Extended depth of field of an imaging system with an annular aperture

A common drawback of high-resolution optical imaging systems is a short depth of field. In this work, we address this problem by considering a 4f-type imaging system with a ring-shaped aperture in the front focal plane of the second lens. The aperture makes the image consist of nearly non-diverging Bessel-like beams and considerably extends the depth of field. We consider both spatially coherent and incoherent systems and show that only incoherent light is able to form sharp and non-distorted images with extraordinarily long depth of field.