grntrdtaco
Adventurer
when you stack 2 linear polarizers or a circular and a linear you get a variable ND filter.  spin the linear polarizer and it lets in less and less light until it is nearly black, something like a nd400
circular polarizers dont work like that
http://www.dmcphoto.com/Articles/VariableND/index.html
	
			
			circular polarizers dont work like that
http://www.dmcphoto.com/Articles/VariableND/index.html
			
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