Aspheric object lens for optical data read-out apparatus

Claim 1

An object lens for an optical data read-out apparatus, comprising first and second refracting aspheric surfaces having a common optical axis, wherein said first refracting aspheric surface satisfies the following aspheric surface equation in which Y denotes height measured from said optical axis, X denotes a distance from a point whose height above the optical axis is Y to a plane which tangentially contacts the apex of said first refracting aspheric surface, C 1 is the curvature of said first refracting aspheric surface at the apex thereof, and K 1 , A.sup.(1) 4 , A.sup.(1) 6 , A.sup.(1) 10 are constants: ##EQU4## and in which said second refracting aspheric surface satisfies the following aspheric surface equation: ##EQU5## where C 2 is the curvature of said second refracting aspheric surface at the apex thereof, and K 1 A.sup.(2) 4 , A.sup.(2) 6 , A.sup.(2) 10 are constant, and furhter in which said first and second refracting aspheric surfaces satisfy the following equations: ##EQU6## in which n denotes the index of refraction of said object lens, f denotes the focal distance of said object lens, r 1 denotes the curvature at the apex of said first refracting aspheric surface and r 2 denotes the curvature at the apex of said second refracting aspheric surface.