Quote Originally Posted by StoneNYC View Post
I never knew this!!!

No wonder some I've my exposures always seemed off, I always thought filter factors were STOPS...

Kind of stupid, why make you do math instead of just putting the stops on the filter? I'm sure it "all goes back to xxxxxxx reason" it's still annoying and dumb.

Thanks for the info
It isn't as stupid as you say.

The filter factors work well with ASA/ISO/EI numbers.

They work well with flash guide numbers.

They work well when you use more than one filter.

They work well with films that have different daylight and tungsten speeds.

They work well with calculations concerning bellows extension.

They fit well within a system.