Re: Sunny 16 Doubter (digest 1597)

[P3D Bob Howard <bobh@xxxxxxxxxxxxxxxxxxxx>]

RE: Greg W. speculates about LA Smog, volcanic eruptions, alpine heights
etc. as something that would defeat Sunny 16 rule. The rule says Clear
Sky..not smog ridden, or filled with volcanic dust. The illumination
from a distant sun is constant within close limits for the time limits
of 10am to 3pm (found on most exposure sheets too.) Agfa did a world
wide study of light variations in designing soem simplified cameras and
found the variations of intensity were not great. What we perceive as
tropical brightness are more stark shadows from high overhead sun! The
16 rule would also allow stop down for high elevation or white sand
(light subject). The former more due to UV than brightness.  This is
what used to cause the overexposure. Many modern cameras are UV filtered
in the cement of the elements or front plate. BobH


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