A birefringent device, which is configured to be mounted in an optical path of an optical system, has an effective area in a pupil plane. The birefringent device affects different polarization states differently and position-dependently. The birefringent device realizes a first pupil function assigned to a first polarization state and a second different pupil function assigned to a second polarization state. The pupil functions may be optimized to achieve various specific optical properties like extended depth of field.