Re: Mirage optical illusion?

wadexkelman@xxxxxxxxxxx wrote:

What's the usual _name_ of this setup, or this illusion?

I don't know that this arrangement has a particular name. (I have
one of these devices, though, and it is very interesting. Kids love
it.)
The two mirrors are actually parabolic. The object placed in the
center of the bottom mirror is at the focus of the upper parabola.
Its light is collimated and directed at the lower mirror, which then
forms a real image (Phil was right!) at its focus at the opening on
the top mirror.
Additional images, seen further off-axis, are due to multiple
bounces. They're not as well imaged, though.

So it doesn't have a common or historical name, in optics texts or
encyclopedias and such? I guess we'll have to refer to it as the
"Hobbs-Kelman illusion" (or the "Kelman-Hobbs delusion" -- you
guys can fight over whose name goes first).

One can actually see two quite distinct images of the object, one
upright and located just above the surface of the opening, the other
upside down and just under that surface.

There's actually a potentially quite useful practical application of a
variant on this idea that's occurred to me -- but I can't publish it
here 'til I talk to my patent attorney . . .
.

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