You may find it necessary under low light conditions to use exposure times of longer than ½ second. All films experience a failure of the laws of reciprocity in low light and under these circumstances and the exposure time indicated by your light meter will give you an underexposed negative. The longer the exposure indicated on the meter, the higher the degree of failure. The chart below will help you to compensate for this phenomenon when using long exposures.

Read your exposure (as indicated by your meter) on the horizontal axis. Find the point on the graph directly above it and read across horizontally to the vertical axis for the actual exposure necessary in order to compensate for reciprocity failure. Many photographers find that the manufacturer’s reciprocity data tends to be conservative and that the actual compensation needs to be greater even than what is indicated above. Nevertheless, the information you derive from this chart will be a good starting point in compensating for the underexposure caused by reciprocity failure. You may want to xerox this page and keep a copy of it in your camera bag for reference when shooting under these conditions.