Transmission of incoherent light between ronchi grids.

The use of Ronchi grids for the detection or measurement of small angular changes is well known. In some applications, such as instruments for the measurement of strain or displacement, the question of linearity of calibration over an extended angular range is important. In this paper we treat the question of such linearity on the basis of physical optics. We conclude that although arbitrary combinations of wavelength or wavelength range, grating space, focal length, and beam width generally yield a nonlinear calibration, special combinations of these parameters result in a highly linear curve over an extended range.