Abstract

New requirements are placed upon the method of reducing the light diffracted by the telescope objective when astrometric measurements are made near the sun. The technique of Lyot greatly reduces the diffracted light, but since the aperture stop in this technique is not rigidly fixed to the objective, sizeable variations in coma and distortion are introduced when the stop moves with respect to the optic axis of the objective.

If, however, instead of the Lyot system, an apodized objective is used to reduce the diffracted light, the aperature stop becomes rigidly fixed to the objective thereby overcoming the above difficulty. It is shown that for an objective apodized with a square aperture the diffracted light is reduced by four orders of magnitude below that for a circular aperture for one-half the azimuthal field and for distances greater than 400 sec from the solar limb.

A general expression for the diffracted intensity from a circular aperture for points exterior to a disk image is obtained, and its leading terms are examined.

© 1965 Optical Society of America

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Equations (24)

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