At 00:35 5/25/01, Rich Lahrson wrote (in part):
Now, I don't fully konw how this works, but I picked it up years ago from
the old Ansel Adams' Basic Photo series books: You get the square root of
the ASA (like ASA 64, square root is 8) of the film you are using. That's
your f-stop (in the example, f/8) and the meter dial indicates a number,
the reciprical of which is the indicated shutter speed (like, 200 c/ft2 is
1/200 sec). Or, f/11 @1/00, etc. That's middle grey, the big arrow
exposure. Those of you with this meter, if you haven't tried, check it out.
Well, enough math. The point is that this system is way faster, as the
simple exposure calculations can be figured in the head So the exposure
dial can be by-passed in many situations.
Rich,
Don't know if what you were thinking to remember was this, but it's how
cd/ft^2 relate to "Brightness Value" (BV) or the subject luminance portion
of EV (the other half is the film Speed Value [SV]):
EV = BV + SV
BV = log(luminance in fL)/log(2)
fL = foot-Lamberts
to convert from Cd/ft^2 to fL, multiply the Cd/ft^2 by pi
This may be the missing piece of the math you were trying to recall.
-- John
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