Bokeh is that magical, dreamy, creamy blur that isolates the subject from background. Translated from japanese the language it means “blur” and is pronounced BOH-ka or BOH-kay. While out of focus backgrounds are achieved via shallow depth of field, Bokeh is the quality of that background.
Shooting for Background Blur
To shoot for good background blur you need to set your camera to manual or aperture priority so that you can set the F-stop. Place your subject a good distance from the background, and yourself close to the subject. The further away the background, and the closer you are to the subject, the more likely you are of achieving a good blurred background. Ideally, you want in excess of 15 feet of space behind your subject.
A second point to note, it’s the lens, not the camera that gives you the dreamy blur. To shoot an image with good bokeh you need a fast lens. A lens that goes below F4 will work, but one that is F2.8 and under is ideal. If you don’t have a fast lens, or have one with a variable F stop rather than a fixed one, a workaround is to increase the distance between the subject and the background. In the case of the eagle below, while it was shot at F7.1, the background was around 40 feet away.
The shape of the reflected light is determined by the diaphragms of the lens. Most new lenses have round blades in the diaphragms, some of the older ones have straight blades resulting in the (seven sided) heptagon shapes, e.g. the Nikkor 50mm is a heptagon. The higher the quality of the lens, the more round blades in the diaphragm, and the better quality, or smoother and more rounded the bokeh becomes.
It’s a well-known fact in photography that not all zoom lenses are created equal. Using a zoom lens will improve the bokeh, but the improvement depends on the quality and optics of the lens. A Canon 75-300 wont give you as creamy a bokeh as the Canon 70-300L