An optical device for a system presenting collimated images through an
off-axis spherical concave mirror. An image can be presented to a user
with correction of eccentric distortion caused by the off-axis spherical
concave mirror without altering the quality of the image. A diffractive
mirror is set in the neighborhood of an intermediate image, and preferably
a second intermediate image. The extent of the neighborhood is limited by
image resolution and, in the neighborhood, the correction by the
diffractive mirror does not alter the resolution. The diffractive mirror
may include a hologram which may be digital or made of a photosensitive
material. A hologram substrate is preferably not planar to operate partly
upon the correction, the residual correction being carried out by the
hologram. Such a device may find application to an aircraft pilot's visor.
