anand@utastro.UUCP (Anand Sivaramakrishnan) (05/14/85)
Here is the truth as I see it : * Set the f-stop to the square root of the ASA of the film. * Meter on some luminance. Placing that luminance on the middle grey (zone V) will require a certain shutter speed, say 1/X of a second. * The luminance that you measured is X foot-candles. More succinctly, the shutter speed needed to produce middle grey using an f-ratio of the square root of the film speed (in ASA or ISO) is numerically equal to the reciprocal of the luminance in foot-candles. This relation can save your skin (or your reputation as a photographer)... in order to use it you can do something like the following: Set the film speed to 125 ASA, and the f-stop to f/11. Meter on an object, and the the shutter speed figure (eg. 30 for 1/30th of a second) IS the luminance in foot candles. Once your eye is calibrated, you can dispense entirely with the meter, and you can remember exposures under various conditions with different films. That is how to make a $300 camera behave like a $10 Weston Master light meter. All this was learnt from Ansel Adams' Basic Photography series.