hmmmm .... actually believe that on an average bright sunny day the incident
reading would be approximately 6400 foot-candles. Ts comes frm the "formula"
fc = C x fsquared / ASA x Exposure Time where C is a constant. Someting like
20 or 25 or so.
If you use 25 and assume that the sunny 16 rule rules then ASA and ET
essentially cancel each other out and you are left with 25 times 16 squared
or 25 times 256 which is 6400 and this would be roughly 6400 x 10.76 = 68864
lux. Methinks ...
Andy
PhotoRoy6@xxxxxxx wrote:
So on a cloudy bright day an exposure for ASA 125 f/11 at 1/125 sec yield
125 foot candles per square foot.
In a message dated 6/29/2007 5:44:24 P.M. Eastern Daylight Time,
elgenper@xxxxxxxxxxxx writes:
Andy, unless I misunderstand you, it sounds as if you´re looking for
Ansel Adams´ famous "Exposure Formula". Here it is, directly from
his book "The Negative": First compute the f/stop value
corresponding to the square root of the film speed in ASA (e.g., for
ASA 125, you get f/11).
Then, the luminance (in candles per square foot) of a surface read by
a correctly calibrated exposure meter is just the reciprocal of the
shutter speed for the above f/stop and film speed.
I haven´t tried it in practice, but these are the words direct from
the holy scriptures of St. Ansel himself, so they must be true...
Good luck!
Per
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