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.
