Imaging optical system, image capture device, and camera system

An imaging optical system consisting of:

• a first lens group having positive power;
• a second lens group having negative power;
• and
• a third lens group having positive power,
• the first lens group, the second lens group, and the third lens group being arranged in this order such that the first lens group is located closer to an object than the second lens group or the third lens group is,
• the second lens group moving along an optical axis of the imaging optical system toward an image plane, while the imaging optical system is focusing to make a transition from an infinity in-focus state toward a close-object in-focus state,
• the first lens group including a negative lens having a convex surface facing the object, the negative lens being located closest to the object in the first lens group,
• the second lens group being located closer to the image plane than an aperture stop is, the second lens group consisting of:
• a positive lens Lp having a convex surface facing the object;
• and
• a negative lens Ln,
• the positive lens Lp and the negative lens Ln being arranged in this order such that the positive lens Lp is located closer to the object than the negative lens Ln is,
• the third lens group consisting of three or more lenses, the three or more lenses including one or more negative lenses, one of the three or more lenses which is located closest to the object in the third lens group being a positive lens,
• the first lens group consisting of:
• a sub-lens group G1a having negative power;
• and
• a sub-lens group G1b having positive power,
• the sub-lens group G1a and the sub-lens group G1b being arranged in this order such that the sub-lens group G1a is located closer to the object than the sub-lens group G1b is, and
• a lens belonging to the sub-lens group G1a which is located closest to the image plane in the sub-lens group G1a being a positive lens belonging to the imaging optical system which is located closer to the object than any other one of a plurality of positive lenses included in the imaging optical system is.

An imaging optical system consisting of:

• a first lens group having positive power;
• a second lens group having negative power;
• and
• a third lens group having positive power,
• the first lens group, the second lens group, and the third lens group being arranged in this order such that the first lens group is located closer to an object than the second lens group or the third lens group is,
• the second lens group moving along an optical axis of the imaging optical system toward an image plane, while the imaging optical system is focusing to make a transition from an infinity in-focus state toward a close-object in-focus state,
• the first lens group including a negative lens having a convex surface facing the object, the negative lens being located closest to the object in the first lens group,
• the second lens group being located closer to the image plane than an aperture stop is, the second lens group consisting of:
• a positive lens Lp having a convex surface facing the object;
• and
• a negative lens Ln,
• the positive lens Lp and the negative lens Ln being arranged in this order such that the positive lens Lp is located closer to the object than the negative lens Ln is,
• the third lens group consisting of three or more lenses, the three or more lenses including one or more negative lenses, one of the three or more lenses which is located closest to the object in the third lens group being a positive lens,
• the imaging optical system satisfying the following Inequality (7):
• 0
• .
• 5
• <
• B
• ⁢
• F
• /
• Y
• <
• 1.
• (
• 7
• )
• where BF is a back focus length of the imaging optical system, and
• Y is a maximum image height.