Reciprocity Failure Calculator

How It Works

Reciprocity failure (the Schwarzschild effect) means film becomes less sensitive to light during very long exposures. Below about 1 second, doubling the time doubles the exposure as expected, but beyond that the relationship breaks down. Each film stock has a characteristic exponent (p). The corrected time is calculated as t_corrected = t_metered^(1/p). Fuji Acros is famous for minimal reciprocity failure, while most B&W films need significant correction beyond a few seconds.