The technique proposed to enhance the resolution of the point spread function (PSF) of an optical system underneath defocussing and spherical aberrations. The method of approach is based on the amplitude and phase masking in a ring aperture for modifying the light intensity distribution in the Gaussian focal plane ($Y_{D} = 0$) and in the defocussed planes ($Y_{D} = \pi$ and $Y_{D} = 2\pi$). The width of the annulus modifies the distribution of the light intensity in the side lobes of the resultant PSF. In the presence of an asymmetry in the phase of the annulus, the Hanning amplitude apodizer [cos($\pi\beta\rho$)] employed in the pupil function can modify the spatial distribution of light in the maximum defocussed plane ($Y_{D} = 2\pi$), results in PSF with improved resolution.

In this work, efficient amplitude-apodization pupils have been presented for tailoring the point spread function (PSF), which results in a decreased full-width at half-maximum (FWHM) and suppressed sidelobes. Comparison of PSF intensity profiles for both the unapodized and apodized cases have been reported. By analysing the resulting PSFs, the well-known effects induced by monochromatic aberrations such as defocussing effect, and the primary spherical aberration have been controlled for various degrees of apodization parameter $\beta$. It is shown that the two-point resolution of the apodized optical system significantly increased in the presence of aberrations. The proposed pupil apodizer is very effective in enhancing the resolution of the optical systems applicable in imaging and focussing applications.