The imaging lens consists of a positive first lens group, a stop, and a positive second lens group in order from the object side to the image side. An Ln lens, which is a negative lens having an absolute value of a curvature radius of an image side surface smaller than an absolute value of a curvature radius of an object side surface, is disposed at a position closest to the image side in the first lens group. In a Cartesian coordinate system in which a horizontal axis is an Abbe number ν and a vertical axis is a partial dispersion ratio θ, ν and θ of the Ln lens are included in a predetermined region.

A light blocking sheet having a central axis includes a central hole and a plurality of inner extended portions. The central axis passes through the central hole, which is enclosed by a hole inner surface. The hole inner surface has a first corresponding circle and a second corresponding circle, wherein a diameter of the first corresponding circle is greater than a diameter of the second corresponding circle. The inner extended portions are adjacent to and surround the central hole, wherein each of the inner extended portions is extended and tapered from the first corresponding circle towards the second corresponding circle and includes an inner surface, and the inner surface includes a line pair. The line pair includes two line sections, wherein one end of one line section thereof and one end of the other line section thereof are towards the second corresponding circle and approach to each other.

A light blocking sheet having a central axis includes a central hole and a plurality of inner extended portions. The central axis passes through the central hole, which is enclosed by a hole inner surface. The hole inner surface has a first corresponding circle and a second corresponding circle, wherein a diameter of the first corresponding circle is greater than a diameter of the second corresponding circle. The inner extended portions are adjacent to and surround the central hole, wherein each of the inner extended portions is extended and tapered from the first corresponding circle towards the second corresponding circle and includes an inner surface, and the inner surface includes a line pair. The line pair includes two line sections, wherein one end of one line section thereof and one end of the other line section thereof are towards the second corresponding circle and approach to each other.

An optical system consists of, in order from an object side to an image side, a front unit, an aperture stop, and a rear unit having positive refractive power as a whole. The rear unit includes a final lens disposed closest to the image side and having positive refractive power. A number of inequalities relating to the spatial relationship between the lenses and their refractive powers are satisfied.

An optical system consists of, in order from an object side to an image side, a front unit, an aperture stop, and a rear unit having positive refractive power as a whole. The rear unit includes a final lens disposed closest to the image side and having positive refractive power. A number of inequalities relating to the spatial relationship between the lenses and their refractive powers are satisfied.

An endoscope objective optical system includes in order from an object side, a front group having a positive refractive power, an aperture stop, and a rear group having a positive refractive power. The front group includes a negative lens which nearest to object, a rear group includes a positive lens which is nearest to image, and the endoscope objective optical system satisfies following conditional expressions (1″′), (2) and (3″′).

−15.0<ff/f1<−4.2  (1″′)

−1.70<f1/f<−0.95  (2)

0.6<g1/g2<1.20  (3″′) where, ff denotes a focal length of the positive lens, f1 denotes a focal length of the negative lens, f denotes a focal length of the overall endoscope objective optical system, g1 denotes a focal length of the front group, and g2 denotes a focal length of the rear group.

An endoscope objective optical system includes in order from an object side, a front group having a positive refractive power, an aperture stop, and a rear group having a positive refractive power. The front group includes a negative lens which nearest to object, a rear group includes a positive lens which is nearest to image, and the endoscope objective optical system satisfies following conditional expressions (1″′), (2) and (3″′).

−15.0<ff/f1<−4.2  (1″′)

−1.70<f1/f<−0.95  (2)

0.6<g1/g2<1.20  (3″′) where, ff denotes a focal length of the positive lens, f1 denotes a focal length of the negative lens, f denotes a focal length of the overall endoscope objective optical system, g1 denotes a focal length of the front group, and g2 denotes a focal length of the rear group.

Embodiments of the present disclosure relate to the technical field of projection, and provide a double telecentric projection lens and a projection system. The double telecentric projection lens includes a first lens group, an aperture stop, and a second lens group that are successively arranged from an object side to an image side, a center of the aperture stop being at a rear focus of the first lens group and a front focus of the second lens group; wherein a focal power of the double telecentric projection lens is greater than 0.03, an object-side numerical aperture of the double telecentric projection lens is 1.7, and an image-side numerical aperture of the double telecentric projection lens is 5.95.

Embodiments of the present disclosure relate to the technical field of projection, and provide a double telecentric projection lens and a projection system. The double telecentric projection lens includes a first lens group, an aperture stop, and a second lens group that are successively arranged from an object side to an image side, a center of the aperture stop being at a rear focus of the first lens group and a front focus of the second lens group; wherein a focal power of the double telecentric projection lens is greater than 0.03, an object-side numerical aperture of the double telecentric projection lens is 1.7, and an image-side numerical aperture of the double telecentric projection lens is 5.95.

An imaging lens includes, successively in order from a position closest to an object side, a positive first lens group that does not move during focusing, a stop, and a positive second lens group that moves during focusing. The second lens group consists of all lenses that integrally move during focusing. The imaging lens satisfies predetermined conditional expressions.