Strange effect with two CPL's

[onform]

Before I start I'm not talking about the variable ND effect that only works when you reverse two CPL's.

I'm referring instead to the strange colour change that occurs when you screw one into the other or the same way round. First you turn it for the normal effect of eliminating reflections then holding one in place rotate the other. The WB changes Right through from cold to warm..

Cool but Why?

Matt

 

[Moreorless]

Not sure but there are variabley colour temprature filters("warm to cool") aswell as ND's that I'd guess use this effect.

 

[Nod]

Are they cheap pols or expensive ones? I would expect expensive ones to stay reasonably neutral under the circumstances above but know that some cheaper pols can introduce a cast (although AWB tends to negate such things on digital sensors - film is less forgiving!