Application of a cubic phase plate to a reflecting telescope for extension of depth of field.

Wavefront coding is an accepted technique to extend the depth of field in incoherent optical systems. We present the design of a reflecting telescope with wavefront coding by employing a cubic phase plate (CPP). We propose a method to reduce the CPP size by changing its position from the aperture stop to a secondary mirror without varying the point-spread function, which is insensitive to defocusing. This change in position reduces the diameter by almost three orders and increases the third-order coefficients of the xy polynomial surface by two orders, thus easing manufacturing.