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Lecture & Vocabulary
Aperture: the opening of a lens, the size of which is controlled by a diaphragm. The term is commonly used to designate f-stops, such as f/4, f/5.6 etc., which are actually arrived at by dividing the focal length of the lens by the diameter of the aperture. Thus, f/11 on a 110mm focal length lens means the opening is 10mm. The wider the opening, the lower the f-number, the more light is let through the lens. Each step in aperture represents a halving or doubling of light. Thus, f/8 allows in half as much light as f/5.6, and twice as much light as f/11.
Shutter speed: an element of exposure; the duration of time in which light is allowed to strike the film.
Shutter: in a focal plane shutter, a set of curtains travels past the film gate and allows light to strike the film within a set period of time. A leaf shutter is located within the lens itself.
Speed: with a shutter, the duration of time in which light strikes the film. With film, the sensitivity to light. With a lens, the maximum aperture. All can be described as either fast, medium, or slow speed.
Shutter priority: an auto exposure mode where the shutter speed is user-selected and the exposure system chooses an appropriate aperture for correct exposure.
Iso: a prefix on film speed ratings that stands for international standards organization, the group that standardizes, among other things, the figures that define the relative speed of films.