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 . An optical lens assembly comprising, in order from an object side to an image side:
 a) a first lens element with positive refractive power having a convex object-side surface;   b) a second lens element with negative refractive power having a thickness d 2  on an optical axis and separated from the first lens element by a first air gap;   c) a third lens element with negative refractive power and separated from the second lens element by a second air gap;   d) a fourth lens element having a positive refractive power and separated from the third lens element by a third air gap; and   e) a fifth lens element having a negative refractive power, separated from the fourth lens element by a fourth air gap and having a thickness d 5  on the optical axis;
 wherein a ratio between an effective focal length (EFL) and a total track length (TTL) of an optical lens system including the lens assembly is smaller than 1.0, wherein a focal length f1 of the first lens element is smaller than TTL/2 and wherein the third air gap is greater than TTL/5. 
   
     
     
         2 . The optical lens assembly of  claim 1 , wherein the first lens element has a convex object-side surface and a convex or concave image-side surface, wherein the second lens element has a meniscus convex object-side surface, wherein the fourth lens element has a positive meniscus and a concave object-side surface, wherein the fifth lens element has a negative meniscus and a concave object-side surface and wherein the fourth air gap is smaller than 1.5d 5 . 
     
     
         3 . The optical lens assembly of  claim 1 , wherein the first, third and fifth lens elements have each an Abbe number greater than 50, and wherein the second and fourth lens elements have each an Abbe number smaller than 30. 
     
     
         4 . The optical lens assembly of  claim 3 , wherein the first lens element has a convex object-side surface and a convex or concave image-side surface, wherein the second lens element has a meniscus convex object-side surface, wherein the fourth lens element has a positive meniscus and a concave object-side surface, wherein the fifth lens element has a negative meniscus and a concave object-side surface and wherein the fourth air gap is smaller than 1.5d 5 . 
     
     
         5 . The optical lens assembly of  claim 3 , wherein the first air gap is smaller than d 2 /2. 
     
     
         6 . The optical lens assembly of  claim 5 , wherein the first lens element has a convex object-side surface and a convex or concave image-side surface, wherein the second lens element has a meniscus convex object-side surface, wherein the fourth lens element has a positive meniscus and a concave object-side surface, wherein the fifth lens element has a negative meniscus and a concave object-side surface and wherein the fourth air gap is smaller than 1.5d 5 . 
     
     
         7 . The optical lens assembly of  claim 1 , wherein all lens elements are made of plastic. 
     
     
         8 . The optical lens assembly of  claim 1 , wherein the first lens element is made of glass and wherein all other lens elements are made of plastic. 
     
     
         9 . The optical lens assembly of  claim 1 , wherein the second lens element is made of glass and all other lens elements are made of plastic. 
     
     
         10 . The optical lens assembly of  claim 1 , wherein the lens assembly has an F number smaller than 3.2. 
     
     
         11 . The optical lens assembly of  claim 3 , wherein the lens assembly has an F number smaller than 3.2. 
     
     
         12 . The optical lens assembly of  claim 5 , wherein the lens assembly has an F number smaller than 3.2. 
     
     
         13 . The optical lens assembly of  claim 1 , wherein all lens element surfaces are aspheric. 
     
     
         14 . The optical lens assembly of  claim 3 , wherein all lens element surfaces are aspheric. 
     
     
         15 . The optical lens assembly of  claim 5 , wherein all lens element surfaces are aspheric. 
     
     
         16 . The optical lens assembly of  claim 1 , wherein f1, a focal length f2 of the second lens element and a focal length f3 of the third lens element fulfill the condition 1.2×|f3|>|f2|>1.5×f1. 
     
     
         17 . The optical lens assembly of  claim 2 , wherein f1, a focal length f2 of the second lens element and a focal length f3 of the third lens element fulfill the condition 1.2×|f3|>|f2|>1.5×f1. 
     
     
         18 . The optical lens assembly of  claim 3 , wherein f1, a focal length f2 of the second lens element and a focal length f3 of the third lens element fulfill the condition 1.2×|f3|>|f2|>1.5×f1. 
     
     
         19 . The optical lens assembly of  claim 5 , wherein f1, a focal length f2 of the second lens element and a focal length f3 of the third lens element fulfill the condition 1.2×|f3|>|f2|>1.5×f1. 
     
     
         20 . The optical lens assembly of  claim 1 , wherein EFL=6.84 mm, F#=2.80 and TTL=5.90 mm.