I have the new cinema series Polar Pro Filters and this is totally N00b question (Sorry!), but how to a work out which stop I need to use? I.e If i want the shutter speed to be 60, and in auto its recommending 1/500th, how do I work out with ND i will need? and on the PL, does anyone know if the markings needs to be vertical or horiztonal relative to the horizon for the PL to function? Sorry again for the N00b questions!