Three-piece infrared single wavelength lens system
A three-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 positive refractive power, a second lens element with a positive refractive power, and a third lens element with a positive refractive power. The focal length of the first lens element is f1, the focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.5<f1/f23<1.0. When the above relation is satisfied, a wide field of view can be obtained and the resolution can be improved evidently.
1. A three-piece infrared single wavelength lens system, in order from an object side to an image side, comprising:
a stop;
a first lens element with a positive refractive power, having an object-side surface being convex near an optical axis and an image-side surface being convex near the optical axis, at least one of the object-side surface and the image-side surface of the first lens element being aspheric;
a second 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, at least one of the object-side surface and the image-side surface of the second lens element being aspheric; and
a third lens element with a positive refractive power, having an object-side surface being convex near the optical axis and an image-side surface being concave near the optical axis, at least one of the object-side surface and the image-side surface of the third lens element being aspheric;
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: 0.5<f1/f23<0.71360; and
wherein the lens system contains only three lens elements with refractive power.
2. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein the focal length of the first lens element is f1, a focal length of the second lens element is f2, and they satisfy the relation: 0.05<f1/f2<0.45.
3. The three-piece infrared single wavelength 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: 0.5<f2/f3<2.6.
4. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein the focal length of the first lens element is f1, a focal length of the third lens element is f3, and they satisfy the relation: 0.05<f1/f3<0.7.
5. The three-piece infrared single wavelength 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: 0.1<f12/f3<0.65.
6. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein a radius of curvature of the image-side surface of the first lens element is R2, a radius of curvature of the object-side surface of the second lens element is R3, and they satisfy the relation: 25<R2/R3<270.
7. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein the three-piece infrared single wavelength lens system has a maximum view angle FOV, and it satisfies the relation: 45<FOV<75.
8. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein a central thickness of the first lens element along the optical axis is CT1, a distance along the optical axis between the first lens element and the second lens element is T12, and they satisfy the relation: 1.4<CT1/T12<2.4.
9. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein a distance along the optical axis between the first lens element and the second lens element is T12, a central thickness of the second lens element along the optical axis is CT2, and they satisfy the relation: 0.5<T12/CT2<1.4.
10. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein a distance along the optical axis between the first lens element and the second lens element is T12, a distance along the optical axis between the second lens element and the third lens element is T23, and they satisfy the relation: 5.4<T12/T23<9.0.
11. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein an Abbe number of the first lens element is V1, an Abbe number of the second lens element is V2, and they satisfy the relation: 30<V1−V2<42.
12. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein an Abbe number of the first lens element is V1, an Abbe number of the third lens element is V3, and they satisfy the relation: 30<V1−V3<42.
13. The three-piece infrared single wavelength lens system as claimed in claim 1 , wherein a f-number of the three-piece infrared single wavelength lens system is Fno, and it satisfies the relation: 1.2<Fno<1.8.