Optical system, optical apparatus and method for manufacturing the optical system

A method for manufacturing an optical system comprising:

• in order from an object on an optical axis, a first lens group having a positive refractive power;
• a second lens group having a negative refractive power;
• a third lens group having a positive refractive power;
• and a fourth lens group having a negative refractive power,
• the method comprising disposing the first to the fourth lens groups in a lens barrel such that, during focusing, the second lens group and the third lens group move on the optical axis and distances between the lens groups adjacent to each other change,
• the method further comprising one of features A or B, wherein
• the feature A comprises:
• satisfying the following conditional expressions,
• 0.20<DG4/TL<0.40,
• 0.15<Bf/f<0.50,
• (L1R2+L1R1)/(L1R2−L1R1)<0.10,
• where DG4:
• a length of the fourth lens group on the optical axis,
• TL:
• an entire length of the optical system upon focusing on infinity,
• Bf:
• a back focus of the optical system upon focusing on infinity,
• f:
• a focal length of the optical system,
• L1R1:
• a radius of curvature of an object-side lens surface of a positive lens disposed closest to the object in the optical system, and
• L1R2:
• a radius of curvature of an image-side lens surface of the positive lens disposed closest to the object in the optical system, and
• the feature B comprises:
• satisfying the following conditional expressions,
• 0.20<DG4/TL<0.40,
• 0.60<L1S/SLn<1.00,
• (L1R2+L1R1)/(L1R2−L1R1)<0.10,
• where DG4:
• a length of the fourth lens group on the optical axis,
• TL:
• an entire length of the optical system upon focusing on infinity,
• L1S:
• a distance on the optical axis from a most object-side lens surface of the optical system to the aperture stop upon focusing on infinity,
• SLn:
• a distance on the optical axis from the aperture stop to a most image-side lens surface of the optical system upon focusing on infinity,
• L1R1:
• a radius of curvature of an object-side lens surface of a positive lens disposed closest to the object in the optical system, and
• L1R2:
• a radius of curvature of an image-side lens surface of the positive lens disposed closest to the object in the optical system.

An optical system comprising:

• in order from an object on an optical axis, a first lens group having a positive refractive power;
• a second lens group having a negative refractive power;
• a third lens group having a positive refractive power;
• and a fourth lens group having a negative refractive power,
• wherein, during focusing, the second lens group and the third lens group move on the optical axis and distances between the lens groups adjacent to each other change, and
• the following conditional expressions are satisfied,
• 0.20<DG4/TL<0.40,
• 0.60<L1S/SLn<1.00,
• (L1R2+L1R1)/(L1R2−L1R1)<0.10,
• where DG4:
• a length of the fourth lens group on the optical axis,
• TL:
• an entire length of the optical system upon focusing on infinity,
• L1S:
• a distance on the optical axis from a most object-side lens surface of the optical system to the aperture stop upon focusing on infinity,
• SLn:
• a distance on the optical axis from the aperture stop to a most image-side lens surface of the optical system upon focusing on infinity,
• L1R1:
• a radius of curvature of an object-side lens surface of a positive lens disposed closest to the object in the optical system, and
• L1R2:
• a radius of curvature of an image-side lens surface of the positive lens disposed closest to the object in the optical system.