Quote Originally Posted by RobertV View Post
Not:
http://www.heliopan.de/produkte/pola...nsfilter.shtml

How they do it is another question but maybe it's one of the secrets of a filter company. All made in Schott glass.
Not "not".

Yes, they know about light and polarisation.
That makes it even more of a mystery why they say a polariser can have a 1/2 stop filter factor.

Polarizers only use glass as covers, to protect the working bit: a 'plastic' foil.