Concentration objective composed of four lenses

Claim 1

A concentrator objective comprising a first group of lenses including first and second converging lenses and a single diverging lens and a second lens group including a single concave-convex lens, said concave-convex lens being arranged with its aplanatic object point coinciding with the image of a point object at infinity given by the lenses of the first group and the successive lenses being separated by a nonzero distance which is small in relation to the smallest focal length of the lenses wherein the dimensions and separations of the lenses are as follows: R1 +211,57 e1 16,70 R2 infinity d1 5,0 R3 +101,19 e2 16,70 R4 +198,38 d2 5,0 R5 +435,66 e3 11,69 R6 +226,60 d3 5,0 R7 + 46,18 e4 16,70 R8 + 58,25 where R1 to R8 are the upstream and downstream radii of curvature of the first and second converging lenses, the single diverging lens and the concave-convex lens respectively, e1 to e4 are their respective thicknesses on the optical axis, and d1 to d3 are the distances between them measured along the optical axis.