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. 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. > > > > -- > 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. > -- David Parsons Photography http://www.davidparsonsphoto.com Aloha Photographer Photoblog http://alohaphotog.blogspot.com/ -- 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.
