THREE-PIECE INFRARED SINGLE WAVELENGTH PROJECTION LENS SYSTEM
A three-piece infrared single wavelength projection lens system, in order from an image side to an image source side: a stop; a first lens element with a positive refractive power having an image-side surface being convex near an optical axis and an image source-side surface being concave near the optical axis; a second lens element with a negative refractive power having an image source-side surface being concave near the optical axis; and a third lens element with a positive refractive power having an image-side surface being concave near the optical axis and an image source-side surface being convex near the optical axis. Such arrangements can provide a three-piece infrared single wavelength projection lens system with better image sensing function.
1 . A three-piece infrared single wavelength projection lens system, in order from an image side to an image source side, comprising:
a stop;
a first lens element with a positive refractive power, having an image-side surface being convex near an optical axis and an image source-side surface being concave near the optical axis, at least one of the image-side surface and the image source-side surface of the first lens element being aspheric;
a second lens element with a negative refractive power, having an image source-side surface being concave near the optical axis, at least one of an image-side surface and the image source-side surface of the second lens element being aspheric; and
a third lens element with a positive refractive power, having an image-side surface being concave near the optical axis and an image source-side surface being convex near the optical axis, at least one of the image-side surface and the image source-side surface of the third lens element being aspheric.
2 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a focal length of the three-piece infrared single wavelength projection lens system is f, a focal length of the first lens element and the second lens element combined is f12, and they satisfy the relation: 0.4<f/f12<1.2.
3 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a focal length of the three-piece infrared single wavelength projection lens system is f, a focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.6<f/f23<1.8.
4 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a focal length of the first lens element is f1, a focal length of the second lens element is f2, and they satisfy the relation: −3.0<f1/f2<−1.2.
5 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a focal length of the second lens element is f2, a focal length of the third lens element is f3, and they satisfy the relation: −1.3<f2/f3<−0.1.
6 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a focal length of the first lens element is f1, a focal length of the third lens element is f3, and they satisfy the relation: 0.7<f1/f3<1.8.
7 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a focal length of the first lens element is f1, a focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.1<f1/f23<1.2.
8 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a focal length of the first lens element and the second lens element combined is f12, a focal length of the third lens element is f3, and they satisfy the relation: 2.3<f12/f3<4.4.
9 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a radius of curvature of the image-side surface of the first lens element is R1, a radius of curvature of the image source-side surface of the first lens element is R2, and they satisfy the relation: 0.01<R1/R2<1.04.
10 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a radius of curvature of the image-side surface of the second lens element is R3, a radius of curvature of the image source-side surface of the second lens element is R4, and they satisfy the relation: −1.65<R3/R4<13.5.
11 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a radius of curvature of the image-side surface of the third lens element is R5, a radius of curvature of the image source-side surface of the third lens element is R6, and they satisfy the relation: 1.6<R5/R6<4.4.
12 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a central thickness of the first lens element along the optical axis is CT1, a central thickness of the second lens element along the optical axis is CT2, and they satisfy the relation: 2.5<CT1/CT2<4.0.
13 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a central thickness of the second lens element along the optical axis is CT2, a central thickness of the third lens element along the optical axis is CT3, and they satisfy the relation: 0.05<CT2/CT3<1.05.
14 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a central thickness of the first lens element along the optical axis is CT1, a central thickness of the third lens element along the optical axis is CT3, and they satisfy the relation: 0.6<CT1/CT3<2.6.
15 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a focal length of the three-piece infrared single wavelength projection lens system is f, a distance from the image-side surface of the first lens element to the image source-side surface along the optical axis is TL, and they satisfy the relation: 0.7<f/TL<1.9.
16 . The three-piece infrared single wavelength projection lens system as claimed in claim 1 , wherein a refractive index of the first lens element is n1, a refractive index of the second lens element is n2, a refractive index of the third lens element is n3, and they satisfy the relations: 1.5<n1<1.7; 1.5<n2<1.7; 1.5<n3<1.7.