Why does this matter? When shooting landscapes with a wide angle lens for instance, you will often put your main subject in the DOF sweet spot – knowing that you have about 1/3rd in front of the focus point to 2/3rds in back of the focus point with which to find that sweet spot. If you do that when shooting a big telephoto lens, the area of the image that you want highlighted will be wrong. Its 50/50 not 33/66. Is this confusing? Yes it can be confusing. That's why I like to point people to an amazing (and free) resource I found called DOFMaster.
Use DOFMaster to learn more about this subject. It’s worth 10-15 minutes of your time. Here’s how:
Select your camera body. Type in the focal length (mm) of the lens you want to learn about. Select an f/stop, and select the subject distance. Then see what sort of DOF you're going to be working with and what the exact near/far distance will be.
If you do take time to visit DOFMaster, you can prove out every theory I proffer here and do so, instantly.
I am using an Olympus E-PM1 camera for this test. I select a 300mm focal length, an f-stop of f/4 and a subject to camera distance of just five feet. In that scenario, my depth-of-field is a mere 0.01 feet!!!
Remember that as camera to subject distance increases, depth-of-field increases. Type in 120 feet instead of five feet and you’ll see that the DOF moves from 0.1 feet to nearly six feet! Type in 1000 feet and the DOF jumps to more than 400 feet at f/4 but the split moves to a 40/60 split.
These concepts may seem vague but they are important. Over time, if you get to be as old as I am, you eventually learn this stuff and just end up knowing what your DOF will be in most situations. But for now, use this DOF calculator to learn it. And remember the concepts.
If you work at close focusing distance with long lenses you will have razor thin DOF and it will generally be evenly split 50/50. This holds true even at very small apertures.
Don’t take my word for it. Try it for yourself. Set your subject close and then far away. Experiment with depth-of-field and you’ll find out that the rule is reliable. Hopefully moving forward, you’ll be able to take this knowledge and improve your percentage of keepers.
ABOUT THE AUTHOR
Scott Bourne is President of US Operations at Skylum Software (Formerly Macphun,) an Olympus Visionary and a professional wildlife photographer, author and lecturer who specializes in birds. He was one of the founders of This Week In Photo, founded Photofocus.com and is co-founder of the Photo Podcast Network.
Scott is a regular contributor to several photography related blogs and podcasts and his photography has appeared in more than 200 books and magazines. He is a trainer at both ThinkTapLearn and lynda.com, and is the author of 11 photography books.
Scott is available to speak to your birding group, photography group and for both private and small group bird photography workshops. For more information on engaging Scott as a speaker or workshop leader, or for image licensing and print information, e-mail email@example.com.