High-Precision Pointing*

Abstract

Two methods permitting high-precision pointing have recently been developed by members of the staff of the Institut d’Optique. The method of Simon for high precision in longitudinal positioning is based on the use of two identical grids, longitudinally separated, one forward and one back of the object point. The position is determined by observing the equality of contrast of the out-of-focus images of the grids. The method of Arnulf and Dupuy for lateral pointing is based on the formation of a system of interference fringes by light from a double slit illuminated by light from a single slit. By placing the entrance pupil of a telescope on a dark fringe, the image of the slits, though very dim, reveals and amplifies any irregularities in the edges of the slits even though the irregularities are very small. If the two slits are separated only by a fine line, the lateral position of this line can be located with high precision.