Yep,
Should apply at the beach as well when viewing from off axis, but
pursuing a larger sample size to confirm this would be prudent.
Mike
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 [at] aol.com 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 account20for 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.
Re: [OT] Center filters, (continued)
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|