JPH1020189A - Objective lens for endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the objective lens wide-angle while the radius of curvature of a front group lens is restrained from getting too small and distortion aberration is corrected to be small without lowering peripheral light quantity so much by constituting the lens of a 1st lens group having negative refractive power as a whole, a brightness diaphragm and a 2nd lens group having positive refractive power as a whole in order from an object side, and satisfying a specified condition. SOLUTION: This lens is constituted of the 1st lens group 10 having the negative refractive power as a whole, the brightness diaphragm S and the 2nd lens group 20 having the positive refractive power as a whole in order from the object side. The 1st lens group 10 is constituted of two single lenses, that is, a 1st lens 11 on the object side and a 2nd lens 12 on an image side, both of which have negative refractive power. The lens satisfies an expression I: -5.0<q1 <-0.9, and an expression II: -0.5<q2 <0.9. Provided that q1 and q2 are the shaping factor of the 1st and the 2nd lenses 11 and 12, that is, (r2+r1)/(r2-r1) and (r4+r3)/(r4-r3), and r1 and r2, and r3 and r4 are the radii of curvature of the surfaces on the object side and the image side of the 1st lens 11 and the 2nd lens 12, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to medical and industrial endoscope objective lenses.

[0002]

2. Description of the Related Art An endoscope objective lens generally requires a wide viewing angle by its nature. For this reason,
Strong negative power is given to the front group (first lens group) ahead of the aperture stop. In recent years, in addition to the increasing demand for a wider angle, in electronic endoscopes, the size of the objective lens has been reduced along with the reduction in the size of the CCD.
The image-side surface of the front group has a smaller radius of curvature.

In order to reduce the size, reduce the diameter, and increase the amount of peripheral light, the endoscope objective lens usually does not correct distortion. However, with a super-wide-angle objective lens whose viewing angle exceeds 120 °, the negative distortion becomes too large and the image is distorted, so that a medical endoscope cannot accurately see a lesion or the like in a body cavity. May be caused. To reduce distortion with a small number of lenses,
For example, an aspherical surface may be used as disclosed in Japanese Patent Application Laid-Open No. 61-162221. However, if the distortion is reduced, there is a problem that the amount of peripheral light decreases.

[0004]

SUMMARY OF THE INVENTION The present invention has two problems that occur when the endoscope objective lens is widened, that is, when the radius of curvature of the front lens group becomes small, and when the distortion is corrected to be small. An object of the present invention is to solve the problem that the peripheral light amount is reduced.

[0005]

SUMMARY OF THE INVENTION According to the present invention, the front group (first lens group) is composed of two negative single lenses having a specific shape, so that a strong negative power is distributed to the two lenses to reduce the curvature. The invention has been completed based on the idea that the peripheral aperture efficiency is increased without increasing the diameter of the front lens without increasing the diameter of the front lens, thereby compensating for the decrease in the amount of peripheral light generated with the wide angle.

The endoscope objective lens according to the present invention comprises, in order from the object side, a first lens group having a negative refractive power as a whole, a brightness stop, and a second lens group having a positive refractive power as a whole. The first lens unit is composed of two single lenses, the first lens on the object side and the second lens on the image side, both having negative refractive power, and satisfies the following conditional expressions (1) and (2). It is characterized by: _{(1) -5.0 <q 1 <} -0.9 (2) -0.5 <q 2 <9.0 where, q _1: shaping factor of the first lens (= (r2
+ R1) / (r2-r1 )) q 2: shaping factor of the second lens (= (r4
+ R3) / (r4-r3)) r1: radius of curvature of the object side surface of the first lens, r2: radius of curvature of the image side surface of the first lens, r3: radius of curvature of the object side surface of the second lens R4: radius of curvature of the image-side surface of the second lens.

It is preferable that the endoscope objective lens of the present invention further satisfies the following conditional expression (3). (3) 0.5 <| f / f I | <1.0, f1 <0 (4) 1.5 <f / f II <2.5 where, f _I: composite focal length of the first lens group, f _II : composite focal length of the second lens group, f: composite focal length of the entire system.

The second lens group preferably employs any one of the following six types. One positive lens, two positive lenses (may be a laminated lens), a positive lens and a negative lens from the object side, a positive lens from the object side, and a cemented lens having a positive refracting power as a whole, in which the positive and negative lenses are cemented Or two positive lenses and a negative lens from the object side, or two positive lenses, a negative lens and a positive lens from the object side.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The endoscope objective lens of the present invention is most characterized in that the first lens group (front group) is composed of two negative single lenses having a specific shape. Conditional expressions (1) and (2) define the shapes of the two negative lenses that form the first lens group. The first lens on the object side of the two negative lenses has a second surface (image side surface) having a smaller radius of curvature than the first surface (object side surface), as defined by conditional expression (1). The second lens on the image side has a concave surface on the object side, the first surface having a radius of curvature smaller than the second surface, as defined by conditional expression (2). Consisting of a negative lens.

By satisfying conditional expressions (1) and (2), it is possible to increase the radius of curvature of the negative lens of the first lens unit including the surface closest to the object. As a result, the angle of incidence on the second lens group (rear group) can be reduced, so that the amount of various aberrations generated in the second lens group can be reduced.

For example, as in the first to third embodiments of Japanese Patent Application Laid-Open No. 61-162021, the first lens group has a negative single lens 1
In the case of a single lens, the radius of curvature of the second surface becomes small, and lens processing becomes difficult. In addition, if an aspherical surface is used, distortion can be reduced, but this causes a problem that the amount of peripheral light decreases. The present invention increases the aperture efficiency of off-axis luminous flux by configuring the first lens group with two negative single lenses having specific shapes defined by conditional expressions (1) and (2). It compensates for the decrease in peripheral light quantity.

In Examples 8 to 10 of JP-A-61-162021, the first lens group is constituted by two negative single lenses, but the second lens has a meniscus lens having a concave surface on the image side. Is different from the present invention. If the second lens is a meniscus lens having a concave surface on the image side, the diameter of the front lens (first lens) increases, which is not preferable as an endoscope objective lens. In the present invention, the second lens of the first lens group has a concave surface on the object side as defined by the conditional expression (2), and therefore, the incident angle of off-axis light to the second lens group is reduced. And the occurrence of various aberrations in the second lens group is reduced. Also, since the effective diameter of the second lens group can be reduced,
It is easy to secure the edge thickness (thickness of the peripheral portion) of the positive lens in the second lens group, and as a result, the overall length of the lens can be shortened.

[0013] Beyond the lower limit of condition (1), the shaping factor q ₁ of the first lens of the first lens group becomes small, the degree of negative meniscus first lens tight (small surfaces of curvature radius) Since it is too much, coma aberration and astigmatism are largely generated on the second surface. In addition, the radius of curvature of the second surface is too small, and as a result, processing becomes difficult, and in addition, the degree of protrusion of the first surface increases, which makes handling difficult.

[0014] Beyond the upper limit of condition (1), the shaping factor q ₁ of the first lens in the first lens group becomes large, the object-side surface of the first face of the first lens becomes concave, and coma The amount of generation of astigmatism increases. In addition, since the first surface of the first lens is concave, there is also a problem that it becomes difficult to clean dust, dirt, and the like that adhere during use such as in-vivo observation. If the surface on the object side is flat or convex, such a problem does not occur.

[0015] Beyond the lower limit of condition (2), since the shaping factor q ₂ of the second lens in the first lens group becomes small, it is impossible to bend the axial ray sufficiently by the first surface of the second lens As a result, the effective diameter of the first surface of the first lens increases.

[0016] Beyond the upper limit of condition (2), the shaping file q ₂ of the second lens in the first lens group becomes large, the degree of meniscus of the second lens becomes too tight (small surfaces of curvature radius) Therefore, in addition to an increase in distortion, coma aberration is generated on the first surface of the second lens, and astigmatism is generated on the second surface.

Conditional expression (3) defines the range of the power of the entire first lens unit having a negative refractive power. If the negative power is smaller than the lower limit of conditional expression (3), the viewing angle cannot be widened. If the negative power is increased beyond the upper limit, the viewing angle can be widened, but the back focus becomes too long, resulting in a longer overall length.

Conditional expression (4) defines the power range of the second lens group having a positive power as a whole. If the lower limit of conditional expression (4) is exceeded and the positive power is reduced, the total length is increased, and the balance with the first lens unit having negative power is lost, resulting in an under-field curvature. When the positive power is increased beyond the upper limit, the overall length can be shortened, but the field curvature becomes under.

Hereinafter, an endoscope objective lens according to the present invention will be described with reference to specific numerical examples. In each of Examples 1 to 10 below, the first negative lens 1 is sequentially arranged from the object side.
The basic configuration includes a first lens group 10 including a first and a second negative lens 12, a brightness stop S, a second lens group 20, and a parallel flat glass G serving as a cover glass of an image sensor. In each embodiment, the parallel flat glass G includes a YAG cut filter YG and a CCD cover glass CG, and the image-side surface of the cover glass CG is an imaging surface.

The second lens group 20 has the following six types. One positive lens (Example 10), two positive lenses (Example 9), a positive lens and a negative lens from the object side (Example 8), a positive lens from the object side, and a positive lens having a positive refractive power as a whole. A negative cemented (laminated) lens (Example 7), two positive lenses and a negative lens from the object side (Example 5,
6), two positive lenses, a negative lens, and a positive lens from the object side (Examples 1, 2, 3, and 4).

[Embodiment 1] FIGS. 1 and 2 show a first embodiment of an endoscope objective lens according to the present invention. FIG. 1 is a lens configuration diagram, and FIG. 2 is a diagram showing various aberrations. is there. Table 1 shows specific numerical data of this lens. In the various aberration diagrams, d
Line, g line, and C line represent chromatic aberration and lateral chromatic aberration represented by spherical aberration at respective wavelengths, S represents sagittal,
M indicates meridional.

In the tables and drawings, F _NO is the F number, F is the focal length of the entire lens system, M is the paraxial lateral magnification, W is the half angle of view of the lens at the reference design distance of 10 mm, and f _B is the back focus. Represent. R designates the radius of curvature, D is the lens thickness or distance between lens, n _d is the refractive index of the d line, [nu _d denotes the Abbe number at the d-line. Back focus f _B is the equivalent air distance distance to the image side surface of the parallel plane glass G from the last surface of the second lens group.

[0023]

[Table 1] f _No = 1: 8.0 f = 2.44 M = -0.259 W = 59.4 ゜ f _B = 0.00 Surface No. RD n _d ν _d 1 ∞ 0.70 1.51633 64.1 2 6.044 0.29--3 -1.528 0.53 1.80518 25.4 4 -3.157 0.04--Aperture ∞ 0.13--5 2.235 0.49 1.72600 53.5 6 -1.129 0.00--7 -3.460 0.60 1.43875 95.0 8 -2.057 0.24--9 -0.875 0.31 1.80518 25.4 10 -86.938 0.43--11 8.621 0.80 1.88300 40.8 12 -4.718 0.58--13 ∞ 1.00 1.53113 62.4 14 ∞ 0.50 1.53000 60.0 15 ∞---

[Embodiment 2] FIGS. 3 and 4 show a second embodiment of the endoscope objective lens of the present invention. FIG. 3 is a lens configuration diagram, and FIG. 4 is a diagram showing various aberrations. Table 2 shows specific numerical data.

[0025]

TABLE 2 _{f No = 1: 8.0 f =} 2.08 M = -0.216 W = 62.6 ° f _B = 0.00 face _{No. R D n d ν d 1} * 6.000 0.70 1.51633 64.1 2 1.483 0.16 - - 3 -1.801 0.33 1.80518 25.4 4 -2.594 0.04--Aperture ∞ 0.13--5 14.814 0.46 1.72600 53.5 6 -0.885 0.00--7 -27.913 0.64 1.43875 95.0 8 -2.694 0.12--9 -1.506 0.12 1.80518 25.4 10 4.952 0.40--11 7.579 0.74 1.88300 40.8 12 -4.927 0.53--13 ∞ 1.00 1.53113 62.4 14 ∞ 0.50 1.53000 60.0 15 ∞---* is a rotationally symmetric aspheric surface. However, a rotationally symmetric aspheric surface is defined by the following formula. x = Ch ² / ｛1+ [1- (1 + K) C
^{2 h 2] 1/2} + A4h} 4 + A6h 6 + A8h 8 + ·
(C is the curvature (1 / r), h is the height from the optical axis, and K is the cone coefficient) Aspherical data No. 1; K = 0.1675, A4 = -0.1052 × 10 ^-1 , A6 = 0.1953 × 10 ^-2 , A8 = -0.4404 × 10 ^-3 , A10 = -0.1085 × 10 ^-3 , A12 = -0.4307 × 10 ^-3

[Embodiment 3] FIGS. 5 and 6 show a third embodiment of the endoscope objective lens of the present invention. FIG. 5 is a lens configuration diagram, and FIG. 6 is a diagram showing various aberrations. Table 3 shows specific numerical data.

[0027]

[Table 3] f _No = 1: 8.0 f = 2.12 M = -0.217 W = 69.8 ゜ f _B = 0.00 Surface No. RD n _d ν _d 1 ∞ 0.70 1.72916 54.7 2 0.900 0.14--3 -1.500 0.30 1.83400 37.2 4 -2.000 0.04--Aperture ∞ 0.01--5 1.375 0.97 1.72600 53.5 6 -1.252 0.00--7 -26.671 0.72 1.43875 95.0 8 -1.142 0.16--9 -0.797 0.37 1.80518 25.4 10 -3.822 0.79--11 9.329 0.71 1.88300 40.8 12 -8.116 0.40--13 ∞ 1.00 1.53113 62.4 14 ∞ 0.50 1.53000 60.0 15 ∞---

[Embodiment 4] FIGS. 7 and 8 show a fourth embodiment of the endoscope objective lens of the present invention. FIG. 7 is a lens configuration diagram, and FIG. 8 is a diagram showing various aberrations. Table 4 shows specific numerical data.

[0029]

Table 4 _{f No = 1: 8.0 f =} 1.40 M = -0.125 W = 60.0 ° f _B = 0.00 face _{No. R D n d ν d 1} * ∞ 0.69 1.51633 64.1 2 1.096 0.29 - - 3 -2.102 0.30 1.80518 25.4 4 -5.142 0.08--Aperture ∞ 0.01--5 2.562 1.27 1.72600 53.5 6 -1.056 0.00--7 -122.520 0.50 1.43875 95.0 8 -1.087 0.12--9 -0.912 0.30 1.84666 23.8 10 11.163 0.40--11 10.011 1.59 1.88300 40.8 12 * -1.610 0.40--13 ∞ 1.00 1.53113 62.4 14 ∞ 0.50 1.53000 60.0 15 ∞---Aspherical data No.1; K = 0.8696 × 10 ¹ , A4 = 0.6727 × 10 ^-1 , A6 = -0.3611 × ^{10 -2, A8 = -0.2045 × 10} -2, A10 = -0.3384 × 10 -4, A12 = 0.6865 × 10 -3 No.12; K = -0.1455 × 10 1, A4 = 0.1055 × 10 -1, A6 = 0.2436 × 10 ^-3 , A8 = -0.1229 × 10 ^-3 , A10 = -0.1277 × 10 ^-4 , A12 = 0.2224 × 10 ^-5

[Embodiment 5] FIGS. 9 and 10 show a fifth embodiment of the endoscope objective lens of the present invention. FIG. 9 is a lens configuration diagram, and FIG. 10 is a diagram showing various aberrations. Table 5 shows specific numerical data.

[0031]

TABLE 5 _{f No = 1: 8.0 f =} 1.89 M = -0.192 W = 60.0 ° f _B = 0.00 face _{No. R D n d ν d 1} 1.751 0.67 1.51633 64.1 2 0.927 0.36 - - 3 -4.721 0.48 1.80518 25.4 4 7.895 0.03--Aperture ∞ 0.13--5 -4.376 0.49 1.72600 53.5 6 -0.750 0.00--7 4.944 0.60 1.43875 95.0 8 -2.818 0.07--9 -8.630 0.18 1.80518 25.4 10 2.630 0.94--11 1.00 1.00 1.53113 62.4 12 ∞ 0.50 1.53000 60.0 13 ∞---

[Embodiment 6] FIGS. 11 and 12 show a sixth embodiment of the endoscope objective lens of the present invention.
1 is a lens configuration diagram, and FIG. 12 is a diagram of various aberrations. Table 6 shows specific numerical data.

[0033]

[Table 6] _{f No = 1: 8.0 f =} 1.86 M = -0.187 W = 59.9 ° f _B = 0.00 face _{No. R D n d ν d 1} 1.944 0.67 1.88300 40.8 2 1.102 0.32 - - 3 -14.755 0.45 1.74400 44.8 4 12.326 0.17--Aperture ∞ 0.13--5 -1.772 0.50 1.72600 53.5 6 -0.736 0.00--7 3.530 0.55 1.51633 64.1 8 -2.294 0.10--9 -5.406 0.18 1.80518 25.4 10 2.651 0.93--11 ∞ 1.00 1.53113 62.4 12 ∞ 0.50 1.53000 60.0 13 ∞---

[Embodiment 7] FIGS. 13 and 14 show a seventh embodiment of the endoscope objective lens of the present invention.
3 is a lens configuration diagram, and FIG. 14 is a diagram of various aberrations. Table 7 shows specific numerical data.

[0035]

TABLE 7 _{f No = 1: 8.0 f =} 1.83 M = -0.181 W = 70.1 ° f _B = 0.01 face _{No. R D n d ν d 1} * 4.955 0.63 1.88300 40.8 2 1.645 0.39 - - 3 -5.000 0.66 1.80518 25.4 4 -27.536 0.03--Aperture ∞ 0.15--5 -1.839 0.79 1.72916 54.7 6 -0.874 0.19--7 3.221 1.19 1.51633 64.1 8 -1.500 0.34 1.80518 25.4 9 50.686 1.09--10 1.00 1.00 1.53113 62.4 11 ∞ 0.50 1.53000 60.0 12 ∞ −
− − Aspherical surface data No. 1; K = −0.9686, A4 = 0.4085 × 10 ⁻² , A6 = 0.6902 × 10 ⁻² , A8 = −0.3954 × 10 ⁻² , A10 = 0.1522 × 10 ⁻² , A12 = −0.1720 × 10 ^-3

Embodiment 8 FIGS. 15 and 16 show an endoscope objective lens according to an eighth embodiment of the present invention.
5 is a lens configuration diagram, and FIG. 16 is a diagram of various aberrations. Table 8 shows specific numerical data.

[0037]

Table 8 _{f No = 1: 8.0 f =} 1.56 M = -0.156 W = 56.1 ° f _B = 0.00 face _{No. R D n d ν d 1} 1.531 0.59 1.88300 40.8 2 0.876 0.23 - - 3 -4.814 0.67 1.69680 55.5 4 ∞ 0.05--Aperture ∞ 0.00--5 -2.811 0.47 1.69680 55.5 6 -0.516 0.06--7 -5.190 0.62 1.75520 27.5 8 3.283 0.55--9 ∞ 1.00 1.53113 62.4 10 ∞ 0.50 1.53000 60.0 11 ∞---

Ninth Embodiment FIGS. 17 and 18 show a ninth embodiment of the endoscope objective lens of the present invention.
7 is a lens configuration diagram, and FIG. 18 is a diagram of various aberrations. Table 9 shows specific numerical data.

[0039]

TABLE 9 _{f No = 1: 8.0 f =} 0.98 M = -0.092 W = 58.0 ° f _B = 0.00 face _{No. R D n d ν d 1} * 2.062 0.59 1.88300 40.8 2 0.875 0.21 - - 3 -1.976 0.55 1.69680 55.5 4 ∞ 0.04--Aperture ∞ 0.08--5 -5.945 0.70 1.65160 58.5 6 -0.748 0.29--7 2.900 0.51 1.69680 55.5 8 * -10.012 0.30--9 1.00 1.00 1.53113 62.4 10 ∞ 0.50 1.53000 60.0 11 ∞--- Aspheric data No.1; K = 0.2790 × 10 ^-1 , A4 = 0.8066 × 10 ^-2 , A6 = 0.2682 × 10 ^-1 , A8 = -0.1842 × 10 ^-1 , A10 = 0.1381 × 10 ^-1 , A12 = 0.1253 × 10 ^-1 , No.8; K = -0.1959 × 10 ^-1 , A4 = 0.1058 × 10 ^-3 , A6 = 0.7133 × 10 ^-1 , A8 = -0.6092 × 10 ^-2 , A10 = -0.3636 × 10 ^-1 , A12 = -0.3702 × 10 ^-1

[Embodiment 10] FIGS. 19 and 20 show a tenth embodiment of the endoscope objective lens of the present invention.
FIG. 19 is a lens configuration diagram, and FIG. 20 is a diagram of various aberrations. Table 1
0 is specific numerical data.

[0041]

Table 10 _{f No = 1: 8.0 f =} 1.19 M = -0.114 W = 59.5 ° f _B = 0.00 face _{No. R D n d ν d 1} 1.449 0.60 1.88300 40.8 2 0.716 0.23 - - 3 -4.789 0.56 1.69680 55.5 4 ∞ 0.04--Aperture ∞ 0.00--5 -2.140 0.53 1.69680 55.5 6 -0.554 0.72--7 ∞ 1.00 1.53113 62.4 8 ∞ 0.50 1.53000 60.0 9 ∞---

Next, Table 11 shows values for the respective conditional expressions in Examples 1 to 10.

[Table 11] Conditional expression (1) Conditional expression (2) Conditional expression (3) Conditional expression (4) Example 1 -1.00 2.88 -0.78 1.32 Example 2 -1.66 5.54 -0.72 1.29 Example 3- 1.00 7.00 -1.84 1.51 Example 4 -1.00 2.38 -0.99 0.50 Example 5 -3.25 0.25 -0.86 1.59 Example 6 -3.62 -0.09 -0.60 1.40 Example 7 -1.99 1.44 -0.85 1.22 Example 8 -3.68 1.00 -0.58 1.11 Example 9 -2.47 1.00 -0.77 1.01 Example 10 -2.95 1.00 -0.61 1.27

As is apparent from Table 11, the numerical values of Examples 1 to 10 satisfy the conditional expressions (1) to (4). Further, as is clear from the aberration diagrams, each aberration is satisfactorily corrected.

[0044]

According to the present invention, it is possible to suppress the radius of curvature of the front lens group from becoming too small and to correct the distortion aberration without reducing the peripheral light amount so much, thereby increasing the angle of the endoscope objective lens. Can be planned.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of an endoscope objective lens according to the present invention.

FIG. 2 is a diagram illustrating various aberrations of the lens of FIG. 1;

FIG. 3 is a lens configuration diagram of a second embodiment of the endoscope objective lens according to the present invention.

FIG. 4 is a diagram illustrating various aberrations of the lens of FIG. 3;

FIG. 5 is a lens configuration diagram of a third embodiment of the endoscope objective lens according to the present invention.

FIG. 6 is a diagram illustrating various aberrations of the lens of FIG. 5;

FIG. 7 is a lens configuration diagram of a fourth embodiment of the endoscope objective lens according to the present invention.

FIG. 8 is a diagram illustrating various aberrations of the lens in FIG. 7;

FIG. 9 is a lens configuration diagram of a fifth embodiment of the endoscope objective lens according to the present invention.

FIG. 10 is a diagram illustrating various aberrations of the lens in FIG. 9;

FIG. 11 is a lens configuration diagram of a sixth embodiment of the endoscope objective lens according to the present invention.

FIG. 12 is a diagram illustrating various aberrations of the lens in FIG. 11;

FIG. 13 is a lens configuration diagram of a seventh embodiment of the endoscope objective lens according to the present invention.

FIG. 14 is a diagram illustrating various aberrations of the lens in FIG. 13;

FIG. 15 is a lens configuration diagram of an eighth embodiment of the endoscope objective lens according to the present invention.

FIG. 16 is a diagram illustrating various aberrations of the lens in FIG. 15;

FIG. 17 is a lens configuration diagram of a ninth embodiment of the endoscope objective lens according to the present invention.

FIG. 18 is a diagram illustrating various aberrations of the lens in FIG. 17;

FIG. 19 is a lens configuration diagram of a tenth embodiment of the endoscope objective lens according to the present invention.

FIG. 20 is a diagram illustrating various aberrations of the lens in FIG. 19;

[Explanation of symbols]

 Reference Signs List 10 first lens group 20 second lens group S stop G parallel flat glass

Claims (8)

[Claims] A first lens group having a negative refractive power as a whole, a brightness stop, and a second lens group having a positive refractive power as a whole; Are composed of two single lenses, a first lens on the object side and a second lens on the image side, both having negative refractive power, and the following conditional expression (1)
An endoscope objective lens satisfying (2). _{(1) -5.0 <q 1 <} -0.9 (2) -0.5 <q 2 <9.0 where, q _1: shaping factor of the first lens (= (r2 + r1) / (r2-r1 )) Q ₂ : shaping factor of second lens (= (r4 + r3) / (r4-r3)) r1: radius of curvature of object-side surface of first lens, r2: radius of curvature of image-side surface of first lens R3: radius of curvature of the object-side surface of the second lens, r4: radius of curvature of the image-side surface of the second lens. 2. The endoscope objective lens according to claim 1, further satisfying the following conditional expression (3). (3) 0.5 <| f / f I | <1.0, f I <0 (4) 1.5 <f / f II <2.5 where, f _I: composite focal length of the first lens group , F _II : composite focal length of the second lens group, f: composite focal length of the entire system. 3. The endoscope objective lens according to claim 1, wherein the second lens group includes one positive lens. 4. The endoscope objective lens according to claim 1, wherein the second lens group includes two positive lenses. 5. An endoscope objective lens according to claim 1, wherein the second lens group includes a positive lens and a negative lens from the object side. 6. The endoscope according to claim 1, wherein the second lens group comprises a positive lens from the object side and a cemented lens having a positive refractive power as a whole, wherein the positive lens and the negative lens are cemented. Objective lens. 7. The endoscope objective lens according to claim 1, wherein the second lens group includes two positive lenses and a negative lens from the object side. 8. The endoscope objective lens according to claim 1, wherein the second lens group includes, from the object side, two positive lenses, a negative lens, and a positive lens.