Patent ID: 7136226

Claim:
The front teleconverter lens system having three lenses or more, and an afocal magnification, upon attaching to an imaging lens, of 1.4 or more, and forming an afocal optical system; the front teleconverter lens system comprising, in order from an object: a first lens group having positive refractive power; and a second lens group having negative refractive power; a diffractive optical surface being arranged in at least one of the first lens group and the second lens group; and wherein the following conditional expression is satisfied: 1.2<φ F/φR< 10 where φF denotes the effective diameter of the most object side lens surface of the first lens group, and φR denotes the effective diameter of the most image side lens surface of the second lens group; wherein an incident angle of the principal ray passing through the maximum image height to the diffractive optical surface is 15 degrees or less.