The resolution (Rayleigh criterion for resolution) of two point sources by a zone plate is analyzed with respect to the number of zones. It is determined that for N (number of zones) less than 200 the limit of resolution is greater than that of a lens with the same aperture diameter, D, if only the zones which contribute light with a positive phase to the point of observation are used, and less than that of the lens if only the zones which contribute light with a negative phase to the point of observation are used. But, in the former case the maximum value of the side lobe (secondary maximum, first ring) is less than that of an equivalent-diameter lens whereas for the latter case the maximum value is greater. For N greater than 200 the resolution and side-lobe values approach those of a lens in both cases.
© 1967 Optical Society of America
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