Thank you for greatly extending and technifying my simple and
incomplete explanation Mike.
However, I always thought that the Slyusarev effect (apparently
increasing pupil size)
was there precisely to counter the fact that the aperture becomes
elliptical
when viewed off-axis, so that it all "evens out".
On 21 Jul 2009, at 12:09 AM, usher99@xxxxxxx wrote:
> Well, not so fast. The inverse square law accounts for only one of
> the cosines in the Cosine**4 law. I think you are describing the
> Slyusarev effect which lens designers utilize to increases the
> apparent
> size of one or both pupils for off-axis points and greatly mitigates
> the cosine**4 law.
>
> A second factor that causes light loss off axis is that the lens pupil
> is no longer round but elliptical when viewed from the periphery. It
> also strikes at an angle off axis. There is additional attenuation
> due
> to the Lambert effect. I think that makes four, but I am tired
> after a
> long day and a couple hours left to go and can no longer count.
>
> Mike (protégé of Dr. Focus)
>
>
> see
>
> http://toothwalker.org/optics/vignetting.html
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|