Re: ATM Re: F@ prolate mirror - why

[Bob Goff <goffaxe@azstarnet.com>]

Having made one of these bastard children of optics while at PE in the 60,
all rays eminating from fhe locus of the focal ring will fall on the
portion of the focal ring on the opposite side of the centroid of the
ellipsoid withour trgard to the direction of the emination. The only
criterion for use is the source being on the focal ring. The ray could go
to Seattle and make it back to the focal ring. Or  the ray could go to the
South Pole and make it back to the focal ring which is coplanar with the
Equator.

Bob


At 04:40 PM 08/25/2001 -0700, you wrote:
>
>At 17:57 2001-08-23 -0700, Donald Qualls wrote:
>
>> > But there's a focal RING for the OBLATE ellipsoid!  What does the
light do
>> > bouncing off that surface?
>>
>>When you observe the full ellipsoid, you're seeing this behavior
>>starting from a circular locus of possible foci; essentially, light
>>generate along a ring will focus to the opposite edge of the ring,
>>providing that ring is the path of the foci of the ellipse while
>>generating the oblate ellipsoid.  This is the "focal ring" of an oblate
>>ellipsoid.
>
>I think it's MUCH messier than that.  So we have convenient terminology, 
>imagine a hollow Earth (an oblate ellipsoid) with the inner surface 
>aluminized.  The focal ring is in the equatorial plane, concentric with the 
>equator.  Take a single point of light on the ring.  We can talk rays for a 
>while (the Earth radius is, what?, 1.16E13 waves of 550 nm 
>light).  Clearly, all rays in the meridional plane through the source will 
>come to a focus at the opposite point on the focal ring.  Consider rays in 
>the equatorial plane - they meet the surface at the circular equator, but 
>they aren't coming from the center of that circle - caustics!  So we're 
>probably looking at messy 3D caustics.
>
>         -- Jim Burrows
>         --              mailto:burrjaw@earthlink.net
>         -- Seattle      N47.47233, W122.36620 (WGS84)
>
>
>
>
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