Image shifts caused by rotating a constant-deviation prism in divergent light.

The use of the constant-deviation prism for producing monochromatic light introduces the problem of image shifts that result from rotating the prism when changing from one spectral line to another. The magnitudes of both the lateral and the axial components of this shift, for a given rotation of the prism, depend upon the position of the axis about which the prism rotates. A position for the axis is known that yields zero lateral shift. The axial shift, however, depends also upon the convergence of the beam and the shape and optical properties of the prism. In this paper a method is presented for locating the positions of the axis of rotation for minimum axial and for minimum total shifts of the foci for both the sagittal and meridian fans of rays.