Depth of Field Differences Between Lenses
Written by: steve
By Steve Russell
Before getting into the specific subject I wanted to discuss depth of field (DOF) and why really knowing, understanding and being able to manipulate DOF can help you become a better photographer.
When we start out as photographers, especially when we get our first DSLR, about the only thing we know, and need to know about DOF is that it exists and that areas in the image that are outside the DOF will not be in focus. After we’ve taken a hundred or so photos we begin to realize that sometimes there are areas of the photo we wanted in focus and aren’t and other areas that are in focus that we wish weren’t. To use DOF to our advantage we have to do two things. First it’s important to study and understand DOF. You can’t make DOF work for you without really understanding it. It’s not difficult even though it may seem that way in the beginning. Second, we have to stop using Automatic and Program modes. In fact, most of the time the best way to control DOF is to shoot in aperture priority mode although manual mode works very well if you’re inclined to shoot that way.
What is DOF, you may ask? In its simplest form, DOF is the area in front of the camera that will be in focus. For example, let’s assume you took a photo of someone and when you looked at it on your computer there was some stuff in the foreground that was out of focus (fuzzy) and some stuff in the background that was fuzzy but the subject and the area close to the subject was nice and clear. The area that is nice and clear, from front to back, is the depth of field.
Someone else took the same photo at the same time and when you looked at their image you noticed that a lot more of theirs was in focus and you wondered why. As you might guess, the answer isn’t overly simple but it also wasn’t necessarily because you did something wrong or the other photographer did something right (or wrong). There are four variables that determine the total DOF, or the total area in front of the camera that’s in focus. Those variables are:
• The distance from the camera to the subject or the focus point
• The size of the camera’s sensor
• The focal length of the lens, and
• The aperture (lens opening)
Because this article is about demonstrating the differences of DOF between lenses, I’m going to focus mainly on the focal length of the lens, camera’s sensor size and aperture. However, keep in mind that as the distance to the subject or focus point changes, so does the DOF.
This table provides the DOF for 6 different lens focal lengths when the aperture is set on f/4 and the subject is 15 feet from the camera. It also illustrates the differences between a camera with a sensor that has a 1.6 crop factor and one with a full frame sensor.
Notice that the longest (200mm) lens has a much shallower DOF than the shortest lens (24mm). Note also that the 1.6 crop factor sensor camera has a somewhat shallower DOF than does the full frame sensor camera using the same lens. Using the short lens allows you to have almost everything in the image in focus which is one of the reasons that landscape photographers tend to use wide-angle lenses. Conversely, photographers that use long lenses, especially in the super telephoto category like a 500mm lens, usually want the subject in sharp focus and all the other things in the image to be out of focus so as not to be distracting to the viewer.
This table is the same as the previous one except that the aperture has been changed from f/4 to f/8. Here the DOF is deeper for each lens. If you were to open the lens wider to f/2.8 the DOF would be shallower.
I wrote another article on DOF on August 1, 2011, and used these same two images. By understanding DOF you can get everything in the image in focus like in the photo of the village in Central Malawi, or render everything but the subject out of focus like the thistle.
If you want to study DOF deeper and gain a better understanding, I recommend you go to Cambridge in Colour a website from the UK that has some really great in-depth information about photography. However, the best way to learn is to go out and experiment. Set you camera mode to aperture priority and take the same photo at different aperture settings (f-stop) and look at the differences. With practice, you’ll be able to visualize the finished result and set your camera’s aperture to achieve the desired result without resorting to trial and error.
Previous Post: Grand Tetons and Yellowstone