Nikon D7000 manual 399

Chapter 12 ■ Making Light Work for You 399

■Evenness of illumination—Con: electronic flash. Electronic flash units, like con- tinuous light sources such as lamps that don’t have the advantage of being located 93 million miles from the subject, suffer from the effects of their proximity. The inverse square law, first applied to both gravity and light by Sir Isaac Newton, dic- tates that as a light source’s distance increases from the subject, the amount of light reaching the subject falls off proportionately to the square of the distance. In plain English, that means that a flash or lamp that’s eight feet away from a subject pro- vides only one-quarter as much illumination as a source that’s four feet away (rather than half as much). (See Figure 12.3.) This translates into relatively shallow “depth- of-light.”

■Action stopping—Con: continuous lighting. Action stopping with continuous light sources is completely dependent on the shutter speed you’ve dialed in on the camera. And the speeds available are dependent on the amount of light available and your ISO sensitivity setting. Outdoors in daylight, there will probably be enough sunlight to let you shoot at 1/2,000th second and f/6.3 with a non-grainy sensitivity setting of ISO 400. That’s a fairly useful combination of settings if you’re not using a super-telephoto with a small maximum aperture. But inside, the reduced illumination quickly has you pushing your D7000 to its limits. For example, if you’re shooting indoor sports, there probably won’t be enough available light to allow you to use a 1/2,000th second shutter speed (although I routinely shoot indoor basketball with my D7000 at ISO 1600 and 1/500th second at f/4). In many indoor sports situations, you may find yourself limited to 1/500th second or slower.

Figure 12.3

A light source that is twice as far away provides only one-quarter as much illumination.