A New Type of Shearing Interferometer for the Measurement of Transfer Functions of the Microscope Objective

A shearing interferometer using polarized light has been devised for the measurement of transfer functions of microscope objectives. In this device, a birefringent system of calcite is employed for obtaining the variable amounts of shear of the aperture. The interferometer is easy to adjust and permits relative lateral shear up to s = 2 corresponding to the resolution limit of a perfect lens, with a great amount of light available in the measurement. Experiments were carried out on an aberration-free 4.3-mm objective, with a numerical aperture of 0.60 under partially coherent illumination, and on an objective having primary spherical aberration of 1.0 λ under incoherent illumination. The experimental results showed fairly good agreement with those of calculation.