I rendered some mirascope animations to easily get an idea of what
configurations would give good results.  To get a good handle on what I
was seeing, I used an object somewhat more complex than a cube, with a
gradient pigment for improved discernment.  The dimensions I used are
annotated at the upper left of the frames, with HEIGHT referring to the
height of the bottom mirror.  For mirascope-02.mp4, I used the
proportions from the illustration at the University of Wisconsin at
Madison at the link BE posted in p.general:

https://www.physics.wisc.edu/ingersollmuseum/exhibits/opticscolor/parabolicmirrorillusion/

That model has a rather small opening, so I rendered mirascope-04.mp4
with double the hole diameter.

It is not easy to see both the object and its reflected apparitions
simultaneously.  With both diameters, there was an angular sweet spot
between when the object itself appears, and when the opening becomes
reflected in the bottom mirror.  At low viewing angles, only the
reflections are visible.  As the viewing angle gets higher, the
reflection of the opening appears soon after the top of the actual
object comes into view, then expands quite rapidly.  At higher viewing
angles, the reflections cannot be seen.

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Attachments:
Download 'mirascope-02.mp4.dat' (260 KB) Download 'mirascope-04.mp4.dat' (306 KB)

Cousin Ricky <ric### [at] yahoocom> wrote:
> To get a good handle on what I
> was seeing, I used an object somewhat more complex than a cube, with a
> gradient pigment for improved discernment.

Yeah, I just used a bozo pigmented cube.

I like the animation - it certainly looks very much like a real mirascope, wrt
the reflections.   I do think that we're missing the "sweet spot" that really
sells the illusion.

https://www.youtube.com/shorts/7gD_aXh6nx4
https://www.youtube.com/watch?v=mbBQ1vK0ELo

I'm gonna say that maybe it's the diameter of the viewing aperture, since I'm
speculating that maybe there aren't too many parabolic mirror dimensions that
satisfy the requirements?

It looks like we need to capture that first real image that appears when you
start looking into the aperture, but make the other reflections not very
visible.  I also get a sense from the videos that maybe the mirrors they are
using are somehow flatter than what you've got.

Your POV-Ray logo has an inverted reflection visible behind the real image, and
the real image sits too deep in the aperture to make it actually look like it's
floating on top of the hole.
It's even worse with the larger aperture.

I'm juggling teen-agers, but maybe you can just use the small aperture to make
another animation where you vary the parabola dimensions, and see if you can get
the logo to "rise up" out of the depths of the device.

Excellent work!

I'm also interested in seeing if the "shine a laser onto the real image" trick
works as well.That's one of the most surprising aspects of the illusion.

- BW

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