Most people who think about an image with strong depth of field (dof) immediately picture landscapes. Why, because a large number of landscape shots are taken to maximize the dof, that is, the photographer wants to ensure that most parts of the image, from the foreground to the mid-ground to the background, are in sharp focus. That is the essence of a strong dof.
So, how do you ensure that your entire picture is in focus when you have parts of the scene at various distances from the camera?
First, you use a small aperture opening. Generally speaking, the smaller your aperture, such as f/16 and above, the more chance you will have of getting everything in focus. But this is not always true.
There are many factors that will determine how strong your depth of field will be. Along with your aperture, the focal length of your lens, the distance of the scene you are attempting to capture from you and your camera, and whether you shoot horizontally or vertically. Those factors that contribute to a strong dof are small aperture openings (at least f/16), wide angle rather than telephoto lenses, subjects that extend far from you and the camera, and a horizontal orientation will tend to give you a stronger dof.
However, it is usually not as easy as all that. To maximize your dof you must focus your lens on the hyperfocal distance. This is the distance at a set aperture and focal length that will provide the most dof. Calculating hyperfocal distance is a mathematical complexity (to me, at least), but you can do a fairly good job of approximating it by focusing your lens one-third into the scene you are photographing. Under many circumstances this is will give you at least a good starting point. Depending on your scene you may need to use other distances, but the most important factor to remember is that you need to focus on a point closer to you and not at the horizon or beyond.
The image you see here was photographed using this method. Focal length was 35mm, using f/22 at 1/90s and 200 ISO.
If your camera has a dof button, use it to preview your image. Don’t rely on your camera’s LCD, it is much too small to give an accurate showing of the dof. If you can zoom in you may get a better idea of how well you’ve maximized dof.
If you are the technical sort and want to delve into hyperfocal distance with a little more depth, the most comprehensive information on this subject can be found at The Dofmaster Website. Here you will find not only informative articles, but various gadgets and software to help you determine the most accurate hyperfocal distance, including apps for the iPhone/iPad Touch. You can find additional aids in the AppStore, such as iDof Calc and PhotoCalc. Also, Expoimaging has a nifty dof dial called Expoaperture2 which can be found at ExpoImaging. But for many of us, the 1/3-in rule should work pretty well.
Now let’s take this a little further. If you follow the 1/3-in rule does that mean your image will be tack sharp? Nope! That’s a whole different can of worms, as they used to say. Stay tuned for a ramble on how to get the sharpest pictures on earth.
As always, questions and comments are most welcome.