PURPOSE: To obtain excellent contrast over the entire image plane by using a Topogon type of four-group, four-element constitution and satisfying specific numerals.

CONSTITUTION: This is the Topogon type of four-group, four-element constitution consisting of a positive meniscus lens L1 having its convex surface on an object side as a 1st group, a negative meniscus lens L2 having its convex surface on the object side as a 2nd group, a negative meniscus lens L3 which has its convex surface on the image side as a 3rd group, a positive meniscus lens L4 which has its convex surface on the image side as a 4th group, and a stop surface r5 which is positioned between the 2nd group lens and the 3rd group lens. Then, they have numerals shown in I. Here, r1, r2Wr4, and r6Wr9 are the radii of curvature of respective refracting surfaces in order from the object side, r5 the stop surface, d1Wd3 and d6Wd8 the surface gaps of the lenses, d4 and d5 the distances from the lens surfaces to the stop surface, n1Wn4 the refractive indexes of the respective lenses, ν1Wν4 the Abbe numbers of the respective lenses, (f) the focal lengths of the lenses, and ω a half field angle. Consequently, the excellent contrast is obtained over the entire image plane.