donald miller , Dec 07, 2002; 12:31 a.m.
Contrast filters are used with variable contrast papers to determine the contrast grade of the paper that you are printing your camera negative on. They are normally used in an enlarger that does not have some type of variable filtration (either dichroic or VC lamphouse).
The contrast grade of the paper will be determined in large part by the density range of the camera negative which is itself determined by the degree of development that it receives.
What one normally attempts to do is arrive at a contrast grade of paper which will give you the degree of shadow detail and highlight detail that you want to display within the print. I hope that this provides you with the answer that you are seeking. Good luck.