You did in 3 sentences what took me 1/2 a page! Concise people irritate me! ;-)
Heh. But you did point out the important difference between aperture and f-stop, and the relationship for consistant exposure.
One other thing to consider is that f-stop simply represents a physical ration between focal length and aperture, and does not take light transference of the lens into account. A lens could have an opaque element and still be considered F/2.8, though you'd find it has quite a different exposure requirement :)
This is not true of cine-lens "T-Stops", which are like F-Stops but also account for light transferrence falloff in different lenses to produce a precise exposure setting.
Love, Light and Peace, - Peter Loveday Director of Development, eyeon Software
