Abstract: A telephoto lens system which composed of a front group comprising, in order from the object side, a positive first lens having a convex surface of large curvature directed toward the object, a positive meniscus second lens having a convex surface of large curvature directed toward the object and a negative third lens having a concave surface of large curvature directed toward the image, and a rear group comprising, in order from the object side, a biconvex fourth lens, a biconcave fifth lens, a positive sixth lens and a seventh lens having a weak positive refractive power, all lenses except the seventh lens being moved in unison to effect focusing. The lens system satisfies conditions which result in a light weight lens system having a focal length of about 100 mm and a large effective aperture ratio of 1:2.0, and which is capable of satisfactory compensation for spherical aberration and astigmatism over a shooting range from infinity to close-up at a magnification of about -0.1.times..