me test my manual setting really quick” shot of this boy running past me. I was so focused on getting settings nailed down that I didn’t even notice he’d fallen until I checked my screen and by then he was up and gone!

For good measure, here is another example with even greater depth of field. To capture this waterfall, I stood pretty close to the edge and shot alongside it while focusing midway across. Because I had a mid-range focal length and had my aperture opening pretty small, all the features in the photo are recognizable. You can clearly see the wall in the background and the rest of the waterfall in the foreground.

Here is an example of how distance and focal length can impact your depth of field. The closer you are to your subject, the more likely you are to blur out the foreground and background of your photo. That probability increases as you increase your focal length by zooming in. I was less than two feet from Mr. Bug here (close enough for him to stare back at me) and had my lens extended all the way. Even though my aperture was set to a mid-range value of f6.3, the fore and backgrounds are pretty blurry, helping the eye focus on the subject in the center of the frame.

From these photos you can clearly see that with minimal effort and a basic understanding of how to control just a single component of your camera, you are able to completely change the texture and appearance of your photos.

Now that you know, what are you going to do about it?

You’ve purchased a camera, you’re out there taking photos, and you’ve made your way to one of the premier resources for all things photography on the web, so I know you want to learn how to create eye-popping photos! With that in mind, here’s an assignment that will help you take your photo taking skills to the next level…

Do this…

Set your camera mode to aperture priority (“A” on Nikon, “Av” on Canon) and work on creating that nice separation from the background. Focus on the ways of doing so that we discussed today.

• Set your aperture opening a bit wider
• Play with focal length (zoom in and out)
• Take the time to step a little bit closer to your subject.

You’ll quickly get the hang of it and be sharing photos that have all your friends praising your photography skills on the social media platform of your choice!