On 10/31/2011 7:02 AM, Collin Brendemuehl wrote:
It also makes the notation of aperture = f/x much more meaningful.
f is your focal length and x is your diameter fraction.
It's why you see apertures listed as f/2 or f/64 and etc. It's
appropriated from a formula.
In addition, what does that letter "f" stand for anyway?
It is a "function".
This formula/function allows you to use two different focal length
lenses and obtain the same exposure. It resolves the problem of
differing aperture sizes and lens focal lengths..
You'll have to ask Ansel Adams what it stands for, he's either started
or popularized the convention, I can't remember which. It's a question
I've seen posed in a number of places with no real satisfactory answer
given.
On Sun, Oct 30, 2011 at 8:08 PM, John Francis<[email protected]> wrote:
On Sun, Oct 30, 2011 at 03:55:21PM -0400, Mark C wrote:
Thanks - I just checked Wikipedia and got the equation for the area
of an f-stop: Area = PI x (focal length / f-stop)^2. Comparing 50mm
and 100mm confirms that the size of a 100mm f-stop is the same as
the f-stop two stops lower in number on a 50mm.
That's doing it the hard way ...
You don't need to calculate area, square any values, etc.
F-stop is simply the ratio between aperture diameter and focal length.
So the same plate (with, by definition, the same diameter aperture)
will have f-stops that differ by a factor of X (two, in your case) when
used with lenses that have focal lengths that differ by a factor of X.
Sincerely,
Collin Brendemuehl
"He is no fool who gives what he cannot keep to gain what he cannot lose"
-- Jim Elliott
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Don't lose heart! They might want to cut it out, and they'll want to avoid a
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