The 85 filters are designed for color film work, to match the color response of the film to the color of the ambient light.
Regardless, an 85 filter will be usable for B+W contrast control. Just try it on a sunny day with clouds in the sky. Shoot pix with and without it. You'll see a change in the rendering of the sky. The blue of the sky will be darkened by the orange in the filter. The clouds will stand out more clearly, through the filter, against the tone of the sky. Without a contrast filter, the clouds will render a bit less differentiated from the sky.
Try one stop compensation for light loss through the filter.
Last edited by CBG; 09-10-2008 at 01:12 AM. Click to view previous post history.