Charles Dias wrote: > Hi, > > ... Imagine you placed three cameras of the same brand and model side by > side, > loaded with the same film and with the same function adjustments. It are > pointed to the same 18% gray panel and the spot light meter are set. One of > the cameras have a 20mm f2.8, other a 35mm f2.8 and the last a 135mm f2.8. > If you set f5.6 in all lenses, will the light meters of the cameras > indicate the same speed for all three cameras?... Charles, The light readings may be different even if the cameras have identical lenses for the simple reason they are three independent systems. Each system is unique. One would hope the variances are limited, but they may be different. They would also be different if they are all three set up on independent tripods at the same time focused on the same gray card because they will must be set up in different positions each with a different angle of reflectance. But, if the gray card is sufficiently large to accommodate the widest lens so that the only thing in the view finder is the card and the card is *evenly* illuminated so that there is no change in reflectance from corner to corner and the cameras are each set upon the same tripod in the same point of view, the different EV readings from each system will be limited to the nuances of each lens and meter. However, If those are truly equal, the readings would also be equal because the intensity of the light would be the same irrespective of focal length. As f-stop is the ratio of aperture opening to focal length, if those ratios are truly identical (which they are not), each lens would then pass the same volume of light through to the film plane and meter. If the shutters are of identical speed (which they are not), the each shutter would all pass the same volume of light for the same amount of time. Exposures would be the same. One way to get to that last point is to use the same body for each lens. This would eliminate the differences in light meters and restrict variances to the lenses themselves. Peace! -- God said, Let there be light! Divine Light: Photography by Rev. Sidney Flack 2507 E. 2nd Street Tulsa, OK 74104-1903 http://www.divinelightphotography.com
