EV can be explained as the range of combinations of shutter speeds and aperture values that correspond to the same final exposure. If you number these ranges, you have EV (Exposure Values). An EV of zero will correspond to the exposure time of one second and the aperture of F/1.0. EV 1 is either a half second and F/1.0 or one-second and F/1.4 and so on. If you combine the exposure value with a specific film speed, EV numbers can be used to indicate the brightness of an object. Without the addition of film speed into the equation, exposure values indicate nothing more than camera settings. Most camera manufacturers use EV to indicate the sensitivity of their AF and metering systems. The Nikon F5 has an AF detection range of EV 1 to EV +19 and a metering range of EV 0 to EV 20 (at a rated 100 ISO). Now, if you mounted a lens with an aperture of F/1.4 to the camera the metering system would be accurate between EV 0 to EV20. However, if you mount a lens with an aperture of F/2.8 the meter now senses three stops less light than with the F/1.4 lens so the metering system is now accurate between EV 3 to EV 23. (All EV ranges are rated at 100 ISO). It is quite easy to set up a chart in excel to set up EV ranges. However, to try to explain it here could take some time. If you would like I have an EV chart in an excel file that I would be happy to email to you.
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