Quote Originally Posted by mporter012 View Post
Hey Bill! Thanks again for the advice. Specifically in reference to the Hoya 25a filter, if you look at this page http://www.bhphotovideo.com/c/produc...d_25A_HMC.html and click on the specifications tab and go down to the filter factor it says: 3 (+2 stops). This has me slightly confused because I am being told 3 stops by most for a 25a. What do you think?
Hi, I'm not going to spend a lot of time trying to convince you, but I think you are mainly being mislead by the B&H numbers. My guess as to what "3 (+2 stops)" means is this: +3 stops for daylight, or +2 stops for tungsten light.

Hoya's own information (p 47 of their catalog) says the filter factor is 8X (3 f-stops). They also say, "The precise filter factor is determined by considering the film type and specific light source."

The reality is that you should be getting your filter factors from film data sheets. A sharp cut filter like this simply does not have a filter factor on its own. The filter factor is based on a combination of the film's spectral sensitivity and the light source. And it assumes a neutral item in the scene; this is the basis of the corrective effect of the filter factor.

I would personally start with the presumption that Hoya's "25A" is roughly the same as a Wratten #25. (I would somehow double check this.) Then, if you look at some Kodak data sheets, you'd find that Tri-X filter factors should be (roughly) 8X for daylight, and 5X for tungsten light. T-max is similar, except only 4X for tungsten. If you look at an obsolete film, such as Tech-Pan, you'd find factors of 3X for daylight and 2X for tungsten light. From this, it should be obvious that metering through the filter is a bad method - the meter doesn't know if your film is more like Tech-Pan or Tri-X.

The Ilford site isn't loading for me tonight, so I can't say what's there, but it's worth checking if you shoot Ilford films. Same for other brands.

As a few other people have mentioned, the exact colors present in the scene are affected differently. So this is something to keep in mind. Likewise for any oddball light sources, such as energy-saving fluorescents, LEDs, etc. So a first roll should maybe be considered partially as a test. Good luck.