JPH02293709A - Objective lens of endoscope - Google Patents

Abstract

PURPOSE:To obtain the objective lens of an endoscope which is short in overall length, small in outside diameter and is well corrected in distortion aberration by adopting the constitution in which a diaphragm is disposed between a front group consisting, successively from an object side, of a negative 1st group and a positive 2nd group and a rear group consisting of only a positive lens group and satisfying specific conditions equations. CONSTITUTION:The front group is constituted, successively from the object side, of the 1st group having a negative power as a whole and the 2nd group consisting of one piece or combined lens and having the positive power. The rear group is constituted of only the positive lens group including the combined lenses of at least one set of the positive lens and negative lens. The diaphragm is disposed between the front group and the rear group. The equations are satisfied when fp is designated as the focal distance of the 2nd group of the front group, f as the focal distance of the entire system and nrp, nrn are designated respectively as the refractive indices of the positive lens and negative lens of the combined lens of the rear group. The effect of decreasing the inclination of the rays emitted from the rear side of the diaphragm when the trays are traced backward from the image plane is provided by disposing the positive refracting power in front of the diaphragm. This lens is thus effective for correcting the distortion aberration.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an objective lens for an endoscope.

[Prior art] As an objective lens for an endoscope, Japanese Patent Application Laid-Open No. 62-173415
Those listed in the number are known. This objective lens had drawbacks such as a long overall length and a lens outer diameter larger than the image diameter.

There is also an objective lens described in Japanese Patent Laid-Open No. 63-26123. Although this objective lens has a narrow angle of view, it suffers from a large amount of distortion, which distorts peripheral images.

[Problems to be Solved by the Invention] An object of the present invention is to provide an endoscope objective lens that has a short overall length, a small outer diameter, a wide angle, and whose distortion is well corrected. be.

[A Thousand Steps to Solve the Problems] The endoscope objective lens of the present invention has the following configuration in order to achieve the above object.

That is, for example, the configuration shown in Fig. 1 is composed of a front group and a rear group with an aperture in between. It is composed of a second group consisting of a cemented lens and having positive power,
Further, the rear group is composed only of a positive lens group including at least one cemented lens of a positive lens and a negative lens. And the next condition m. This is a lens system that satisfies (21).

(1) 0.33f < f. < 11.5f (21
lnrp-nJ > 0.2 where fp is the focal length of the second group of the front group, f is the focal length of the entire system, n, . p. n
− is the refractive index of each of the positive lens and the lens having negative power of the cemented lens in the rear group.

By arranging a positive refractive power et valve in front of the diaphragm, the optical system of the present invention has the effect of reducing the inclination of the rays emerging from behind the diaphragm when rays are traced backward from the image plane. This is advantageous for correcting distortion aberration.

Furthermore, this positive refractive power lens has the effect of alleviating the asymmetrical nature of the lens system caused by configuring only negative lenses in front of the diaphragm, which is advantageous for correcting coma aberration.

If the focal length of the positive lens component in front of this aperture is 11.5 times or more the focal length of the entire system, that is, if it exceeds the upper limit of condition (1), it will be difficult to correct the lower coma positively. Therefore, it becomes difficult to correct distortion aberration. On the other hand, if it is less than 0.33 times the focal length of the entire system, that is, if the lower limit of 11 is exceeded, the power of each lens in the front group becomes too strong, making it difficult to correct coma and astigmatism.

Furthermore, the cemented lens in the rear group is designed to correct spherical aberration and upper coma aberration by creating a difference in refractive index between both lenses. If the refractive index difference between the positive lens and the negative lens of this cemented lens exceeds condition (2) and is 0.2 or less, it becomes difficult to correct spherical aberration and upper coma aberration.

In the objective lens of the present invention, it is desirable that the cemented lens be placed closest to the image plane in the rear group.

The objective lens described in the above-mentioned Japanese Patent Application Laid-Open No. 173415/1980 has a meniscus lens with a relatively large outer diameter arranged near the final surface of the lens system. However, meniscus lenses are difficult to work with, and because they are thin throughout the lens, their strength is weak, and they are highly affected by eccentricity, which causes astigmatism, which can cause problems in optical systems such as endoscopes. It is not preferable to use such a meniscus lens. In addition, the conventional objective lens has drawbacks such as a large total length due to the large number of lens elements, and a decrease in peripheral light intensity because the exit pupil of off-axis light approaches the image plane.

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

Furthermore, in the objective lens of the present invention, it is desirable that the positive lens component disposed in the front group be a cemented lens so that the following condition (3) is satisfied.

(3) lnfr-nrr1>0.1 but n t
f*n tr is the refractive index of the object-side lens and the image-side lens of the cemented lens.

In this way, by creating a difference in refractive index between both lenses of the positive cemented lens placed in front of the diaphragm, it is possible to correct spherical aberration and lower coma aberration at the cemented surface.

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

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 cemented lens placed closest to the image side.

By doing as described above, the cemented lens of the rear group can be separated from the diaphragm, and therefore off-axis rays can be made to pass through a high position of the cemented surface of this cemented lens. This makes it possible to effectively correct chromatic aberration of magnification, and because the distance to the concave lens in the front group can be increased, the power of each lens can be weakened, which is advantageous for correcting coma and astigmatism. be. It is also desirable to insert an optical filter in the above-mentioned interval to cut out light of wavelengths unnecessary for imaging, such as infrared rays.

If the value of D in condition (4) is too small and falls below the lower limit of this condition, it will not be possible to arrange the optical elements such as optical filters at sufficient intervals. On the other hand, if the value of D is too large and exceeds the upper limit of the conditions, the total length of the lens system becomes long, resulting in a problem that it cannot be made compact.

Further, in the endoscope objective lens of the present invention, by using an aspheric surface, distortion aberration and field curvature can be favorably corrected.

In the embodiment described later, the object-side surface of one of the lenses in the front group arranged before the aperture stop S is a surface whose curvature gradually becomes stronger as it moves away from the optical axis. Either, or the image-side surface of one of the lenses in the front group placed before the aperture stop S has a surface whose curvature gradually weakens as it moves away from the optical axis. The object-side surface of one lens in the rear group that has one or more surfaces, or is located behind the aperture stop S, has a curvature that gradually weakens as it moves away from the optical axis. The image-side surface of one lens in the rear group located behind the aperture stop S has a surface whose curvature gradually becomes stronger as it moves away from the optical axis. It has at least one surface on either side.

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

The reason why a conventional endoscope objective lens with the configuration shown in Fig. 21 generates strong negative distortion is because when the principal ray is traced backwards from the image side, the brightness of the principal ray increases as the image height increases. Aperture S
The object is refracted in a direction that widens the angle of view by the front group that is in front of the aperture stop and the rear group that is after the aperture stop. Therefore, strong negative distortion can be corrected by providing in the lens system an aspheric surface whose refractive power for the chief ray becomes weaker as it moves away from the optical axis.

To do this, the object-side surfaces of the l lenses in the front group before the aperture stop S should include a portion where the curvature of the surface becomes stronger as the distance from the optical axis increases, or Either the image-side surface of one lens in the group includes a portion where the curvature gradually weakens as it moves away from the optical axis, or one lens in the rear group behind the aperture stop S. Either the object-side surface of the lens should include a portion where the curvature of the surface becomes weaker as it moves away from the optical axis, or the image-side surface of one lens in the rear group should have a curvature of the surface that becomes weaker as it moves away from the optical axis. It is sufficient to include a portion where the curvature is strong.

An aspherical 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, the curvature is considered including its sign, and is negative if the center of the contact circle at a certain point on the surface is on the object side of the surface, and positive if it is on the image side. Therefore, the example shown in Fig. 22 is an example in which the curvature increases as it moves away from the optical axis (increasing from a negative curvature that is concave toward the object to a positive curvature that is convex toward the object), including the sign. It is. Also the 23rd
The example shown in the figure is an example in which the curvature increases once and then decreases.

The reason why distortion can be corrected even on the surface shown in FIG. 23 is that it is practically acceptable even if the aberration curve of distortion has undulations as shown in FIG.
This is because the peripheral portion of the aspherical surface shown in FIG. 3 is not related to distortion aberration correction because the principal ray does not pass therethrough even though the lower ray passes therethrough.

In addition, as an example of a curved surface including a portion where the curvature of the image-side surface of the lens gradually weakens as the light rays leave,
Figure 5. There is also a shape as shown in FIG.

As explained above, when the aspherical 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 aspherical surface may also have a surface as shown in FIGS. 22 and 23. Including, at least one surface includes a portion where the curvature gradually becomes stronger, and when it is provided on the image side surface, it is shown in FIG. 25. This is a surface that includes at least a portion where the curvature gradually increases, including the surface shown in FIG. 26. An objective lens including at least one aspherical surface can satisfactorily correct distortion.

Generally, an aspherical surface can be expressed by the following formula.

x = {Cy2/ fl10FF lower [? ) }+By2
+Ey'+Fy6+Gy8+=-Here, x and y are the second
As shown in Figure 7, the coordinate value when the optical axis is taken as 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, C is an aspheric surface near the optical axis. , P is the conic constant, B. E. F. G. -... are respectively secondary. 4th order. These are the 6th and 8th order aspheric coefficients.

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

+51 0.0006/f3<E<0.6/f3(6
) B. 0001/f5<F'<b. In order to sufficiently correct distortion with the aspheric surface used in the l/f5 front group, 0.0006/f3<E must be satisfied. In other words, if the lower limit of the above condition (5) is exceeded, distortion aberration will not be sufficiently corrected. Moreover, if the upper limit of condition (5) is exceeded, astigmatism cannot be suppressed, and the processability of the lens also deteriorates.

On the other hand, by setting the value of F to satisfy condition (6), the same effect as described above regarding the value of E can be obtained.

In this condition (6), if the lower limit is exceeded, distortion aberration will not be sufficiently corrected. Moreover, if the upper limit is exceeded, astigmatism cannot be corrected sufficiently and the processability of the lens becomes poor.

If it is necessary to correct only distortion in the lens system of the present invention, it is sufficient to arrange an aspherical surface as described above only on one side of the aperture. However, in that case, the bulge of the meridional field curvature at the intermediate image height becomes large, and the image quality at the intermediate image height is significantly degraded. Therefore, if aspheric surfaces are placed in both the front group and the rear group, the sign, or minus, of the bulge in the meridional field curvature due to the aspheric surface provided in the front group, and the bulge in the meridional field curvature due to the aspheric surface provided in the rear group. Since the signs, that is, plus and minus, are opposite signs, they cancel each other out, and the above-mentioned bulge can be removed.

In addition, in the endoscopic objective of the present invention, it is desirable to arrange the aspherical surface of the rear group at a position that satisfies the following condition (7): This is the air equivalent length up to the spherical surface.The air equivalent length here is the sum of the inner thickness of the lens divided by the refractive index when a lens is inserted between them.

In this way, by placing the aspherical surface of the rear group somewhat close to the aperture, it is possible to increase the difference in height between the upper and lower rays passing through the aspherical surface, which is advantageous for correcting coma aberration. be. Also, if the aperture is too close to the aperture, it becomes difficult to correct astigmatism, which is undesirable.

Also, Seidel's aberration coefficient is calculated using the following formula fil. (ii)
Define it like this. This is general-purpose lens design program A
This is the same one used in CCOS-V.

However, in A'CCO S-V, the object distance is set to OB. The numerical aperture of the marginal ray is NA, and the refractive index of the medium on the object side from the first surface is n. The ray height H at the first surface of the paraxial ray when it is closed. is Ho=OBx tayt. {δt几−' (NA/
No) }, whereas in this application, Ho
= OBX (determined by NA/n.1. Therefore, in this application, H determined by the latter
. Based on this, paraxial tracking is performed to find each aberration coefficient. Note that NA=1/2F. ．． It is.

8Y = (SA31Y” + (CMA31Y2H) for the meridian ray (X=O)
+ {3 [AST3) -1- (PTZ31 }Y
H2+ fDIs3) H”+ (SA51Y50(C
MA51Y'H + (TOBSA)Y3H2+ tE
tcua+rn3+ {5 (AST5) + (PTZ
5) }yu4ten(DIS51H5+ (SA71Y'
・−・・−・・・・・・−(1) Sagittal ray (Y=0)
For Δx = (SA31X3+ {(AST3)
TZ3))XH2+ (SA5)X5+ (SOBSA
IX3H2+ {(AST5} + (PTZ5)}
XH'+ (SAT)X7...(ii) The above formula (i
l is the deviation between the paraxial image point (the image point when there is no aberration) and the actual image point for the Meridian ray, which is ΔY.
Y is the incident position of the paraxial chief ray on the image plane normalized by the maximum image height, and F is the incident position of the marginal ray on the pupil plane normalized by the pupil diameter. Also SA3. SA5. SA7 is the 3rd, 5th and 7th order spherical aberration, CMA3 and CMA5 respectively.
are respectively tertiary. 5th order Tanginine Charcoma, AST3.
AST5 is 3rd order respectively. Fifth-order astigmatism, PTZ3. P.T.
Z5 is the 3rd and 5th order Beppard sum, DIS3. D
IS5 is the third-order and fifth-order distortion aberration, TOBSA is the fifth-order oblique tangential spherical aberration, and E L C M
A. is the fifth-order elliptic coma, and SOBSA is the fifth-order oblique sagittal spherical aberration.

Now, assuming that the i-th surface in the rear group is an aspherical surface, the i-th surface can be considered to be a spherical surface to which a predetermined amount of displacement is added. Here, the third-order coma aberration coefficient that occurs on the original spherical surface is S, and the third-order coma aberration coefficient that occurs due to displacement from the spherical surface is A. SR, . S.A. shall be.

Also, when there are multiple aspheric surfaces in the rear group, the sum of each aspheric surface is taken and expressed as follows.

AR=ΣAR, SR=ΣSR+ Further, when the sum of the third-order coma aberration coefficients generated on the surface with negative refractive power of the front group is A2, the following condition (8). It is desirable to satisfy (9).

(8) -13<A2/(AR+SRl<-0.0
3(9) -0.2 < AR < 0.2 In general, the objective lens of an endoscope has a strong negative surface in the front group in order to widen the angle of view, and significant coma aberration occurs here. It is necessary to cancel this aberration with aberrations generated in the rear group and correct coma aberration as a whole to improve performance. Note that when the first group consists of multiple lenses as shown in Figures 28 and 30, the air contact surface on the image side is on the upper side, and in the case of Figure 29, the air contact surface on the image side of the object side lens is on the upper side. It is necessary to use the rear group to cancel out the negative coma aberration that occurs on this plane. Therefore, it is desirable that S2 and (AR+SR) have the same absolute value and different signs. However, in practice, condition (8)
It is allowed within the range expressed by .

Furthermore, if the value of AR is too large, other aberrations will also become large, making it difficult to correct the other aberrations. If the value of AR is too small, coma aberration in the front group cannot be fully corrected, so it is desirable that the value be within the range of condition (9).

[Example] Next, examples of the endoscope objective lens of the present invention will be shown.

Example 1 f=1.000. F/5.3, 2ω=13
5.9゜IH=1.0 r1=(capital) d, =0.2949 n. =1.88300
v. =40.78r2 = 0. 7248 d2= 0.7077 r3=9.8296 d3= 0.6225 174=-2.3211 d. =B. 1966 r5=oo (aperture) d5=0.2425 rs=-4.3689 d6=0.5308 r7=-1.1894 d7=b. 0983 r. =3-1298 d. = 0.8519 r9 == -o. 9450 d9=0.2621 r,. =-3.1625 dlo =0.0655 r11 :oo d,, =0.2621 n2= 1.84666 n3= 1.51633 n4 1.58913 n5= 1.84666 ne” 1.51633 ν5 rl2 = (fund) ?1■ = 0.0197 r+3 23.78 dl3 0.4063 r mouth = (fund) dl4 = 0.0197 r15 : ″l d,5 = 0.2621 r+a = ″l = 64.15 ct, 6 = 0 .7864 rat = ■ dl7 0.6553 60.97 =23.78 64.15 r18 :"l fp=2.271, Example 2 f = 1.000, IH=0.91 r+" ■ d.=0 .2653 r2= 0.6775 d2= 0.4894 r3=4.9752 1.52000 = 74.00 na" 1.51633 64.15 ns" 1.51633 64.15 nrp-nrn 0.25753 F/4. 1 2 ω = 114.76 n, = 1.88300 = 40.78 ?3 = 0.2948 r4 = 1.6392 d. = 0.5896 r5 = -2.5071 d5 = 0.0590 r6 = oo (aperture ) d, t= 0.1887 i”7=-13.0601 d7= 0.4953 r8=-1.3779 d. = 0.2182 r9 = 4.1999 d. =B. 7134 rto =-0.8974 d,. =0.2358 r++ =-2.4858 d,, =O. l769 r1■ = (fund) n2=1.51633 1.69895 n4= 1.58913 n5= 1.58913 Q6= 1.84666 ν2 υ4 ? ．． ■ = 0.2358 r+t” 1.516
33=64.15 30.12 60.97 = 60.97 = 23.78 =64.15 d+3 =0.0177 r,4=OO d14 = 0.3656 ns= 1.520
00=74.00 rl5 = 00 dl5 0.0177 rl6:c1o dl6 rI7 :oo dl7 r18 = (fund) 0.2358 0.7429 dl8 0.5896 r寞9:oo fI,=2.148 . ntt-ntr Example 3 f=1. Ro00. IH=0.92 rl=00 d,= 0.3114 11,= 1.51633 =64.15 nlo 1.51633 ν,. =64.15 nrp-nrn 0.18262 0.25753 F/4.1 2 ω= 1136 1.88300 =40.78 r2=0.7131 d2= 0.5689 r3= 4.1434 d3=0.2509 r4 =0.6116 d4=0.5957 r5=-1.9478 d. = 0.1076 r6=oo (aperture) d6= 0.0599 r7=-5.5688 d,= 0.4497 1"8=-1.1870 d8= 0.3346 rc+=ω d.= 0.4192 rlG = (fund) n2= 1.77250 Q3= 1.62004 n4 1.72916 n5= 1.52000 d+o = 0.2395 na1.51633 r11 ” (fund) d. ．． =0.0599? , ■ = 2.7131 ν2 = 49.66 ν. =36.25 ν4254. 68 d1. = 0.2255 r,3 =1,ro896 d. 3 = 0.9748 n, = 1.84666 118 = 1.51633 23.78 = 64.15 r+4 = -3.2795 d. ．． =1.1464 r15 :oo dI5 = 0.5988 n9 = 1.51633
νe = 64.15r16: oO fp = 3.842. nrp-nrn
= 0.33033nte-ntr = 0.1
5246. D=0.768 Example 4 f=l. ooO. F/4.2, 2ω=114.
3°IH=0.92 r,=oo ν5 74.00 d. = 0.3393 ν6 = 64.15 r2 = 0.7795 d2 = 0.7857 r3 = 3.3429 d. = 0.2232 r4 = 0.8393 n r = 1 . 88300 na=1.77250 =40.78 =49.66 d4=0.5804 n3 1.62606 r5=-2.2304 d5=0.0893? 6=oO d. = 0.0446 r7=-13.5125 dt=b. 4464 r8=-1.6062 d8=0.0893 r9=00 d9=1.3393 r10: OO d. o =0.0893 r++ =2.1268 d++ =0.2500 r1■ = 1.0464 d1. = 0.9732 n4 = 1.72916 n s = 1. 516 3 3 n6 = 1.84666 ny = 1.51633 r++ = -3.8661 d+a = 0.6230 i' 1 4 - (Xl ν3 = 39.21 dl4 0.8929 r, 5 = OO ν4 = 54.68 υ5 = 64.15 23.78 64.15 f. = 3.04 white . nff-nyr Example 5 f = 1.0 Roro . IH = 1.0 O r, = oo (aspherical surface) d. = 0. 3026 r2=0.6320 d2=0.5326 r3" 1. 4455 d.= 0.2291 r4 = -6. 7934 d4= 0.6325 r5=-1.2679 d5= 0.1332 r6=oo (aperture) d6 = 0.1724 r, = 2.4437 rrp-nrn = 0.33033 = 0.l46
44 D=1.0621.51633 F/4.7 2 ω=106° 1.80610 n. =1.75520 1.56883 =64.15 40.95 =27.51 = 56.34 d7= 0.5403 n4= 1.51633
r8=-1.8760 do" 0.2195 n-= 1.84666
r9=-2.8190 (aspherical surface) d. = 0.1332 rlo ” ■ d+.=0.9[179 n6=1.5200Or,
,=OO dz =0.2766 rI2 :oO? +■ =0.6053 n7=1.51633ν5 ν6 ν7 23.78 =74. OO 64.15 Intr-nrrl = 0.18637,D
A=0.647FIA. =0.00526 ,A2/
(AR-SRl=-0.996 Example 6 f=1.000. F/4.5, 2ω= 113
．． 0°IH=1.14 r,=oo (aspherical surface) d. =o. 3459 n,=1.80610
v. =40.95?2=0.7439 d2=0-3459 ra=2.6052 d. = 0.5328 r4 = -0.8588 d4 = 0.5535 1”5 = 266.4111 d. = 0.0692 r6 = ■ (aperture) d. = 0.1683 r7: 24.8283 d7 = 0.4559 r8 = 2.0198 do = 0.4690 n5 = re = -1.3623 (aspherical surface) d9 = 0.1
730 rlG = ■ d+o = 1.0378 ns r11 = Suzu d1 ■ = 0.3407 12: 1.72825 n3 = 1.58913 n4 = 1.53172 1.84100 1.52000 28.46: 60.97 = 48. 90 = 43.23 = 74.00 r, 2 = CIQ? ．． ■ =0.6919 n, =1.51633r
ta ” ■ Aspheric coefficient = 64.15 (first surface) P = 1.0000 B = O.14569E = 0
．． 29823 X to-' F =-0.1302
0X 10' (9th surface) P = 1.7759. B=O. E = 0
．． 14285F=0.10574 fp=2.348. nrp-nrn =0.3
0928Intt-ntl =” 0.13912
．． 0A=0.7207AR=0.0025. A
2/(AR+SRl=-0.596 Example 7 f=t.oooo.F/4.7.2ω=1
13.0°IH=1.15 r,=OQ (aspherical surface) d+=low 348O n. =1.806'lO
v. =40.95r2=0.6177 d2=0.5740? 3 = 2.4828 d3 = 0-5111 n2 = 1.72825
r4=-0.6841 da"" 0.5569 n3= 1.5892
1rs=-3.2002 ds"0.0696 r6"■ (aperture) d,= o. 1798 r7=2.2304 d,= 0.3829 n4= 1.84666
ra" 1.1621 d." 0.3921 ns= 1.51633
r. = -1. 1830 (aspherical surface) d9=0.1
740 r,o=OO d. o ” 1.0441 n6= 1.520
00th =■ d++ =0.3554 r+2 = (A) d1■ = 0.6961 r+y= 1.516
33 = 28.46 = 41.08 = 23.78 = 64, l5 = 74.00 = 64.15 r13 = ■ Aspheric coefficient (first surface) P = 1.0000. B=O. 11531E =
0.26826XIO゜'. F = 0.98377
X to-3 (9th side) P = 2.8824, B = O. E = 0
．． 24847F = 0.77271 G = -0
．． 48669x 10-'fp=1.623. n
rp-nrn =0-33033ntt-nfr1
= 0.13904. 1) A=0.645
7AR=0.00135, A2/(AR+S.
l=-1.328 Example 8 f=1.0 lo 0. F/4.6. 2
ω=112.4°IH=l. l2 r,=oo (aspherical surface) d+=0.3382 n1= L80610
v+ =40.95r2=0.7123 d2=0.3382 ra=4.2817 da=0.6242 n2=172825
V228.46? ．． =-1.0308 d, =0.5411 rs=-14.9956 ds=Q. 0676 r. 1691 rlo ”■ d+o =1.0146 nfir11 =■ d. ．． =0.3466 r1■ = (fund) Q4= 1.53172 ns=1.58913 1.84100 1.52000 ? ．． ■ r13 = (capital) Aspheric coefficient 0.6765 n, = 1.51633 = 60.
97 = 43.23 74.00 64.15 (first page) P=1. O(lt11(1.B=0.23401
E = 0. F = 0.93316 x 10-
2 (9th side) P = -0.0306. B: 0, E=
0.33663X t'o-'. F =
0.5i1lo7×lOf,=3.033.
lrorp-nrnl ”0.30928nrt-n
rrl=0.13912, DA=0
．． 5338AR=-Q-01Q8. A2/(AR+
S, I1=-0.502 Example 9 f=1.000, F/4.6, 2ω=l0
6°I H = 1.00 r, = 00 (aspherical surface) d. ”'0.302'6 n.=1.80610
1/l =40.95r2=0.6333 d. = 0.5326 rs=1.7941 d3="0.2287 n2=1.75520
v2=27.51r4=-2.6805 d4=0.6325 n. :! :1.56883
1/3==56.34?5=-1.1728 d5=0.1332 r6=cx:+(aperture) d. = 0.1721 rt" 4.7481 d, = 0.5368 n4 = 1.51633
r8=-3.0936 d. = 0.2169 Q5 = 1.84666
r. =-2.4248 (Aspherical surface) d9= 0.1332 r+o ” ■ d,. = 0.9079 06= 1.520
0Or,, :00 d,, =0.2713 r1■ = (fund) d. ．． ” 0.6053 n, = 1.516
33r13 = (a) Aspheric coefficient (first surface) P = 1.0000 B = 0.83810XIO 64.15 = 23.78 74. DO 64.15 E = 0, F = 0.75968 x
10-2 (9th surface) P=0.3802 B=O E=0.14794 F=0.21801xlO-
'f. =l. l77. lnrp-nrnl =0.3
3033ntt-ntr=0. 18637,
DA: 0.6436AR=0.00353. A2
/[AR+SRl=-1.334 Example 10 f =1.000. F/3.7. 2
ω = 135.9°I H = 1.41' r, =■ (aspherical surface) d. = o. 4132 n. ”1.88300
v. =40.78r2=0.9706 d2=0.9885 r3=10. 5419 d3=0.8724 n2=1.84666
v2=23.78r4=-3.2037 d4=0.2755 rs=■(aperture) ds"0.3449 ?6=-3.5233 ds" 0.7526 n3= 1.51633
v- = 64.15r7 = -1.6611 d, = 0.1412 r8 = 3.2843 d. =1.1786 n4=1.58913
v4 = 60.97 r9 = -1.2919 (aspherical surface) d9 = 0.3673 n5 = 1.84666
V6 = 23.78r,o: -2.28
45 d. . =0.0918 rth = ■ d,. =1. '3774 ns=1.51633
v6 =64.15rl2= (″d1■ = 0.3398 r13 :″l d1a =0.6428 nt=1.51633
v7 = 64.15rl4 ” ■ Aspheric coefficient (first surface) P = 1.0000. B = 0.53237 xlO
'E=0.37136 xlO'. F=-0
．． l0040xlOG = 0.13094 x 1
0-2 (9th side) P = 0.8681. B=O. E=-0.1
4223. F=0.39404 xlO-'G
=-0.62118x 10-'fp" 2.989, n.-nrn" 0.
25753. Da=1. 724A. =0.
0108. A2/(AR+SRl=-0.605
However, rl+r2+... is the radius of curvature of each lens surface,
d1, d2. ... is the wall thickness and air spacing of each lens,
n l Tn 2 1... is the refractive index of each lens, ν1
, ν2. ... is the Apé number of each lens.

The above embodiments 1 to 10 are shown in FIGS. 1 to 10, respectively.
As shown in the figure, these aberration situations are respectively 11th
As shown in FIGS. 20 to 20.

Among these examples, in Examples 2 to 9, the positive lens component in front of the aperture in the front group is a cemented lens, and the condition (
3).

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

[Effects of the Invention] As explained in detail above and as is clear from the examples, the endoscope objective lens of the present invention has a short overall length, a small outer diameter, a wide angle, and a well-corrected distortion aberration for an endoscope. It is an objective lens.

[Brief explanation of drawings]

1 to 10 are cross-sectional views of Examples 1 to 10 of the endoscope objective lens of the present invention, and FIGS. 11 to 20 respectively.
The figures are aberration curve diagrams of Examples 1 to 10 and 21.
The figure is a cross-sectional view of a conventional endoscope objective lens.
Figure 3 is a cross-sectional view of an example of an aspheric lens whose object side is an aspherical surface, Figure 24 is a diagram showing an example of distortion, and Figure 25. FIG. 26 is a cross-sectional view of an example of an aspherical lens whose image side is an aspherical surface, FIG. 27 is a diagram showing the coordinate system of the aspherical equation, and FIGS. 28 to 30 are front views of the objective lens of the present invention. It is a sectional view showing other examples of a group.

Claims (1)

[Scope of Claims] (1) Consisting of a front group and a rear group arranged with an aperture in between, the front group is composed of a first group having an overall negative power from the object side and one lens or cemented lens. An endoscope objective lens comprising a second group having a positive power consisting of a second group, the rear group consisting of only a positive lens group including a cemented lens consisting of at least a negative lens and a positive lens, and satisfying the following conditions. (1) 0.33f<f_p<11.5f (2) |n_r_p−n_r_n|>0.2 However, f
_p is the focal length of the second group, f is the focal length of the entire system, n_p
, n_n are the refractive indices of the positive lens and negative lens of the cemented lens in the rear group, respectively. (2) Consisting of a front group and a rear group arranged with an aperture in between, 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 aspherical surface, and if the aspherical surface in the front group is provided on the object side of the lens, the curvature of the aspherical surface gradually becomes stronger as it moves away from the optical axis. If the aspherical surface is provided on the image-side surface of the lens, it has a shape that includes a portion whose curvature gradually weakens as it moves away from the optical axis. When the aspherical surface is provided on the object side surface of the lens, it has a shape that includes a portion whose curvature gradually weakens as it moves away from the optical axis; If so, the endoscope objective lens has a shape that includes a portion whose curvature gradually becomes stronger as it moves away from the optical axis, and further satisfies the following conditions. 0.2f<D_A<3f where D_A is the air-equivalent distance from the aperture stop to the aspherical surface in the rear group.