Objective lens system

Claim 1

An objective lens system comprising, in order from the object side: a first lens unit consisting of a lens element having a homogeneous lens medium and having a negative refracting power, said first lens unit being the most object-side lens unit of said objective system; and a second lens unit consisting of a lens element having a radial type gradient refractive index and having a positive refractive power, said second lens unit being the second most object-side lens unit of said objective system, wherein only one radial type gradient index lens element, which has a refractive index distribution in a radial direction from an optical axis, is disposed in said second lens unit and in the lens system as a whole, wherein said radial type gradient index lens element has a planar surface on at least one side, and wherein said radial type gradient index lens element satisfies the following condition (6): 1/V.sub.10 <0.01 (6) wherein the reference symbol V 10 represents a dispersing power of said radial type gradient index lens element which is given by the formula (c) shown below: V.sub.10 =N.sub.10d /(N.sub.10F -N.sub.10c) wherein the reference symbols N 10d , N 10F and N 10C designate values of a coefficient of a term r 2 for the d-line, F-line and C-line, respectively, when a refractive index of said radial type gradient index lens element is expressed as a polynomial of r.