Patent ID: 8164836

Claim:
A zoom objective lens for endoscopes, characterized by having an angle of view (2ω) of 100° or greater at a wide-angle end, and comprising, in order from an object side thereof, a positive first group, a negative second group and a positive third lens group, wherein: said third group comprises a positive first (3-1) subgroup and a positive second (3-2) subgroup, the second group comprises subgroups, wherein a lens subgroup in at least said second group moves to (1) bring about a change in a focal length of a whole system and (2) correct an image position for movement in association with a focal length change, and one subgroup in said second group and said third group moves to an image side from a longer working distance (WD) side being a far end toward a shorter working distance side being a near end to correct a focal position for movement in association with a working distance change, and wherein said zoom objective lens for endoscopes satisfies the following conditions: 0.4<( D 12 t−D 12 w )/ fw≦ 1.077 (1)′ 0.02<Δ Dwd/fw< 0.4 (2) 0<( rb+ra )/( rb−ra )<2 (3) −0.7<1/β wd< 0.2 (4) where fw is a focal length of a whole system at the wide-angle end, a figure being obtained in a far end-defining working distance; D 12 w is a spacing between the first group and the second group at the wide-angle end; D 12 t is a spacing between the first group and the second group at a telephoto end; ΔDwd is an amount of movement of a moving group upon changing of the working distance from a far end to a near end, provided that a plus sign is indicative of a direction of movement of the moving group to an image side; ra is a radius of curvature of an image-side surface of a first lens in the first group; rb is s radius of curvature of an object-side surface of a second lens in the first group; and βwd is an imaging magnification of the moving group upon a working distance change, a figure being obtained at the wide-angle end in a far end-defining working distance.