Patent ID: 8755132

Claim:
A wide angle optical system comprising: a first lens group of negative refractive power; and a second lens group of positive refractive power; the first lens group and the second lens group being arranged in the above-mentioned order from the object side; the second lens group including: a cemented doublet SU 21 ; an aperture diaphragm; a lens SU 22 ; and a positive refractive power biconvex lens L 25 ; the cemented doublet, the aperture diaphragm, the lens and the positive refractive power biconvex lens being arranged immediately following one another in the above-mentioned order from the object side; the largest air space on the axis being a combination of the front and rear air spaces of the aperture diaphragm except for air spaces after the final lens to the focal plane; the wide angle optical system being divided into the first lens group and the second lens group at the second largest air space operating as a boundary, the air space not including an air space adjacent to the diaphragm the wide angle optical system being divided into the first lens group and the second lens group at the second largest air space operating as a boundary, the air space not including an air space adjacent to the diaphragm.