Photographing lens

Abstract

The present invention is directed to a photographing lens containing, in order from an object side: a first lens having a positive refractive power and a convex surface facing the object side; a second lens having a negative refractive power; a third lens having a positive refractive power; and a fourth lens having a negative refractive power and at least one aspheric surface, the photographing lens satisfying the following conditional expressions: L T f ≤ 1.2 0.5 ≤ f 3 f ≤ 1.0 where L T denotes the distance on the optical axis between the object side of the first lens and the image side of the fourth lens; f denotes the total focal length of the photographing lens; and f 3 denotes the focal length of the third lens.

What is claimed is: 
     
       1. A photographing lens comprising, in order from an object side:
 a first lens having a positive refractive power and a convex surface facing the object side;   a second lens having a negative refractive power;   a third lens having a positive refractive power; and   a fourth lens having a negative refractive power and at least one aspheric surface,   the photographing lens satisfying the following conditional expressions:   
       
         
           
             
               
                 
                   L 
                   T 
                 
                 f 
               
               ≤ 
               1.2 
             
           
         
         
           
             
               0.5 
               ≤ 
               
                 
                   f 
                   3 
                 
                 f 
               
               ≤ 
               1.0 
             
           
         
       
       wherein L T  denotes the distance on the optical axis between the object side of the first lens and the image side of the fourth lens; f denotes the total focal length of the photographing lens; and f 3  denotes the focal length of the third lens. 
     
     
       2. The photographing lens as claimed in  claim 1 , wherein the third lens has at least one aspheric surface. 
     
     
       3. The photographing lens as claimed in  claim 1 , wherein the photographing lens further satisfies the following conditional expressions: 
       
         
           
             
               0.5 
               ≤ 
               
                 
                   f 
                   1 
                 
                 f 
               
               ≤ 
               
                 2.0 
                 ⁢ 
                 
                   
 
                 
                 - 
                 1.2 
               
               ≤ 
               
                 
                   f 
                   2 
                 
                 f 
               
               ≤ 
               
                 - 
                 0.4 
               
             
           
         
       
       wherein f 1  denotes the focal length of the first lens; and f 2  denotes the focal length of the second lens. 
     
     
       4. The photographing lens as claimed in  claim 1 , wherein the photographing lens further satisfies the following conditional expressions:
   |n 3 −n 4 |≧0.1
   
       wherein n 3  denotes the refractive index of the third lens; and n 4  denotes the refractive index of the fourth lens. 
     
     
       5. The photographing lens as claimed in  claim 1 , wherein the photographing lens further satisfies the following conditional expressions: 
       
         
           
             
               
                 - 
                 20 
               
               ≤ 
               
                 
                   f 
                   4 
                 
                 f 
               
               ≤ 
               
                 - 
                 1 
               
             
           
         
       
       wherein f 4  denotes the focal length of the fourth lens. 
     
     
       6. A photographing lens comprising, in order from an object side:
 a first lens having a positive refractive power and a convex surface facing the object side;   a second lens having a negative refractive power;   a third lens having a positive refractive power; and   a fourth lens having a negative refractive power and at least one aspheric surface, the photographing lens satisfying the following conditional expressions:   
       
         
           
             
               0.75 
               < 
               
                 
                   f 
                   1 
                 
                 / 
                 f 
               
               < 
               2.0 
             
           
         
         
           
             
               
                 
                   L 
                   T 
                 
                 f 
               
               ≤ 
               1.2 
             
           
         
         
           
             
               0.5 
               ≤ 
               
                 
                   f 
                   3 
                 
                 f 
               
               ≤ 
               1.0 
             
           
         
       
       wherein L T  denotes the distance on the optical axis between the object side of the first lens and the image side of the fourth lens; f denotes the total focal length of the photographing lens; f 1  denotes the focal length of the first lens; and f 3  denotes the focal length of the third lens.  
     
     
       7. The photographing lens as claimed in claim 6, wherein the third lens has aspheric surfaces on both sides and the fourth lens has aspheric surfaces on both sides. 
     
     
       8. The photographing lens as claimed in claim 6, wherein the photographing lens further satisfies the following conditional expressions: 
       
         
           
             
               
                 - 
                 20 
               
               ≤ 
               
                 
                   f 
                   4 
                 
                 f 
               
               ≤ 
               
                 - 
                 1 
               
             
           
         
       
       wherein f 4  denotes the focal length of the fourth lens.  
     
     
       9. The photographing lens as claimed in claim 6, wherein the photographing lens comprises an iris diaphragm located on the object side of the first lens. 
     
     
       10. The photographing lens as claimed in claim 6, wherein the first lens has aspheric surfaces on both sides and the fourth lens has aspheric surfaces on both sides.