> An f-stop is simply the ratio between the principal focal length of
the lens
> and the principle diameter of the aperture, Nothing more, nothing
less.
>
> This because the diameter needed to get an certain f-stop depends
also on
> the place of the aperture blades in the beam. Where this place is,
depends
> totaly on the design of an lens, and in a zoom-lens this place,
combined
> with the optical-design determines what influence this has on the
maximim
> f-stop it can reach.
>
> Drikus
Darn it ... I just replied then saw this ... yes, that is correct.
It is a common misconception that the actual hole left by the
diaphragm blades is the "aperture". I do wonder how the manufacturers
calculate this. is it by ray-tracing (for axial beams) or is it by
measuring light transmission and assuming an attenuation factor.
Ultimately who cares?
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