This is a reprint of Phil Davis' article on Reciprocity from the D-Max Newsletter, December 2002.

Phil tested the reciprocity of 9 films and 5 film developers. His procedure is described in the article. The end result was calibrated reciprocity data for about 80 film and developer combinations. This reciprocity information is included in the BTZS Plotter program and is used when exporting film test data to the BTZS Expo/Dev software for the Palm Pilot.

The Expo/Dev program makes calculating exposure and development easy. When you enter the f/stop the Expo/Dev program calculates the exposure time including any correction needed for reciprocity along with the developing time.

Fred Newman