Patent ID: 9746648
Date: 2017-08-29
CPC Classifications: G02B

Claim:
1. A four-piece infrared single wavelength lens system, in order from an object side to an image side, comprising: a first lens element with a refractive power, having an object-side surface being concave 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 stop; a second lens element with a positive refractive power, having an object-side surface being convex 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 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 third lens element being aspheric; and a fourth 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 fourth 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: −210<f1/f23<365.