Patent ID: 8687291

Claim:
An optical system comprising: in order from an object side to an image side, a first lens unit configured to be fixed during a focusing operation, the first lens unit having a positive refractive power as a whole; a second lens unit configured to move in an optical axis direction during the focusing operation, the second lens unit having a negative refractive power as a whole; and a third lens unit positioned at the image side relative to the second lens unit, the third lens unit having a positive or negative refractive power as a whole, wherein the first lens unit is, in order from the object side to the image side, configured by a first partial lens unit, a second partial lens unit, and a third partial lens unit, wherein the first partial lens unit is configured by two positive lens components, wherein the second partial lens unit is configured by one cemented lens having a negative combined refractive power configured by cementing at least one positive lens and one negative lens, or configured by one positive lens and one negative lens having a negative combined refractive power, wherein the third partial lens unit is positioned between the second partial lens unit and the second lens unit, the third partial lens unit having a positive refractive power as a whole, and wherein following conditional expressions are met: 0.20 < f 1 Ã— L Ã— Fno â¢ / â¢ f 2 < 1.30 0.50 < ï˜ƒ âˆ i = 1 L â¢ â¢ 1 â¢ num â¢ Î² i ï˜„ Ã— L f < 9.00 where f is a focal length of a total system during focusing on infinity, f 1 is a focal length of the first lens unit, f 1A is a focal length of the first partial lens unit, L is a length from an apex of a surface closest to the object side of the optical system to an image plane, Fno is a full open F-number when focusing on an infinite object, L 1 num is a sum of a number of lens components from the first partial lens unit to the second partial lens unit, and Î² i is a combined lateral magnification of all lenses at the image side relative to an i-th lens component in order from the object side when focusing on the infinite object.