To: "scottythefiddler" 
From: Stan Truitt 
Cc: 
Reply-To: Stan Truitt 


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Aloha Scotty,

>Especially curious, (for me, anyways), is why does the optical surface of m=
y
>uncoated black vitrious ceramic mirror appear black from every angle, and
>still become more reflective at low angles of incidence?   It is hard to
>attribute reflectivity to surface smoothness alone, when coating the same
>surface with silver or aluminum will increase its reflectivity several
>times.
>
>Wutsup?

Of the many modes of reflection, there are two main types of interest to
ATMs, specular and diffuse.  How much of each type contributes to
reflections of glassy (dielectric) surfaces is a function of surface finish
and polarization.  A roughened surface has mostly diffuse reflections, and
a smooth (polished) one has mostly specular reflections.  Graphs of those
Fresnel (specular) reflectances are at the bottom of:

http://www.infoline.ru/g23/5495/Physics/English/rays_txt.htm

And you will notice that both polarizations have very high reflectance at
high angles of incidence, consistent with your personal observations of
dielectric materials.

Metallic reflections are a bit different.


Hope this helps,

Stan Truitt            20=B0 51'  N,  156=B0 22'  W,    511 meters MSL
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ATM Fresnel reflection, was Ebony Star et
al.

Aloha Scotty,

Especially curious, (for me,
anyways), is
why does the optical surface of my uncoated black vitrious
ceramic mirror appear black from every angle, and
still become more reflective at low angles of
incidence?   It is hard to
attribute reflectivity to surface smoothness alone, when coating the same
surface with silver or aluminum will increase its reflectivity several
times.

Wutsup?

Of the many modes of reflection, there are two main types of
interest to ATMs, specular and diffuse.  How much of each type
contributes to reflections of glassy (dielectric) surfaces is a function of
surface finish and polarization.  A roughened surface has mostly
diffuse reflections, and a smooth (polished) one has mostly specular
reflections.  Graphs of those Fresnel (specular) reflectances are
at the bottom of:

http://www.infoline.ru/g23/5495/Physics/English/rays_txt.htm
>

And you will notice that both polarizations have very high
reflectance at high angles of incidence, consistent with your personal
observations of dielectric materials.

Metallic reflections are a bit different.


Hope this helps,

Stan
Truitt           
20=B0 51'  N,  156=B0 22' 
W,    511 meters MSL


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