Well, to me, "lens opening" is synonymous with "the size of the hole in the
diaphragm," a/k/a the f-stop. Otherwise, that 4-inch lens with a one inch
diameter would always be f/4 -- unless somebody's figured out a way to compress
glass and metal so as to change the diameter.
Walt, aiding and abetting the counting of angels
--
"Anything more than 500 yards from
the car just isn't photogenic." --
Edward Weston
-------------- Original message ----------------------
From: Moose <olymoose@xxxxxxxxxxxxxxx>
> Walt Wayman wrote:
>
> >"The lens aperture is simply the diameter of the lens opening, expressed as
> >a
> fraction of its focal length. Thus, a lens of 4-inch focal length with a
> diameter of one inch has a relative aperture of 4/1, or 4. the aperture
> designation is expressed as f/4, indicating that the aperture is the focal
> length/4. Another 4-inch lens that has a diameter of 1/2 inch would be an
> f/8
> lens.
> >
> He also wrote earlier:
>
> Moose,
>
> I've never heard an f-stop defined by its relation to the front element.
>
>
>
> Well, now you not only have heard of it, but are quoting it. :-)
>
> Moose
>
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