Low Intensity Reciprocity Failure d

Low Intensity Reciprocity Failure describes thephenomenon where if the same total exposure is givento photographic material over a longer period of timethen the density of the image generated is lower(effective speed is reduced).It is caused by a reduced efficiency in forming stabledevelopment centres with lower levels of light.Our Film Fact Sheets use graphs based on a singlefactor for all our films. We have carried out work tocalculate this speed reduction for each individualcamera film. Instead of showing the results in a graphwe believe it will be more flexible to give a factor foreach film and a calculation method. Exposure times ofone second or less will not require any compensation.Use a calculator to calculate the Reciprocity FailurecorrectionThis uses the equation Tc = TmpWhere Tm is the metered (indicated) time and Tc is thecorrected time. P is a factor calculated following arange of exposure timesEnter into the calculator the metered (indicated) time inseconds.Press the xy button and enter the factor for the productfrom the table below and then the = button.So, for example, using HP5+ at a metered time of 10seconds gives us:Tc = 10 exp 1.31 = 20.4 secondsRound this result off to give an exposure of 20 seconds.