An evaluation,by Fourier analysis,of some of the errors introduced in reflectance measurements

In order to evaluate the errors which can be introduced in the measurement of reflectance, we have made a study of data obtained for several minerals and in two immersion media on turning the microscope stage to a succession of positions relatively orientated by 45°. Fourier analysis of the results allows an estimate of the different errors as a function of the periodicity with which they appear on a full rotation of the stage. The mean magnitude of two of the Fourier coefficients is shown to provide a measure of the quality of the measurements further allowing evaluation of the equipment used, the orthogonality of the sample in relation to the incident light, and other errors of different periodicity.