Patent ID: 8947793
Filing Date: 2015-02-03
Classification: G02B

Abstract:
1. An inner focus lens system comprising, in order from an object side to an image side, a first lens unit, an aperture stop, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power, wherein a total number of lens units in the inner focus lens system is four, which is the first lens unit, the second lens unit, the third lens unit, and the fourth lens unit, wherein the first lens unit has at least two negative lenses and at least one positive lens, the second lens unit has at least one negative lens and at least one positive lens, the third lens unit has at least one negative lens, the fourth lens unit has at least one positive lens, at a time of focusing on an object at a short distance from an object at infinity, the third lens unit moves to the image side so as to lengthen a distance to the second lens unit and to shorten a distance to the fourth lens unit, and the following conditional expression (1) is satisfied: where f f is a focal length of the inner focus lens system at the time of focusing on the object at infinity.