Miniature telephoto lens assembly

Abstract

An optical lens assembly includes five lens elements and provides a TTL/EFL<1.0. In an embodiment, the focal length of the first lens element f1<TTL/2, an air gap between first and second lens elements is smaller than half the second lens element thickness, an air gap between the third and fourth lens elements is greater than TTL/5 and an air gap between the fourth and fifth lens elements is smaller than about 1.5 times the fifth lens element thickness. All lens elements may be aspheric.

What is claimed is: 
     
         1 . A lens system, comprising:
 a) a lens assembly comprising a plurality of refractive lens elements arranged along an optical axis with a first lens element on an object side, wherein at least one surface of at least one of the plurality of lens elements is aspheric, and wherein the lens assembly has an effective focal length EFL; and   b) a window positioned between the plurality of lens elements and an image plane,
 wherein the lens system has a total track length TTL of 6.5 mm or less, a ratio TTL/EFL smaller than 1.0, a F number smaller than 3.2, and a ratio L 11 /L 1   e  between a largest optical axis thickness L 11  and a circumferential edge thickness L 1   e  of the first lens element smaller than 4. 
   
     
     
         2 . The lens system according to  claim 1 , wherein the ratio L 11 /L 1   e  smaller than 3.5. 
     
     
         3 . The lens system according to  claim 1 , wherein the ratio L 11 /L 1   e  smaller than 3.2. 
     
     
         4 . The lens system according to  claim 1 , wherein the ratio L 11 /L 1   e  smaller than 3.1. 
     
     
         5 . The lens system according to  claim 1 , wherein the ratio L 11 /L 1   e  smaller than 3.0. 
     
     
         6 . The lens system of  claim 2 , wherein the F number is smaller than 2.9. 
     
     
         7 . The lens system of  claim 2 , wherein the TTL is equal or smaller than 6.0 mm. 
     
     
         8 . The lens system of  claim 2 , wherein the plurality of lens elements includes, in order from an object side to an image side, a first group comprising the first lens element, a second lens element with negative refractive power and a third lens element, and a second group comprising a fourth lens element and a fifth lens element, wherein the first and second groups are separated by a gap that is larger than twice any other gap between lens elements, wherein the first lens element has positive refractive power and wherein the fourth and the fifth lens elements have opposite refractive powers. 
     
     
         9 . The lens system of  claim 2 , wherein the plurality of lens elements includes, in order from an object side to an image side, a first group comprising the first lens element, a second lens element with a focal length f2 and a third lens element with a focal length f3, and a second group comprising a fourth lens element and a fifth lens element, wherein the first element has a focal length f1 and positive refractive power, wherein the second lens element has negative refractive power, wherein 1.2×|f3|>|f2|>1.5×f1 and wherein the fourth and fifth lens elements have opposite refractive powers. 
     
     
         10 . The lens system of  claim 2 , wherein the plurality of lens elements comprises, in order from an object side to an image side, a first lens element with a focal length f1 and positive refractive power, a second lens element with a focal length f2 and negative refractive power and a third lens element with a focal length f3, the focal length f1, the focal length f2 and the focal length f3 fulfilling the condition 1.2×|f3| >|f2|>1.5×f1, wherein a center thickness along the optical axis of each one of the plurality of lens elements is at least 0.2 mm, wherein the F number is smaller than 2.9 and wherein the plurality of lens elements further comprises a fourth lens element, the third and fourth lens elements being separated by an air gap greater than TTL/5. 
     
     
         11 . The lens system of  claim 2 , wherein the plurality of refractive lens elements comprises, in order from an object plane to an image plane along the optical axis, a first lens element having positive optical power, a pair of second and third lens elements having together a negative optical power, and a combination of fourth and fifth lens elements, the fourth lens element separated from the third lens element by an air gap greater than TTL/5, and wherein a center thickness along the optical axis of each one of the plurality of lens elements is at least 0.2 mm. 
     
     
         12 . The lens system of  claim 8 , wherein f1<TTL/2. 
     
     
         13 . The lens system of  claim 8 , wherein 1.2×|f3|>|f2|>1.5×f1. 
     
     
         14 . The lens system of  claim 8 , wherein a combined power of the second and third lens elements is negative. 
     
     
         15 . The lens system of  claim 8 , wherein the third lens element has negative refractive power. 
     
     
         16 . The lens system of  claim 8 , wherein the gap between the fourth and fifth lens elements is smaller than 1.5×d5, where d5 is a thickness of the fifth lens element along the optical axis. 
     
     
         17 . The lens system of  claim 8 , wherein the fourth and fifth lens elements are separated by a gap smaller than TTL/20. 
     
     
         18 . The lens system of  claim 8 , wherein the fourth and fifth lens elements are made of different lens materials having different Abbe numbers, such that one lens element has Abbe number that is smaller than 30 and the other lens element has an Abbe number that is larger than 50.