Using the Built-in Flash

Working with the D5100’s built-in flash (as well as external flash units like the Nikon SB-900) deserves detailed coverage, and I’m providing the information you need (see Chapter 12). But the built-in flash is easy enough to work with that you can begin using it right away, either to provide the main lighting of a scene or as supplementary illumination to fill in the shadows. For example, if you choose Matrix or Center-weighted metering (as described earlier), you can even use the flash in full daylight, as the D5100 will even automatically balance the amount of light emitted from the flash so that it illuminates the shadows nicely, without overwhelming the highlights and producing a glaring “flash” look. (Think Baywatch when they’re using too many reflectors on the lifeguards!)

The D5100’s flash has a power rating of 12/39 (meters/feet) at ISO 100, using the GN (guide number) system that dates back to the film era and before electronic flash units had any sort of automatic features. I’ll explain guide numbers (which can be a little confusing) in more detail in Chapter 12, but in plain terms, the flash’s rating means that the unit is powerful enough to allow proper illumination of a subject that’s 10 feet away at f/4 at the ISO 100 (sensitivity) setting of your camera. Boost the ISO (or use a wider f/stop) and you can shoot subjects that are located at a great distance. For example, at ISO 800, the D5100’s flash is good enough for a subject at 20 feet using f/5.6 or, alternatively, you can expose that scene at the original 10 feet distance at f/11. Ordinarily, the D5100 takes care of all these calculations for you. If you need a bigger blast of light, you can add an external flash, like the Nikon SB-900, which lets you reach out to 3245 feet at ISO 200 and f/5.6 (or even farther at larger f/stops).