On 6/1/2013 12:09 PM, Mike Lazzari wrote:
>> And that's only the labeled f/stop. The actual f/stop is only valid at
>> infinity. The effective f/stop get numerically larger as the extension
>> increases.
> Isn't it just the physical aperture which is at issue with diffraction?
Somebody told me that, and I believed it for a while. The physical diameter of
the opening, relative to the wave length
of the light does indeed determine the amount of angular diffraction.
However, the greater the distance from aperture to chemical or electronic
sensor, the greater the displacement of the
diffracted rays from those not so affected. Another way to put it is that
greater lens extension magnifies the effect,
along with a part of the projected image.
I think I've got that right. In any case, it turns out that the math works
properly using only the actual focal ratio,
as opposed to the f-stop at infinity focus, without needing to use the physical
diameter directly.
Open Aperture Moose
--
What if the Hokey Pokey *IS* what it's all about?
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|