Imaging optical system, and image capture device and camera system using the imaging optical system

An imaging optical system comprising:

• a front group having positive power;
• an aperture stop;
• a single lens Fn arranged adjacent to the aperture stop and having negative power;
• and
• a rear group having power,
• the front group, the aperture stop, the single lens Fn, and the rear group being arranged in this order such that the front group is located closer to an object than any of the aperture stop, the single lens Fn, or the rear group is and that the rear group is located closer to an image than any of the front group, the aperture stop, or the single lens Fn is,
• the front group including:
• a first lens having positive power;
• a second lens having negative power;
• and
• a lens LG1R having positive power,
• the first lens, the second lens, and the lens LG1R being arranged in this order such that the first lens is located closest to the object and that the lens LG1R is located closest to the image,
• the rear group including a lens LGnR having negative power and located closest to the image, wherein
• while the imaging optical system is focusing to make a transition from an infinity in-focus state to a close-object in-focus state, neither the front group nor the rear group moves but the single lens Fn moves along an optical axis toward the image, and
• the imaging optical system satisfies the following Inequality (1):
• 0.38<fLG1R/fG1<1.75 (1)
• where fG1 is a focal length of the front group and fLG1R is a focal length of the lens LG1R.