Circular vs non circular polarizers...

[DocFrankenstein]

I know circular works with AF SLRs...

But what's the difference in terms of how the lines are arranged? Non circular consists of "just" straight lines close to each other.

How does the circular polarizer structure works?

[daveh]

I vaguely remember building one of these in high school physics. It's just a linear polarizer followed by a quarter wave plate aligned 45 degrees to the axis of polarization.

You get the benefit of what a linear polarizer does (because the light has passed through one) but then you adjust the polarization so as not to fool autoexposure and autofocus systems. (Linearly polarized light hitting the mirror will be reduced in strength depending on it's angle - ie - same property you're using when you use a polarizer to cut glare from glass/metal/water etc.)

[DocFrankenstein]

What's a quarter wave plate?

At least I undertand this part:
Linearly polarized light hitting the mirror will be reduced in strength depending on it's angle
:D

[ron chappel]

interesting thread,i've allways wondered exactly how it works.


(Linearly polarized light hitting the mirror will be reduced in strength depending on it's angle - ie - same property you're using when you use a polarizer to cut glare from glass/metal/water etc.)

That helps alot :)

[daveh]

Now you're really pushing my memory but it's a material which has two indices of refraction (based on the direction of polarization). By lining it up right, the light combing out of the polarizer is split into components traveling at different speeds and the thickness of the wave plate is cut such that one component emerges one quarter of a wavelength late. When they reemerge and recombine on the other side, you have light with polarization that rotates over time. (Imagine a corkscrew wave.)

Or something like that :)

Fun with circular polarizes: place it up to a mirror. With the front out, it goes black, flip it around and it's light gray. In the front out case, light gets polarized, circularly polarized, reflected, gets converted back from circular to linear by a second pass through the wave plate but at 90 degrees different to where it started and doesn't get back through the linear polarizer.

[DocFrankenstein]

Now you're really pushing my memory but it's a material which has two indices of refraction (based on the direction of polarization). By lining it up right, the light combing out of the polarizer is split into components traveling at different speeds and the thickness of the wave plate is cut such that one component emerges one quarter of a wavelength late. When they reemerge and recombine on the other side, you have light with polarization that rotates over time. (Imagine a corkscrew wave.)

OMG! That's genius man!