On the diffraction theory of microscopic vision

Abstract

The changes that take place in the resultant diffraction pattern when a black crossed-grating on a white ground is viewed through a very long rectilinear slit, the axis of which is inclined at an angle of 45° to the lines of the grating and when the slit width is gradually decreased, are described, and reproductions of photographs of typical stages in the image distortion are given. It is shown that when the slit is sufficiently narrow the diffraction field consists of a series of equidistant bright and dark lines at right angles to the chief axis of the slit. The elemental case of a single black 90° cross on a white ground, when viewed through a slit which is parallel to the bisector of a pair of vertical angles of the cross, is subjected to approximate mathematical analysis, and the contour lines are given both numerically and graphically. It is explained how a synthesis of the elemental pattern accounts, qualitatively at least, for the more general case.