What's this weird dial on my polarizer?

[keller]

I've noticed on a polarizer, you can spin it around with this little dial (without detaching the actual polarizer from the lens). What does this do? I've noticed no effects through my viewfinder. Is it some kind of control?

 

[binglemybongle]

It allows you to adjust the amount of polarisation that the lens..... gives.

If you look at an object through the lens that has quite a lot of highlight (say an apple in bright light - odd choice I know) and spin the filter, you should notice that the highlight dims then comes bright again with about 180' of rotation.

I thinks thats what its for anyway. I stand to be corrected.

 

[Big Mike]

That's right. You can adjust the amount of polarization right down to none.

If you are not seeing a difference when you spin the filter, then that's not a shot that a polarizer will help...inside, for example.

Try it outside in bright sun light...hopefully with a blue sky and or reflective water.

Also note that a polarizer has it's strongest affect when pointed at 90 degrees to the sunlight.

 

[markc]

It's not the amount, but the angle of polarization. When light bounces off a surface, it can end up polarized. Instead of the light waves "waving" along a random axis, they all align based on the surface they bounced off of. Light bouncing off the water align horizontaly. If the "slit" is aligned horizontally, all that light gets through and the camera see as your eyes do (all the light). If you rotate the "slit" 90 degrees so that it's vertical, the horizontal light can't get through. The other light does by shifting to align with the slit, but it's too far for the 90 degree light to make it. You see all the light except for the light bouncing off the surface. Without that glare, you can then see the dimmer light that comes from under the surface.

It's more complex than that, but that's a basic explanation.

http://polarization.com/
http://www.bobatkins.com/photography/tutorials/polarizers.html
http://en.wikipedia.org/wiki/Polarisation

 

[MyCameraEye]

Mark K just posted what I was going to correct, "It's not the amount, but the angle of polarization".

Scott

 

[airgunr]

I notice the effect most when there is a section of blue sky or looking at a reflection in water or off a window. It will not elimiate or reduce reflections from metalic objects like chrome on a car.

 

[keller]

After reading that article, there's one thing I don't get - if the polarizer takes away the surface reflection, can our eyes actually see the reflection, or do we have inbuilt "polarizers" in our eyes/mind?

 

[airgunr]

We see the reflection and the polarizer reduces it or elimiates it. Say you are looking at a stream and there is a strong reflection of sky in it. With a polarizer you may be able to eliminate it and see the bottom of the stream.