Reciprocity failure calculator
For long exposures, film loses sensitivity. Enter your metered time to estimate the corrected time.
Estimate only — always check your film's data sheet for exact corrections. No correction is needed below ~1 second.
About this tool
For long exposures, film loses sensitivity and needs more time than the meter suggests, an effect called reciprocity failure. This tool takes your metered long exposure time and the film type, then returns the corrected, longer exposure time. It prevents the dark, underexposed negatives you would otherwise get in dim light and night photography.
How to use it
- Enter the metered exposure time your light meter suggested.
- Select the film type or its reciprocity characteristic.
- Read the corrected, longer exposure time the tool calculates.
- Set that adjusted time on your camera or use bulb mode with a timer.
FAQ
When does reciprocity failure start to matter?
It usually becomes significant once metered times reach about one second or longer, and it grows quickly beyond that. Short daylight exposures are unaffected.
Is the correction the same for every film?
No. Each emulsion behaves differently, so films like Fuji Acros need very little correction while others need several times the metered time.