Hey, you're way, way beyond Dr. Focus. Anything to the 4th power is
way, way beyond Dr. Focus and he's all for mitigating it, except for
them off-axis ellipticals. Is that anything like what Nathan sees at
the beach?
Dr. Focus
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
>
>
>
> have a neat trick where the aperture
>> is optically magnified (increasing the apparent size)
>> as you move off-axis, it's quite neat to see when looking into the
>> front of the lens.
>
>
>
> However, this still can't account for the fact that the light has to
>> travel more than 2x as far to the corners of
>> the film plane, than what it has to the centre. This, and only this,
>> causes the light falloff, and it's this that the
>> centre filter tries to correct.
--
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