Imaging lens unit

Abstract

Disclosed herein is an imaging lens unit, including: a first lens having a positive (+) power; a second lens having a negative (−) power; a third lens selectively having one of a positive (+) and negative (−) power; a fourth lens having a negative (−) power; and a fifth lens having a negative (−) power, wherein the first lens, the second lens, the third lens, the fourth lens, and fifth lens are arranged in order from an object to be formed as an image, and the fourth lens is concave toward an image side.

What is claimed is: 
     
         1 . An imaging lens unit, comprising:
 a first lens having positive (+) power;   a second lens having negative (−) power;   a third lens selectively having one of positive (+) and negative (−) power;   a fourth lens having negative (−) power; and   a fifth lens having negative (−) power,   wherein the first lens, the second lens, the third lens, the fourth lens, and fifth lens are arranged in order from an object to be formed as an image, and the fourth lens is concave toward an image side.   
     
     
         2 . The imaging lens unit as set forth in  claim 1 , wherein the fourth lens is a meniscus-shaped lens. 
     
     
         3 . The imaging lens unit as set forth in  claim 1 , wherein an Abbe number v4 of the fourth lens satisfies the following conditional expression:
   0 <v 4<30.   
     
     
         4 . The imaging lens unit as set forth in  claim 1 , wherein the second lens and the fourth lens are made of a high dispersion material. 
     
     
         5 . The imaging lens unit as set forth in  claim 1 , wherein an Abbe number v1 of the first lens satisfies the following conditional expression:
   50 <v 1.   
     
     
         6 . The imaging lens unit as set forth in  claim 1 , wherein an Abbe number v2 of the second lens satisfies the following conditional expression:
   0 <v 2<30.   
     
     
         7 . The imaging lens unit as set forth in  claim 1 , wherein the first lens has a convex form toward an object side. 
     
     
         8 . The imaging lens unit as set forth in  claim 1 , wherein the second lens has a concave form toward the image side. 
     
     
         9 . The imaging lens unit as set forth in  claim 1 , wherein the fifth lens has an inflection point toward the image side. 
     
     
         10 . The imaging lens unit as set forth in  claim 1 , wherein the third lens has negative (−) power. 
     
     
         11 . The imaging lens unit as set forth in  claim 1 , wherein the third lens has positive (+) power. 
     
     
         12 . The imaging lens unit as set forth in  claim 10  or  11 , further comprising an aperture stop disposed in front of the first lens to adjust a light amount. 
     
     
         13 . The imaging lens unit as set forth in  claim 10  or  11 , further comprising an aperture stop disposed between the first lens and the second lens to adjust a light amount. 
     
     
         14 . The imaging lens unit as set forth in  claim 1 , wherein the first lens, the second lens, the third lens, and the fourth lens are all made of a plastic material. 
     
     
         15 . The imaging lens unit as set forth in  claim 1 , wherein a total focal length f of the imaging lens unit, a curvature radius r7 of the fourth lens on the object side, and a curvature radius r8 of the fourth lens on the image side satisfy the following conditional expression:
   0<( r 7 +r 8)/( r 7 −r 8)<−2.5.
   
     
     
         16 . The imaging lens unit as set forth in  claim 1 , wherein a total focal length f of the imaging lens unit and a distance tt from a vertex of the first lens on the object side to the image side satisfy the following conditional expression:
   0 <tt/f< 1.3.   
     
     
         17 . The imaging lens unit as set forth in  claim 1 , wherein an Abbe number v1 of the first lens, an Abbe number v2 of the second lens, an Abbe number v3 of the third lens, and an Abbe number v4 of the fourth lens satisfy the following conditional expression:
   0.7<( v 1 +v 2)/( v 3 +v 4)<1.0.