To obtain an optical system which performs excellent eccentricity adjustment with the constitution of small number of lenses and whose producing performance is hardly deteriorated in comparison with designing performance by assembling a 1st lens component from the object side of a lens chamber and a 2nd lens component from the image side of the lens chamber and satisfying specified conditions.

The 1st lens component L12 is assembled in the lens chamber 1 from the object side of the lens chamber 1 and the 2nd lens component L13 is assembled in the chamber 1 from the image side of the chamber 1, and at least either of the components L12 and L13 has a lens surface formed to be a spherical. Then, the conditions being (r11-R12)/(r11+r12)<0.3, r22/r21<0.2, -0.5<(r11-r22)/(r11+r22)<0.5 are satisfied, where r11 and r12 are the radii of curvature of the lens surfaces of the 1st lens component L12 on the object side and the image side, and r21 and r22 are the radii of curvature of the lens surfaces of the 2nd lens component L13 on the object side and the image side.