Film and lens speeds are similar to shutter speeds. When someone refers to the speed of a lens, it refers to the smallest number f-stop the lens has. A lens whose smallest f-stop number is 1.2, for example, is “faster” than a lens with the smallest number of 5.6. This is because it has the ability to allow more light through the lens since it can open wider (remember, the larger the opening, the smaller the f-stop number). Film that is said to be “fast” is film that requires less light for proper exposure. ISO 800 film, for instance, is … Continue reading →