ABSTRACT
Aperture settings are arranged so that changing from one "standard" f/stop to another causes either doubling or halving of the admitted light. The same applies to shutter speeds and ISO settings and exposure compensation dials. The guide number (GN) of many flashes assumes that the camera in use is set to ISO 100. Flashes equipped with a zoom function will assume the particular zoom setting at the specified guide number. A histogram applies to images produced by any kind of light, including ambient light. The red, green, and blue (RGB) histogram shows simultaneously, but independently, a histogram for each of the RGB color channels. The histogram display on the camera covers a certain number of stops, essentially the dynamic range of the sensor. The handheld flash exposure meter provides another means of measuring the light from a flash. They must be set for flash use because they also serve as ambient light meters.
