Depth Of Field In Depth

I deliberately chose a commonly written about topic for this week’s tip to encourage everyone to take every piece of information deep to heart and integrate these concepts into your workflow. If you’re new to it, may this reading be the start of your using it. If you’re somewhat familiar, may depth of field become one with you. And if you’re a frequent user of it, may it help further reinforce its importance.

The Basics

There’s a direct relationship in how much depth of field is created in a photo to extremely important variables: the focal length of the lens, the aperture at which the photo is made, how close the subject is to the background, how far away the subject resides from the camera and how much the subject is magnified. (This assumes a DSLR is used to make the image. A point and shoot inherently provides a lot of depth of field due to its small sensor size.)

Proximity To The Background

The farther away the subject is from the background, the more the background can be thrown out of focus. If the subject is very close to the background, it’s not possible to make the background go soft even if you use a super-telephoto lens and set the aperture to ƒ/4. In the photo of the kingfisher, the background was a significant distance from where the bird perched. The focal length was 400mm with an aperture of ƒ/8. Note the plane of sharpness lies solely on the bird. Even the stick upon which it’s perched falls out of the range of focus. (I used flash as a source of fill because the bird was photographed in a forest.)

The Aperture

The wider open the lens, the less depth of field. The more the aperture is stopped down, the greater the depth of field. In other words, ƒ/4 nets shallower depth of field than ƒ/22 based on a fixed focal length. It’s important to realize the connection to focal length in addition to how far away from the background the subject resides. If you use a telephoto lens with a wide-open aperture, you stand a greater chance of throwing the background/foreground out of focus. Understanding how the combinations go hand in hand is absolutely imperative to comprehend. In the side-by-side portrait, the image on the left was made at ƒ/13 and the image on the right at ƒ/4.

Focal Length

The more telephoto the lens, the less potential for near-to-far depth of field. The wider the lens, the greater the potential. For instance, an image made with a 28mm lens will inherently display more depth of field than a 100mm lens at the same aperture. So if you want to create shallow depth of field and you use a wide lens, it may not be possible. Hand in hand, if you use a telephoto lens and want a subject close to the lens and a distant object to both be in focus, it may not be possible. The red rock scenic was made at ƒ/20 with a 20mm lens.

Subjects On Multiple Planes/Distance From Camera

In order to fully comprehend depth of field, you need to understand the concept of infinity. Infinity occurs when all the elements in the photo start where the lens focuses at its farthest distance. The wildebeest photo was made at 166mm at ƒ/5.6. Even though the aperture was wide open and a medium telephoto zoom setting was utilized, everything is in focus in that all planes are at “infinity,” so every layer is sharp.

If the subject is very close to the camera and the focus point is placed on the subject, there’s more potential to create shallow depth of field than if the subject is significantly farther away. This concept is tied into the above explaining subjects on multiple planes. Again, there’s a very specific relationship of the focal length, the aperture, how far the background is from the subject and the distance the subject is from the camera.

Scenics for Maximum Depth

Decades ago, I realized the importance of depth of field when I began to make scenics. I pieced together the facts that wide-angle lenses are most often used, stopped-down apertures are needed and it’s good to maintain sharpness on all planes—foreground, midground and background. In the scenic made in Yellowstone, I used the grasses as my foreground, trees and lake for the mid, and mountains and dramatic sky as the backdrop. The focal length was 45mm, the aperture was ƒ/14, and I placed the focus point on the foreground spit that juts into the lake. 

Selective Focus

Mostly incorporated into portraiture and macro photography, a technique known as selective focus is utilized so the eye is drawn to a single slice of one plane of focus. In the photo of the California poppy and spider, I wanted the viewer’s eye to zero in on just the silhouette of the spider and top of the poppy. When I made the photo, I was actually photographing just the backlit poppies, so I dialed in a stopped-down aperture in order to get the entire flower in focus. When the spider entered the scene, I quickly adjusted the lens opening to ƒ/4 to make the spider the focal point. Because the majority of the image content falls out of focus, the viewer is drawn to the spider since it’s one of the few sharp planes.

Subject Magnification

The closer you get to a macro subject, depth of field quickly falls off. This concept of depth of field is more specialized and it really is a subject unto itself. I bring it up for the sole purpose to let you know it’s an important variable. Study the side-by-side images of the Columbine bud. The image on the left was made at ƒ/4 and the one on the right at ƒ/16. The focal length for both was 100mm. In that I zeroed in on a single bud, I had to fully stop down to ƒ/16 to get sufficient depth of field. (Note that it also tries to increase the depth of field of the background so the flower has to compete with it.)

Since there’s a ton of info to digest just above, I simply bring up the following two concepts that should be explored and are extremely important in controlling depth of field: hyperfocal distance and focus stacking. Digital photography has opened the door to focus stacking and requires knowledge of software to utilize it. Hyperfocal distance is reliant upon where in the composition the focus point is located and how it interacts with the focal length and aperture—definitely worth looking at both if you already comprehend the other info in this week’s tip.  Enjoy your journey into the depths of depth of field!

To learn more about this subject, join me on a photo safari to Tanzania. Visit www.russburdenphotography.com to get more information.