 Conversely some films that are "slow" under normal exposure duration retain their light sensitivity better at low light levels.For example, for a given film, if a light meter indicates a required EV of 5 and the photographer sets the aperture to f/11, then ordinarily a 4-second exposure would be required; a reciprocity correction factor of 1.5 would require the exposure to be extended to 6 seconds for the same result.Reciprocity failure generally becomes significant at exposures of longer than about 1 sec for film, and above 30 sec for paper.