This was originally posted on my old web site, and now I am moving over to my blog. - Andy
Wildlife photography comes with many challenges, both creatively and technically. On the creative side, composition is the single most important decision you will make in your images. Other things are certainly important, but composition will carry an image if other aspects are not as strong. On the other hand, if you already have your creative areas covered and need more help with the technical aspects of your images, consider this brief introduction to depth of field for wildlife photography a good start.
"Why worry about depth of field? I mean, I spent all of this money on a fast telephoto lens, why not shoot wide open all of the time?" I often hear this type of statement while out on safari, along with additional tidbits like "don't I always want the fastest shutter speed possible?" or "I don't want to have to think about my depth of field. Shooting wide open takes that decision away." Ok. Let's dive in.In my photographs, before I click the shutter I have already decided what is the most important part of the image. In other words, I have already decided what the subject is. It is this decision that will determine the technical aspects of my photos. Using different apertures on my lenses will help determine, or display, what is important and what is not important to the viewers of my photographs. Increasing or decreasing the depth of field allows me the control that I need. The challenge arises when I want to accomplish many things that appear contradictory. For example, in the image below, I wanted to have the eyes and nose all in focus, but have the background blurred. If I have to stop down (increase the aperture number) from f/4 to about f/5 or f/5.6 to have enough depth of field to have the eyes and nose sharp, I really haven't given up my blurred background.
Canon 1DsMkII, 400mm f/4 DO IS, f/5.0 @ 1/640sec, ISO 250
Here is a quick crop of the eyes and nose. I could have stopped down a little more, but I was trying to strike the balance between a blurred background, which usually requires f/2.8 to f/4 at moderate distances, and a sharp subject. One of the techniques that I use is mid-point focusing. In other words, if I need both the eyes and nose in focus, I will focus in the space in between them. This image is a near-miss, but I am still happy with it. Notice that the eyes are sharp, as well as the teeth, but not quite on the nose.
Here is another example of a missed opportunity. Somewhat of a grab shot, but I always try to take images with babies or action in them. Here we have a mother and baby giraffe in Serengeti National Park, Tanzania. I used a 500mm lens on a Canon 5D camera, and I had only a second to grab a shot before they walked away. Well, I only had one shot, and the shot didn't work out, as I grabbed the shot at f/4. Not enough depth of field for both the mother's head and the baby's head. If you look closely at the image, you can easily see that the mother's head is likely to be 4 to 6 feet behind the baby's head. Something to think about when examining a scene.
Canon 5D, 500mm f/4 L IS, 1/200sec @ f/4, ISO 200
And here is the cropped area. Notice how the mother is dead sharp and the baby isn't sharp at all. Strike that up to not enough depth of field. The entire head area was important to me on both of them, so I missed the mark on this shot.
So how does one determine the proper aperture for a given goal? Here are some great resources that illustrate both depth of field concepts and products that you can take with you out in the field. Understand the relationship between focal length, subject distance and aperture. All three are related to each other, and it takes a while to get a hang of it. I know instinctively that with my 500mm f/4 lens at 50 feet, I am usually shooting between f/8 and f/14, depending on how large my subject is. I will need much more depth of field for a zebra that is looking directly at the camera than if I am shooting a bird of prey that is looking sideways, or a profile look. The zebra will require about 24 inches of depth of field from its nose to is ears, and an eagle that is looking sideways might only require 4 inches of depth of field. When in doubt, stop down more than you think you need. F/14 is very common in my world. You will be surprised at how you can still reach your goal of having a blurred background, while having all of your subject in focus.
Here is an example of when you can have a tack sharp subject and a blurred background. One of the tricks is to try to avoid cluttered background, which helps separate your subject from the rest of the image. In this next shot, I used f/11 to make sure that I had all of the fine detail of the grass in focus. So my subject increased from the lioness to the surrounding area. The lines of the grass complement the angle of the lioness, so I chose to emphasize this by increasing the depth of field. I have found that for my 500mm f/4 lens in east Africa, where my subjects range from 25 to 75 feet away, I use f/8 to f/11 75% of the time. And I tend to stop down more to f/14 or more on a regular basis. I rarely use f/4 to f/5.6, unless I am in dire need of a faster shutter speed.
Canon 1DMkII, 500mm f/4 L IS, f/11 @ 1/200 sec, ISO 250
Depth of field control is both a tool to convey what is important in your image, as well as it is a control to help de-emphasize what is not important in your image. Learn what the depth of field is at common apertures for different focal lengths at different distances. Your understanding of these variables will go a long way in controlling how your subjects are portrayed in your images.