Imaging lens
The present invention is an imaging lens in which various aberrations are favorably corrected, the optical length is short, and a sufficient back focus is secured. The imaging lens is constituted by arranging a first lens L 1 , an aperture diaphragm S 1 , a second lens L 2 , and a third lens L 3 in succession from the object side to the image side. The first lens L 1 is a lens having a positive refractive power and a meniscus shape in which the convex surface faces the object side, the second lens L 2 is a lens having a negative refractive power and a meniscus shape in which the convex surface faces the image side, and the third lens L 3 is a lens in which the convex surface faces the object side.
1. An imaging lens comprising a first lens L 1 , an aperture diaphragm S 1 , a second lens L 2 , and a third lens L 3 , and constituted such that said first lens L 1 , aperture diaphragm S 1 , second lens L 2 , and third lens L 3 are arranged in succession from the object side to the image side,
wherein said first lens L 1 is a lens having a positive refractive power and a meniscus shape in which the convex surface faces the object side,
said second lens L 2 is a lens having a negative refractive power and a meniscus shape in which the convex surface faces the image side, and
said third lens L 3 is a lens in which the convex surface faces the object side,
both surfaces of said first lens L 1 and said second lens L 2 being aspheric, and at least one surface of said third lens L 3 being aspheric, and
said imaging lens satisfying the following conditions:
0.35<r 1 /r 2 <0.45 (1)
0.07<D 2 /f<0.1 (2)
0.01<D 4 /f<0.04 (3)
1.00<d/f<1.30 (4)
0.3<b f /f<0.5 (5)
where f is the combined focal length of the imaging lens,
r 1 is the radius of curvature (axial radius of curvature) of the object-side surface of the first lens L 1 in the vicinity of the optical axis,
r 2 is the radius of curvature (axial radius of curvature) of the image-side surface of the first lens L 1 in the vicinity of the optical axis,
D 2 is the distance between the first lens L 1 and second lens L 2 ,
D 4 is the distance between the second lens L 2 and the third lens L 3 ,
d is the distance (atmospheric) from the object-side surface of the first lens L 1 to the imaging surface, and
b f is the distance (atmospheric) from the image-side surface of the third lens L 3 to the imaging surface.
2. The imaging lens according to claim 1 , wherein said first lens L 1 , said second lens L 2 , and said third lens L 3 constituting said imaging lens are formed from a material having an Abbe number within a range of thirty to sixty.
3. The imaging lens according to claim 1 , wherein said first lens L 1 , said second lens L 2 , and said third lens L 3 constituting said imaging lens are formed using cycloolefin plastics as a material.
4. The imaging lens according to claim 1 , wherein said first lens L 1 and said third lens L 3 constituting said imaging lens are formed using cycloolefin plastics as a material, and said second lens L 2 is formed using polycarbonate as a material.
5. The imaging lens according to claim 1 , wherein said first lens L 1 and said third lens L 3 constituting said imaging lens are formed using cycloolefin plastics as a material,
said second lens L 2 is formed using polycarbonate as a material, and
said third lens L 3 is a lens having a negative refractive power and a meniscus shape in which the convex surface faces the object side.