Imaging lens

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 negative refractive power;
• and
• a fifth lens having negative refractive power, arranged in this order from an object side to an image plane side,
• wherein said first lens is formed in a shape so that a curvature radius of a surface thereof on the object side is positive,
• said second lens is formed in a shape so that 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 both positive,
• said third lens is formed in a shape so that a curvature radius of a surface thereof on the object side is positive,
• said fifth lens is formed in a shape so that 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 both positive,
• each of said first lens, said third lens, said fourth lens, and said fifth lens has an Abbe's number greater than 45,
• said second lens has an Abbe's number less than 35,
• said first lens has a focal length f1, said second lens has a focal length f2, said third lens has a focal length f3, said fourth lens has a focal length f4, and said fifth lens has a focal length f5 so that the following conditional expressions are satisfied:
• f1<f3 and |f2|<f3
• f3<|f4| and |f2|<|f5|, and
• a whole lens system has a focal length f so that the following conditional expression is satisfied:
• 5.0<f3/f<20.0.

An imaging lens comprising:

• a first lens having positive refractive power;
• a second lens;
• a third lens having positive refractive power;
• a fourth lens;
• and
• a fifth lens, arranged in this order from an object side to an image plane side,
• wherein said first lens is formed in a shape so that 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 both positive,
• said second lens is formed in a shape so that a surface thereof on the image plane side is aspherical, and a curvature radius of a surface thereof on the object side and a curvature radius of the surface thereof on the image plane side are both positive,
• said third lens is formed in a shape so that at least one of a surface thereof on the object side and a surface thereof on the image plane side is aspherical,
• said fourth lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side are aspherical, and a curvature radius of the surface thereof on the image plane side is negative,
• said fifth lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side are aspherical,
• said second lens has a focal length f2, said third lens has a focal length f3, said fourth lens has a focal length f4, and said fifth lens has a focal length f5 so that the following conditional expressions are satisfied:
• f3<|f4| and |f2|<|f5|.

An imaging lens comprising:

• a first lens having positive refractive power;
• a second lens;
• a third lens;
• a fourth lens;
• and
• a fifth lens having negative refractive power, arranged in this order from an object side to an image plane side,
• wherein said first lens is formed in a shape so that a curvature radius of a surface thereof on the object side is positive,
• said second lens is formed in a shape so that 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 both positive,
• each of said first lens and said third lens has an Abbe's number greater than 45,
• said second lens has an Abbe's number less than 35,
• said third lens has a focal length f3, and a whole lens system has a focal length f so that the following conditional expression is satisfied:
• 5.58≦|f3|/f≦16.23, and
• said second lens and said third lens are arranged so that the surface of the second lens on the image plane side is situated away from a surface of the third lens on the object side by a distance dA on an optical axis, and said third lens and said fourth lens are arranged so that a surface of the third lens on the image plane side is situated away from a surface of the fourth lens on the object side by a distance dB on the optical axis so that the following conditional expression is satisfied:
• 0.3<dA/dB<1.5.