One of the most interesting concepts artistically that my students want to achieve is called the Figure/Ground Principle. It is one of the Gestalt Principles. These principles were developed by a group of German psychologists in the 1920’s and determined how we perceived various visual stimuli. “Gestalt” means “unified whole” so in other words, it is how we see the world, or in this case photographic compositions as a whole.
Figure-ground articulation is how we see the foreground against the background. In order for the foreground to visually be separated from the background there may be a difference in color, a difference in depth or one object on a closer plane versus a distant plane, and a distinct line separating one area from another. When using this principle in photography, we cannot create lines that are not there except through depth-of-field (DOF). We create sharp lines on blurred backgrounds with narrow DOF. Those lines become less sharp as the DOP becomes broader.
Notice in the examples above, shot with a 200mm focal length lens, how the seed pods become more distinct and delineated against the background as the DOF is decreased. This artistic choice isolates the subject for the viewer and allows for less visual confusion. Just how much DOF is the right amount is up to you. Even at f/8 the background is less intrusive than at f/22 and there are still several non-standard aperture choices between f/8 and f/4.
So, what determines your depth-of-field? It is not just about your aperture. Your DOF is determined by your choice of lens, your aperture and where you focus. A great resource to bookmark is the Depth of Field Master which allows you to choose your make/model of your camera (both film and digital), your focal length and your focus distance to your subject and it will give you your depth of field. Notice in the example below for the 50mm lens used below the focus is set at 6 feet in front of the camera. The depth of field extends 5.4 feet in front of that focus point (44%) as well as 6.8 feet behind that focus point (56%).
Using my NikonD300s as guide with a static focus distance of 6 feet here is a table to show a correlation between lens and aperture and your DOF ratios between your near limit and far limit of acceptable sharpness :
|16mm||30%/70%||10%/90%||100% (3.2 ft to infinity)|
Thanks to the gurus at DepthofFieldMaster.com your can create and print tables for your camera/lens or stream tables to your iPhone or iPod, download the app to your iDevice and for Android users an app is coming but for now you can bookmark this mobile site for use on your devices.
One last addendum to this post, when shooting macro/micro photography your DOF will reduce dramatically no matter what. Your scale will go from having a DOF measured in feet to millimeters/micro-millimeters so be prepared. Your focus will be super-critical as will your understanding of your near and far ranges. A tripod will be most handy to have as will a shutter release cable. In lieu of a cable, you can also use your self-timer.
Another handy tool will be your Depth-of-field Preview Button if your camera is so equipped. This can eliminate the need for tables and such as you will be able to SEE in the viewfinder the amount of focus and where it begins to drop off in the composition before you even release the shutter.