weird polarizer interaction

[bwanaaa]

I noticed something playing with a linear and circular polarizer. If you flip the circular polarizer so that its female threads are facing the female threads of the linear polarizer then something interesting happens. As you rotate one relative to the other from 0 to 90 degrees, you dont get extinction but rather the colors go from warm to cold.

I wish I could explain that.

 

[watdahel]

You should report it to National Geographic.

 

[Mark R]

Likely due to the construction of the circular polarizer.

Circular polarizers are actually linear polarizers (otherwise rotation wouldn't alter their effect on the sky, reflections, etc.). However, on their back side, they have a "quarter wave plate" which then shifts the polarization from linear to circular.

If you put the circular polarizer filter round backwards, then you can get all sorts of weird effects due to imperfections in the linear->circular conversion. Those imperfections then show up as extinction by the crossed linear polarizers.