EV
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Exposure Value. A number representing equivalent shutter speeds and lens apertures combinations for the same exposure, given a scene brightness. At ISO 100, 0 represents (f/1.0 at 1 sec); 1 = (f/1.4 at 1 sec) or (f/1.0 at 1/2 sec); 2 = (f/2.0 at 1 sec) or (f/1.4 at 1/2 sec) or (f/1.0 at 1/4 sec) and so on. For a fixed aperture, as the EV increases 1, the shutter speed increases one step; for fixed shutters speeds, as the EV increases 1, aperture decreases one f/stop. Long exposures are for (or have) negative EV. A light meter sensitivity is usually defined as having the capacity to read an EV range for a given ISO speed.
