Patent ID: 7738182

Claim:
An image pickup optical system comprising: a first lens unit having negative refractive power; a second lens unit having positive refractive power and being disposed closer to an image side than the first lens unit, which moves at the time of focusing; and an aperture; wherein the image pickup optical system includes one or more cemented lenses disposed closer to the image side than the aperture; and one or more negative lenses disposed closer to an object side than the aperture; and wherein a diffraction optical part is provided on the joint surface of a first cemented lens of the one or more cemented lenses, and the conditional expressions of −0.1 <f /(ν RN ×f RN )<−0.02, 80<ν FN <97, | r avr /r DOE |<3, and −0.02 P ΘgF −(−1.625×10 −3 ×ν RP +0.642)<0.03 are satisfied in which f represents the focal length of the whole system, ν RN and f RN represent the Abbe number of the material of a negative lens of a second cemented lens of the one or more cemented lenses, and the focal length of the negative lens of the second cemented lens of the one or more cemented lenses within the air, respectively, ν FN represents the maximum Abbe number, of the Abbe number of the material of a negative lens disposed closer to the object side than the aperture, r avr represents the average value between the curvature radius of a face closest to the object side and the curvature radius of a face closest to the image side of the first cemented lens including the diffraction optical part, r DOE represents the curvature radius of the diffraction optical part, P ΘgF represents the partial dispersion ratio of a positive lens having the maximum difference of a partial dispersion ratio as to a reference line of the material of a positive lens disposed closer to the image side than the aperture, and ν RP represents the Abbe number of the material of a positive lens having the maximum difference of a partial dispersion ratio as to a reference line of the material of a positive lens disposed closer to the image side than the aperture.