Archived posting to the Leica Users Group, 1999/02/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>>EV is strictly a function of shutter speed and aperture. Just look at any >>Hasselblad C or CF lens to convince yourself. Specifying exposure requires >>both EV and film speed. >> >>Dan C. >> > > >>>> The EV is a function >>>>of light AND film speed. >>> > >Are we talking at cross-purposes here? >I understood Mark's original statement to mean that the required EV was >dependent on the intensity of light and the sensitivity of the film - that >is true, surely. However, EV itself is solely a function of speed and >aperture and is independent of film speed and the amount of light. These >are not contradictory statements. Any apparent contradiction is the fault >of my inability to explain myself! CORRECT! EV is in and of itself SOLELY a function of the aperture and shutter speed combination. But the EV that will be appropriate for a given intensity of light IS dependant on film speed ( I know -- "DUH!" ). And measuring EV on a handheld meter requires the Film speed be selected ( and of course the light being measured :-). The minimum and maximum EV that can be measured by the light meter is dependant on the photocell sensitivity and the supporting electronics. For a TTL meter on a camera the "measuring" F-ratio of the lens comes into play and shifts the min-max values up or down depeding on weather its a fast or slow lens. That is why when you look at specs of how sensitive a light meter is on a camera it is typically -- by industry standard I suppose -- given as something like EV -1 to 17 @F1.4 and ASA100. I think that addresses the issues posted today about this thread. May it rest in peace! :-)