Imaging lens

Abstract

An imaging lens comprises, in order from an object side: a first lens having a positive refractive power; a second lens having a negative refractive power whose concave surface faces to the object; and a third lens having a positive refractive power and having a meniscus form that has a convex surface, facing to the object, in a portion at and around an optical axis of the imaging lens; wherein the first, second and third lenses have at least one aspheric surface, and wherein the imaging lens satisfies conditional expressions given below: 0.7<f1/f<1.3   (1) 0.3<D2/f<0.5   (2) 1.0<|f2/f|<3.0   (3) 1.2<f3/f<4.0   (4) where f: a focal length of an overall system, f 1: a focal length of the first lens, f 2: a focal length of the second lens, f 3: a focal length of the third lens, and D 2: a spacing, on the optical axis, between the first lens and the second lens.

1. An imaging lens comprising, in order from an object side:
 a first lens having a positive refractive power; 
 a second lens having a negative refractive power whose concave surface faces to the object; and 
 a third lens having a positive refractive power and having a meniscus form that has a convex surface, facing to the object, in a portion at and around an optical axis of the imaging lens; 
 wherein the first, second and third lenses have at least one aspheric surface, and 
 wherein the imaging lens satisfies conditional expressions given below:
   0.7<f1/f<1.3   (1)
 
   0.3<D2/f<0.5   (2)
 
   0.21≦D2/f<0.5   (2′) 
 
   1.0<|f2/f|<3.0   (3)
 
   1.2<f3/f<4.0   (4)
 
 
 
       where
 f: a focal length of an overall system, 
 f 1 : a focal length of the first lens, 
 f 2 : a focal length of the second lens, 
 f 3 : a focal length of the third lens, and 
 D 2 : a spacing, on the optical axis, between the first lens and the second lens. 
 
     
     
       2. An imaging lens according to  claim 1 ,
 wherein a conditional expression given below is further satisfied:
   20<ν1−ν2   (5)
 
 
 
       where
 ν1: Abbe number of the first lens, and 
 ν2: Abbe number of the second lens. 
 
     
     
       3. An imaging lens according to  claim 1 ,
 wherein the first lens has: an object-side surface having a convex form in a portion at and around the optical axis; and an image-side surface having all aspheric form and having a positive refractive power increasing as a peripheral portion thereof is neared, and 
 the second lens has a meniscus form in a portion at and around the optical axis. 
 
     
     
       4. An imaging lens according to  claim 2 ,
 wherein the first lens has: an object-side surface having a convex form in a portion at and around the optical axis; and an image-side surface having an aspheric form and having a positive refractive power increasing as a peripheral portion thereof is neared, and 
 the second lens has a meniscus form in a portion at and around the optical axis.