US 12,455,430 B2
Optical system, optical apparatus, and method of manufacturing optical system
Saburo Masugi, Kawasaki (JP); and Tomoyuki Sashima, Tokyo (JP)
Assigned to Nikon Corporation, Tokyo (JP)
Appl. No. 17/052,794
Filed by Nikon Corporation, Tokyo (JP)
PCT Filed May 18, 2018, PCT No. PCT/JP2018/019268
§ 371(c)(1), (2) Date Mar. 22, 2021,
PCT Pub. No. WO2019/220617, PCT Pub. Date Nov. 21, 2019.
Prior Publication US 2021/0247596 A1, Aug. 12, 2021
Int. Cl. G02B 9/12 (2006.01); G02B 15/22 (2006.01); G02B 13/18 (2006.01)
CPC G02B 9/12 (2013.01) [G02B 15/22 (2013.01); G02B 13/18 (2013.01)] 13 Claims
OG exemplary drawing
 
1. An optical system comprising:
a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power, arranged in order from an object, wherein
when focusing, the second lens group moves along an optical axis,
the third lens group comprises at least one positive lens and at least one negative lens, and
the optical system satisfies the following conditional expressions
0.200<f1/f2<2.500
0.70<TLa/(−f3)<4.00
0.82<TLa/f1<4.00
0.100<BFa/f<0.320
where f1 is a focal length of the first lens group,
f2 is a focal length of the second lens group,
f3 is a focal length of the third lens group,
TLa is a total distance on the optical axis from the lens surface closest to the object in the optical system to an image surface, wherein a portion of the total distance, the portion being the distance from a lens surface closest to the image surface in the optical system to the image surface, is an air equivalent distance,
f is a focal length of the optical system, and
BFa is the air equivalent distance on the optical axis from the lens surface on the image side to the image surface for the lens disposed farthest on the image side in the optical system.