Imaging lens

Abstract

An imaging lens includes, in this order from an object side, an aperture stop ST, a positive first lens L 1, a negative second lens L 2 having a meniscus shape that directs a convex surface on the object side near an optical axis, a positive third lens L 3, a positive fourth lens L 4 having a meniscus shape that directs a concave surface on the object side near an optical axis, and a negative fifth lens L 5 having a meniscus shape that directs a convex surface on the object side near an optical axis.

What is claimed is: 
     
       1. An imaging lens comprising:
 a first lens having positive refractive power;   a second lens having negative refractive power;   a third lens having positive refractive power;   a fourth lens having positive refractive power; and   a fifth lens having negative refractive power in this order from an object side to an image side,   wherein said second lens is formed in a shape so that both a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image side are positive,   said fourth lens is formed in a shape so that both a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image side are negative,   said first lens and said second lens have a composite focal length f12, and said third lens and said fourth lens have a composite focal length f34 so that the following conditional expression is satisfied:
   1.592≤f34/f12<4.0, and
 
   said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, said third lens has an Abbe's number νd3, said fourth lens has an Abbe's number νd4, and said fifth lens has an Abbe's number νd5 so that the following conditional expressions are satisfied:
   50<νd1<85
 
   νd2<30
 
   50<νd3<85
 
   50<νd4<85
 
   50<νd5<85.
 
   
     
     
       2. The imaging lens according to  claim 1 , wherein said fifth lens is formed in a shape so that both a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image side are positive. 
     
     
       3. The imaging lens according to  claim 1 , wherein said third lens and said fourth lens have a composite focal length f34 and a whole lens system has a focal length f so that the following conditional expression is satisfied:
   0.5<f34/f<5.0.   
     
     
       4. The imaging lens according to  claim 1 , wherein said first lens has a focal length f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
   0.4<|f1/f2|<1.0.   
     
     
       5. An imaging lens comprising:
 a first lens having positive refractive power;   a second lens having negative refractive power;   a third lens;   a fourth lens; and   a fifth lens, arranged in this order from an object side to an image plane side,   wherein said second lens is formed in a shape so that a curvature radius of a surface thereof on the image plane side is positive,   said fourth lens is formed in a shape so that a curvature radius of a surface thereof on the image plane side is negative,   said fifth lens is formed in a shape so that both a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image plane side are positive,   said first lens and said second lens have a composite focal length f12, and said third lens and said fourth lens have a composite focal length f34 so that the following conditional expression is satisfied:
   1.592≤f34/f12<4.0, and
 
   said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, said third lens has an Abbe's number νd3, said fourth lens has an Abbe's number νd4, and said fifth lens has an Abbe's number νd5 so that the following conditional expressions are satisfied:
   50<νd1<85,
 
   νd2<30,
 
   50<νd3<85,
 
   50<νd4<85,
 
   50<νd5<85. 
 
   
     
     
       6. The imaging lens according to claim 5, wherein said third lens has positive refractive power.  
     
     
       7. The imaging lens according to claim 5, wherein said fourth lens has positive refractive power.  
     
     
       8. The imaging lens according to claim 5, wherein said fifth lens has negative refractive power.  
     
     
       9. The imaging lens according to claim 5, wherein said second lens is formed in the shape so that a curvature radius of a surface thereof on the object side is positive, and
 said fourth lens is formed in the shape so that a curvature radius of a surface thereof on the object side is negative.