PRIMARY SPHERICAL ABERRATION WITH TWO-ZONE APERTURES

Abstract

Apodisation improves some selected properties of an imaging system at the cost of some others. Apodisation can be accomplished either by aperture shading or aperture shaping. The former alters the shape of the aperture and the later alters the aperture transmission characteristics. Aperture shaping can be accomplished by altering the shape of the aperture from circular to non-circular. Aperture shading can be achieved by modifying the pupil transmission function. In the case of aperture shaping, the entrance pupil covers by the spatial filter resultantly; the transmission characteristics of the aperture are altered. Thus aperture shading results in a non-uniform amplitude transmission of the pupil from point to point (MONDAL and VENKAT REDDY, 1987). In addition to these two methods of apodisation, there is one more method of apodisation in which narrowing the central part below the classical Rayleigh limit of 3.832 units