Err....,Originally Posted by Francis247
Or you can put:
ND2 - Reduce light by 1 stop
ND4 - Reduce light by 2 stops
ND8 - Reduce light by 3 stops
So, if Pol-Cir reduce light by about 2 stop (1.33 stop to 2 stop depending of manufacturer), it nearer to ND4. Yes, Pol-Cir filter will make the colour slightly blue, while ND filter will not alter the colour. Slightly blue can be treated by using Camera White balance, or later in PC.
Your statement is correct Pol-Cir is not ND2