As a 35mm SLR Photographer, I never have had any trouble with filter factors, as the light was always read through the lens. Of course I realize I can hold the filters up in front of my Spot meter and take a reading through them, but would like to know the filter factors for the filters I use, and how to apply this inf ormation to my exposior. I only use three filters as I am an outdoor Photographe r and do not like to use many. The filters concerend are an 81C, A Cokin Medium graduated nuetral density, and a polerizer. If someone could advise me as to fac tors and exposior info for these, I would appreciate it. Also I would like to kn ow if you find these calculations are more helpful them simply holding the filte r befor the Spot Meter???