Learn How To Understand Depth Of Field
Using a long zoom lens with a relatively wide aperture can have many advantages in wildlife photography. Wider apertures produce narrower depth of field, allowing the subject to be isolated from a busy or uninteresting background by blurring the background with beautiful bokeh. Of course, you must take care to keep the critical parts of your subject sharp, with careful attention to where you are focusing. Going “wide open” means using the widest aperture that your lens supports, usually ƒ/2.8, ƒ/4, or even ƒ/5.6 for some zoom lenses. For smaller animals, this will often result in the entire animal being in focus. For larger animals, the photographer should ensure the eyes are in focus, with acceptable depth of field—typically extending at least from the nose back to the ears (left). Sometimes this requires selecting a narrower (smaller) aperture than you would for a smaller animal.
With groups of animals, using a wider aperture can isolate one animal from the rest of a group (right). This can help produce a feeling of depth in a line of animals, or emphasize a behavior. Sometimes though, a photographer wishes to ensure all animals in the group are in focus. A solid understanding of depth of field, and how it is influenced by various factors, can help you make choices that best match your creative vision. Understanding depth of field at various settings Depth of field (DoF) is the distance between the nearest and farthest points in an image that appears sharp. Depth of field is affected by three factors: focal length of lens, aperture, and distance to subject. As the focal length of a lens is increased, the depth of field becomes shallower. Wider apertures also lead to a shallower depth of field, as does a decreased distance from your subject. Conversely, shorter focal lengths, narrower apertures, and a longer distance to your subject mean greater depth of field.
While these generalities are easy and helpful, the math behind calculating the actual depth of field can be complex and impractical in the field unless you have tools to help with the calculation. One such tool is an app called PhotoPills. This app offers a wide array of tools for photographers and can be a relatively quick way to calculate complicated things like depth of field and hyperfocal distance. Let’s use PhotoPills to calculate some depth of field examples. The image at left depicts the PhotoPills depth of field calculator, which allows you to input camera model, focal length, aperture, and subject distance to calculate the depth of field. The image at right depicts the PhotoPills depth of field calculator showing both the near and far limit of the depth of field based on focal length, aperture and subject distance. On the next page, there’s a table with depth of field calculations at various focal lengths, apertures, and subject distances. Examples are from a full frame camera.
Obviously, the combinations of subject distance, focal length and aperture are limitless, and these tables are just a few samples to illustrate the key points. I encourage photographers to use an app like PhotoPills to explore the various depth of field for their own lenses at varying subject distances
Aperture setting for photographing large animals When photographing small single animals, wide apertures will generally lead to the entire animal being in focus. This can also be true when shooting a side profile of larger animals. Smaller apertures are needed when shooting a larger animal head-on if sharp focus is desired from the tip of the nose to ears (the longer the nose, the more this is true!). For example, if you are photographing the face of a bear at 500mm that is 13 meters away from you, an aperture of ƒ/5.6 is going to result in a depth of field of only 22 cm. This won’t be enough to have both the eyes and snout in focus, so a smaller aperture is going to be required to get its entire face in focus. Much smaller apertures are needed if you are looking for the entire length of a large animal to be in focus as it approaches you directly.
Aperture setting for photographing groups of animals Wildlife photos of groups of animals can be quite compelling. Showing the interaction of mother and cubs or highlighting group behaviors and interaction often makes for high-interest photos. While narrow depth of field can be useful for isolating an animal in a group, sometimes the photographer wishes to have all animals in a given group in focus. In this case, the aperture must be made small enough to achieve the desired wider depth of field. When I am shooting groups of animals, I adjust my aperture as I shoot, using a few basic observations.
First, how many animals are there in the group? More animals generally mean they are staggered at greater depth and will require smaller apertures to capture them all.
Second, how close are the animals, and how long of a zoom lens am I using? If I am shooting using a relatively wide-angle lens, say my 24-70 mm, depth of field is usually not an issue. But if I am using a 500 mm lens and the animals are only 20 m away, I know that I need quite small apertures to get a group of animals in focus.
Based on these factors, I will make my decision on which aperture setting I wish to use. An aperture of ƒ/7.1 or ƒ/8 with a smaller group of smaller amount of stagger in their positions. ƒ/9, ƒ/11 or ƒ/13 when there are more animals and more stagger in their positions. I’ll go as high as ƒ/16 or ƒ/18 for a group that spans a significant depth or when they are particularly close when using a long zoom lens.
If a group of animals is stationary, I will often take a series of photos in quick succession using smaller and smaller apertures. Once I download to the computer, I can choose which setting has the optimal sharpness.
If I am photographing an action shot of a group of animals, I will often work with a smaller aperture to keep them all in focus (or at least all animals that are involved in the action. Of course, this must be balanced with a higher enough shutter speed to freeze the action!
My primary creative decision when shooting wildlife, apart from framing and composition, is choosing the aperture setting. Sometimes that will be wide open to isolate a single animal, but for groups of animals or large animals, I have to constantly remind myself to make my apertures smaller to maintain an adequate depth of field. I will then make sure that my ISO is adequate to allow me sufficiently fast shutter speeds for the image I’m trying to obtain. When shooting wildlife, some guidelines I go with are 1/320-1/500 sec for relatively stationary animals, 1/1000 – 1/1600 sec for faster moving action, and 1/2000-1/2500 sec for very fast action like birds in flight.