Patent ID: 6980365

Claim:
An optical system comprising: (A) a microdisplay; and (B) a magnifier for producing a magnified image of the microdisplay for viewing by a human eye, said magnifier having a focal length fo, a long conjugate side in the direction of the human eye, a short conjugate side in the direction of the microdisplay, and an f-number f# for light passing from the long conjugate to the short conjugate, said magnifier, in order from the long conjugate side to the short conjugate side, comprising: (I) a first element having a first surface which is convex in the direction of the long conjugate, said first element having a focal length f 1 ; (II) a block of optical material; and (III) a second element having a second surface which is convex in the direction of the short conjugate, said second element having a focal length f 2 ; wherein: (a) f 1 >0; (b) f 2 >0; (c) the first surface is a diffractive surface, or the second surface is a diffractive surface, or the magnifier comprises a diffractive surface which is separate from the first and second surfaces; (d) axial light passing through the optical system from the long conjugate to the short conjugate and converging at the microdisplay has a beam diameter at the diffractive surface whose maximum value is d; and (e) the beam diameter value d, the focal length f 0 , and the f-number satisfy the relationship: ( f#·d ) /f 0 >0.4.