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Re: [OM] [OT] Center filters

Subject: Re: [OM] [OT] Center filters
From: usher99@xxxxxxx
Date: Mon, 20 Jul 2009 18:51:53 -0400
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) 
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