An image capturing optical system includes four lens elements which are, in order from an object side to an image side along an optical path: a first lens element, a second lens element, a third lens element and a fourth lens element. The first lens element with negative refractive power has an image-side surface being concave in a paraxial region thereof. The second lens element has positive refractive power. The third lens element with positive refractive power has an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof. The image capturing optical system further includes an aperture stop located between the second lens element and the third lens element.

A four-piece optical lens for capturing image and a five-piece optical module for capturing image are provided. In the order from an object side to an image side, the optical lens along the optical axis includes a first lens with positive refractive power; a second lens with refractive power; a third lens with refractive power; and a fourth lens with refractive power; and at least one of the image-side surface and object-side surface of each of the four lens elements are aspheric. The optical lens can increase aperture value and improve the imagining quality for use in compact cameras.

There is provided a small-sized and bright objective optical system for endoscope with a wide angle of view and thin diameter, which enables to achieve a highly-defined image.

The objective optical system for endoscope includes in order from an object side: a front lens group having a negative refractive power as a whole, an aperture stop; and a rear lens group having a positive refractive power as a whole, wherein the front lens group includes in order from the object side, a first lens which is a single lens having a negative refractive power and a second lens which is a single lens having a positive refractive power, and the rear lens group includes a third lens which is a single lens having a positive refractive power and a cemented lens of a fourth lens having a positive refractive power and a fifth lens having a negative refractive power, and an object-side surface of the first lens is a flat surface, and the second lens has a meniscus shape having a convex surface directed toward an image side, and the third lens has a biconvex shape, and the objective optical system for endoscope satisfies the following conditional expressions (1) and (2)

−2.0≦f.sub.1/Ih≦−1.39  (1)

−0.2≦SF.sub.3≦0.61  (2) where, f.sub.1 denotes a focal length of the first lens, Ih denotes the maximum image height of the objective optical system for endoscope, and SF.sub.3 denotes a shape factor which is expressed by SF.sub.3=(R.sub.3L+R.sub.3R)/(R.sub.3L−R.sub.3R), when a radius of curvature of an object-side surface of the third lens is let to be R.sub.3L and a radius of curvature of an image-side surface of the third lens is lens to be R.sub.3R.

There is provided a small-sized and bright objective optical system for endoscope with a wide angle of view and thin diameter, which enables to achieve a highly-defined image.

The objective optical system for endoscope includes in order from an object side: a front lens group having a negative refractive power as a whole, an aperture stop; and a rear lens group having a positive refractive power as a whole, wherein the front lens group includes in order from the object side, a first lens which is a single lens having a negative refractive power and a second lens which is a single lens having a positive refractive power, and the rear lens group includes a third lens which is a single lens having a positive refractive power and a cemented lens of a fourth lens having a positive refractive power and a fifth lens having a negative refractive power, and an object-side surface of the first lens is a flat surface, and the second lens has a meniscus shape having a convex surface directed toward an image side, and the third lens has a biconvex shape, and the objective optical system for endoscope satisfies the following conditional expressions (1) and (2)

−2.0≦f.sub.1/Ih≦−1.39  (1)

−0.2≦SF.sub.3≦0.61  (2) where, f.sub.1 denotes a focal length of the first lens, Ih denotes the maximum image height of the objective optical system for endoscope, and SF.sub.3 denotes a shape factor which is expressed by SF.sub.3=(R.sub.3L+R.sub.3R)/(R.sub.3L−R.sub.3R), when a radius of curvature of an object-side surface of the third lens is let to be R.sub.3L and a radius of curvature of an image-side surface of the third lens is lens to be R.sub.3R.

A four-piece infrared single wavelength lens system includes, in order from the object side to the image side: a stop, a first lens element with a refractive power having an object-side surface being convex near an optical axis, a second lens element with a positive refractive power, a third lens element with a positive refractive power having an object-side surface being concave near the optical axis and an image-side surface being convex near the optical axis, a fourth lens element with a negative refractive power having an object-side surface being convex near the optical axis and an image-side surface being concave near the optical axis. Such arrangements can provide a four-piece infrared single wavelength lens system which has a wide field of view, large stop, short length and less distortion.

A four-piece infrared single wavelength lens system includes, in order from the object side to the image side: a stop, a first lens element with a refractive power having an object-side surface being convex near an optical axis, a second lens element with a positive refractive power, a third lens element with a positive refractive power having an object-side surface being concave near the optical axis and an image-side surface being convex near the optical axis, a fourth lens element with a negative refractive power having an object-side surface being convex near the optical axis and an image-side surface being concave near the optical axis. Such arrangements can provide a four-piece infrared single wavelength lens system which has a wide field of view, large stop, short length and less distortion.

An optical image capturing system is provided. In the order from an object side to an image side, the optical image capturing system includes a first lens with positive refractive power; a second lens with refractive power; a third lens with refractive power; and a fourth lens with refractive power; and at least one of the image-side surface and object-side surface of each of the four lens elements is aspheric. The optical lens can increase aperture value and improve the imagining quality for use in compact cameras.

An optical image capturing system is provided. In the order from an object side to an image side, the optical image capturing system includes a first lens with positive refractive power; a second lens with refractive power; a third lens with refractive power; and a fourth lens with refractive power; and at least one of the image-side surface and object-side surface of each of the four lens elements is aspheric. The optical lens can increase aperture value and improve the imagining quality for use in compact cameras.

An imaging lens is substantially constituted by: a negative first lens group; a positive second lens group; an aperture stop; a positive third lens group; and a negative fourth lens group; provided in this order from an object side. The first lens group is constituted only by two or more negative lenses. The second lens group has a positive lens at the most object side thereof. The third lens group has a negative lens having a concave surface toward the object side at the most object side thereof. The fourth lens group is constituted by a single negative lens. The fourth lens group moves from the object side to an image side when changing focus from an object at infinity to an object at an extremely close distance. Only the fourth lens group moves during focusing operations.

An objective optical system for endoscope includes, a first group having a positive refractive power, an aperture stop, and a second group having a positive refractive power, wherein the first group includes a first lens having a negative refractive power, and a second lens having a positive refractive power, the second group includes a cemented lens, and the cemented lens includes a third lens having a positive refractive power and a fourth lens having a negative refractive power, and the following conditional expressions (1), (2), (3), (4), (7) and (9) are satisfied:

0.13≦La/Lb≦0.17   (1),

−2.7≦f4/f≦−2.2   (2),

−0.7≦(ne2×f2)/(ne4×f4)≦0   (3),

2.5≦νd3/νd4≦3.5   (4)

−2.6≦r2o/rcc≦−2   (7), and

−1.2≦r2i/f2≦−0.9   (9).