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Here's a simple enough question...
Is it possible for a transparent substance to be non-reflective? Or are all
transparent substances inherantly reflective to a certain degree?
Just wondering...
Andrew.
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> Is it possible for a transparent substance to be non-reflective? Or
are all
> transparent substances inherantly reflective to a certain degree?
I doubt such a substance exists. If something was truly non-reflective,
it would be perfectly invisible, unless it was absorbing light against a
background or was emitting light itself. I can't think of anything that
is perfectly invisible like that, though I should think that some gases
come close, but perhaps only on account of their low density under
Earthly conditions.
And there would also be the problem of total internal reflection.
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Andrew Coppin wrote:
> Here's a simple enough question...
>
> Is it possible for a transparent substance to be non-reflective? Or are
> all transparent substances inherantly reflective to a certain degree?
>
> Just wondering...
> Andrew.
Certainly within the realm of the visible. You don't see your reflection in
the air do you?
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Hmm... gases don't *appear* reflective... but does a gas have a surface???
Andrew.
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On Thu, 8 May 2003 08:32:30 +0100, "Andrew Coppin" <orp### [at] btinternet com> wrote:
> Hmm... gases don't *appear* reflective... but does a gas have a surface???
Between your eye and gas ?
ABX
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> Is it possible for a transparent substance to be non-reflective? Or are all
> transparent substances inherantly reflective to a certain degree?
I always assumed that if light travels into a denser medium (with higher
ior), some of it will be reflected, because "the light does not want to
go through the trouble of traveling through a dense medium". On the other
hand there will be no reflection (except total reflection), when light
travels into a coarser (?English? less dense?) medium.
To make this post on-topic: That's why I always switch reflection off for
the interior_texture of glass and water materials.
Now all of that was assumptions. Can anybody who knows better please
- tell us if that was right?
- give us a formula for the correct reflection value between different
ior's (assuming it does not depend on anything else)?
--
merge{#local i=-11;#while(i<11)#local
i=i+.1;sphere{<i*(i*i*(.05-i*i*(4e-7*i*i+3e-4))-3)10*sin(i)30>.5}#end
pigment{rgbt 1}interior{media{emission x}}hollow}// Mark Weyer
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OK, well, a lump of shashed up ice doesn't look reflective at all... but
take a bit and polish it to give it a nice smooth surface and you find that
it actually IS reflective. Was thinking, if you have a layer of gas, it's
surface probably isn't smooth, which might explain why it doesn't look
reflective.
If that makes sense.
Andrew.
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On Thu, 8 May 2003 08:48:09 +0100, "Andrew Coppin" <orp### [at] btinternetcom> wrote:
> OK, well, a lump of shashed up ice doesn't look reflective at all...
But I think it is reflective, just with a lot of blur :-)
> Was thinking, if you have a layer of gas, it's
> surface probably isn't smooth, which might explain why it doesn't look
> reflective.
On desert you can see images in the air. You know how ?
http://www.islandnet.com/~see/weather/graphics/photos/supmirag.gif
ABX
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Andrew <ast### [at] hotmailcom> wrote:
> If something was truly non-reflective,
> it would be perfectly invisible
A transparent object which refracts light is never invisible.
--
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}// - Warp -
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Andrew Coppin wrote:
>
> Here's a simple enough question...
>
> Is it possible for a transparent substance to be non-reflective? Or are all
> transparent substances inherantly reflective to a certain degree?
Reflection is an inherent effect on all interfaces between materials of
different optical density (i.e. ior, speed of light in the material)
The amount of reflection depending on the incident angle and the materials
can be calculated with the fresnel equations. This works for both a
transit from less dense to more dense medium as well as the other way
round. More information can be found in the links from:
http://www-public.tu-bs.de:8080/~y0013390/pov/water/water_app1.html#reflect
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______
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At school a teacher told us that reflection is caused if the surface is
electroconductive (at the frequency of the light-wave). In that case it
will "short-circuit" the "electric part" of the wave (light is an
electromagnetic-wave) - because the electric and the magnetic vectors
are perpendicular the angle of reflection is equal to the angle of
incidence.
I have got no idea if this is true - could be complete nonsense...
-sascha
Christoph Hormann wrote:
>
> Andrew Coppin wrote:
>
>>Here's a simple enough question...
>>
>>Is it possible for a transparent substance to be non-reflective? Or are all
>>transparent substances inherantly reflective to a certain degree?
>
>
> Reflection is an inherent effect on all interfaces between materials of
> different optical density (i.e. ior, speed of light in the material)
>
> The amount of reflection depending on the incident angle and the materials
> can be calculated with the fresnel equations. This works for both a
> transit from less dense to more dense medium as well as the other way
> round. More information can be found in the links from:
>
> http://www-public.tu-bs.de:8080/~y0013390/pov/water/water_app1.html#reflect
>
> Christoph
>
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> A transparent object which refracts light is never invisible.
...unless it's an even-thickness slab, viewed exactly square-on *grin*
Andrew.
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> Reflection is an inherent effect on all interfaces between materials of
> different optical density (i.e. ior, speed of light in the material)
Right. That would seem to explain why no one has ever managed to make
invisible glass for windows yet...
> The amount of reflection depending on the incident angle and the materials
> can be calculated with the fresnel equations. This works for both a
> transit from less dense to more dense medium as well as the other way
> round. More information can be found in the links from:
>
>
http://www-public.tu-bs.de:8080/~y0013390/pov/water/water_app1.html#reflect
...and once again I'm left saying I'll check it out later... oh to have more
time! lol
Thanks.
Andrew.
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On Thu, 8 May 2003 21:54:54 +0100, "Andrew Coppin"
<orp### [at] btinternetcom> wrote:
>...unless it's an even-thickness slab, viewed exactly square-on *grin*
You'll see the edges and side walls due to perspective unless the side
walls are parallel to the viewing rays, but then again you'll have to
look at it with one eye closed.
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG e-mail : pet### [at] tagpovrayorg
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In article <3eb95e52@news.povray.org>,
"Andrew Coppin" <orp### [at] btinternetcom> wrote:
> Is it possible for a transparent substance to be non-reflective? Or are all
> transparent substances inherantly reflective to a certain degree?
All known substances are reflective to some degree. (Though neutronium
may be an exception...)
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/
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In article <3eba0869@news.povray.org>,
"Andrew Coppin" <orp### [at] btinternetcom> wrote:
> Hmm... gases don't *appear* reflective... but does a gas have a surface???
Mirages. The varying density can cause reflections.
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/
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In article <3eba0c14$1@news.povray.org>,
"Andrew Coppin" <orp### [at] btinternetcom> wrote:
> OK, well, a lump of shashed up ice doesn't look reflective at all...
Ice is very reflective. That's why you can see it.
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/
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Christopher James Huff <cja### [at] earthlinknet> wrote:
> Mirages. The varying density can cause reflections.
You don't mean variable refraction?
--
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -
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In article <3ebbd2fb@news.povray.org>, Warp <war### [at] tagpovrayorg>
wrote:
> > Mirages. The varying density can cause reflections.
>
> You don't mean variable refraction?
I do, and don't. The varying density causes varying optical density,
which produces variable refraction. If things are set up properly, you
can end up with reflections from a layer of hot air which look a lot
like water.
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/
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> Is it possible for a transparent substance to be non-reflective? Or are
all
> transparent substances inherantly reflective to a certain degree?
Every transparent substance is reflective and is not.
If you are in water, a glass with ior of water won't reflect anything.
If you have an interface, it's reflection, if you have a gradient of ior
(like hot air on the road), you have some refraction.
That's all.
Now, try to think about a relation between ior and reflectivity...
selsek
new feature requested: auto_reflection :-))
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> On desert you can see images in the air. You know how ?
> http://www.islandnet.com/~see/weather/graphics/photos/supmirag.gif
On hot roads too, you know...
It's an ior gradient.
You can easily reproduce this phnomenon in pov... and get max_trace_level
very high. (you put boxes with progressive ior and check the result).
selsek
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On Wed, 07 May 2003 15:26:48 -0400, Andrew Coppin wrote:
> Here's a simple enough question...
>
> Is it possible for a transparent substance to be non-reflective? Or are
> all transparent substances inherantly reflective to a certain degree?
If you work at it hard enough ... If you look at it as an impedance
mismatch causing the reflection then you can layer materials on a surface
which "match" the impedance of air to glass. That gives a number of
smaller reflections which sum to less than the single reflection without
them. That is all the anti-reflection coatings do on lenses.
If you could apply a single layer that smoothly transitioned the IOR from
air to glass you would theoretically have no reflection as there would not be a
point of different IORs -- unless a low pressure front moves in or the
humidity changes.
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On Thu, 08 May 2003 06:17:03 -0400, Warp wrote:
> Andrew <ast### [at] hotmailcom> wrote:
>> If something was truly non-reflective, it would be perfectly invisible
>
> A transparent object which refracts light is never invisible.
Observable and invisible are different things. A gravitational lens is
invisible but observable. The hot air over a road is invisible but
observable by the turbulent distortion.
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On Wed, 07 May 2003 15:26:48 -0400, Andrew Coppin wrote:
> Here's a simple enough question...
>
> Is it possible for a transparent substance to be non-reflective? Or are
> all transparent substances inherantly reflective to a certain degree?
>
Also the turbulent hot air over a road in summer is an example of
smoothly varying IOR that does not in itself reflect. We cannot see the
turbulence whorls themselves as they do not reflect because of the
smoothly varying IOR.
The shallow angle mirage is somewhat different phenomenon.
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On Thu, 08 May 2003 03:48:09 -0400, Andrew Coppin wrote:
> OK, well, a lump of shashed up ice doesn't look reflective at all... but
> take a bit and polish it to give it a nice smooth surface and you find
> that it actually IS reflective. Was thinking, if you have a layer of
> gas, it's surface probably isn't smooth, which might explain why it
> doesn't look reflective.
>
> If that makes sense.
>
Smoothed up it is specular reflection which is a special case of
reflection. The gas has a smoothly varying IOR so it does not have a
reflective surface.
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On Tue, 13 May 2003 17:02:50 -0400, selsek wrote:
>> On desert you can see images in the air. You know how ?
>> http://www.islandnet.com/~see/weather/graphics/photos/supmirag.gif
>
> On hot roads too, you know...
> It's an ior gradient.
> You can easily reproduce this phnomenon in pov... and get
> max_trace_level very high. (you put boxes with progressive ior and check
> the result).
>
Shallow angle reflection is a different issue. A sheet of glass is
totally reflective at a shallow angle.
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simian <sim### [at] localhostlocaldomain> wrote:
> Observable and invisible are different things.
Right. They are opposite things.
> The hot air over a road is invisible but
> observable by the turbulent distortion.
It can't be invisible if it's observable. :)
--
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}// - Warp -
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"Andrew Coppin" <orp### [at] btinternetcom> a écrit dans le message de news:
3eba0869@news.povray.org...
> Hmm... gases don't *appear* reflective... but does a gas have a surface???
The point is IOR variation : on a hot tarmac you can observe air reflecting
the sky because the temperature of the air film is higher than the ambient
air.
If you have density variation between 2 medias or inside a media, you get
refraction (and reflection if the ior gradient is high enough).
Marc
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In article <3ec4ecee@news.povray.org>,
"Marc Jacquier" <jac### [at] wanadoofr> wrote:
> "Andrew Coppin" <orp### [at] btinternetcom> a écrit dans le message de news:
> 3eba0869@news.povray.org...
> > Hmm... gases don't *appear* reflective... but does a gas have a surface???
> The point is IOR variation : on a hot tarmac you can observe air reflecting
> the sky because the temperature of the air film is higher than the ambient
> air.
> If you have density variation between 2 medias or inside a media, you get
> refraction (and reflection if the ior gradient is high enough).
Also, I've read somewhere about the possibility of using high-density
plasma as a mirror. This was in the context of a nuclear-pumped X-ray
laser, where the mirror didn't have to exist for more than a few
microseconds.
I'm not sure about the exact principles behind that one though...since
light interacts through electromagnetic effects, I'm guessing a
highly-ionized plasma will have quite different optical properties
compared to the neutral gas, maybe acting more metallic. One place I
know of this kind of difference is in atmospheric nitrogen lasers...they
lase in the ultraviolet range, but produce very short pulses because the
lasing medium (atmospheric pressure air with a corona discharge through
it) becomes highly opaque to the wavelength being emitted.
And this is all about specular reflection...gases do reflect diffusely,
scattering in other words. For example, our atmosphere scatters blue
wavelengths more than red ones, making the sky appear blue except for at
sunrise and sunset, where you're seeing the wavelengths that weren't
scattered as highly. This effect is enhanced by dust in the air, but I
don't think it depends on it.
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/
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On Fri, 16 May 2003 11:16:15 -0400, Christopher James Huff
<cja### [at] earthlinknet> wrote:
>For example, our atmosphere scatters blue
>wavelengths more than red ones, making the sky appear blue except for at
>sunrise and sunset, where you're seeing the wavelengths that weren't
>scattered as highly. This effect is enhanced by dust in the air, but I
>don't think it depends on it.
It's just that the nitrogen molecule scatters blue. Dust can be of any
color, making up for some gorgeous sunsets after a sandstorm (we had
some last month when a heat wave from North Sahara hit us.)
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG e-mail : pet### [at] tagpovrayorg
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On Fri, 16 May 2003 08:57:32 -0400, Warp wrote:
> simian <sim### [at] localhostlocaldomain> wrote:
>> Observable and invisible are different things.
>
> Right. They are opposite things.
>
>> The hot air over a road is invisible but observable by the turbulent
>> distortion.
>
> It can't be invisible if it's observable. :)
Assume wise expression and far away look.
Can you see the wind, Grasshopper?
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simian wrote:
> Assume wise expression and far away look.
> Can you see the wind, Grasshopper?
Trees moving back and forth makes the wind blow.
--
Tim Cook
http://home.bellsouth.net/p/PWP-empyrean
-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------
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In article <9l1acvo9rnd6u8ci0pehb6qv6pvguudkla@4ax.com>,
Peter Popov <pet### [at] vipbg> wrote:
> It's just that the nitrogen molecule scatters blue. Dust can be of any
> color, making up for some gorgeous sunsets after a sandstorm (we had
> some last month when a heat wave from North Sahara hit us.)
Well, dust can be of any colored substance, but particles of the size
that will stay in the atmosphere for any significant amount of time are
small enough that they scatter blue wavelengths more. Similar to the
reasons shorter wavelengths are used for higher magnification microscopy.
Try pouring a little milk into a glass of water and shine a flashlight
through it...depending on the angle you observe it at, the scattered
beam will appear blue or orange.
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/
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On Fri, 16 May 2003 21:39:44 -0400, Tim Cook wrote:
> simian wrote:
>> Assume wise expression and far away look. Can you see the wind,
>> Grasshopper?
>
> Trees moving back and forth makes the wind blow.
Is the rippling grass to be ignored because we trample it underfoot?
Are the clouds to be forgotten because we cannot reach them?
Is the man off stage with the big fan to be given no credit?
You have only answers, Grasshopper, should you not be asking questions?
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On 16 May 2003 08:57:32 -0400, Warp <war### [at] tagpovrayorg> wrote:
>
> It can't be invisible if it's observable. :)
>
You can observe something without seeing it. The meaning of "observe" is not
the same as the meaning of visible.
Regards
Stephen
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"sascha" <sas### [at] userssourceforgenet> wrote in message
news:3eba479a@news.povray.org...
> At school a teacher told us that reflection is caused if the surface is
> electroconductive
Interesting anyway. Seems this discussion is including refraction as being a
part of reflection, then I happened to think about how shallow angles cause
more reflection (Fresnel) and so could easily be thought of as a refractive
effect instead of purely a reflective one. That being to do with air or an
atmospheric effect anyhow. I don't know if this holds true for solid objects
and absolute voids (vacuum of space) or not. Never learned enough from
physics, myself, to know.
But going by what you said there, glancing lightwaves could be electrically
different than ones bouncing directly off of a surface.
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