On the uniqueness of the method of plotting blackening curves of spectral photoplates using a two-step attenuating device

Abstract It is shown that, when the method using the two-step attenuating device is applied to obtain blackening curves, one and the same set of blackening pairs can yield a series of different blackening curves the shapes of which are determined by the method used to obtain the blackening curve. This effect is eliminated with the application of the preliminary curve method which gives a unique curve, its shape being independent of (1) the method of plotting, (2) the value Δ Y m of the attenuating device constant, (3) the actual values of the measured set of blackening pairs and (4) the type of preliminary curve.