Great Idea! and some replies

[T3D <JValaVIDI@xxxxxxx>]

  What an excellent idea, Thank you John for including me!  I'm going to
compile a few responses into one so please read on.

About 3D SEM:  From what I recall about how an SEM actually captures an image
it seems as though the only way it could work is by tilt!  Correct me if I
start loosing it here but, what you get from the camera is the result of an
incredibly slow electron beam scanning over the surface of your specimen at
the same rate an electron beam is scanning over the phosphor screen of the
CRT in the camera.  The intensity of the phosphor is directly related to the
amount of current flowing down the single stream from the electron gun, to
the sample, out the stage, and into the amplifier to the CRT, or in the case
of back-scattered, into the detector.  I can't see any element along the way
that would act as a "lensing" element which we could apply to standard
geometric optics.  The way I see it, imaging with an SEM is a fortunate
phenomenon and shouldn't be confused with customary optical imaging.  What I
see the "tilt" doing is slightly modifying the "infliction" of the electron
beam with the sample causing the subtle variations in both position and
surface luminance that we will later perceive as stereo.  Did that make
sense?

About Parabolic reflectors:  Those are funny things!  Actually, the "output"
of a parabolic reflector more closely resembles the output of a point source
X distance from a flat surface.  Imagine a point source 3 inches from a white
surface.  The area of the surface closest to the source would be the
brightest and fall off as you moved farther away from "ground Zero" (of
coarse).  The same thing happens with a parabolic reflectors projected beam.
 The rays that originate from points closer to the optical axis (the Vertex)
will be "brighter" than those that had to diverge and travel some distance
before they were reflected by the mirror surface and sent on their way out.
 Therefore, there will be a higher "density" of rays near the optical axis
which will fall off in intensity as they get farther off axis. BUT!!..... the
nice feature is they will be PARALLEL or collimated, and that's not something
just any old reflector can do!

About Lambertian Surfaces:  By far the best reflector for the type of viewer
we usually discuss here would be one which has a spherical or (more feasibly)
a cylindrical shape.  In this case the "point source" would be positioned at
the center of curvature.  All light rays would travel the same distance
before hitting the surface and would therefore be the same intensity upon
incidence (remember the surface of a parabola just keeps getting farther and
farther away in distance from the source as you go from the Vertex to the
Latus Rectum!).  Since the surface is coated with a Lambertian material, it
really won't matter how close or far away the reflecting surface is to the
film gate, it will all look the same intensity.  Remember...., that rule
about light intensity falling off with the square of the distance ONLY
applies to point sources of light!  NOT distributed sources like wide area
Lambertian surfaces.  I have done a lot of work with Lambertian coated
Integrating Spheres and have always been amazed at how surprisingly uniform
they can make light based on such a simple principle.  I was so impressed by
it I got some patents for a light source that employed the principle.

   Again, I think this new list is an excellent idea and I applaud you guys
for organizing and maintaining it.  I was really getting tired of gleaning
through Photo-3d looking for something good to read.

John Vala


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