Patent ID: 11867889
Assignee: NITTOH INC.
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. A lens system for imaging consisting, in order from an object side, of a first lens group that has negative refractive power, a second lens group that has positive refractive power, a third lens group that has positive refractive power, a stop, and a fourth lens group that has positive refractive power,
wherein the third lens group includes, at a position closest to an image plane side, a cemented lens disposed on the object side of the stop and including an image plane side-surface with a surface that is concave on the object side,
the fourth lens group includes, at a position closest to the object side, a cemented lens disposed closest to the image plane side of the stop and including an object side surface with a surface that is concave on the image plane side, and
the cemented lens disposed on the object side of the stop and the cemented lens disposed on the image plane side of the stop have negative refractive powers,
a radius of curvature g3er of the surface that is concave on the object side, a radius of curvature g4fr of the surface that is concave on the image surface side, a focal length B2f of the cemented lens disposed on the object side of the stop and a focal length B3f of the cemented lens disposed on the image plane side of the stop satisfy following conditions:

2.5≤|g4fr/g3er|≤4.0, and

1.7≤B3f/B2f≤3.0.