Patent ID: 11960060
Assignee: RICOH COMPANY, LTD.
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 7:
8. An imaging lens, comprising:
a first group having negative refractive power:
a second group having positive refractive power;
an aperture stop;
a third group having positive refractive power; and
a fourth group having positive refractive power, wherein
the first group, the second group, the aperture stop, the third group, and the fourth group are arranged in that order from an object side toward an image side,
the first group consists of three lenses, the three lenses including two negative lenses and one positive lens, the two negative lenses including one negative lens at the object side and another negative lens at the image side,
in the first group, the one negative lens, the one positive lens, and the another negative lens are arranged in that order from the object side toward the image side,
the second group includes one positive lens,
the third group consists of three lenses, the three lenses including two positive lenses and one negative lens,
in the third group, at least two of the three lenses at the object side are joined together to form a compound lens,
the compound lens is immediately adjacent to the image side of the aperture stop of,
both sides of each lens in the first group, the second group and the third group are spherical surfaces,
the fourth group includes one positive lens in which both sides are aspherical surfaces,
the imaging lens has a fixed focal length and an angle of view of 120 degrees or more, and
conditional expressions (1), (2), (3), and (4) below are satisfied:

−2.7≤f1/f≤−0.7  (1)

2.2≤f2/f≤6.6  (2)

3.9≤f3/f≤14.3  (3)

2.8≤f4/f≤11.0  (4)

where
fi denotes focal length of i-th group with respect to a d-line,
i denotes one of 1 to 4, and
f denotes focal length of an entirety of the imaging lens with respect to the d-line.