Kodak put out a couple books back in the day. The first pub is Transmission of Wratten Filter, and the second is KODAK Photographic Filters Handbook. Another great pub to refer to is the Kodak Reference Handbook from the 1940s. They all give the amount of light transmitted for a wide variety of filters. For instance the red 25 passes about 12.5% of light at 590nm wavelength, hence the filter factor of 8, or 3 stops. At above 600nm, it passes in the mid 80s range. The total light passed by a #25 filter runs about 15% of all light averaged, hence the generic factor. Find a good color/wavelength chart to go with the pub, and you can compare your lighting and make your adjustments according to your scene. Relying only on a published factor can often be disappointing.
The books can be found on Amazon for a reasonable price, and will help you get the most from your filters.
?Here's a link to some tables for a few common filters http://www.mat.uc.pt/~rps/photos/other-filters.html
Last edited by kintatsu; 01-23-2013 at 12:11 PM. Click to view previous post history.
Reason: Added link