PURPOSE: To form a compact lens system whose various aberrations are sufficiently corrected by constituting the lens system of four groups and specifying the system with specific conditions.

CONSTITUTION: The lens system is constituted of a 1st group consisting of a positive meniscus resin lens turning its convex face to the object side, a 2nd group consisting of a resin lens having concave faces on both the sides, a 3rd group consisting of a glass lens having projected faces on both the sides and a 4th group consisting of a negative meniscus resin lens turning its concave face to the object side which are successively arranged from the object side and the lens groups are satisfied with the conditions shown by inequalities. In the inequalities, N1WN3 are the refractive indexes of the 1stW3rd groups. Consequently, the lightweight lens system having about 60° picture angle and about 1.0 telescopic ratio, constituted of four lenses in four groups and sufficiently corrected at its various aberrations can be obtained.