JP2596827B2 - Endoscope objective lens - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an objective lens of an endoscope.

[Prior Art] As an objective lens of an endoscope, a lens described in JP-A-62-173415 is known. This objective lens has disadvantages such as a long overall length and a lens outer diameter that is larger than the image diameter.

There is also an objective lens described in JP-A-63-26123. This objective lens has a drawback in that although the angle of view is narrow, a large amount of distortion occurs and the peripheral image is distorted.

[Problems to be Solved by the Invention] The present invention has a short overall length, a small outer diameter, a wide angle,
It is an object of the present invention to provide an endoscope objective lens in which distortion is satisfactorily corrected.

[Means for Solving the Problems] The endoscope objective lens of the present invention has the following configuration to achieve the above object.

That is, for example, in a configuration as shown in FIG. 1, the front unit and the rear unit are sandwiched by an aperture.
The first lens unit includes a first unit having a negative power as a whole and a second unit having one or more cemented lenses and having a positive power. The rear unit includes at least one cemented lens of a positive lens and a negative lens. It comprises only a positive lens group. The lens system satisfies the following conditions (1) and (2).

_{(1) 0.33f <f p <} 11.5f (2) | n rp -n rn |> 0.2 , however, f _p is the focal length of the second lens group of the front group, f is the focal length of the entire system, n _rp, n _rn is the refractive index of each of the positive and negative power lenses of the cemented lens in the rear group.

The optical system of the present invention, by arranging a positive refractive power in front of the stop, can have a function of reducing the inclination of light rays emitted from the rear side of the stop when tracing light backward from the image plane. This is advantageous for correcting distortion. In addition, the lens having the positive refractive power has a function of alleviating the lens system from being asymmetric by forming only the negative lens in front of the stop, which is advantageous for correction of coma.

If the focal length of the positive lens component before this stop is 11.5 times or more of the focal length of the entire system, that is, if the upper limit of the condition (1) is exceeded, it becomes difficult to correct the lower coma positively. Correction of distortion is also difficult. On the other hand, if the focal length of the entire system is 0.33 times or less, that is, if the lower limit of the condition (1) is exceeded, the power of each lens in the front group becomes too strong, and it becomes difficult to correct coma and astigmatism.

In the cemented lens of the rear group, the spherical aberration and the upper coma are corrected by giving the refractive index difference between the two lenses. If the refractive index difference between the positive lens and the negative lens of the cemented lens is out of the condition (2) and is 0.2 or less, it becomes difficult to correct spherical aberration and upper coma.

Further, in the objective lens according to the present invention, it is desirable that the cemented lens is arranged closest to the image plane in the rear group.

In the objective lens described in the above-mentioned Japanese Patent Application Laid-Open No. Sho 62-173415, a meniscus lens having a relatively large outer diameter is arranged near the final surface of the lens system. However, the meniscus lens is poor in workability, and has a low strength due to the thinness over the entire lens, and is greatly affected by eccentricity, thereby causing astigmatism. It is not preferable to use such a meniscus lens. In addition, the conventional objective lens has a drawback that the total length is long due to the large number of lens elements, and the peripheral light quantity is reduced because the exit pupil of off-axis light approaches the image plane.

In the present invention, by disposing the cemented lens closest to the image, it is not necessary to use a weak meniscus lens, and chromatic aberration of magnification can be corrected.

Further, in the objective lens according to the present invention, it is desirable that the positive lens component arranged in the front group be a cemented lens so as to satisfy the following condition (3).

(3) | n _ff −n _fr |> 0.1 where n _ff and n _fr are the refractive indices of the object-side lens and the image-side lens of the cemented lens.

In this way, by providing a refractive index difference between the two lenses of the positive cemented lens disposed before the stop, it is possible to correct spherical aberration and lower coma at the cemented surface.

If this refractive index difference is less than 0.1, spherical aberration and lower coma cannot be satisfactorily corrected.

Furthermore, it is preferable that the objective lens of the present invention satisfies the following condition (4).

(4) 0.2f <D <5f where D is the maximum air-equivalent length between the lens closest to the object in the rear group and the lens closest to the image among the cemented lenses.

In this manner, the cemented lens in the rear group can be moved away from the stop, and thus the off-axis rays can pass through a high position of the cemented surface of the cemented lens. Thereby, the chromatic aberration of magnification can be favorably corrected, and the distance to the concave lens in the front group can be increased, so that the power of each lens can be weakened, which is advantageous for correction of coma and astigmatism. . In addition, an optical filter that cuts light having a wavelength unnecessary for imaging, such as infrared light, can be inserted into the above-mentioned interval, which is desirable.

If the value of D in the condition (4) is too small and falls below the lower limit of the condition, the interval for arranging optical elements such as an optical filter cannot be obtained. On the other hand, if the value of D is too large and exceeds the upper limit of the condition, the overall length of the lens system becomes long, which causes a problem that it cannot be made compact.

Furthermore, in the endoscope objective lens of the present invention, distortion and image surface curvature can be favorably corrected by using an aspherical surface.

In an embodiment to be described later, the surface on the object side of one of the lenses of the front group disposed before the aperture stop S has a surface whose curvature gradually increases as the distance from the optical axis increases. Or the image-side surface of one of the lenses in the front group disposed before the aperture stop S has a surface whose curvature gradually becomes weaker as the distance from the optical axis increases. One or more surfaces, or the object-side surface of one of the lenses in the rear group disposed behind the aperture stop S has a portion where the curvature gradually decreases as the distance from the optical axis increases. Whether the surface on the image side of one of the lenses in the rear group disposed behind the aperture stop S has a surface whose curvature gradually increases as the distance from the optical axis increases. At least one surface It is obtained by way.

Next, the reason why the endoscope objective lens as described above can sufficiently correct both distortion and field curvature will be described.

The reason that the conventional endoscope objective lens having the configuration shown in FIG. 21 generates a strong negative distortion is that when the principal ray is traced in reverse from the image side, the principal ray becomes brighter as the image height increases. Aperture S
That is, the light is refracted in a direction in which the angle of view is widened by the front group before the lens and the rear group after the aperture stop. Therefore, strong negative distortion can be corrected by providing an aspherical surface in the lens system in which the refractive power of the principal ray becomes weaker as the distance from the optical axis increases.

For this purpose, the surface on the object side of one of the lenses in the front group before the aperture stop S includes a portion where the curvature of the surface increases as the distance from the optical axis increases, or Either include a portion where the curvature gradually decreases as the image-side surface of one of the lenses on the image side moves away from the optical axis, or one of the lenses in the rear group after the aperture stop S. The object-side surface may include a portion where the curvature of the surface becomes weaker as the distance from the optical axis increases, or the image-side surface of one lens in the rear group moves away from the optical axis. What is necessary is just to include the part which curvature becomes strong.

An aspheric surface as shown in FIGS. 22 and 23 is also effective as a surface whose curvature gradually increases as the distance from the optical axis increases. In this case, considering the curvature including the sign,
If the center of the osculating circle at a certain point on the surface is on the object side of the surface, it is negative; if it is on the image side, it is positive. Therefore, the example shown in FIG. 22 is an example in which the curvature increases with increasing distance from the optical axis (the negative curvature that is concave on the object side increases to the positive curvature that is convex on the object side), including the sign. is there. The example shown in FIG. 23 is an example in which the curvature once increases and then decreases.

The distortion can be corrected even on the surface as shown in FIG. 23 because the distortion curve of distortion cannot be practically used even if it has undulation as shown in FIG. 24, and the aspherical surface shown in FIG. Of these, the peripheral portion does not pass through the lower ray but does not pass through the principal ray, and thus has no relation to the correction of distortion.

Further, as an example of a curved surface including a portion in which the curvature of the image-side surface of the lens gradually becomes weaker as the light rays move away,
25 and 26 are also available.

As described above, when the aspheric surface provided in the front group of the endoscope objective lens of the present invention is provided on the object-side surface of the lens, the surface as shown in FIGS. Including,
At least one surface includes a portion where the curvature gradually increases.
26, including the surface as shown in FIG. 26 and FIG. 26, the surface includes a portion where the curvature gradually increases. The objective lens including at least one aspheric surface can satisfactorily correct distortion.

 Generally, an aspheric surface can be represented by the following equation.

Here, x and y are coordinate values when the optical axis is the x-axis, the image direction is the positive direction, the intersection with the optical axis is the origin, and the direction orthogonal to the x-axis is the y-axis, as shown in FIG. C is the reciprocal of the radius of curvature of the circle in contact with the aspheric surface near the optical axis, P is the conic constant, B, E, F,
G,... Are second-order, fourth-order, sixth-order, and eighth-order aspherical coefficients, respectively.

In the endoscope objective lens of the present invention, when the shape of the aspherical surface on the object side of the front group is considered as the amount of deviation from the plane, that is, the fourth-order aspherical surface coefficient E and 6
It is desirable that the next aspheric coefficient F satisfies at least one of the following conditions.

(5) 0.0006 <f ³ <E <0.6 / f ³ (6) 0.0001 <f ⁵ <F <0.1 / f ^{5 In} order to satisfactorily correct distortion with the aspheric surface used in the front group, 0.0006 <f ³ f ³ <E. That is, when the value goes below the lower limit of the condition (5), the correction of the distortion becomes insufficient. When the value exceeds the upper limit of the condition (5), astigmatism cannot be suppressed and the workability of the lens deteriorates.

On the other hand, when the value of F satisfies the condition (6), the value of E
The same effect as described above for the value of is obtained.

If the lower limit of the condition (6) is exceeded, correction of distortion will not be sufficient. If the value exceeds the upper limit, astigmatism cannot be sufficiently corrected, and the workability of the lens deteriorates.

If only the distortion needs to be corrected in the lens system of the present invention, the above-described aspherical surface may be disposed only on one side of the stop. However, in this case, the swelling of the meridional field curvature at the intermediate image height increases, and the image quality at the intermediate image height remarkably decreases. Therefore, when the aspherical surfaces are arranged in both the front group and the rear group, the sign of the bulge of the meridional field curvature due to the aspherical surface provided in the front group, that is, minus, and the bulge of the meridional field curvature due to the aspherical surface provided in the rear group. Since the sign, that is, the plus sign is the opposite sign, the bulge can be canceled by canceling each other.

In the endoscope objective according to the present invention, it is desirable that the aspherical surface of the rear group is disposed at a position satisfying the following condition (7).

_{(7) 0.2f <D A <} 3f However D _A is air-equivalent length to aspherical from the aperture stop. The air conversion length referred to here is a value obtained by adding a value obtained by dividing the thickness of the lens by the refractive index when a lens is interposed therebetween.

In this way, by disposing the aspherical surface of the rear group at a position close to the stop to a certain extent, it is possible to increase the difference between the heights of the upper and lower rays passing through the aspherical surface, which is advantageous in correcting coma. is there. If the aperture is too close to the stop, it becomes difficult to correct astigmatism, which is not preferable.

Also, Seidel's aberration coefficient is defined as in the following equations (i) and (ii). This is a general-purpose lens design program ACCOS
Same as used in -V. However, AC
In COS-V, the object distance is OB and the numerical aperture of the marginal ray is
NA, when the refractive index of the medium on the object side from the first surface is n ₀ , the ray height H ₀ of the paraxial ray on the first surface is H ₀ = OB × tan {sin ^-1 (NA / n ₀ )} In the present application, it is determined by H ₀ = OB × (NA / n ₀ ). Therefore, in the present application, H ₀ determined by the latter
Is used to perform paraxial tracking to obtain each aberration coefficient. NA = 1 / 2F _NO .

Meridional ΔY to light rays (= 0) = (SA3) 3 + (CMA3) 2 + {3 (AST3) + (PTZ3)} 2 + (DIS3) 3 + (SA5) 5 + (CMA5) 4 + (TOBSA ^{) 3 2 + (ELCMA) 2} 3 + {5 (AST5) + (PTZ5)} 4 + (DIS5) 3 + (SA7) 7 ............ (i) ΔX relative sagittal rays (= 0) = ( ^{SA3) 3 + {(AST3)} + (PTZ3)} 2 + (SA5) 5 + (SOBSA) 3 2 + {(AST5) + (PTZ5)} 4 + (SA7) 7 ... (ii) above formula (i ) Shows the deviation between the paraxial image point (image point when there is no aberration) and the actual image point with respect to the meridional ray by ΔY
Is the incident position of the paraxial chief ray on the image plane standardized by the maximum image height, and F is the incident position of the marginal ray standardized by the pupil diameter on the pupil plane. SA3, SA5, SA
7 is the 3rd, 5th and 7th order spherical aberration, respectively, CMA3 and CMA5 are 3 respectively
Next, 5th order tanjinjinkoma, AST3, AST5 are 3rd,
Fifth-order astigmatism, PTZ3, PTZ5 are third- and fifth-order Petzval sums, DIS3, DIS5 are third-, fifth-order distortions, and TOBSA is five.
The next oblique tangential spherical aberration, ELCMA is the fifth elliptical coma, and SOBSA is the fifth oblique sagittal spherical aberration.

Now, assuming that the i-th surface in the rear group is an aspherical surface, it can be considered that the i-th surface is obtained by adding a displacement of a predetermined magnitude to the spherical surface. Here, the third-order coma aberration coefficient generated on the original spherical surface is S _i , the third-order coma aberration coefficient generated on displacement from the spherical surface is A _i, and S _Ri , A _Ri .

When a plurality of aspherical surfaces exist in the rear group, the sum of the respective aspherical surfaces is expressed as follows.

A _R = ΣA _Ri S _R = ΣS _{Ri When} the sum of the third-order coma aberration coefficients generated on the surface having a negative refractive power of the front group is A ₂ , the following conditions (8) and (9) are satisfied. It is desirable to be satisfied.

_{(8) -13 <A 2 /} (A R + S R) <- 0.03 (9) -0.2 <A R <0.2 objective lens generally endoscope, negative surface strong in front group for wider angle Where significant coma occurs. It is necessary to cancel out this aberration with the aberration generated in the rear group and correct the coma as a whole to improve the performance. When the first group is composed of a plurality of lenses as shown in FIGS. 28 and 30, the air contact surface on the image side is in the case of FIG. 29. In terms of
It is necessary to cancel the negative coma generated on this surface in the rear group. Therefore, it is desirable that S ₂ and (A _R + S _R ) have the same absolute value and opposite signs. However, practically, it is permissible within the range represented by the condition (8).

Also the value of A _R is too large, becomes larger other aberrations, it becomes difficult to correct other aberrations. If the value of A _R is too small, the coma in the front group cannot be corrected completely, so it is desirable to be within the range of the condition (9).

EXAMPLES Next, examples of the endoscope objective lens of the present invention will be described.

Example 1 f = 1.000, F / 5.3, 2ω = 135.9 ° IH = 1.0 r ₁ = ∞ d ₁ = 0.2949 n ₁ = 1.88300 ν ₁ = 40.78 r ₂ = 0.7248 d ₂ = 0.7077 r ₃ = 9.8296 d ₃ = 0.6225 n ₂ = 1.84666 v ₂ = 23.78 r ₄ = −2.3211 d ₄ = 0.1966 r ₅ = ∞ (aperture) d ₅ = 0.2425 r ₆ = −4.3689 d ₆ = 0.5308 n ₃ = 1.51633 v ₃ = 64.15 r ₇ = −1.1894 d ₇ = 0.0983 r ₈ = 3.1298 d ₈ = 0.8519 n ₄ = 1.58913 ν ₄ = 60.97 r ₉ = -0.9450 d ₉ = 0.2621 n ₅ = 1.84666 ν ₅ = 23.78 r ₁₀ = -3.1625 d ₁₀ = 0.0655 r ₁₁ = ∞ d ₁₁ = 0.2621 n ₆ = 1.51633 ν ₆ = 64.15 r ₁₂ = ∞ d ₁₂ = 0.0197 r ₁₃ = ₁₃ d ₁₃ = 0.4063 n ₇ = 1.52000 ν ₇ = 74.00 r ₁₄ = ∞ d ₁₄ = 0.0197 r ₁₅ = ∞ d _{15 = 0.2621 n 8 = 1.51633 ν 8} = 64.15 r 16 = ∞ d 16 = 0.7864 r 17 = ∞ d 17 = 0.6553 n 9 = 1.51633 ν 9 = 64.15 r 18 = ∞ f p = 2.271, | n rp -n rn | = 0.25753 Example 2 f = 1.000, F / 4.1, 2ω = 114.7 ° IH = 0.91 r ₁ = ∞ d ₁ = 0.2653 n ₁ = 1.88300 ν ₁ = 40.78 r ₂ = 0.6775 d ₂ = 0.4894 r _{3 = 4.9752 d 3 = 0.2948 n 2} = 1.51633 ν 2 = 64.15 r 4 = 1.6392 d 4 = 0.5896 n 3 = 1.69895 ν 3 = 30.12 r 5 = -2.5071 d 5 = 0.0590 r 6 = ∞ d 6 = 0.1887 r 7 = _{-13.0601 d 7 = 0.4953 n 4 =} 1.58913 ν 4 = 60.97 r 8 = -1.3779 d 8 = 0.2182 r 9 = 4.1999 d 9 = 0.7134 n 5 = 1.58913 ν 5 = 60.97 r 10 = -0.8974 d 10 = 0.2358 n 6 = 1.84666 ν ₆ = 23.78 r ₁₁ = −2.4858 d ₁₁ = 0.17769 r ₁₂ = ∞ d ₁₂ = 0.2358 n ₇ = 1.51633 ν ₇ = 64.15 r ₁₃ = ∞ d ₁₃ = 0.0177 r ₁₄ = ∞ d ₁₄ = 0.3656 n ₈ = 1.52000 ν ₈ = 74.00 r ₁₅ = ∞ d ₁₅ = 0.0177 r ₁₆ = ∞ d ₁₆ = 0.2358 n ₉ = 1.51633 ν ₉ = 64.15 r ₁₇ = ∞ d ₁₇ = 0.7429 r ₁₈ = ∞ d ₁₈ = 0.5896 n ₁₀ = 1.51633 ν _{10 = 64.15 r 19 = ∞ f} p = 2.148, | n rp -n rn | = 0.25753 | n ff -n fr | = 0.18262 example 3 f = 1.000, F / 4.1,2ω = 113 ° IH = 0.92 r 1 _{= ∞ d 1 = 0.3114 n 1} = 1.88300 ν 1 = 40.78 r 2 = 0.7131 d 2 = 0.5689 r 3 = 4.1434 d 3 = 0.2509 n 2 = 1.77250 ν 2 = 49.66 r 4 = _{0.6116 d 4 = 0.5957 n 3 =} 1.62004 ν 3 = 36.25 r 5 = -1.9478 d 5 = 0.1076 r 6 = ∞ ( _{stop) d 6 = 0.0599 r 7 =} -5.5688 d 7 = 0.4497 n 4 = 1.72916 ν 4 = 54.68 r ₈ = -1.1870 d ₈ = 0.3346 r ₉ = ∞ d ₉ = 0.4192 n ₅ = 1.52000 ν ₅ = 74.00 r ₁₀ = ∞ d ₁₀ = 0.2395 n ₆ = 1.51633 ν ₆ = 64.15 r ₁₁ = ∞ d ₁₁ = 0.0599 r ₁₂ = 2.7131 d ₁₂ = 0.2255 n ₇ = 1.84666 ν ₇ = 23.78 r ₁₃ = 1.0896 d ₁₃ = 0.9748 n ₈ = 1.51633 ν ₈ = 64.15 r ₁₄ = -3.2795 d ₁₄ = 1.1464 r ₁₅ = ∞ d ₁₅ = 0.5988 n _{9 = 1.51633 ν 9 = 64.15 r 16} = ∞ f p = 3.842, | n rp -n rn | = 0.33033 | n ff -n fr | = 0.15246, D = 0.768 example 4 f = 1.000, F / 4.2,2ω = _{114.3 ° IH = 0.92 r 1 =} ∞ d 1 = 0.3393 n 1 = 1.88300 ν 1 = 40.78 r 2 = 0.7795 d 2 = 0.7857 r 3 = 3.3429 d 3 = 0.2232 n 2 = 1.77250 ν 2 = 49.66 r 4 = 0.8393 d _{4 = 0.5804 n 3 = 1.62606 ν} 3 = 39.21 r 5 = -2.2304 d 5 = 0.0893 r 6 = ∞ d 6 = 0.0446 r 7 = -13.5125 d 7 = 0.4464 n 4 = 1.72916 ν ₄ = 54.68 r ₈ = -1.6062 d ₈ = 0.0893 r ₉ = ∞ d ₉ = 1.3393 n ₅ = 1.51633 ν ₅ = 64.15 r ₁₀ = ∞ d ₁₀ = 0.0893 r ₁₁ = 2.1268 d ₁₁ = 0.2500 n ₆ = 1.84666 ν _{6 = 23.78 r 12 = 1.0464 d} 12 = 0.9732 n 7 = 1.51633 ν 7 = 64.15 r 13 = -3.8661 d 13 = 0.6230 r 14 = ∞ d 14 = 0.8929 n 8 = 1.51633 ν 8 = 64.15 r 15 = ∞ f p = 3.048, | n _rp −n _rn | = 0.30333 | n _ff −n _fr | = 0.14644, D = 1.62 Example 5 f = 1.000, F / 4.7, 2ω = 106 ° IH = 1.00 r ₁ = ∞ (aspherical surface ) D ₁ = 0.3026 n ₁ = 1.80610 ν ₁ = 40.95 r ₂ = 0.6320 d ₂ = 0.5326 r ₃ = 1.4455 d ₃ = 0.2291 n ₂ = 1.75520 ν ₂ = 27.51 r ₄ = −6.7934 d ₄ = 0.6325 n ₃ = 1.56883 ν ₃ = 56.34 r ₅ = -1.2679 d ₅ = 0.1332 r ₆ = ∞ (aperture) d ₆ = 0.1724 r ₇ = 2.4437 d ₇ = 0.5403 n ₄ = 1.51633 ν ₄ = 64.15 r ₈ = -1.8760 d ₈ = 0.2195 n ₅ = 1.84666 ν ₅ = 23.78 r ₉ = -2.8190 (aspheric surface) d ₉ = 0.1332 r ₁₀ = ∞ d ₁₀ = 0.9079 n ₆ = 1.52000 ν ₆ = 74.00 r ₁₁ = ∞ d ₁₁ = 0.2766 r ₁₂ = ∞ d ₁₂ = 0.6053 n ₇ = 1.51633 ν ₇ = 64.15 r ₁₃ = ∞ (first surface) P = 1.000 B = 0.23263 × 10 ^-1 E = 0.3
4082 × 10 ⁻¹ F = −0.48683 × 10 ⁻² (Ninth surface) P = −6.7002 B = 0 E = 0.17408 F
= −0.69257 × 10 ⁻¹ f _p = 1.153, | n _rp −n _rn | = 0.30333 | n _ff −n _fr | = 0.18637, D _A = 0.6475 A _R = 0.00526, A ₂ / (A _R −S _R ) = −0.996 Example 6 f = 1.000, F / 4.5, 2ω = 113.0 ° IH = 1.14 r ₁ = ∞ (aspherical surface) d ₁ = 0.3459 n ₁ = 1.80610 ν ₁ = 40.95 r ₂ = 0.7439 d ₂ = 0.3459 r _{3 = 2.6052 d 3 = 0.5328 n} 2 = 1.72825 ν 2 = 28.46 r 4 = -0.8588 d 4 = 0.5535 n 3 = 1.58913 ν 3 = 60.97 r 5 = 266.4111 d 5 = 0.0692 r 6 = ∞ ( stop) d ₆ = _{0.1683 r 7 = 24.8283 d 7 =} 0.4559 n 4 = 1.53172 ν 4 = 48.90 r 8 = 2.0198 d 8 = 0.4690 n 5 = 1.84100 ν 5 = 43.23 r 9 = -1.3623 ( aspheric _{surface) d 9 = 0.1730 r 10 =} ∞ d ₁₀ = 1.0378 n ₆ = 1.52000 ν ₆ = 74.00 r ₁₁ = ∞ d ₁₁ = 0.3407 r ₁₂ = ∞ d ₁₂ = 0.6919 n ₇ = 1.51633 ν ₇ = 64.15 r ₁₃ = ∞ Aspherical coefficient (first surface) P = 1.0000, B = 0.14569 E = 0.29823 × 10 ⁻¹ , F = −0.13020 × 10 ⁻¹ (9th surface) P = 1.759, B = 0, E = 0.14285 F = 0.10574 f _p = 2.348, | n _rp −n _rn | = 0.30928 │n _ff -n _fr │ = 0.13912, D _A = 0.7207 A _R = 0.0025, A ₂ / (A _R + S _R ) =-0.596 Example 7 f = 1.000, F / 4.7, 2ω = 13.0 ° IH = 1.15 r ₁ = ∞ (aspherical surface) d ₁ = 0.3480 n ₁ = 1.80610 ν ₁ = 40.95 r ₂ = 0.6177 d ₂ = 0.5740 r ₃ = 2.4828 d ₃ = 0.5111 n ₂ = 1.72825 ν ₂ = 28.46 r ₄ = −0.6841 d _{4 = 0.5569 n 3 = 1.58921 ν} 3 = 41.08 r 5 = -3.2002 d 5 = 0.0696 r 6 = ∞ ( _{stop) d 6 = 0.1798 r 7 =} 2.2304 d 7 = 0.3829 n 4 = 1.84666 ν 4 = 23.78 r 8 = _{1.1621 d 8 = 0.3921 n 5 =} 1.51633 ν 5 = 64.15 r 9 = -1.1830 ( aspheric _{surface) d 9 = 0.1740 r 10 =} ∞ d 10 = 1.0441 n 6 = 1.52000 ν 6 = 74.00 r 11 = ∞ d 11 = 0.3554 r ₁₂ = ∞ d ₁₂ = 0.6961 n ₇ = 1.51633 ν ₇ = 64.15 r ₁₃ = ∞ aspheric coefficient (first surface) P = 1.0000, B = 0.15331 E = 0.26826 × 10 ⁻¹ , F = 0.98377 × 10 ^-3 (ninth surface) P = 2.8824, B = 0 , E = 0.24847 F = 0.77271, G = -0.48669 × 10 -1 f p = 1.623, | n rp -n rn | = 0.33033 | n ff -n fr | = 0.1390 4, D _A = 0.6457 A _R = 0.00135, A ₂ / (A _R + S _R ) = − 1.328 Example 8 f = 1.000, F / 4.6,2ω = 112.4 ° IH = 1.12 r ₁ = ∞ (aspherical surface) d _{1 = 0.3382 n 1 = 1.80610 ν} 1 = 40.95 r 2 = 0.7123 d 2 = 0.3382 r 3 = 4.2817 d 3 = 0.6242 n 2 = 1.72825 ν 2 = 28.46 r 4 = -1.0308 d 4 = 0.5411 n 3 = 1.58913 ν 3 _{= 60.97 r 5 = -14.9956 d 5} = 0.0676 r 6 = ∞ ( _{stop) d 6 = 0.1112 r 7 =} 10.0801 d 7 = 0.4259 n 4 = 1.53172 ν 4 = 48.90 r 8 = 5.8518 d 8 = 0.2662 n 5 = 1.84100 ν ₅ = 43.23 r ₉ = −1.1895 (aspherical surface) d ₉ = 0.1691 r ₁₀ = ∞ d ₁₀ = 1.0146 n ₆ = 1.52000 ν ₆ = 74.00 r ₁₁ = ∞ d ₁₁ = 0.3466 r ₁₂ = ∞ d ₁₂ = 0.6765 n ₇ = 1.51633 ν ₇ = 64.15 r ₁₃ = ∞ Aspheric coefficient (first surface) P = 1.0000, B = 0.23401 E = 0, F = 0.93316 × 10 ^-2 (ninth surface) P = -0.0306, B = 0 ^{, E = 0.33663 × 10 -1,} F = 0.51107 × 10 -1 f p = 3.033, | n rp -n rn | = 0.30928 | n ff -n fr | = 0.13912, D A = 0.5338 A R = -0.0108, A ₂ / (A _R + S _R ) = − 0.502 Example 9 f = 1.000, F / 4.6, 2ω = 106 ° IH = 1.00 r ₁ = ∞ (aspherical surface) d ₁ = 0.3026 n ₁ = 1.80610 ν ₁ = 40.95 r ₂ = 0.6333 d _{2 = 0.5326 r 3 = 1.7941 d 3} = 0.2287 n 2 = 1.75520 ν 2 = 27.51 r 4 = -2.6805 d 4 = 0.6325 n 3 = 1.56883 ν 3 = 56.34 r 5 = -1.1728 d 5 = 0.1332 r 6 = ∞ ( aperture ) D ₆ = 0.1721 r ₇ = 4.7481 d ₇ = 0.5368 n ₄ = 1.51633 ν ₄ = 64.15 r ₈ = −3.0936 d ₈ = 0.169 n ₅ = 1.84666 ν ₅ = 23.78 r ₉ = −2.4248 (aspherical surface) d ₉ = 0.1332 r ₁₀ = ∞ d ₁₀ = 0.9079 n ₆ = 1.52000 ν ₆ = 74.00 r ₁₁ = ∞ d ₁₁ = 0.2713 r ₁₂ = ∞ d ₁₂ = 0.6053 n ₇ = 1.51633 ν ₇ = 64.15 r ₁₃ = ∞ Aspherical coefficient One surface) P = 1.0000, B = 0.83810 × 10 ^-1 E = 0, F = 0.75968 × 10 ^-2 (9th surface) P = 0.3802, B = 0 E = 0.14794, F = 0.21801 × 10 ^-1 f _p = 1.177, | n _rp −n _rn | = 0.30333 | n _ff −n _fr | = 0.18637, D _A = 0.6436 A _R = 0.00353, A ₂ / (A _R + S _R ) = − 1.334 Example 10 f = 1.000, F / 3.7,2ω _{135.9 ° IH = 1.41 r 1 =} ∞ ( _{aspherical) d 1 = 0.4132 n 1 =} 1.88300 ν 1 = 40.78 r 2 = 0.9706 d 2 = 0.9885 r 3 = 10.5419 d 3 = 0.8724 n 2 = 1.84666 ν 2 = 23.78 r ₄ = -3.2037 d ₄ = 0.2755 r ₅ = ∞ (aperture) d ₅ = 0.3449 r ₆ = -3.5233 d ₆ = 0.7526 n ₃ = 1.51633 ν ₃ = 64.15 r ₇ = -1.6611 d ₇ = 0.1412 r ₈ = 3.2843 d ₈ = 1.1786 n ₄ = 1.58913 ν ₄ = 60.97 r ₉ = -1.2919 (aspheric surface) d ₉ = 0.3673 n ₅ = 1.84666 ν ₅ = 23.78 r ₁₀ = -2.2845 d ₁₀ = 0.0918 r ₁₁ = ∞ d ₁₁ = 1.3774 n ₆ = 1.51633 ν ₆ = 64.15 r ₁₂ = ∞ d ₁₂ = 0.3398 r ₁₃ = ∞ d ₁₃ = 0.6428 n ₇ = 1.51633 ν ₇ = 64.15 r ₁₄ = ∞ Aspheric coefficient (first surface) P = 1.0000, B = 0.53237 × 10 ⁻¹ E = 0.37136 × 10 ⁻¹ , F = −0.10040 × 10 ⁻¹ G = 0.13094 × 10 ⁻² (9th surface) P = 0.8681, B = 0, E = −0.14223, F = 0.39404 × 10 ^{-1 G = -0.62118 × 10 -1 f} p = 2.989, | n rp -n rn | = 0.25753, D A = 1.724 A R = 0.0108, A 2 / (A R + S R) = - 0.605 However r _1, r ₂ ... the radius of curvature of each lens surface, d _1, d _2,
... the thickness and air space of the lens, n _1, n _2, ... is the refractive index of each lens, ν _1, ν _2, ... is the Abbe number of each lens.

The first to tenth embodiments are as shown in FIGS. 1 to 10, respectively, and the aberration states thereof are as shown in FIGS. 11 to 20, respectively.

In Examples 2 to 9 among these examples, the positive lens component before the stop in the front group is a cemented lens, and is configured to satisfy the condition (3).

Embodiments 3 and 4 satisfy the condition (4) and have a configuration in which an optical element such as an infrared cut filter can be arranged in the rear group.

[Effects of the Invention] The endoscope objective lens of the present invention has a short overall length, a small outer diameter, a wide angle, and excellent correction of distortion, as described in detail above and as apparent from the examples. It is an objective lens.

[Brief description of the drawings]

1 to 10 are sectional views of Examples 1 to 10 of the endoscope objective lens of the present invention, and FIGS. 11 to 20 are aberration curve diagrams of Examples 1 to 10, respectively. FIG. 21 is a cross-sectional view of a conventional endoscope objective lens, FIGS. 22 and 23 are cross-sectional views of an example of an aspheric lens having an aspherical object side, and FIG. 24 is a view showing an example of distortion aberration. 25 and 26 are cross-sectional views of an example of an aspherical lens having an aspherical surface on the image side, FIG. 27 is a diagram showing a coordinate system of an aspherical expression, and FIGS. 28 to 30 are objectives of the present invention. It is sectional drawing which shows the other example of the front group of a lens.

Claims (6)

(57) [Claims] 1. A front unit comprising a front unit and a rear unit arranged with a diaphragm interposed therebetween, wherein the front unit comprises a first unit having a negative power as a whole from the object side and a positive power comprising one lens or a cemented lens. An endoscope objective lens that satisfies the following condition, wherein the second lens unit includes a second lens unit, and the rear unit includes only a positive lens unit including a cemented lens including at least a negative lens and a positive lens. _{(1) 0.33f <f p <} 11.5f (2) | n rp -n rn |> 0.2 , however, f _p is the focal length of the second lens group of the front group, f is the focal length of the entire system, n _p, n _n is the refractive index of the positive lens and the negative lens of the cemented lens in the rear group, respectively. 2. The endoscope objective lens according to claim 1, wherein said second group is a cemented lens, and satisfies the following condition. (3) | n _ff −n _fr |> 0.1 where n _ff and n _fr are the refractive indices of the object-side lens and the image-side lens of the cemented lens. 3. The method according to claim 1, wherein the following condition (4) is satisfied.
Endoscope objective lens. (4) 0.2f <D <5f where D is the maximum air-equivalent length between the lens closest to the object in the rear group and the lens closest to the image among the cemented lenses. 4. A lens system comprising: a front group and a rear group disposed with a stop interposed therebetween; wherein the front group includes a lens component having a negative refractive power, and the rear group has a positive refractive power; Each of the front group and the rear group has at least one aspheric surface, and when the aspheric surface is provided on the object side of the lens, the curvature gradually increases as the distance from the optical axis increases. When the aspheric surface is provided on the image-side surface of the lens, the shape is such that the curvature gradually decreases as the distance from the optical axis increases. When the aspheric surface is provided on the object-side surface of the lens, the middle aspheric surface is shaped so as to include a portion whose curvature gradually becomes weaker as the distance from the optical axis increases, and the aspheric surface is the image-side surface of the lens. , As the curvature moves away from the optical axis, Gradually is shaped to include a strongly becomes part, an endoscope objective lens further satisfies the following conditions. 0.2F <D _A <3f However D _A is the equivalent air distance to the aspherical surface in the rear lens from the aperture stop. 5. The endoscope objective lens according to claim 4, wherein the aspherical surface provided on the side surface of the object in the front group satisfies the following conditions (5) and (6). (5) 0.0006 / f ³ <E <0.6 / f ³ (6) 0.0001 / f ⁵ <F <0.1 / f ⁵ where E is a fourth-order aspherical coefficient, and F is a sixth-order aspherical coefficient. 6. The aspherical surface in the rear group has the following condition (8):
The endoscope objective lens according to claim 4, which satisfies (9). (8) −13 <A ₂ / (A _R + S _R ) <− 0.03 (9) −0.2 <A _R <0.2 where A ₂ is a third-order frame generated on the surface having negative refractive power of the front group. The sum of the aberration coefficients, A _R is the third-order coma aberration coefficient of the aspheric surface, and S _R is the third-order coma aberration coefficient of the original spherical surface of the aspheric surface. is there.