How do circular polarizer work? Majic?

I just tried out a circular polarizer I bought for one of my lenses awhile ago. I am amazed that I still cannot understand how it works. I searched online but it gets a little to complicated. All I know is that when I turn it, some reflections get darker, but how? :idea:

I think one side of the lens is darker than the other. Much like an ND grad. Most CPs have a line on the side that indicates the darkest. I usually point the line up. If you go from portrait to landscape it is easy to forget that though. You can get polorizers that are not darker on one side and no need to turn them.

Others can probably explain better than I can, but...

Light waves normally oscillate in all directions. But when light is reflected off of some materials, most of the light is absorbed and only light oscillating in one plane is reflected. Sort of like squirting a hard surface with a hose - a round stream hits the surface, but what bounces off is more like a flat fan. So light reflected off of glass or water is mainly oscillating in only one plane and light that reflects off of the air (actually the water in the air, I believe) in the atmosphere (blue reflects the most, so the sky looks blue) is also mainly oscillating in one plane.

Polarized glass is made to remove light oscillating in a certain plane, so when you turn the glass and get the plane that is being removed lined up with the plane off the reflected light, the reflected light is removed. Since some light is removed, it is also somewhat darker.

TF

Correct. Reflections off of water and objects are normally horizontally polarized. Scattered blue light is also polarized. The polarizer on your lens chooses how much of that polarized light gets through.

FWIW, A circular polarizer is the same thing as a linear polarizer but has a quarter wave retarder plate on the back. This plate "spirals the light" making it suitable for any beam splitter that comes after it.

Quote:

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"Sort of like squirting a hard surface with a hose - a round stream hits the surface, but what bounces off is more like a flat fan. So light reflected off of glass or water is mainly oscillating in only one plane and light that reflects off of the air (actually the water in the air, I believe) in the atmosphere (blue reflects the most, so the sky looks blue) is also mainly oscillating in one plane."

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I like that analogy a lot, thanks old clicker.

Thanks to everyone that replied, that really did help. Now I can take more photos with a circular polarizer with out scratching my head wondering. I particularly use this filter when someone wears sun glasses and I want to eliminate its reflections.

Another use not often mentioned is when you are getting blown out leaves in a shot. It's the reflection that is causing the problem and the polarizer will help. - TF

Any sufficiently advanced technology is indistinguishable from magic.

http://www.fas.harvard.edu/~scidemos...arization.html