The invention provides an optical instrument including means (1, 2) to
produce an optical image to be viewed by an observer including a
diffractive element (7) located at an intermediate focal or image plane
(4) of the optical instrument and comprising a pattern of a plurality of
areas effective to cause diffraction interference in light passing
through the optical instrument and thereby produce an expanded exit pupil
(6) comprising a combination of a multiplicity of exit pupils displaced
relative to one another transverse to an optical axis (3) of said
instrument.