One sided mirror

I am looking for a mirror that should be transparent from one side and
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

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.

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"PV" wrote in message
...
I am looking for a mirror that should be transparent from one side and
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

This is true, but you could get around the problem by shining a very
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" wrote in message
. com...
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.

--
http://www.chapelhillnoir.com
home of The Camera-ist's Manifesto
The Improved Links Pages are at
http://www.chapelhillnoir.com/links/mlinks00.html
New email - Contact on the Menyou page.
"PV" wrote in message
...
I am looking for a mirror that should be transparent from one side and
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

Use a thin sheet of glass between the light source and the object at 45
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 wrote in article
...
I am looking for a mirror that should be transparent from one side and
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

Right. If it were possible to truly do this, one could make Maxwell's
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

webpage- http://www.usfamily.net/web/stauffer

Using polarised light you could get quite close to using all the light. But
probably the reflected light from the object of not completely polarised
anymore....

Rob.

"PV" wrote in message
...
I am looking for a mirror that should be transparent from one side and
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

In , Charlie D wrote:

Here's one.
http://www.scientificsonline.com/ec/...ategoryID=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 )

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.
Thanks in advance.
PV

David wrote:
I believe the mirror in question would be a Brewster's mirror. These are
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.

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

On Sat, 5 Jul 2003 07:06:29 +0000 (UTC), "Luke" wrote:

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.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com