What was once a perplexing and mysterious photo accessory, electronic flash has evolved into an easy to utilize tool. It seamlessly couples to the camera body’s hot-shoe and interfaces with the in-camera computer. The days of manually setting ƒ-stops, calculating guide numbers or measuring flash to subject distance is done automatically and yields perfectly balanced and exposed digital files.
Flash is used for many purposes. It adds light to a dimly lit subject, helps freeze motion due to its very short duration, allows lower ISOs to be used when it becomes a main light, it’s an extremely versatile source to fill in shadows, it can be used creatively to provide stroboscopic or slow motion effects and, when used as a primary source of light, greater depth of field can be achieved by powering it up and stopping down the lens. It’s best used when its inclusion goes undetected so the viewer gets the impression the scene was naturally lit.
With all of the above benefits mentioned, it needs to be understood that flash has limitations. They have a given distance as to their capability to illuminate a subject. The guide number of the flash determines its power. If distances are exceeded, the flash has little to no effect. The reason this occurs is light from a flash falls off quickly once it reaches its maximum output. Factors that determine how effective flash can be include: