One sided mirror
PV
reflective from other side. Could anyone please help me where I can find
it? My application is to illuminate the object from the transparent side
and reflected image will be used from the other side for image collection.
Thanks in advance
PV
Tony Spadaro
transparent on both sides (which if you think about it, is the only posible
way). The side that is lit is visible from the side that is dark. Change the
lighting so the dark chamber is light and the light one goes dark and the
"transparancy" will shift.
All those movies with one way mirrors are very inaccurate unless the
viewing room is shown as being dark.
--
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home of The Camera-ist's Manifesto
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"PV" <psiv...@hotmail.com> wrote in message
news:3F04E711...@hotmail.com...
Luke
directed, parrallel, beam of light through the glass and then taking the
shot at an angle to the half silvered side.
I think you would find it easier to just shoot the subject in a normal
mirror, at an angle. If you possition the lights carefully you will be albe
to light the subject with light reflected off the mirror without the light
source appearing in the image. You can start with a light just next to your
cammera, a standard flash for example.
Luke
"Tony Spadaro" <tspa...@ncmaps.rr.com> wrote in message
news:CJ5Na.230401$jp.60...@twister.southeast.rr.com...
Charlie D
<http://www.scientificsonline.com/ec/Products/Display.cfm?CategoryID=1928
41>
--
Charlie Dilks
Newark, DE USA
Joseph Meehan
suggesting. However by lighting around a smaller mirror or by reflecting
light off the mirror to illuminate the back of the object you should be able
to do what you want.
It really sounds like you may want to use a light tent with a mirror
inside.
--
Joseph E. Meehan
26 + 6 = 1 It's Irish Math
"PV" <psiv...@hotmail.com> wrote in message
news:3F04E711...@hotmail.com...
David Lee
degrees to the line between them. A fraction of the light will pass
through the glass and illuminate the object whilst the rest will be
reflected at 90 degrees. Likewise with light returning from the object -
part will be transmitted and will return along the same path to the light
source whilst the rest will again be reflected a 90 degrees but in the
opposite direction to that directly from the light source. Thus you divide
the light into two at each pass through the mirror and separate the light
from the object from the 'waste' light from the lamp. It's easier to
imagine than to describe. I'm not good at ASCII art but the sketch below
may help. This is the closest you will get to an "optical check valve".
The mirror can either be a piece of plain glass, in which case you will
maximize the illumination of the object, or else a partially silvered
mirror in which case you will get less illumination but maximize the
collection of light from the object. Plain glass is usually fine.
This is a standard way of illuminating objects for microscopy or macro
photography and also the principle of operation of the autocue and Pepper's
Ghost.
HTH
David
mirror (at 45 degrees)
^ /
| /
| /
| /
|/
LIGHT - - - - - - - >/<-·-·-·-·-·-·-> OBJECT
/·
/ ·
/ ·
/ ·
/ ·
·
V
CAMERA
PV <psiv...@hotmail.com> wrote in article
<3F04E711...@hotmail.com>...
Don Stauffer
demon, and end up with a really need solar power system.
Joseph Meehan wrote:
>
> As the others have said, I don't think you can do exactly what you are
> suggesting.
--
Don Stauffer in Minnesota
stau...@usfamily.net
webpage- http://www.usfamily.net/web/stauffer
H.J.P. Vink
probably the reflected light from the object of not completely polarised
anymore....
Rob.
"PV" <psiv...@hotmail.com> wrote in message
news:3F04E711...@hotmail.com...
Don Klipstein
>Here's one.
><http://www.scientificsonline.com/ec/Products/Display.cfm?CategoryID=1928
>41>
This is a beam splitter. It does not work even to a partial extent as a
check valve. The "loss" (diversion) along/from any given path would be
the same in both directions.
Optical check valves appear impossible to me because:
Suppose you have a closed system which consists of a blackbody chamber -
say, some isolated completely closed room. This room is at some
certain temperature and blackbody radiation exists in it.
Now, suppose you had an "optical check valve" wall and divided this room
with it. There would be a net flow of energy from one side of the wall to
the other. The temperature would rise on one side and fall on the other
side. You would be able to string a pair of thermocouples in this room,
one on each side, and have that turn en electric motor to do work. Or you
could set up some other heat engine in this divided room to do work. Have
the heat coming from friction in whatever work you are doing go into the
hot side. Maybe the motor could just turn a fan or something decorative
to demonstrate the principle.
Obviously, this would have the entropy in the closed system decrease
from where it was before the optical check valve started doing its thing.
And it would be a perpetual motion machine. As far as I understand it,
the assumption that such things cannot work has been used to prove
Einstein's photoelectric loss, and a similar (bandwidth and intensity
dependent) loss in photovoltaic semiconductors.
This brings me to directional couplers (a radio frequency device) which
I have heard of but I don't know exactly what they do nor how they work.
But if you had a divided blackbody chamber with blackbody radiation
including some radio frequency, I doubt you can make a perpetual motion
machine by putting an antenna in each side and putting a directional
coupler between them.
- Don Klipstein (d...@misty.com)
David
used in LASER applications and are very common. I have several 2 inch square
ones now. They came from old grocery store check stand scanners. You should
be able to find them at a LASER hobbyist store. :)
PV
help me get one.
Thanks you all the others for your valuable discussion and ideas.
I wonder, whether I can find a beamslitter which should has one side
with higher transparency and other side with higher reflection.
Where can I find such a beamsplitter? Any help.
Thanks in advance.
PV
Chris L Peterson
>I really like to try this Brewster's Mirror. Could you or someone please
>help me get one.
>Thanks you all the others for your valuable discussion and ideas.
>I wonder, whether I can find a beamslitter which should has one side
>with higher transparency and other side with higher reflection.
>
>Where can I find such a beamsplitter? Any help.
Sorry, this won't work. The simple fact is that there is no such thing as an
optical element that is transparent in one direction and reflective in the
other.
Brewsters windows seem a bit like they work this way, but in fact this is only
because of the way polarized light reflects. A Brewster window is nothing more
than a piece of glass tilted at the correct angle.
Unless you can very specifically control the polarization of the light, and
maintain it after it reflects from you object, the closest you are going to come
to your goal is by using a beam splitter. The more reflective the splitter, the
more light from your object will reflect, but the less light from your source
will make it through.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
Luke
>
> Sorry, this won't work. The simple fact is that there is no such thing as
an
> optical element that is transparent in one direction and reflective in the
> other.
>
This is true, but you can get an element which has the same transmission
from both directions but also high reflectivity on one side and low
reflectivity but high absorption on the other:
(usual physical terminology would be 'emissivity' rather than 'absorption',
but the two are aways equal)
Conservation of energy says that transmission through the entire optical
system must be the same from both directions (as someone suggested look up
'Maxwell's demon' if you want convincing).
Conservation of energy (COE) does not imply that the other optical
properties of the surfaces must be the same. What it does say is:
transmission + reflection + absoption = 1
(it is worth noting the reflection may be diffuse or specular, that doesn't
effect COE but does effect the optical properties.)
So it is possible to have a sheet of glass that is say 50% transmissive in
both directions and 50% reflective from one side but 0% reflective and 50%
absorbative from the other side. This is what people try to achive when
making one way mirrors.
Yes there is no such thing as a perfect one way mirror, but they do only
function as a mirror from one direction.
Luke
Chris L Peterson
>This is true, but you can get an element which has the same transmission
>from both directions but also high reflectivity on one side and low
>reflectivity but high absorption on the other:
Sure, the best example being a plate of matte black material that is aluminized
on one side. [Approximately] 100% reflective on one side, 100% absorptive on the
other. But it sure doesn't do what PV is looking for!
I think the best he's going to get is 50% reflectivity, 50% transmissivity.
>So it is possible to have a sheet of glass that is say 50% transmissive in
>both directions and 50% reflective from one side but 0% reflective and 50%
>absorbative from the other side. This is what people try to achive when
>making one way mirrors.
I think typical one-way mirrors are more like 75% reflective. And they don't
have any preferred side- you can install them either way and they work just the
same.
Dave Martindale
> This brings me to directional couplers (a radio frequency device) which
>I have heard of but I don't know exactly what they do nor how they work.
There are a number of different ways to build directional couplers, but
(as you surmised) they don't provide a perpetual motion machine, nor are
they a one-way valve. They just control where a signal goes to.
One type of directional coupler is the splitter/tap used in cable TV
systems. A signal that arrives at the "input" is distributed to each
of the "outputs" in a specified power ratio. If the splitter is on
the pole in front of your house, there's one output that receives
almost all the signal, which is the main cable feed continuing down the
street, and one or more house-feed taps that may get a signal that's 20
or 30 dB down from what's on the main cable. But it's a passive device,
so the sum of the signal power in all of the outputs is always less than
the input power.
Its use as a splitter is pretty mundane, but any passive splitter also
works as a combiner when the signals arrive from the other direction. A
signal coming in one of the "outputs" is passed through to the "input",
without also being fed to the other "outputs". In other words, a signal
headed "upstream" continues upstream, without the other "downstream"
outputs seeing it. That's why it's called a directional coupler:
direction of the signal matters.
Dave
PV
0/50 beam splitter. If anyone (mmm..Laser people:-) has any idea where I
can get the Brewster's mirror, please let me know...
I really like this thread to go on and discuss further, since I am
interested in knowing any other solutions for this problems/or similar.
It is really great to read all your valuable ideas...and Thanks YOU ALL
againa and again.
PV
Chris L Peterson
>Thank you all. I am going to try both the Brewster's mirror and 5the
>0/50 beam splitter. If anyone (mmm..Laser people:-) has any idea where I
>can get the Brewster's mirror, please let me know...
There is no such thing as a Brewster's mirror- it is just a flat piece of glass.
When you have a plane wavefront incident on the boundary between materials with
different indices of refraction, there is an angle where linearly polarized
light is 100% transmitted. This angle is called Brewster's angle, and is around
57 degrees for an air/glass interface. A Brewster window is very useful when
working with lasers, as it provides a mechanism for getting the beam out of a
sealed tube without losses. But in a natural setting, the only implication of
Brewster's angle is a very minor variation in reflectivity off the surface
depending on the angle and polarization of light hitting it. It is unlikely you
would be able to detect this visually.
Daniel P. B. Smith
"Tony Spadaro" <tspa...@ncmaps.rr.com> wrote:
> SO called one way mirrors are actually half silvered. THey are partially
> transparent on both sides (which if you think about it, is the only posible
> way). The side that is lit is visible from the side that is dark. Change the
> lighting so the dark chamber is light and the light one goes dark and the
> "transparancy" will shift.
> All those movies with one way mirrors are very inaccurate unless the
> viewing room is shown as being dark.
Such a mirror plays a role in Arthur C. Clarke's novel "Childhood's
End." The protagonists have interviews with an alien creature who will
only talk to them from behind a pane of "one-way" glass. So they
smuggle in very bright battery-powered light concealed in an attach
case. The light has a hood arrangement; by jamming it against the
one-way glass and turning it on, they light the room on the far side
brightly enough to see what's in it.
Another thing to be noted about "one-way" mirrors is that in real life
they're usually easy to spot, for a couple of reasons. First, if you
start paying attention to how _bright_ the reflection in a mirror is,
you'll see that for a real mirror, the reflection is _almost_ a match
for the scene being reflected, looking only _slightly_ dimmer. In a
"one-way" mirror the reflectivity is usually low enough so that the
reflection looks suspiciously dim, noticeably dimmer than the scene
being reflected. Other giveaway, of course, is that such mirrors are
often in locations that aren't very logical places for mirrors. And
frequently are mounted in a frame that looks much more like a
windowframe than a picture frame. I remember an airport in Venezuela
that had a whole row of "mirrors" that were mounted on a wall about
fifteen feet above the floor. Of course, it's quite possible that they
didn't care at all whether people thought they were mirrors; the
important thing was that you couldn't tell whether or not you were being
watched.
--
dpbsmith at world dot std dot com
(replace "at" with at-sign and "dot" with period and remove spaces)
Dave Martindale
>A Brewster window is very useful when
>working with lasers, as it provides a mechanism for getting the beam out of a
>sealed tube without losses.
Isn't it also what's used to force a beam to be polarized in the first
place? The idea that a piece of glass at Brewster's angle allows one
polarization to pass back and forth without loss, while the orthogonal
polarization suffers some loss in each pass and is attenuated to
extinction. This works with external-mirror lasers, where the Brewster
window is part of the tube envelope, and with integral-mirror lasers
where there's just a piece of glass at the right angle inside the tube.
Dave
Chris L Peterson
wrote:
Exactly. And since the stimulated emission (the SE in LASER) maintains the
polarization of the stimulating photon, the polarization selected by the
Brewster window ends up being the only one the cavity will support.
James Horn
instance, if you have a two polarizers in parallel with their axes rotated
45 degrees from each other and put a polarization rotating medium between
them that rotates the light 45 degrees (a solution of sugar for home
experimenters), light travelling one way will only have the ganged
polarizer loss (about 50%) but the other way will see *crossed* polarizers
(over 99%). Small units for directional control in fiber optics are
available off the shelf.
For radio frequencies, look up "circulators" - a staple in microwave
systems.
Jim Horn, WB9SYN/6
Chris L Peterson
>By the way, non-reciprocal optical devices exist and are available. For
>instance, if you have a two polarizers in parallel with their axes rotated
>45 degrees from each other and put a polarization rotating medium between
>them that rotates the light 45 degrees (a solution of sugar for home
>experimenters), light travelling one way will only have the ganged
>polarizer loss (about 50%) but the other way will see *crossed* polarizers
>(over 99%). Small units for directional control in fiber optics are
>available off the shelf.
Unfortunately for the original poster, however, such devices won't do what he
wants. I don't know of anything that can do this with white light that has
scattered off a random object (like a person) of varying color and texture.
There might be some exotic non-linear optical element like this, but certainly
not something the size of a normal mirror!
Harvey
"James Horn" <jim...@svn.net> wrote in message
news:vgk4v64...@corp.supernews.com...
It will *not* work with the sugar solution or any other optically active
material.
It has to be a material exhibiting the Faraday efffect, in a magnetic field,
often a high Verdet constant glass (often Tb doped) or crystal (a garnet as
I recall.)
Microwave circulators & isolators use the same effects in ferrites, & also
need a magnetic field.
Harvey
Paul Hovnanian P.E.
>
[snip]
> I remember an airport in Venezuela
> that had a whole row of "mirrors" that were mounted on a wall about
> fifteen feet above the floor. Of course, it's quite possible that they
> didn't care at all whether people thought they were mirrors; the
> important thing was that you couldn't tell whether or not you were being
> watched.
Post offices use these quite often. They are used by postal inspectors
looking for theft. The employees know what the mirrors are for but have
no way of knowing when inspectors are watching them.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Where am I going, and what am I doing in this handbasket?
Tzortzakakis Dimitrios
? "Paul Hovnanian P.E." <pa...@hovnanian.com> ?????? ??? ??????
news:47AF9DED...@hovnanian.com...
> "Daniel P. B. Smith" wrote:
> >
> [snip]
> > I remember an airport in Venezuela
> > that had a whole row of "mirrors" that were mounted on a wall about
> > fifteen feet above the floor. Of course, it's quite possible that they
> > didn't care at all whether people thought they were mirrors; the
> > important thing was that you couldn't tell whether or not you were being
> > watched.
>
> Post offices use these quite often. They are used by postal inspectors
> looking for theft. The employees know what the mirrors are for but have
> no way of knowing when inspectors are watching them.
>
> --
you!
--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr