Objective lens for endoscopes
First Claim
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 an 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, andthe rear lens unit comprising;
a third lens element with positive refracting power, with an absolute value of a radius of curvature of an image-side surface being lower than an absolute value of a radius of curvature of an object-side surface;
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
0.93<
(D1+D2−
f1)/(2×
f3)<
1.13where 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 a radius of curvature of an image-side surface of the first lens element is denoted by R2;
D is an equivalent air length along an optical axis 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 along the optical axis from a vertex of the object-side surface of the first lens element to the aperture stop;
D2 is an equivalent air length along the optical axis from the aperture stop to a vertex of the image-side surface of the third lens element;
f1 is a focal length of the first lens element; and
f3 is a focal length of the third lens element.
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Accused Products
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 and a second lens element with positive refracting power, and the rear lens unit includes a third lens element with positive refracting power, 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; D is a distance 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 from the aperture stop to a vertex of 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.
69 Citations
8 Claims
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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 an 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 an absolute value of a radius of curvature of an image-side surface being lower than an absolute value of a radius of curvature of an object-side surface; 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
0.93<
(D1+D2−
f1)/(2×
f3)<
1.13where 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 a radius of curvature of an image-side surface of the first lens element is denoted by R2;
D is an equivalent air length along an optical axis 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 along the optical axis from a vertex of the object-side surface of the first lens element to the aperture stop;
D2 is an equivalent air length along the optical axis from the aperture stop to a vertex of the image-side surface of the third lens element;
f1 is a focal length of the first lens element; and
f3 is a focal length of the third lens element.- View Dependent Claims (2, 3, 4)
-
-
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 an 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 facing an image side configured as an aspherical surface whose curvature moderates in going from a center to a periphery; 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)<
1.13where 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 a radius of curvature of an image-side surface of the first lens element is denoted by R2;
D is an equivalent air length along an optical axis 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 along the optical axis from a vertex of the object-side surface of the first lens element to the aperture stop;
D2 is an equivalent air length along the optical axis from the aperture stop to a vertex of the image-side surface of the third lens element;
f1 is a focal length of the first lens element; and
f3 is a focal length of the third lens element.- View Dependent Claims (6, 7, 8)
-
Specification