Objective lens for endoscopes

• US 20090161234A1
• Filed: 12/18/2008
• Published: 06/25/2009
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Medical Systems Corporation (Olympus Corporation)
• Inventors: Sasamoto, Tsutomu
• Granted Patent: US 8,098,441 B2
• Time in Patent Office: Days
• US Class Current: 359/717
• CPC Class Codes: G02B 13/04 Reversed telephoto objectives
• CPC Class Codes: G02B 23/2407 Optical details

Abstract

An objective lens for endoscopes has a front lens unit and a rear lens unit with an aperture stop between them. The front lens unit includes a first lens element with negative refracting power of a meniscus shape, with a convex surface facing the object side and a second lens element with positive refracting power, and the rear lens unit includes a third lens element with positive refracting power, with a surface of the minor radius of curvature facing the image side and a cemented lens component of a fourth lens element with positive refracting power and a fifth lens element with negative refracting power. The objective lens satisfies the following conditions:

−2<SF<−0.9

0.94<D/(f×sin θ)<1.7

0.86<(D₁+D₂−f₁)/(2×f₃)<1.13

where SF is the shape factor of the first lens element and is a value expressed by SF=(R2+R1)/(R2−R1) when the radius of curvature of the object-side surface is denoted by R1 and the radius of curvature of the image-side surface is denoted by R2; D is a distance (an equivalent-air medium length) from the vertex of the image-side surface of the first lens element to the aperture stop; f is the combined focal length of the entire system; θ is a half angle of view; D₁ is an actually measured distance from the vertex of the object-side surface of the first lens element to the aperture stop; D₂ is a distance (an equivalent-air medium length) from the aperture stop to the image-side surface of the third lens element; f₁ is the focal length of the first lens element; and f₃ is the focal length of the third lens element.

Claims

1. An objective lens for endoscopes having a front lens unit and a rear lens unit with an aperture stop between the front lens unit and the rear lens unit,

the front lens unit comprising, in order from the object side:

a first lens element with negative refracting power of a meniscus shape, with a convex surface facing the object side; and

a second lens element with positive refracting power, and

the rear lens unit comprising;

a third lens element with positive refracting power, with a surface of a minor radius of curvature facing an image side;

a fourth lens element with positive refracting power; and

a fifth lens element with negative refracting power,

wherein the fourth lens element and the fifth lens element are cemented and the objective lens satisfies the following conditions;

−

2<

SF<

−

0.9

0.94<

D/(f×

sin θ

)<

1.7

0.86<

(D₁+D₂−

f₁)/(2×

f₃)<

1.13

where SF is a shape factor of the first lens element and is a value expressed by SF=(R2+R1)/(R2−

R1) when a radius of curvature of an object-side surface of the first lens element is denoted by R1 and the radius of curvature of an image-side surface is denoted by R2;

D is a distance (an equivalent-air medium length) from a vertex of the image-side surface of the first lens element to the aperture stop;

f is a combined focal length of an entire system;

θ

is a half angle of view;

D₁ is an actually measured distance from the vertex of the object-side surface of the first lens element to the aperture stop;

D₂ is a distance (an equivalent-air medium length) from the aperture stop to the image-side surface of the third lens element;

f₁ is a focal length of the first lens element; and

f₃ is the focal length of the third lens element.

2. An objective lens for endoscopes according to claim 1, satisfying the following condition:

−

1.5<

SF<

−

1.0

3. An objective lens for endoscopes according to claim 1, satisfying the following condition:

0.90<

(D₁+D₂−

f₁)/(2×

f₃)<

1.06

4. An objective lens for endoscopes according to claim 1, wherein the third lens element is a lens element with positive refracting power, with a surface configured as an aspherical surface whose curvature moderates in going from a center to a periphery facing the image side.

5. An objective lens for endoscopes having a front lens unit and a rear lens unit with an aperture stop between the front lens unit and the rear lens unit,

the front lens unit comprising, in order from the object side:

a first lens element with negative refracting power of a meniscus shape, with a convex surface facing the object side; and

a second lens element with positive refracting power, and

the rear lens unit comprising;

a third lens element with positive refracting power, with a surface configured as an aspherical surface whose curvature moderates in going from a center to a periphery facing the image side;

a fourth lens element with positive refracting power; and

a fifth lens element with negative refracting power,

wherein the fourth lens element and the fifth lens element are cemented and the objective lens satisfies the following conditions;

−

2<

SF<

−

0.9

0.65<

D/(f×

sin θ

)≦

0.94

0.86<

(D₁+D₂−

f₁)/(2×

f₃)<

1.13

where SF is a shape factor of the first lens element and is a value expressed by SF=(R2+R1)/(R2−

R1) when a radius of curvature of an object-side surface of the first lens element is denoted by R1 and the radius of curvature of an image-side surface is denoted by R2;

D is a distance (an equivalent-air medium length) from a vertex of the image-side surface of the first lens element to the aperture stop;

f is a combined focal length of an entire system;

θ

is a half angle of view;

D₁ is an actually measured distance from the vertex of the object-side surface of the first lens element to the aperture stop;

D₂ is a distance (an equivalent-air medium length) from the aperture stop to the image-side surface of the third lens element;

f₁ is a focal length of the first lens element; and

f₃ is the focal length of the third lens element.

6. An objective lens for endoscopes according to claim 5, satisfying the following condition:

−

1.5<

SF<

−

1.0

7. An objective lens for endoscopes according to claim 5, satisfying the following condition:

0.90<

(D₁+D₂−

f₁)/(2×

f₃)<

1.06

8. An objective lens for endoscopes according to claim 5, satisfying the following condition:

0.8<

D/(f×

sin θ

)≦

0.94