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Old Aug 23, 2003, 7:09 PM   #1
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Default de-polarising filter?

is there such thing as a de-polarising filter?
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Old Aug 23, 2003, 8:27 PM   #2
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Default Maybe

There are filters that block polarized light.
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Old Aug 23, 2003, 8:28 PM   #3
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what give out polarized light?
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Old Aug 23, 2003, 11:17 PM   #4
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Default Re: de-polarising filter?

Quote:
Originally Posted by Jayson
is there such thing as a de-polarising filter?
What is your source of polarized light, a laser? There are optics which have 2 wedged birefringent materials constructed in such a way that the light sent through it is "depolarized". You can find them here:

http://www.ofr.com/optics/polarizer_oc-251.htm

Sending the light through a multi-mode fiber will tend to scramble the light also.

Technically a circular polarizer is a "depolarizer". But I doubt there is a camera filter made specifically to "depolarize" light.

~Laserjock~
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Old Aug 24, 2003, 3:37 PM   #5
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Default Reflections

I am not a physicist but as a person who takes pictures and uses a filter the source of most polarized light is reflections from water, windows, and so forth.
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Old Aug 25, 2003, 12:50 AM   #6
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I forgot most of this stuff, but I think I can explain the gist of why you need a polarizer.

Light travels as a wave. The wave goes up and down in a single direction. The light is called "polarized" because it only 'waves' up and down in one direction. A laser will create a perfectly polarized beam of light. The sun's rays are fairly polarized as well. All the light rays that are coming out of the laser or the sun are pretty much in sync.

Up Down Up Down Up Down... etc.

However, when a wave hits a barrier, it bounces. If you look at a swimming pool, a wave travels from the middle of the pool and hits the wall and then bounces back. BUT! After the bounce, the wave is UPSIDE DOWN compared to the original wave. If you have a lot of waves reflecting multiple times, you will have a big mess of waves all traveling out of sync with each other, just like all the little waves in a pool. The same thing with light. The polarized light gets reflected off of glass, water, walls, even the air will reflect light. So the light that you see at the earth's surface is not polarized, it is a big mess of light waves all travelling out of sync with each other.

This unpolarized light is the cause of glare. Glare is the light that you don't want in your photo because it will wash out the other light that you do want. So you put a polarizing lens on the camera to fix this. The polarizing lens will filter out all of the little waves that you don't want that are out of sync with the light waves that you do want. The filter only lets through the type of light that is polarized in the direction that you want. The polarizer will allow you to see 'through' the glare by filtering the bad light waves.


Quote:
is there such thing as a de-polarising filter?
I don't know. Do you mean a polarizing filter?
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Old Aug 25, 2003, 8:23 PM   #7
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Most light is UNPOLARIZED or more precisely RANDOMLY POLARIZED. Sunlight, lamplight, candlelight, flashes, specular and diffuse reflections from surfaces such as water, glass etc. are all examples of RANDOMLY POLARIZED light. Meaning that the light waves eminate from the source in random directions. Contrary to popular belief, most lasers such as pointers and HeNe's project UNPOLARIZED light (unless a polarizing filter is inserted into the lasing cavity). Lasers do not inherently give out polarized light, just COHERENT light. Bouncing (reflected) light does not become more or less randomly polarized as it bounces around.

Randomly polarized light reflected off a surface incident to an angle known as Brewster's angle will be linearly polarized. Light can be polarized in three ways, Linear, Circular and Elliptical.

Are we clear now? :-)

~Laserjock~
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Old Aug 26, 2003, 4:04 AM   #8
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well i think i understand now.

thanks all!
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