Compensating for Filter Factor
I am currently using a Nikon FM which doesn't meter through the lens and I've just mounted a Circular Polarizer which has a filter factor of between 2.3 to 2.8. To simplify things lets average this number to 2.5. The film in my camera is 400 ISO, so in theory I can directly compensate by changing the ISO so the filter factor which equates to about 1 1/3 stops. Can somebody tell me if I'm on the right path? What would I have to change my ISO setting to on my camera for it to meter correctly?
P.S hope I didn't write that in a overly confusing way :P