The phenomenon of polarization has now become important in the field of optical imagery. It is well-known that the imaging properties of optical systems are determined by the diffraction properties of their apertures. This calls for a systematic study of diffraction properties of different apertures in presence of zonal masking devices. In the present paper, we study the diffraction properties of a circular aperture where the zonal polarization masks are mutually orthogonal. The variation of the PSF and OTF of such a system with the orientation of the analyzer placed at the output side have been studied. © 2012 Elsevier GmbH. All rights reserved.