requirement 1 is fulfilled further taking the axial direction as the x axis and the direction perpendicular to the optical axis as the y axis stipulating that the quantity measured in a direction in which the light progresses shall have the positive sign and locating the original point at the intersection of the vertex of the front surface of the 4th component and the x axis the difference u03b4x between the aspheric surface and a spherical surface assumed to have a radius of curvature equal to that of curvature of the paraxial region of the aspheric surface which contributes to the determination of the focal length is expressed by the following formula equ4 where r 7 is the radius of curvature of the paraxial region of the front surface of the 4th lens component r 7 is the radius of the curfature of the reference spherical surface of the lens defined by the following formula equ5 bi is the coefficient of the i th odd numbered power term then letting u03b4x 0 7r 7 denote the value of u03b4x at the height r 7 x0 7 in y coordinate and u03b4x 0 5r 7 the value of u03b4x at the height r 7 x0 5 the following requirements 2 and 3 are fulfilled equ6 in this embodiment the 1st to 4th lens components take the form of a positive meniscus lens a bi concave lens a bi convex lens and a negative meniscus lens respectively the significance of each of these inequalities is as follows when the lower limit of inequality 1 is.