Conventional polariscope set‐ups like the plane polariscope or the dark or bright field set‐ups specify the positions of the various optical elements with respect to the polarising axes of the photoelastic model for determining the isoclinic and isochromatic parameters.In this paper, it is shown that such specification is not necessary since, for any light path, the positions of the optical elements for an absolute minimum in intensity of the light emerging from the analyser are unique. To illustrate this, the case of a general retarder introducing a retardation 2δ at an azimuth θ with respect to the axis of the polariser is discussed and the conditions for the determination of the isoclinics and isochromatics are obt