FILM SPEED, SHUTTER SPEED AND f/stops — What Are They?
Each of these four factors is represented by a series of numbers. Your camera may have only a portion of each series indicated. Exposure Value: In most light meters, photons of light that are reflected from your subject put pressure on a photo-sensitive receptor in your light meter and are converted into electricity (this is why some meters do not require batteries). The greater the number of photons, the greater the electricity that is produced. Internationally accepted standards specify exactly how much light pressure equals a certain EV number. This value is measured by the following number series (for ISO 100 film): 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 Easy! However, even though this appears to be a linear progression, each number represents twice as much light as the numbers increase. This provides an easily memorized scale to clarify the concept of “absolute value of the amount of light falling on a subject”. This term is related to il
