Film Reciprocity Failure Calculator
Pick your film stock and enter the time your light meter gives you. At long shutter speeds film under-exposes because the light-sensitive reaction slows down — this tool tells you the extra time you actually need to set on your camera. Nothing uploaded.
Exposure Bracket
| −⅓ stop | Corrected | +⅓ stop |
|---|---|---|
| — | — | — |
Learn more about film reciprocity failure
What is reciprocity failure?
Reciprocity failure is the phenomenon where film requires progressively more exposure than the meter indicates for exposures longer than about 1 second. The degree of failure varies by film stock. The Schwarzschild formula models it precisely.
How bad is Ilford HP5 reciprocity failure?
HP5 has moderate failure. At 10s metered you need about 25s actual. At 100s metered the correction becomes very significant. The calculator uses Ilford's published exponent for precise results.
Why does my film come out thin at night?
If you are using the metered time directly for exposures over 1 second, you are under-exposing due to reciprocity failure. Apply the correction from the calculator for your specific film stock.