Sorry for continuing to pick all your brains in this fashion but there is a big upside: I am currently working in a camera store and have become known as "the resident film guy". All the local university/college art students come to me with questions and I pass on all information I can plus the forum's address as often as possible. I recently purchased some Hoya filters and was testing them out yesterday by setting up a gray card in sunlight, taking a reading with my spot meter (known to be reliable) and then holding the filter in front of the spot meter and taking a second reading. The change in readings are quite different than the filter factors published online. The yellow K2 had less than 1/3 stop change (as opposed to the supposed filter factor of 2 or 1 stop); the red 25 had a full stop change (compared to the 8 filter factor or 3 stop) and the circular polarizer had a 4 stop change (compared to the factor of 4 or 2 stops) regardless of position. Any ideas which adjustment to make?