A Simple Azimuth and Phase Half-Shade of Variable Sensitivity

Abstract

The azimuth half-shade component consists of two thin adjoining glass plates mounted on and in front of the analyzer at an angle of about 90° with each other. The common edge is in the plane of polarization of the analyzer, the glass strips making equal angles with this plane. The phase half-shade component is an approximately quarter-wave mica plate placed in front of the glass slips (away from the analyzer), its planes of polarization being in and perpendicular to that of the analyzer. It is so cut and mounted that its free edge bisects the field of view in a line perpendicular to the common edge of the glass slips. End-point setting is complete when (1) the intensities in adjacent quadrants in the field of view not back of the mica phase plate are equal (azimuth), and (2), they are also equal in the quadrants back of the mica. Azimuth and phase sensitivity are both varied equally by changing the angle of inclination of the common edge of the glass slips with the axis of rotation of the analyzer. Due to the method of construction, all adjustments for proper operation can be made optically at any time. No high constructive skill is needed in making the apparatus and the preliminary adjustments are not critical. The photometric dividing line between quadrants for both settings (1) and (2) is one obtuse adjoining edge of one of the glass slips which is easily made imperceptible. The sensitivity in both azimuth and phase is equal to that of any of the usual variable sensitivity half-shade devices.