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05/04/2006 11:17:51 AM · #1 |
| I still dont understand how these things work, when i put another one on to see what it did it gets SUPER dark. Like adding a welders mask at one point. |
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05/04/2006 11:25:23 AM · #2 |
Originally posted by BowerR64:
I still dont understand how these things work, when i put another one on to see what it did it gets SUPER dark. Like adding a welders mask at one point. |
Think of it this way.
Light vibrates in all directions when unpolarized. Not each photon stream, but just as a whole.
When you add two together, and the polarization points are turned 90 degrees from each other, it will block most of the light entering your lens because it's not an exactly perfect 1 degree of polarization, theres about 20% around the edges that get through.
don't quote me on that, I probably just got an F in my physics class.
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05/04/2006 11:25:45 AM · #3 |
polarize = align
If you rotate one to line up at 90 degrees to the other you should be able to block nearly all of the light.
It is kind of a cool thing. In big cities, some adjacent high rise buildings coat their windows with polarizing film (aligned orthogonally to each other) so that looking out your window you cannot see in the window directly across from you.
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05/04/2006 11:28:36 AM · #4 |
A polorizer is a light filter basically how it works is this:
Light normally goes to the camera in all directions basically looks like this-> O . So when you add a polarizer it is-> - or | of the light comoing through it. So as you rotate 2 polarized glass peices it turns to this-> + at 90 degrees. and the available light comming through
is-> . I hope that made sense. |
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05/04/2006 11:29:34 AM · #5 |
I don't know if this trick will work with circular polarizers, but it does with regular ones and polarized sunglasses:
Imagine a light photon as a little particle holding a flag. With regular light, these flags are at all different orientations. A polarizer is basically a grill that will only allow photons whose flag is oriented the correct way to slip through.
So - if you take one polarizer and orient a second at 90 degrees, you would expect that very little light would get through - that is what you observe when you see the super dark.
Now, here is the fun part - take a third polarizer. What would happen if you put it between the first two - should get even darker, right? But that is not what happens - if you put it in, oriented at 45 degrees to the 1st 2, you will actually see that MORE light gets in.
This, I have been told, is an observable quantum event. I have seen it with my own eyes using sunglasses. The explantion is somewhat like this: in quantum physics, everything is a probability. The amount of light going through a pair of polarizers depends on the cosine of the angle between their orientations - so when they are in alignment, all (or nearly all) the light will get through, when at 90 degress none of it should. When you put the 3rd between the first two, instead of one probability of 0, you get a non-zero chance the photon will make it through the first 45 degree pair and then another non-zero chance it will make it through the second - resulting in a non-zero chance for the photon to make it all the way through. |
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05/04/2006 11:30:24 AM · #6 |
Originally posted by MQuinn:
A polorizer is a light filter basically how it works is this:
Light normally goes to the camera in all directions basically looks like this-> O . So when you add a polarizer it is-> - or | of the light comoing through it. So as you rotate 2 polarized glass peices it turns to this-> + at 90 degrees. and the available light comming through
is-> . I hope that made sense. |
excellent use of symbols.
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05/04/2006 11:30:55 AM · #7 |
Originally posted by MQuinn:
A polorizer is a light filter basically how it works is this:
Light normally goes to the camera in all directions basically looks like this-> O . So when you add a polarizer it is-> - or | of the light comoing through it. So as you rotate 2 polarized glass peices it turns to this-> + at 90 degrees. and the available light comming through
is-> . I hope that made sense. |
sure Matt! I think you confused him even more :P
LOL! |
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05/04/2006 11:30:55 AM · #8 |
Hi Mike, a polarizer only allows light with a specific polarization to pass through. Although we use circular polarizers, it is easier to understand with linear polarizers.
Imagine you have two polarizers: one only allows vertically polarised light to pass, the other only horizontally polarised light. If you stack the two with the vertical one in the front you will only have vertically polarised light coming into the second polarizer. This one only allows horizontally polarised light to pass, but there is now no more horizontal component because the first filter has filtered it out! That is why the result is very dark.
Using two stacked polarizers is great to watch solar eclipses with because it dramatically reduces the bright light.
Wow, 4 posts in a minute - and I'm the slow-coach!
Message edited by author 2006-05-04 11:32:45. |
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05/04/2006 11:33:15 AM · #9 |
I used to own a watch that featured this effect. There was a polarizer on the inner surface of the watch and there was a disc of polarized plastic that rotated as the second hand. As it rotated, it moved from clear to black.
Totally slick watch. I loved that watch. It was a gift from my mother. We all get good gifts and bad gifts from our parents. That was one of the best in my memory.
I think I still have it somewhere.
Sadly, the watch seemed to have some sort of fault in it's design because it burned through batteries in a few weeks... Bummer.
As to how they work, try this out.
Turn out all the lights. Spread your fingers on one hand and put a directional light source behind them. They will cast alternatively shadow and light.
Now, if you used venetian blinds (I hope you know what these are) instead of fingers, this would have a similar effect of casting alternately shadow then light. Now, venetian blinds are designed to BLOCK light, but polarizing filters are just tring to directionalize it while preserving the quantity. Therefore, if you made the blinds reflective, not so much light would be lost, and the areas of brightness would actually be brighter because the light would be condensed as it passed through the reflective filter (some light would pass straight through, other light would bounce once, then twice to get through).
A polarizing filter does this.
Now theoretically, the above description allows for 100% light permissiveness via perfect reflectivity.
It doesn't really work like that though. A fair bit of light is excluded. Most particularly in the case of an actual polarizer would be light that comes in at bad angles. This is the purpose of the polarizer. It helps you to choose which light it permits. Light that comes at bad angles does not pass through.
Enter the second polarizer.
Now that you have selected only light from certain angles AND conditioned the permitted light (like the alternating shadow/light pattern coming through the venetian blinds), you can then turn the 2nd polarizer so that it excludes the light coming in from the angles that are permitted by the original polarizer.
It's like having a gay bar for men, but staffing it with a bouncer who only likes ladies... Ok, maybe a bit of a stretch... |
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05/04/2006 11:33:21 AM · #10 |
A polarizer sorta "combs" wavelengths of light. Imagine it like a series of black and white stripes (or bars on a window). If you take another polarizer whose stripes are perpendicular to the first, you'll block all the light. As you rotate the one in relation to the other it will be lighter and then darker again (90 and 180 degrees).
I don't know much about photography, but I know physics and engineering.
The purpose of a polarizer is it cleans out the light that's all bouncing around from different directions.
Light is a particle.
Light is a wave. |
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05/04/2006 11:34:33 AM · #11 |
//alienryderflex.com/polarizer/
article with pictures...explains the basics along with an interesting twist of what happens when one adds a 3rd polarizer at a 45degree angle to the others. |
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05/04/2006 11:37:35 AM · #12 |
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05/04/2006 03:10:05 PM · #13 |
Can you get a reverse polarizer? that like increases the light?
Or what if you put the polarizer on the flash? will it light up the opbject with no reflections? |
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05/04/2006 11:05:40 PM · #14 |
You can buy polarizing lamps for reading. Check them out at your local department store or lighting store.
They all share one common characteristic. VERY low output. Polarizers tend to cut out a lot of light. Putting it on your flash will require a significant adjustment in flash output. Your camera MAY not be able to figure this out. I think the S2 is so-so with flash metering if I recall correctly. I don't use flash all that much.
Worth a look though if you are thinking about eliminating reflections and glare. Very soft light coming out of them.
You can probably do just as well with cheap diffusers though.
A reverse polarizer would be a diffuser. It doesn't increase the light.
The light that is available is the light that is available. If you want more light, you have to actually gather more light.
Treating light will always generate loss, whether it's directionalizing it or de-directionalizing it.
Think about those venetian blinds. Which direction can you turn the blinds that they allow more light through than is being put off by the source?
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05/04/2006 11:22:12 PM · #15 |
LAYMAN TERMS:
do not stack 2 (or more) polarizers
and read this to understand how polarizer works (PDF file)
Message edited by author 2006-05-04 23:24:22. |
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05/04/2006 11:31:07 PM · #16 |
| Just curious though, could 2 stacked polarizers be used as a variable Nuetral Density filter? :) |
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05/06/2006 02:07:37 PM · #17 |
| So, did I stump everyone? Could you use stacked polarizers as an adjustable ND filter? Thanks for the help? |
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05/06/2006 03:15:04 PM · #18 |
I used 2 poloriser for this challenge entry
One in front of the single light source pointing directly back at the camera which had a poloriser too, but rotated through 90 degrees. then a normal 99p ruler in between
Steve
edit for clarity
Message edited by author 2006-05-06 15:16:22. |
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05/06/2006 04:04:28 PM · #19 |
| The super dark effect from two stacked polarizers that you saw is in effect a manifestation of tunable neutral density filter effect- The reasons fully explained above. You wont get eny extra polarization from the second filter but you can use it to block out variable amount (nearly all if you wish) of the light that makes it through the first one. Could be useful for long exposures in bright light conditions where conventional 2x, 4x 8x filters might be insuficient. |
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05/08/2006 02:32:12 PM · #20 |
Originally posted by armin:
The super dark effect from two stacked polarizers that you saw is in effect a manifestation of tunable neutral density filter effect- The reasons fully explained above. You wont get eny extra polarization from the second filter but you can use it to block out variable amount (nearly all if you wish) of the light that makes it through the first one. Could be useful for long exposures in bright light conditions where conventional 2x, 4x 8x filters might be insuficient. |
Cool idea! |
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