FOUR-MIRROR LENS Russian patent published in 2015 - IPC G02B17/06 

FIELD: physics.

SUBSTANCE: lens includes a first mirror in the form of an off-axis fragment of a concave spherical converging mirror, facing the object plane with its concave side, a second mirror in the form of a convex spherical diverging mirror, facing the first mirror with its convex side, a third mirror in the form of an off-axis fragment of a concave aspherical converging mirror, facing a fourth mirror with its concave side, a fourth mirror in the form of a fragment of a concave aspherical converging mirror, facing the image plane with its concave side, and an aperture diaphragm. The centres of curvature of all optical surfaces lie on a common axis. In the meridian section, the second mirror is symmetrical relative to the optical axis, the first mirror lies below the optical axis, the third mirror is above the optical axis and the fourth mirror is above the third mirror. The aperture diaphragm coincides with the holder of the second mirror.

EFFECT: absence of central screening, high image quality and improved manufacturability.

2 dwg, 1 tbl