Quote Originally Posted by alex


i hadn't thought about the 0.6 being basically equivalent to the CP.



Yep. In fact, the the Singh-Ray Vari-ND filter is essentially two stacked polarizers (one circular and one linear) - when rotated so the polarizing grids are in the same orientation, it's a 2 stop ND, and as you rotate one of them the apparent density of the filter increases (and actually keeps on increasing - if rotated so the grids are 90° to one another, no light passes, which is why Singh-Ray states that you can get >8 stops of reduction, but they don't recommend it because it results in interference artifacts).