OBJECTIVE OPTICAL SYSTEM FOR ENDOSCOPE

• US 20170038563A1
• Filed: 10/24/2016
• Published: 02/09/2017
• Est. Priority Date: 10/30/2014
• Status: Active Grant

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Corporation
• Inventors: SATO, Shinya
• Granted Patent: US 9,766,437 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 1/00096 Optical elements
• CPC Class Codes: G02B 13/04 Reversed telephoto objectives
• CPC Class Codes: G02B 23/243 Objectives for endoscopes
• CPC Class Codes: G02B 7/105 with movable lens means specially adapted for focusing at close distances
• CPC Class Codes: G02B 9/60 having five components only

Abstract

There is provided an objective optical system for endoscope with a lesser number of lenses and high-performance optical characteristics, equipped with a long back focus and a focusing function, and in which the aberration fluctuation accompanied by focusing is small.

The objective optical system for endoscope includes in order from an object side, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power, wherein the third group includes in order from the object side, a positive cemented lens and a positive lens, and observation from a normal observation state up to a close observation state is possible by moving the second group along an optical axis and the first group includes a cemented lens, and the first group includes in order from the object side, a negative lens having a concave surface directed toward an image side, and the cemented lens, and the cemented lens is a negative cemented lens, and the second group includes a positive meniscus lens having a convex surface directed toward the object side, and the objective optical system for endoscope satisfies the following conditional expression (1).

4≦FB/f≦7   (1)

• • where,
  • FE denotes a hack focus of the objective optical system for endoscope, and
  • f denotes a focal length of the overall objective optical system for endoscope in the normal observation state.

Claims

1. An objective optical system for endoscope, comprising in order from an object side:

a first group having a negative refractive power;

second group having a positive refractive power; and

a third group having a positive refractive power, wherein

the third group includes in order from the object side, positive cemented lens and a positive lens, and

observation from a normal observation state up to a close observation state is possible by moving the second group along an optical axis, and

the first group includes a cemented lens, and

the first group includes in order from the object side, a negative lens having a concave surface directed toward an image side, and the cemented lens, and

the cemented lens is a negative cemented lens, and

the second group includes a positive meniscus lens having a convex surface directed toward the object side, and

the objective optical system for endoscope satisfies the following conditional expression (1)

4≦

FB/f≦

7  

 

(1)

where,

FB denotes a back focus of the objective optical system for endoscope, and

f denotes a focal length of the overall objective optical system for endoscope in the normal observation state.

2. The objective optical system for endoscope according to claim 1, wherein the objective optical system for endoscope satisfies the following conditional expression (2)

8≦

|f_c1/f|≦

22  

 

(2)

where,

f_c1 denotes a focal length of the cemented lens in the first group, and

f denotes the focal length of the overall objective optical system for endoscope in the normal observation state.

3. The objective optical system for endoscope according to claim 1, wherein the objective optical system for endoscope satisfies the following conditional expression (3)

1≦

|f_c1/f_c3|≦

2.8  

 

(3)

where,

f_c1 denotes a focal length of the cemented lens in the first group, and

f_c3 denotes a focal length of the positive cemented lens in the third group.

4. The objective optical system for endoscope according to claim 1, wherein the objective optical system for endoscope satisfies the following conditional expression (4)

4≦

f_c3/f≦

12  

 

(4)

where,

f_c3 denotes a focal length of the positive cemented lens in the third group, and

f denotes the focal length of the overall objective optical system for endoscope in the normal observation state.