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

Claim 0:
1. 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 second group follows the first group without any lenses in between the first group and the second group,
the first group consists of two negative lenses,
the second group consists of one positive lens,
the third group consists of three lenses, the three lenses being two positive lenses and one negative lens,
in the third group, one of the two positive lenses and the one negative lens are joined together to form a compound lens, and the other one of the two positive lenses is separate from the compound lens and on the image side of the compound lens,
the compound lens is immediately adjacent to the image side of the aperture stop,
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.