JP3455309B2 - Objective lens for endoscope - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens used for endoscopes, rigid endoscopes and the like, and more particularly to an objective lens having a short overall length and a small number of constituents.

[0002]

2. Description of the Related Art Generally, the angle of view required for endoscopes, rigid endoscopes, etc. is about 90 to 120 °, which is a very wide angle. Therefore, the distortion produced by the objective lens tends to be large, and in general, it is about -36 at an angle of view of 100 °.
%, At an angle of view of 120 ° it becomes about -50%. As means for reducing such distortion aberration, Japanese Patent Laid-Open No. 61-16202
The use of aspherical lenses is known, as shown in Japanese Patent Publication No. 1 and the like.

However, since an objective lens such as an endoscope is required to have a diameter as small as possible, aspherical surface processing such as polishing is difficult as compared with a 35 mm camera lens. Further, as a method of manufacturing such a small-diameter aspherical lens, a glass molding method has been conventionally reported. However, this method can be applied to a glass material having a low transition point and easily softened.

On the other hand, in endoscopes and rigid endoscopes, the amount of illumination light introduced from the outside is small and a bright objective lens is required. On the other hand, a bright objective lens tends to have a large total length and diameter. is there. Therefore, by using a glass material having a high refractive index to increase the power of each lens and reduce the number of lens components, it is possible to create an objective lens having a wide angle, a small diameter, and a short total length.

However, most of such glass materials having a high refractive index have high transition points and are not suitable for the glass molding method.
If you try to apply it, the amount of heat required to soften the glass material will increase, the energy consumption will increase, overheating and slow cooling will take a long time, the life of the mold will be shortened, and the cost will increase. is there. Further, in the design of an objective lens using a glass material that is easy to mold, the degree of freedom is reduced, and there arises a problem that it is difficult to obtain desired performance.

Further, in the objective lens of the endoscope, it is customary to give power to the front lens group which is arranged on the object side of the aperture stop. Therefore, by eliminating the front lens group, the total length of the lens can be shortened. However, if the front lens group is abolished, the power of the rear lens group must be increased. However, if the power of the rear lens group is increased, performance deterioration such as distortion occurs. In order to increase the power of the rear lens group, it is necessary to increase the refractive index of the rear lens group, and the introduction of an aspherical surface is effective for good aberration correction. However, the high refractive index glass material that can be molded by the molding method in which the aspherical surface is easily formed is extremely limited as described above,
It is difficult to form an aspherical lens by a molding method using a glass material having a high refractive index. Therefore, it is practically difficult to form an endoscope objective lens having a short total length and a small distortion.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the conventional objective lens for an endoscope, and is easy to process, has a small distortion, has a short total length, and has a small number of constituents. An object is to provide an objective lens.

[0008]

SUMMARY OF THE INVENTION The invention according to claim 1 that achieves this object comprises, in order from the object side, a cover glass, an aperture stop, and a rear lens group having a positive power.
Lens is a glass lens, composed of a transparent member layer adhering to the surface of the glass lens, it is one of the composite aspherical lens surface that does not adhere to the glass lens of the transparent member layer is made of a non-spherical surface, The glass lens of the composite type aspherical lens is characterized in that the refractive index n is n> 1.65. The invention according to claim 2 is
From the object side, in order, from the aperture stop and a rear group lens having a positive power, the rear group lens comprises a glass lens and a transparent member layer adhered to the surface of the glass lens. It is one composite type aspherical lens in which the surface not attached to the glass lens is an aspherical surface, and the refractive index n of the glass lens of the composite type aspherical lens is
Is characterized in that n> 1.65.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on illustrated embodiments. FIGS. 1 and 2 show Example 1, FIGS. 3 and 4 show Example 2, FIGS. 5 and 6 show Example 3, FIGS. 7 and 8 show Example 4, FIGS. 9 and 10 show Example 5, and FIGS. 16 shows the lens configuration and various aberration characteristics of Example 6. Examples 1 to 5 are objective lenses used in a fiberscope, and Example 6 is an objective lens used in an electronic scope. Example 1 has a cover glass and Examples 2-6 do not have a cover glass. Examples 1 and 2 have a rear lens group with one lens, Examples 3 to 6 have a rear lens group with two lenses, and third to fifth examples have a positive lens from the object side.
The sixth embodiment is a combination of a positive lens and a negative lens from the object side. Although only the optical elements are shown in the drawing, these are fixed to a lens barrel or the like and attached to the tip portion of an endoscope, a rigid endoscope, or the like.

In Embodiments 1 and 2, the rear lens group 12,
21 is formed of a glass lens having a refractive index n> 1.65, and transparent member layers 13 and 22 are formed by pressing a synthetic resin on the image side surfaces NO. 4 and NO. The image side surfaces of these transparent member layers 13 and 22 are NO. 5 and N.
The rear lens group 12 and the transparent member layer 13, the rear lens group 21 and the transparent member layer 2 have O.3 (the surfaces of the glass lenses 12 and 21 not adhered to the surfaces NO.4 and NO.2) as an aspherical surface.
A composite aspherical lens consisting of 2 is formed. Also,
The brightness diaphragms 12S and 21S are arranged in a space closer to the object side than the rear group lenses 12 and 21.

In the third embodiment, at least the second lens 32 among the two rear group lenses 31 and 32 having positive power is used.
Is formed of a glass lens having a refractive index n> 1.65, and a synthetic resin is added to the image side surface NO.4 of the second lens 32 to provide a pressed transparent member layer 33. The image side surface NO.5 of the transparent member layer 33 (the surface NO.4 of the second lens 32)
A surface of the composite aspherical lens composed of the second lens 32 and the transparent member layer 33 is formed with the surface (on the side not attached to the) as an aspherical surface. Further, the aperture stop 31S is arranged in the space closer to the object side than the first lens 31.

In the fourth embodiment, at least one of the three rear group lenses consisting of the first lens 41 having positive power, the second lens 42 having negative power, and the third lens 43 having positive power is used. The third lens 43 is formed of a glass lens having a refractive index n> 1.65, and the image side surface NO.
Transparent member layer 44 obtained by adding synthetic resin to 5 and pressing.
Is provided. The image side surface N of the transparent member layer 44
O.6 (surface not attached to surface NO.5 of third lens 43)
As an aspherical surface, the third lens 43 and the transparent member layer 44
And a compound type aspherical lens is formed. Further, the aperture stop 41S is arranged in the space closer to the object than the first lens 41.

In the fifth embodiment, among the three rear group lenses consisting of the first lens 51 having positive power, the 253th lens having negative power, and the third lens 54 having positive power,
The first lens 51 is formed of a glass lens having a refractive index n> 1.65, and a synthetic resin is added to the image side surface NO.2 of the first lens 51 to provide a transparent member layer 52 which is pressed. Then, the image side surface NO.3 of this transparent member layer 52 (the surface not attached to the surface NO.2 of the first lens 51) is made an aspherical surface,
A composite aspherical lens composed of the first lens 51 and the transparent member layer 52 is formed. Also, the aperture stop 51S
Are arranged in a space closer to the object side than the first lens 51.

In the sixth embodiment, at least the first of the three rear group lenses including the first lens 61 having a positive power, the second lens 63 having a negative power, and the third lens 64 having a positive power is used. The lens 61 is composed of a glass lens having a refractive index n> 1.65, and the image side surface N of the first lens 61.
Transparent member layer 6 made by adding synthetic resin to O.2 and pressing
2 is provided. The image side surface of the transparent member layer 52
A composite type aspherical lens composed of the first lens 61 and the transparent member layer 62 is formed with NO.3 (the surface of the first lens which is not attached to the surface NO.2) as an aspherical surface. Further, the aperture stop 61S is arranged in the object side space of the first lens 61. Note that reference numerals 65 and 66 in the figure denote a cover glass and an adhesive layer of the CCD image pickup device used in the electronic endoscope.

In the above embodiments, the angle of view 2w is 2w = 100 ° in Examples 1, 5 and 6, and 2w = 80 in Example 2.
2 ° = 90 ° in Example 3, and 2w = 92 ° in Example 4. Regarding the F number, Examples 1 to 3 have F = 1.8, Example 4
Is F = 4.0, Example 5 is F = 2.9, and Example 6 is F = 5.6.
Is. The F number is a value for an object distance of infinity, and the angle of view 2w is a value for a designed object distance.
Here, the designed object distance is 8.0 mm in Examples 1 and 2, 5.0 mm in Example 3, and 6.0 mm in Examples 4, 5 and 6.

In this embodiment, the glass lens has
A glass material called LAH58 (glass material name of OHARA INC.) Is used in view of chemical resistance, aberration correction requirement in optical design, polishing and processing characteristics. This glass material has a high transition point of 730 ° C. and is unsuitable for the glass molding method. Further, there is no other glass material having a refractive index and an Abbe number similar to those of the glass material LAH58, which has a sufficiently low transition point and is suitable for the glass molding method.

On the other hand, in the transparent member layer forming the aspherical surface,
Although the thermosetting resin is used, other resin materials such as a photo-curing resin can also be used. Furthermore, there is no particular limitation on the refractive index of the resin material.

Specific numerical data of Examples 1 to 6 are shown in the table below, and various aberrations are shown in FIGS. 2, 4, 6, 8, 10, and 12. In the figure, SA is spherical aberration, SC is sine condition, d-line, g-line, and C-line are chromatic aberration and chromatic aberration of magnification due to spherical aberration at respective wavelengths, S is sagittal in the astigmatism diagram, and M is astigmatism. Each meridional in the aberration diagram is shown.

In the table and figures, F _NO is the F number, f is the focal length (mm), M is the lateral magnification, W is the half angle of view (°), f _B is the back focus (mm), and r is the lens surface. Paraxial radius of curvature (mm), d is the distance between lens surfaces (mm), nd is the refractive index of the d line, and νd is the Abbe number of the d line.

[Example 1]

[Table 1] F _NO = 1.8 f = 0.33 M = -0.040 W = 50 f _B = 0.29 Surface NO. R d n _d νd 1 ∞ 0.20 1.88300 40.8 2 ∞ 0.16 Aperture ∞ 0.03 3 2.222 0.49 1.88300 40.8 4 -0.389 0.05 1.52010 50.8 5 * -0.244---* is aspherical surface NO.5: K = -2.38716, A4 = -4.55994, A6 = 0.26567 × 10 ² , A8 = 0.00000, A10 = 0.00000, A12 = 0.00000 However, aspherical surface It is defined by the following formula. x = cy ² / [1+ {1- (1 + K) c ² y ² } ^1/2 ] + A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰ + A
The aspherical surfaces of the examples of 12y ^{12 and} below are also defined by the same formula.

[Embodiment 2]

[Table 2] F _NO = 1.8 f = 0.43 M = -0.054 W = 40 f _B = 0.38 surface NO. Rd n _d νd Aperture ∞ 0.11 1 1.848 0.51 1.88 300 40.8 2 -0.410 0.05 1.52010 50.8 3 * -0.394-- -* Is aspherical NO.3: K = -1.98384, A4 = -0.03256, A6 = 7.81836, A8 = 0.00000, A10 = 0.00000, A12 = 0.00000

[Embodiment 3]

[Table 3] F _NO = 1.8 f = 0.39 M = -0.077 W = 45 f _B = 0.34 surface NO. Rd n _d νd Aperture ∞ 0.04 1 -1.121 0.30 1.51633 64.1 2 -0.897 0.05--3 0.880 0.40 1.65830 57.3 4 -0.510 0.05 1.52010 50.8 5 * -0.309---* is aspherical NO.5: K = -2.87113 A4 = -2.62966, A6 = 0.26542 × 10 ² , A8 = -0.32503 × 10 ² , A10 = -0.35704 × 10 ³ , A12 = 0.12321 × 10 ⁴

[Embodiment 4]

[Table 4] F _NO = 4.0 f = 0.91 M = -0.152 W = 46 f _B = 1.01 surface NO. r d n _d ν d Aperture ∞ 0.04 1 -0.540 0.23 1.88300 40.8 2 -0.525 0.05--3 -11.419 0.47 1.80518 25.4 4 0.910 0.73 1.72916 54.7 5 -1.200 0.20 1.52010 50.8 6 * -0.700---* is an aspherical NO. 6: K = -2.18934, A4 = -0.29640, A6 = -0.23181, A8 = 0.00000, A10 = 0.00000, A12 = 0.00000

[Embodiment 5]

[Table 5] F _NO = 2.9 f = 0.89 M = -0.151 W = 50 f _B = 0.00 Face NO. Rd n _d νd Aperture ∞ 0.04 1 -1.449 0.51 1.88 300 40.8 2 -0.440 0.05 1.52010 50.8 3 * -0.589 0.05 --4 -1.100 0.30 1.80518 25.4 5 1.596 0.78 1.72916 54.7 6 -0.920---* is aspherical NO.3: K = -0.83413, A4 = 0.42655, A6 = 0.41254, A8 = 0.00000 A10 = 0.00000, A12 = 0.00000

[Sixth Embodiment]

[Table 6] F _NO = 5.6 f = 1.19 M = -0.235 W = 50 f _B = 0.00 Plane NO. Rd n _d νd Aperture ∞ 0.06 1 -1.774 0.51 1.88 300 40.8 2 -0.472 0.05 1.52010 50.8 3 * -0.732 0.16 --4 -6.062 0.30 1.80518 25.4 5 1.142 0.34 1.72916 54.7 6 2.620 0.30--7 ∞ 0.60 1.53000 50.0 8 ∞ 0.40 1.54000 40.0 9 ∞---* is aspheric NO.3: K = -0.74470, A4 = -0.20247 , A6 = -0.26087, A8 = 0.00000 A10 = 0.00000, A12 = 0.00000

As described above, in Examples 1 and 2, astigmatism, field curvature and distortion are improved as compared with the case where no aspherical surface is used.

In the third embodiment, the rear lens group is replaced by the first lens 31.
By separating the lens into the second lens 32 and the second lens 32, the radius of curvature r of each surface of the lens is increased as compared with the first and second embodiments, manufacturing is facilitated, and the occurrence of spherical aberration is reduced. Further, the distortion aberration is improved from -27% to -19% as compared with the same lens configuration using no aspherical surface.

In Examples 4 and 5, the generation of chromatic aberration is reduced by bonding the object side lenses 42 and 53 of the rear group lens and the image side lenses 43 and 54 to each other. Furthermore, since the surfaces of the transparent member layers 44 and 52 that are not attached to the glass lenses are made aspherical, distortion is particularly reduced in Example 4 and astigmatism is reduced in Example 5.

Example 6 (FIGS. 11 and 12) is an example of an objective lens used in an electronic endoscope. Although not shown, an image pickup device such as a CCD is arranged in close contact with the adhesive layer 66 closest to the image side. The sixth embodiment is, for example, the fifth embodiment.
Compared with, since the image angle is the same but the image height is high, when the same lens configuration as that of the fifth embodiment is used, the focal length becomes long and the total length tends to become long. Therefore, the total length can be shortened by making the most image-side lens unit have a negative power. The total length of only the lens is the same as in Example 5.
Compared with, it is reduced by about 20%. Also, distortion aberration is reduced.

[0030]

As is apparent from the above description, the present invention is
The front lens group is abolished, and the rear lens group having a diaphragm and a rear lens group having positive power is arranged in order from the object side.
Lens, glass lens, composed of a transparent member layer adhering to the surface of the glass lens, a double <br/> case type non that surface not attached to the glass lens of the transparent member layer is made of aspherical constituted by a spherical lens, and a glass lens of the composite aspherical lens, the refractive index n was formed by the glass material which satisfies n> 1.65, the total length is short, can provide a small endoscope objective lens diameter . Moreover, since it has an aspherical surface,
Various aberrations such as spherical aberration, axial chromatic aberration, lateral chromatic aberration, astigmatism, and distortion are reduced.

[Brief description of drawings]

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

FIG. 2 is a diagram of various aberration characteristics of the first example.

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

FIG. 4 is a diagram of various aberration characteristics of the second embodiment.

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

FIG. 6 is a diagram of various aberration characteristics of the third example.

FIG. 7 is a lens configuration diagram of Example 4 of the objective lens for an endoscope of the present invention.

FIG. 8 is a diagram of various aberration characteristics of the fourth embodiment.

FIG. 9 is a lens configuration diagram of Example 5 of the objective lens for an endoscope of the present invention.

FIG. 10 is a diagram of various aberration characteristics of the fifth example.

FIG. 11 is a lens configuration diagram of Example 6 of the endoscope objective lens of the present invention.

FIG. 12 is a diagram of various aberration characteristics of the sixth example.

[Explanation of symbols]

11 cover glass 12 lens (glass lens) 12S aperture 13 Transparent member layer 21 1st lens (glass lens) 21S aperture stop 22 Transparent member layer 31 1st lens (glass lens) 31S aperture stop 32 Second lens (glass lens) 33 Transparent member layer 41S aperture stop 43 Third lens (glass lens) 44 Transparent member layer 51 1st lens (glass lens) 51S aperture stop 52 Transparent member layer 61 lens (glass lens) 61S aperture stop 62 transparent member layer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-1-151880 (JP, A) JP-A-1-245211 (JP, A) JP-A-6-14819 (JP, A) JP-A-4- 125608 (JP, A) JP 62-273505 (JP, A) JP 62-94812 (JP, A) JP 2-176612 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 13/18 G02B 13/00 G02B 9/00

Claims (6)

(57) [Claims] 1. A cover glass, an aperture stop, and a rear group lens having a positive power in order from the object side. The rear group lens includes a glass lens and a transparent member layer attached to the surface of the glass lens. The surface of this transparent member layer that is not attached to the glass lens is an aspherical surface.
An objective lens for an endoscope, which is one composite aspherical lens, wherein a refractive index n of the glass lens of the composite aspherical lens is n> 1.65. 2. An aperture stop and a rear lens group having a positive power, in order from the object side. The rear lens group includes a glass lens and a transparent member layer attached to the surface of the glass lens. The surface of this transparent member layer that is not attached to the glass lens is an aspherical surface.
An objective lens for an endoscope, which is one composite aspherical lens, wherein a refractive index n of the glass lens of the composite aspherical lens is n> 1.65. 3. The cover glass and the brightness in order from the object side.
A rear lens group having a stop and a positive power, the rear lens group having a positive power and a negative lens group.
Is composed of a second lens group having a power of
One group is a glass lens and this glass lens
This transparent member layer is composed of a transparent member layer adhered to the surface.
Surface of the glass lens that is not attached to the
A case aspherical lens, the refractive index n of the glass lens of the composite aspherical lens, n> 1.65 is further when the half angle of the w, 80 ° = <2w = <120 ° Objective lens for endoscopes. 4. An aperture stop and a positive aperture are arranged in order from the object side.
A rear lens group having a power, a first lens group having a positive power in the rear lens group, and
Consists of a second lens group having negative power,
At least one group is a glass lens and this glass lens
This transparent member consists of a transparent member layer attached to the surface of
The surface of the layer that is not attached to the glass lens is aspherical
It is a composite aspherical lens, the refractive index n of the glass lens of the composite aspherical lens, n> 1.65 is further when the half angle of the w, 80 ° = <2w = <120 ° Objective lens for endoscopes. 5. An aperture stop and a positive aperture are arranged in order from the object side.
It consists rear lens group having a power, a first lens group which the rear lens group has a positive power and a positive
And a second group lens having a power of
At least one group is a glass lens and this glass lens
This transparent member consists of a transparent member layer attached to the surface of
The surface of the layer that is not attached to the glass lens is aspherical
A composite aspherical lens, the refractive index n of the glass lens of the composite aspherical lens, an endoscope objective lens, which is a n> 1.65. 6. The method according to any one of claims 3 to 5.
In the objective lens for an endoscope , the first lens group of the rear group lens is the composite aspherical lens, and the objective lens for an endoscope.