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01/31/2005 04:43:18 PM · #1 |
| If you have two polarized lenses, is it possible to orient them so that they block out virtually all incoming light? Is there any way to do it with one? |
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01/31/2005 04:51:24 PM · #2 |
I think that's called a lens cap.
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01/31/2005 04:53:33 PM · #3 |
Originally posted by micknewton:
I think that's called a lens cap. |
actually i think it's called cross-polarization but idk how to do that..
i prefer the thumb-over-lens method of only letting some light in by accident of course
Lee
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01/31/2005 04:53:50 PM · #4 |
If you have linear polarized lenses, you should be able to rotate them at 90 degrees from one another to block out most light - you can do that with a couple pairs of polarized sunglasses. I'm not sure what circular polarizers would do.
There is a neat trick that you can do with three polarized lenses - orient 2 so they block nearly all the light, then what happens when you insert a 3rd between them? All of a sudden, you can see light again! This is an example of a macro-world observable quantum phenomenon.
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01/31/2005 05:11:18 PM · #5 |
Originally posted by joebok:
If you have linear polarized lenses, you should be able to rotate them at 90 degrees from one another to block out most light - you can do that with a couple pairs of polarized sunglasses. I'm not sure what circular polarizers would do.
There is a neat trick that you can do with three polarized lenses - orient 2 so they block nearly all the light, then what happens when you insert a 3rd between them? All of a sudden, you can see light again! This is an example of a macro-world observable quantum phenomenon. |
Wow, does it open a hole into another dimension or something?
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01/31/2005 05:12:07 PM · #6 |
Only one of the polarizes need to be linear, the first one.
You can in fact do it with two circular polarizes but the first one would need to be mounted backwards (thread side facing out).
What we call a circular polarizes is in fact a filter that only passes on linear polarization but then uses a 1/4 wave plate to make it circular as it leaves the filter. The reason to do this is beam splitters don’t work very well with linear polarized light. If the light come in the back side and goes out the front it will not filter out any linear polarized light but what leaves the filter will be linear polarized.
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01/31/2005 05:59:27 PM · #7 |
does a circular polarizer by itself function normally backwards?
i think it does. but don't know the specifics.
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01/31/2005 07:23:37 PM · #8 |
Originally posted by joebok:
This is an example of a macro-world observable quantum phenomenon. |
What QM phenomenon are we witnessing exactly?
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01/31/2005 07:29:42 PM · #9 |
If memory serves me correctly, you are experiencing the particle-wave duality of light.
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01/31/2005 07:33:14 PM · #10 |
hahaha
an excuse to buy another CPL (or possibly 2 more) just to check this out. All in the name of science, you know.
On the practical side, how do you figure out the orientation of a CPL? Is there any way of doing that? (I mean orientation as in what wave-dimension it is blocking).
Cheers
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01/31/2005 07:41:22 PM · #11 |
Originally posted by Gauti:
hahaha
an excuse to buy another CPL (or possibly 2 more) just to check this out. All in the name of science, you know.
On the practical side, how do you figure out the orientation of a CPL? Is there any way of doing that? (I mean orientation as in what wave-dimension it is blocking).
Cheers |
you can check out which side is the camera side of the filer by putting it over something shiny, like a quarter. The quarter should look dark when the thread side it towards it and shiny when the threads are pointed out. If it is a linear polarizing filer then the quarter will look shiny both ways. |
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01/31/2005 07:45:08 PM · #12 |
Originally posted by scottwilson:
Originally posted by Gauti:
hahaha
an excuse to buy another CPL (or possibly 2 more) just to check this out. All in the name of science, you know.
On the practical side, how do you figure out the orientation of a CPL? Is there any way of doing that? (I mean orientation as in what wave-dimension it is blocking).
Cheers |
you can check out which side is the camera side of the filer by putting it over something shiny, like a quarter. The quarter should look dark when the thread side it towards it and shiny when the threads are pointed out. If it is a linear polarizing filer then the quarter will look shiny both ways. |
I was more thinking on the lines of when I turn the CPL what 3D movement of light is blocked, so that when I get 2 (or 3) I don't have to experiment too much.
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01/31/2005 08:04:56 PM · #13 |
Originally posted by Gauti:
Originally posted by scottwilson:
Originally posted by Gauti:
hahaha
an excuse to buy another CPL (or possibly 2 more) just to check this out. All in the name of science, you know.
On the practical side, how do you figure out the orientation of a CPL? Is there any way of doing that? (I mean orientation as in what wave-dimension it is blocking).
Cheers |
you can check out which side is the camera side of the filer by putting it over something shiny, like a quarter. The quarter should look dark when the thread side it towards it and shiny when the threads are pointed out. If it is a linear polarizing filer then the quarter will look shiny both ways. |
I was more thinking on the lines of when I turn the CPL what 3D movement of light is blocked, so that when I get 2 (or 3) I don't have to experiment too much. |
Well I am not sure what you mean by 3D movement of light. Light reflecting off a surface light glass or water at a glancing angle will tend to be polarized with the electric field in a vertical direction, assuming the water or glass surface is flat. If the sun is behind you the sky light is also polarized in this orientation, so normally a polarizing filter is set to pass light with the E field in the horizontal direction which will tend to block the reflected light. On my filter there are a couple of small marks to show the orientation for the E field that will pass through the filter. Keep in mind that the light that comes out of the filter is messed up, on purpose, by the 1/4 wave plate, this is the circular part of the filter.
The filter passes light of one linear polarization but what comes out is not longer linear but rather circular. If you look at the E field of circular polarized light you see the E field rotating like the hands of a clock, rotating really fast, like 600,000,000,000,000 times a second
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01/31/2005 08:05:17 PM · #14 |
One of mine has a line marking the blocking axis, the other has the name of the manufacturer 90 degrees from the blocking axis - don't know for sure if this was on purpose or just happened that way, but I like to believe the former.
I'm not sure if this is what Scott was trying to describe, but find a shiney surface, preferably water or metal, where the sun or another bright light is shining on it. Stick the polarizer in front of your eye, look at the surface, and turn the polarizer. You should see the reflections go in and out. At the point the reflection is least, that's the blocking angle.
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01/31/2005 08:07:25 PM · #15 |
Ok,
Will try that ASAP, but now very soon since I still have only one CPL and am trying to fix up my brand new appartment.
Thanks for the info and ideas.
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01/31/2005 08:15:53 PM · #16 |
| do digital cam sensors know the difference when rotating a circular polarizer? |
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01/31/2005 08:20:30 PM · #17 |
the filter is changing the light that hits the sensor, - so i guess no
Message edited by author 2005-01-31 20:21:03.
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