Objective optical system

• US 6,943,959 B2
• Filed: 06/30/2004
• Issued: 09/13/2005
• Est. Priority Date: 07/04/2003
• Status: Active Grant

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Corporation
• Inventors: Homma, Hiroyuki
• Primary Examiner(s): Dang, Hung Xuan
• Assistant Examiner(s): MARTINEZ, JOSEPH P
• Application Number:
  US10/879,086
• Publication Number:
  US 20050030639A1
• Time in Patent Office: 440 Days
• Field of Search: 359/682, 359/676, 359/677, 359/687, 359/681, 600/176, 600/160, 600/168
• US Class Current: 359/682
• CPC Class Codes: G02B 15/143507 arranged -++

Abstract

In a nearer order from its object, a first lens group which has a negative refractive power, a brightness diaphragm, and a second lens group which has a positive refractive power, and a moving lens group which moves on an optical axis, conditions such as 2≦D_L/f_W≦6, and −2≦D_VH/f_W≦0.37 are satisfied under condition that D_L (mm) indicates an air-converged length from an end surface near an image in the first lens group to an end surface nearer to an object in the moving lens group, f_W (mm) indicates a focal length in an entire system in a wide angle end, D_VH (mm) indicates a distance from the end surface near the object in the moving lens group to a front principal point. By doing this, it is possible to provide an objective optical system which can obtain a high magnification while securing a sufficient distance between the diaphragm which is disposed behind the optical axis direction converting element such as a prism to the moving lens group.

Claims

1. An objective optical system which is provided with, in a nearer order from its object, a first lens group which has a negative refractive power, a brightness diaphragm, and a second lens group which has a positive refractive power, and a moving lens group which moves on an optical axis;

wherein

conditions 2≦

D_L/f_W≦

6, and −

2≦

D_VH/f_W≦

0.37 are satisfied under condition that D_L (mm) indicates an air-converged length from an end surface near an image in the first lens group to an end surface nearer to an object in the moving lens group, f_W (mm) indicates a focal length in an entire system in a wide angle end, D_VH (mm) indicates a distance from the end surface near the object in the moving lens group to a front principal point.

2. An objective optical system according to claim 1 wherein

the focal length f_V (mm) of the moving lens group satisfies a condition 2.5≦

f_V/f_W≦

4.

3. An objective optical system according to claim 1 wherein

a magnification β

_VT in an telephoto end of the moving lens group satisfies a condition −

1.2≦

β

_VT≦

−

0.83.

4. An objective optical system according to claim 1 wherein

the moving lens group is provided with, in an order from nearer the object, at least a lens which has a positive refractive power and a lens which has a negative refractive power.

5. An objective optical system according to claim 4 wherein

the moving lens group has another lens which has a positive refractive power between the lens which has positive refractive power and the lens which has negative refractive power.

6. An objective optical system according to claim 1 wherein

the air-converged length D_A (mm) from the end surface near an image of the first lens group to a position of the diaphragm satisfies a condition 1.674(mm)≦

D_A≦

4(mm).

7. An objective optical system according to claim 1 wherein an

infra-red-ray-cutting filter is disposed between the diaphragm and the moving lens group.

8. An objective optical system according to claim 1 wherein a focal length f_T (mm) in an entire system at a telephoto end satisfies a condition 2(1/mm)≦

D_L/(f_W/f_T)≦

4(1/mm).

9. An objective optical system according to claim 1 wherein

a prism is disposed between the first lens group and the diaphragm.