>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.. >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 -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
