Patent ID: 6788442
Filing Date: 2004-09-07
Classification: G02B

Abstract:
An optical device for a helmet viewfinder presenting a collimated image to a user, comprising:an imager configured to form an image; a diffractive field mirror; and an off-axis spherical concave mirror, wherein a first intermediate image is formed between said diffractive field mirror and said off-axis spherical concave mirror, said diffractive field mirror is configured to correct an image distortion caused by the off-axis spherical concave mirror, said image distortion being an off-centering distortion of the second kind corresponding to an absence of symmetry of revolution caused by the spherical concave mirror being viewed at an oblique angle with respect to an axis thereof, and a second intermediate image is formed in a vicinity of said diffractive field mirror, the vicinity having an extent limited to a maximum distance of the image beyond which resolution of the image at a center of a field of the device is degraded.