Imaging lens and imaging device
View Patent ↗The imaging lens is provided and includes: in order from the object side, a negative first lens whose concave surface is directed toward the image side; a second lens of a planoconcave lens whose flat surface is directed toward the object side or a biconcave lens whose surface having a larger absolute value of radius of curvature is directed toward the object side; a third biconvex lens; a stop; a positive fourth lens whose surface having a smaller absolute value of radius of curvature is directed toward the image side; and a cemented lens of a positive fifth lens of biconvex shape and a negative sixth lens of meniscus shape, the cemented lens having a positive refractive power, and an Abbe number ν 3 at d-line of the third lens satisfies a conditional expression (1) ν 3 <43.
1. An imaging lens comprising: in order from an object side of the imaging lens,
a first lens having a negative refractive power and having a concave surface directed toward an image side of the imaging lens;
a second lens that is one of a planoconcave lens having a flat surface directed toward the object side and a biconcave lens whose surface having a larger absolute value of radius of curvature is directed toward the object side;
a third biconvex lens;
a stop;
a fourth lens whose surface having a smaller absolute value of radius of curvature is directed toward the image side, the fourth lens having a positive refractive power; and
a cemented lens having a positive refractive power, the cemented lens including a fifth lens and a sixth lens, the fifth lens having a positive refractive power and having a biconvex shape, the sixth lens having a negative refractive power and having a meniscus shape,
the imaging lens satisfying conditional expressions:
ν 3 <43 (1)
0.05< N n −N p <0.45 (5)
2.8≦ν p /ν n <5.5 (6′)
wherein ν 3 represents an Abbe number of the third lens at the d-line, and wherein N p represents a refractive index of the positive lens constituting the cemented lens at the d-line, N n represents a refractive index of the negative lens constituting the cemented lens at the d-line, ν p represents an Abbe number of the positive lens constituting the cemented lens at the d-line, and ν n represents an Abbe number of the negative lens constituting the cemented lens at the d-line.
2. The imaging lens according to claim 1 , further satisfying a conditional expression:
0.5 <|f 12 /f|< 2 (7)
wherein f 12 represents a composite focal length of the first lens and the second lens, and f represents a focal length of the imaging lens.
3. The imaging lens according to claim 2 , further satisfying a conditional expression:
f 123 <0 (8)
wherein f 123 represents a composite focal length of the first lens, the second lens, and the third lens.
4. The imaging lens according to claim 3 , further satisfying a conditional expression:
3< f 56 /f< 10 (9)
wherein f 56 represents a composite focal length of the fifth lens and the sixth lens, and f represents a focal length of the imaging lens.
5. The imaging lens according to claim 4 , further satisfying a conditional expression:
7< L/f< 14 (10)
wherein L represents a distance along an optical axis from an object-side surface of the first lens to an image-side focal plane of the imaging lens, provided that the distance from the third biconvex lens to the image-side focal plane is converted into air, and f represents a focal length of the imaging lens.
6. An imaging device comprising:
an imaging lens according to claim 5 ; and
an imaging element that converts an optical image formed by means of the imaging lens into an electric signal.
7. The imaging lens according to claim 1 , further satisfying a conditional expression:
f 123 <0 (8)
wherein f 123 represents a composite focal length of the first lens, the second lens, and the third lens.
8. The imaging lens according to claim 1 , further satisfying a conditional expression:
3 <f 56 /f< 10 (9)
wherein f 56 represents a composite focal length of the fifth lens and the sixth lens, and f represents a focal length of the imaging lens.
9. The imaging lens according to claim 1 , further satisfying a conditional expression:
7 <L/f< 14 (10)
wherein L represents a distance along an optical axis from an object-side surface of the first lens to an image-side focal plane of the imaging lens, provided that the distance from the third biconvex lens to the image-side focal plane is converted into air, and f represents a focal length of the imaging lens.
10. An imaging device comprising:
an imaging lens according to claim 1 ; and
an imaging element that converts an optical image formed by means of the imaging lens into an electric signal.