A versatile shearing double refracting interference microscope for investigation of transparent specimens is presented. The shearing system used is capable of giving uniform and fringe interference fields with both the great and differential image doubling imparted by different shears. This variability of interference methods is achieved with some combinations of two simultaneously acting birefringent prisms inserted between two polarizers. One of these prisms, of the Nomarski type, is incorporated in objectives and is rotatable round the objective axis of the microscope. The other birefringent prism of the Nomarski or Wollaston type is placed in the microscope tube and can be slid in a direction perpendicular to the axis of the objective. The accuracy of optical path difference measurements that can be obtained with the microscope by using the minimum intensity, minimum visibility and half-shade methods is examined and discussed.
