Font Size: 

In this paper, the mean intensity of the field radiated by the circular aperture focused in the Fresnel region is investigated in the presence of random phase errors of a illumination field. Expressions for the average intensity in the focal plane and for the focal spot width are obtained. Computation results showing dependencies of the intensity distribution type, the focal spot width and the intensity value on the optical axis on the phase errors and the distance from the aperture are presented.