JPH08179226A - Objective optical system for endoscope - Google Patents

Abstract

PURPOSE: To obtain a wide-angle objective optical system of endoscope which is constituted so that both of the housing space of a luminous flux direction conversion optical element and the long back focus of a side-viewing type endoscope are obtained and whose optical performance is excellent. CONSTITUTION: This system is provided with a front group 10 having negative focal length, a diaphragm and a rear group 20 having positive focal length in turn from an object side. Besides, it is constituted so as to satisfy the conditional expressions of (1) -1.10<ff /f<-0.80, (2) 1.00<df /f<2.00 and (3) 1.20<fr /f<1.70. Provided that (f) is the focal length of the whole of an objective optical system, (ff ) is the focal length of the front group 10, fr is the focal length of the rear group 20 and df is an air conversion distance to the object- side surface of the lens of the rear group 20 positioned on the most object side from the image-side surface of the lens of the front group 10 positioned on the most object side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective optical system for a medical or industrial endoscope, and in particular, it requires a space for inserting a light beam direction changing optical element between a front group and a rear group (diaphragm). The present invention relates to an objective optical system suitable for a side-viewing (perspective) endoscope.

[0002]

2. Description of the Related Art Inspection and surgery, laser treatment, and the like of an affected area using an endoscope as a medical device are performed by inserting a body insertion portion (tube) of the endoscope into the body of a patient. In order to reduce the burden on the patient, it is desired to reduce the diameter of the tube, and the objective optical system is also required to be downsized. However, since an objective optical system for an endoscope is generally desired to have a wide angle, the height from the optical axis through which the most peripheral light flux passes becomes higher at the lens closest to the object side or the image side, and therefore the lens outer diameter increases. Tend.

The endoscope has a direct-view type in which a first lens of an objective optical system is provided at the end of the distal end of the tube, and other lenses and CCDs are arranged linearly on the optical axis of the first lens. There is a side view (perspective) type in which the same first lens is provided on the side of the tip of the tube, and the optical axis of this first lens is bent by a prism or the like and other lenses or CCDs are arranged on the bent optical axis. They are used properly depending on the insertion location into the body and the purpose of inspection. In this side-view endoscope, a light beam direction changing optical element such as a prism is generally required, and in order not to prevent the diameter of the tube of the endoscope from being reduced, this light beam direction changing optical element is used as much as possible. It is desirable to be close to the diaphragm. The lens system must have a sufficient space for accommodating the direction changing optical element and be compact in consideration of downsizing of the tube itself.

Further, in the case of an electronic endoscope for forming an image of an objective optical system on a CCD (solid-state image pickup device), even a miniaturized CCD protects the CCD and prevents infrared light and the like. Thick coverglasses and filters are needed to remove observable harmful light. In order to incorporate these cover glasses and filters, the back focus of the objective optical system must be lengthened. However, there is a limit to the total length of the objective optical system due to the requirements such as the improvement of the tip bendability and the miniaturization of the CCD tip. Therefore, in a side-view electronic endoscope that requires both a long back focus and a space for accommodating the light beam direction changing optical element, it becomes difficult to design the optical system of the objective optical system, and the lens that configures the optical system is thin. However, there is no choice but to take measures such as reducing the number of lenses. As a result, not only is it difficult to process and assemble the lens, but also the optical performance is sacrificed.

[0005]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to obtain an objective optical system for an endoscope which has both a space for accommodating a light beam direction changing optical element and a long back focus, and has a wide angle and good optical performance. And

[0006]

SUMMARY OF THE INVENTION The objective optical system of the present invention is a well-known retrofocus type which is composed of a front group having a negative focal length, a rear group having a positive focal length, and a diaphragm located between the front and rear groups. It is based. Then, in this basic type, the height of the axial marginal ray in the rear group is increased by giving a sufficient distance between the front and rear groups in consideration of the insertion space of the light beam direction changing optical element, and a long back focus that has never been seen before. It was completed by finding out that the required performance can be obtained by ensuring the above and satisfying a specific condition regarding the power sharing of the negative power of the front group and the positive power of the rear group.

That is, according to the present invention, in the objective optical system for an endoscope having, in order from the object side, a front group having a negative focal length, a diaphragm, and a rear group having a positive focal length, It is characterized by satisfying (1), (2) and (3). _{(1) -1.10 <f f /f<-0.80} (2) 1.00 <d f /f<2.00 (3) 1.20 <f r /f<1.70 where, f Focal length of the whole objective optical system, f _f ; focal length of the front group, f _r ; focal length of the rear group, d _f ; from the image side surface of the lens closest to the object side of the front group The air-equivalent distance to the object-side surface of the lens located closest to the object in the rear group.

In the present invention, the first lens on the object side of the front group is a negative lens, and this negative lens is conditional expression (4).
Is preferably satisfied. (4) 1.70 <n _f1 where n _f1 is the refractive index of the negative lens with respect to the d-line.

Further, in the objective optical system of the present invention, it is preferable that the first lens on the object side of the rear group is a positive lens, and this positive lens satisfies the conditional expression (5). (5) 0.00 <f / r _r1 <0.80 where r _r1 is the radius of curvature of the object-side surface of the positive lens.

Furthermore, it is preferable that the rear group includes at least one cemented lens of a positive lens and a negative lens, and satisfies the conditional expression (6). (6) 0.08 <n _N −n _F where n _{N is the} refractive index of the negative lens in the cemented lens with respect to the d line, n _{P is the} refractive index of the positive lens with respect to the d line in the cemented lens, .

When used in a side-viewing type endoscope, a light beam direction changing optical element can be arranged between the front group and the rear group (diaphragm).

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to illustrated embodiments. The objective optical system for an endoscope of the present invention adopts a retrofocus type having, in order from the object side, a front group having a negative focal length, a diaphragm, and a rear group having a positive focal length. Conditional expression (1) represents the range of the focal length of the front lens group in this retrofocus type. If the negative focal length becomes longer than the lower limit, the refracting power is weakened, the required viewing angle cannot be obtained, and the back focus becomes short. If the negative focal length becomes shorter than the upper limit,
Although the refracting power is increased to widen the viewing angle and lengthen the back focus, on the other hand, the negative distortion aberration becomes too large, and the spherical aberration and the chromatic aberration become excessive, which deteriorates the imaging performance.

Conditional expression (2) represents the range of the air gap between the front group and the rear group. If the distance between the front lens group and the rear lens group becomes shorter than the lower limit, the distance between the front lens group of negative power and the rear lens group of positive power becomes closer under the condition that the focal length of the entire system is constant.
A long back focus cannot be obtained. If the upper limit is exceeded and the distance between the front group and the rear group becomes long, a long back focus can be obtained, but the height of incidence of off-axis light rays on the rear group will become high, and the lens outer diameter will become large. It becomes difficult to downsize.

Conditional expression (3) represents the range of the focal length of the rear lens group. If the focal length becomes shorter than the lower limit,
It becomes difficult to secure a long back focus, spherical aberration and astigmatism increase, and good performance cannot be maintained.
If the positive focal length becomes longer than the upper limit, it becomes easy to secure a long back focus and various aberrations decrease, but the total length from the first lens surface to the image surface increases, which is not preferable for compactness.

The objective optical system of the present invention preferably further satisfies the conditional expression (4) in order to keep the outer diameter of the lens of the front group small. For this reason, the conditional expression (4) represents the range in which the refractive index of the first negative lens in the front group should be set. When the refractive index of the first lens is reduced below the lower limit, the refractive power is weakened, the incident height of the off-axis light beam on the first surface of the first negative lens is increased, and the lens effective diameter is increased.

The objective optical system of the present invention preferably further satisfies the conditional expression (5) in order to keep the outer diameter of the lens in the rear group small while maintaining good optical performance. For this reason, the conditional expression (5) shows the range of the radius of curvature of the object side surface of the first lens in the rear group. When the radius of curvature becomes smaller than the lower limit, the angle of incidence of the incident light beam on this surface becomes large, resulting in astigmatism and field curvature,
Optical performance deteriorates. If the radius of curvature increases beyond the upper limit, the angle of incidence of the incident light beam on this surface decreases,
The refracting power for the off-axis light beam weakens, and the incident height on the subsequent lens increases, which eventually increases the lens outer diameter.

The objective optical system of the present invention further satisfies conditional expression (6) in order to correct astigmatism and to facilitate lens assembly and processing in the cemented lens for correcting chromatic aberration in the system. Is preferred. For this reason, the conditional expression (6) indicates the range in which the refractive index difference between the positive and negative lenses constituting the cemented lens included in the rear group should be taken. If the difference in refractive index disappears below the lower limit, the refracting power for light rays at the cemented surface becomes weak, and it becomes impossible to correct spherical aberration, astigmatism, and the like.
Further, in order to obtain the refractive power of the cemented surface, it is necessary to reduce the radius of curvature of the cemented surface, which makes it difficult to secure the edge thickness of the lens having the cemented surface as a convex surface, which increases processing difficulty.

Next, concrete numerical examples will be described. [Embodiment 1] FIG. 1 shows a first embodiment of the objective optical system of the present invention. From the object side, a negative front group 10 composed of a single lens, a light beam direction changing optical element 11, and a diaphragm. It consists of S and a positive rear group 20. The rear group 20, from the object side,
It is composed of a positive lens 21, and a cemented lens of a positive lens 22 and a negative lens 23. The infrared light absorption filter 12 and the cover glass 13 of the CCD are located behind the negative lens 23. The image side surface of the cover glass 13 is an image surface (CCD image pickup surface). Light flux direction changing optical element 11
Is a developed prism, for example, and is depicted as a plane-parallel plate in FIG. FIG. 17 shows an arrangement example of optical elements of a side-view endoscope in which the light beam direction changing optical element 11 of FIG. 1 is drawn as a prism. In FIG. 17, d ₃
Is the distance from the entrance point A to the prism 11 to the exit point B.

Specific numerical data of this optical system are shown in Table 1, and various aberrations are shown in FIG. In various aberration diagrams, SA is spherical aberration, SC is sine condition, d line, g line, and C line are chromatic aberration and chromatic aberration of magnification indicated by spherical aberration at respective wavelengths, diaphragm S is sagittal, and M is meridional. ing.

In the tables and drawings, FE is the effective F number, f
Is the focal length of the entire system, ω is the half angle of view, M is the paraxial lateral magnification, Y is the image height, f _B is the back focus (the distance from the final lens surface to the imaging surface), and U _-1 is the reference design distance. Represent r is the radius of curvature, d is the lens thickness or lens spacing, N _d is the d-line refractive index, and ν _d is the d-line Abbe number. The numerical value of the lens interval including the diaphragm S is shown by two numerical values with the diaphragm as a boundary in the table.

[0021]

[Table 1] FE = 1: 5.76 f = 1.47 f _f = -1.35 f _r = 2.07 ω = 50.20 ° M = -0.094 f _B = 3.84 U _-1 = -1.5 surface No. rd N _d ν _d 1 ∞ 0.47 1.88300 40.8 2 1.196 0.66 3 ∞ 3.05 1.88300 40.8 4 ∞ 0.05 Aperture ∞ 0.13 5 2.400 0.85 1.53172 48.9 6 -2.400 0.20 7 3.680 1.48 1.51633 64.1 8 -1.100 0.31 1.80518 25.4 9 -5.577 0.84 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3rd and 4th surfaces are light beam direction changing optical elements.

[Embodiment 2] FIG. 3 shows a second embodiment of the objective optical system of the present invention. The basic arrangement of optical elements is the same as that of Embodiment 1 of FIG. Table 2 shows specific numerical data of this optical system, and FIG. 4 shows various aberrations.

[0023]

[Table 2] FE = 1: 5.73 f = 1.50 f _f = −1.33 fr _r = 2.23 ω = 49.98 ° M = -0.096 f _B = 3.94 U ₋₁ = -1.5 plane No. r d N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.171 1.00 3 ∞ 1.89 1.88300 40.8 4 ∞ 0.05 Aperture ∞ 0.26 5 3.551 0.85 1.53172 48.9 6 -2.209 0.85 7 3.442 1.50 1.51633 64.1 8 -1.494 0.30 1.92286 21.3 9 -4.064 0.94 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3rd and 4th surfaces are light beam direction changing optical elements.

[Embodiment 3] FIG. 5 shows a third embodiment of the objective optical system of the present invention. The basic arrangement of optical elements is as follows.
The same as Example 1 of FIG. 1 except that the cemented lens in the rear group is composed of a negative lens 24 and a positive lens 25 from the object side. Table 3 shows specific numerical data of this optical system.
And various aberrations are shown in FIG.

[0025]

[Table 3] FE = 1: 5.72 f = 1.47 f _f = -1.37 f _r = 2.22 ω = 50.02 ° M = -0.094 f _B = 3.75 U _-1 = -1.5 surface No. rd N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.212 0.84 3 ∞ 2.00 1.88300 40.8 4 ∞ 0.05 Aperture ∞ 0.29 5 10.276 0.85 1.88300 40.8 6 -2.732 0.92 7 6.545 1.00 1.84666 23.8 8 1.354 1.00 1.72916 54.7 9 -11.001 0.75 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞ -3rd and 4th surfaces are light beam direction changing optical elements.

[Fourth Embodiment] FIG. 7 shows a fourth embodiment of the objective optical system of the present invention. The basic arrangement of optical elements is as follows.
This is the same as the first embodiment in FIG. Table 4 shows specific numerical data of this optical system, and FIG. 8 shows various aberrations.

[0027]

[Table 4] FE = 1: 5.74 f = 1.48 f _f = -1.31 f _r = 1.98 ω = 49.99 ° M = -0.095 f _B = 3.70 U _-1 = -1.5 surface No. rd N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.157 0.59 3 ∞ 1.50 1.88300 40.8 4 ∞ 0.26 Aperture ∞ 0.08 5 3.755 1.88 1.88300 40.8 6 -2.854 0.38 7 5.687 1.09 1.58913 61.2 8 -1.354 0.31 1.92286 21.3 9 -5.148 0.70 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3rd and 4th surfaces are light beam direction changing optical elements.

[Fifth Embodiment] FIG. 9 shows a fifth embodiment of the objective optical system of the present invention. The basic arrangement of optical elements is as follows.
This is the same as the first embodiment in FIG. Table 5 shows specific numerical data of this optical system, and FIG. 10 shows various aberrations.

[0029]

[Table 5] FE = 1: 5.77 f = 1.48 f _f = -1.38 f _r = 2.11 ω = 50.16 ° M = -0.095 f _B = 3.91 U _-1 = -1.5 surface No. rd N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.220 0.73 3 ∞ 3.05 1.72916 54.7 4 ∞ 0.05 Aperture ∞ 0.24 5 2.128 0.85 1.53172 48.9 6 -2.660 0.30 7 3.139 1.20 1.51633 64.1 8 -1.059 0.30 1.80518 25.4 9 -12.820 0.91 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3rd and 4th surfaces are light beam direction changing optical elements.

[Sixth Embodiment] FIG. 11 shows a sixth embodiment of the objective optical system of the present invention. The basic arrangement of the optical elements is the same as that of the first embodiment shown in FIG. Table 6 shows specific numerical data of this optical system, and FIG. 12 shows various aberrations.

[0031]

[Table 6] FE = 1: 5.72 f = 1.49 f _f = -1.33 f _r = 2.35 ω = 50.10 ° M = -0.095 f _B = 4.12 U _-1 = -1.5 surface No. rd N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.175 0.73 3 ∞ 2.00 1.51633 64.1 4 ∞ 0.05 Aperture ∞ 0.28 5 6.428 0.85 1.88300 40.8 6 -2.946 1.01 7 149.282 1.30 1.75700 47.8 8 -1.161 0.30 1.84666 23.8 9 -5.567 1.12 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3rd and 4th surfaces are light beam direction changing optical elements.

[Embodiment 7] FIG. 13 shows a seventh embodiment of the objective optical system according to the present invention. The basic arrangement of optical elements is such that a light beam direction converting optical element is arranged between the front group 10 and the rear group 20. Element 1
The third embodiment is the same as the third embodiment shown in FIG. 5, except that the first embodiment is not arranged and is configured as a direct view type. Table 7 shows specific numerical data of this optical system, and FIG. 14 shows various aberrations.

[0033]

[Table 7] FE = 1: 5.70 f = 1.49 f _f = -1.45 f _r = 2.49 ω = 50.00 ° M = -0.094 f _B = 4.06 U _-1 = -1.5 surface No. r d N _d ν _d 1 ∞ 0.39 1.88300 40.8 2 1.278 2.12 Aperture ∞ 0.29 3 10.135 0.88 1.83400 37.2 4 -2.634 1.22 5 12.142 0.30 1.84666 23.8 6 1.430 1.30 1.72916 54.7 7 -5.735 1.06 8 ∞ 2.00 1.52400 65.5 9 ∞ 1.00 1.53996 59.5 10 ∞-

[Embodiment 8] FIG. 15 shows an eighth embodiment of the objective optical system of the present invention. The basic arrangement of the optical elements is the same as that of Embodiment 1 of FIG. Table 8 shows specific numerical data of this optical system, and FIG. 16 shows various aberrations.

[0035]

[Table 8] FE = 1: 5.74 f = 1.49 f _f = -1.50 f _r = 2.19 ω = 49.91 ° M = -0.095 f _B = 4.02 U _-1 = -1.50 Surface No. rd N _d ν _d 1 ∞ 0.30 1.72916 54.7 2 1.097 0.47 3 ∞ 3.05 1.88300 40.8 4 ∞ 0.05 Aperture ∞ 0.26 5 3.444 0.85 1.53172 48.9 6 -2.192 0.20 7 4.131 1.46 1.51633 64.1 8 -1.364 0.30 1.84666 23.8 9 -3.946 1.02 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3rd and 4th surfaces are light beam direction changing optical elements.

Table 9 shows each numerical value of each conditional expression (1) to (6) for each embodiment.

[Table 9] Conditional expression (1) Conditional expression (2) Conditional expression (3) (f _f / f) (d _f / f) (f _r / f) Example 1 -0.9208 1.6722 1.4075 Example 2 -0.8846 1.5490 1.5181 Example 3 -0.9311 1.5217 1.5081 Example 4 -0.8868 1.1672 1.3423 Example 5 -0.9363 1.8886 1.4295 Example 6 -0.8950 1.6001 1.5782 Example 7 -0.9708 1.6212 1.6666 Example 8 -1.0121 1.6191 1.4718 Conditional Expression (4) Conditional Expression (5) Conditional expression (6) (n _f1 ) (f / r _r1 ) (n _N -n _P ) Example 1 1.88300 0.6129 0.2888 Example 2 1.88300 0.4222 0.4065 Example 3 1.88300 0.1435 0.1175 Example 4 1.88300 0.3935 0.3337 Implementation Example 5 1.88300 0.6934 0.2888 Example 6 1.88300 0.2313 0.0897 Example 7 1.88300 0.1471 0.1175 Example 8 1.72916 0.4316 0.3303

As is apparent from Table 9, the numerical values of Examples 1 to 8 satisfy the conditional expressions (1) to (6). Further, in the objective optical system for an endoscope of the present invention, various aberrations are well corrected as shown in various aberration diagrams.

[0038]

According to the present invention, both an accommodation space for a light beam direction changing optical element and a long back focus required for a side-viewing endoscope can be obtained, and an endoscope having a wide angle and good optical performance is obtained. The objective optical system can be obtained.

[Brief description of drawings]

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

FIG. 2 is a diagram of various types of aberration of the lens system in FIG.

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

FIG. 4 is a diagram of various types of aberration of the lens system in FIG.

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

FIG. 6 is a diagram of various types of aberration of the lens system in FIG.

FIG. 7 is a lens configuration diagram showing a fourth example of the endoscope objective optical system according to the present invention.

FIG. 8 is a diagram of various types of aberration of the lens system in FIG.

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

FIG. 10 is a diagram of various types of aberration of the lens system in FIG.

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

12 is a diagram of various types of aberration in the lens system of FIG.

FIG. 13 is a lens configuration diagram showing a seventh embodiment of the objective optical system for an endoscope according to the present invention.

14 is a diagram of various types of aberration of the lens system in FIG.

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

16 is a diagram of various types of aberration in the lens system of FIG.

17 is an optical configuration diagram in which the light beam direction changing optical element of the lens system of FIG. 1 is drawn as a prism.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 front group 11 luminous flux direction changing optical element S diaphragm 20 rear group 12 infrared absorption filter 13 cover glass

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] October 4, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

Specific numerical data of this optical system are shown in Table 1, and various aberrations are shown in FIG. In the various aberration charts, SA is spherical aberration, SC is sine condition, d line, g line and C line are chromatic aberration and chromatic aberration of magnification indicated by spherical aberration at respective wavelengths, S is sagittal and M is meridional. There is.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

[0021]

[Table 1] FE = 1: 5.76 f = 1.47 f _f = -1.35 f _r = 2.07 ω = 50.20 ° M = -0.094 f _B = 3.8 4 surface No. r d N _d ν _d 1 ∞ 0.47 1.88300 40.8 2 1.196 0.66 3 ∞ 3.05 1.88 300 40.8 4 ∞ 0.05 Aperture ∞ 0.13 5 2.400 0.85 1.53172 48.9 6 -2.400 0.20 7 3.680 1.48 1.51633 64.1 8 -1.100 0.31 1.80518 25.4 9 -5.577 0.84 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞ -3 The surfaces 4 and 4 are light beam direction changing optical elements.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

[0023]

[Table 2] FE = 1: 5.73 f = 1.50 f _f = -1.33 f _r = 2.28 ω = 49.98 ° M = -0.096 f _B = 3.9 4 faces No. r d N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.171 1.00 3 ∞ 1.89 1.88 300 40.8 4 ∞ 0.05 Aperture ∞ 0.26 5 3.551 0.85 1.53172 48.9 6 -2.209 0.85 7 3.442 1.50 1.51633 64.1 8 -1.494 0.30 1.92286 21.3 9 -4.064 0.94 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3 The surfaces 4 and 4 are light beam direction changing optical elements.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

[0025]

[Table 3] FE = 1: 5.72 f = 1.47 f _f = -1.37 f _r = 2.22 ω = 50.02 ° M = -0.094 f _B = 3.7 5 surface No. r d N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.212 0.84 3 ∞ 2.00 1.88300 40.8 4 ∞ 0.05 Aperture ∞ 0.29 5 10.276 0.85 1.88300 40.8 6 -2.732 0.92 7 6.545 1.00 1.84666 23.8 8 1.354 1.00 1.72916 54.7 9 -11.001 0.75 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3 faces The four surfaces are light beam direction changing optical elements.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

[0027]

[Table 4] FE = 1: 5.74 f = 1.48 f _f = -1.31 f _r = 1.98 ω = 49.99 ° M = -0.095 f _B = 3.7 0 surface No. r d N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.157 0.59 3 ∞ 1.50 1.88300 40.8 4 ∞ 0.26 Aperture ∞ 0.08 5 3.755 1.88 1.88300 40.8 6 -2.854 0.38 7 5.687 1.09 1.58913 61.2 8 -1.354 0.31 1.92286 21.3 9 -5.148 0.70 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3 The surfaces 4 and 4 are light beam direction changing optical elements.

[Procedure correction 6]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

[0029]

[Table 5] FE = 1: 5.77 f = 1.48 f _f = -1.38 f _r = 2.11 ω = 50.16 ° M = -0.095 f _B = 3.9 One surface No. r d N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.220 0.73 3 ∞ 3.05 1.72916 54.7 4 ∞ 0.05 Aperture ∞ 0.24 5 2.128 0.85 1.53172 48.9 6 -2.660 0.30 7 3.139 1.20 1.51633 64.1 8 -1.059 0.30 1.80518 25.4 9 -12.820 0.91 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3 The surfaces 4 and 4 are light beam direction changing optical elements.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

[0031]

[Table 6] FE = 1: 5.72 f = 1.49 f _f = -1.33 f _r = 2.35 ω = 50.10 ° M = -0.095 f _B = 4.1 2 surface No. r d N _d ν _d 1 ∞ 0.30 1.88300 40.8 2 1.175 0.73 3 ∞ 2.00 1.51633 64.1 4 ∞ 0.05 Aperture ∞ 0.28 5 6.428 0.85 1.88300 40.8 6 -2.946 1.01 7 149.282 1.30 1.75700 47.8 8 -1.161 0.30 1.84666 23.8 9 -5.567 1.12 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3 The surfaces 4 and 4 are light beam direction changing optical elements.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction content]

[0033]

[Table 7] FE = 1: 5.70 f = 1.49 f _f = -1.45 f _r = 2.49 ω = 50.00 ° M = -0.094 f _B = 4.0 6 faces No. r d N _d ν _d 1 ∞ 0.39 1.88300 40.8 2 1.278 2.12 Aperture ∞ 0.29 3 10.135 0.88 1.83400 37.2 4 -2.634 1.22 5 12.142 0.30 1.84666 23.8 6 1.430 1.30 1.72916 54.7 7 -5.735 1.06 8 ∞ 2.00 1.52400 65.5 9 ∞ 1.00 1.53996 59.5 10 ∞ −

[Procedure Amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

[0035]

[Table 8] FE = 1: 5.74 f = 1.49 f _f = -1.50 f _r = 2.19 ω = 49.91 ° M = -0.095 f _B = 4.0 2 surface No. r d N _d ν _d 1 ∞ 0.30 1.72916 54.7 2 1.097 0.47 3 ∞ 3.05 1.88300 40.8 4 ∞ 0.05 Aperture ∞ 0.26 5 3.444 0.85 1.53172 48.9 6 -2.192 0.20 7 4.131 1.46 1.51633 64.1 8 -1.364 0.30 1.84666 23.8 9 -3.946 1.02 10 ∞ 2.00 1.52400 65.5 11 ∞ 1.00 1.53996 59.5 12 ∞-3rd and 4th surfaces are luminous flux direction changing optical elements.

Claims (5)

[Claims] 1. An objective optical system for an endoscope having, in order from the object side, a front group having a negative focal length, an aperture stop, and a rear group having a positive focal length, the following conditional expression (1): , (2) and (3) are satisfied, The objective optical system for endoscopes characterized by the above-mentioned. _{(1) -1.10 <f f /f<-0.80} (2) 1.00 <d f /f<2.00 (3) 1.20 <f r /f<1.70 where, f Focal length of the whole objective optical system, f _f ; focal length of the front group, f _r ; focal length of the rear group, d _f ; from the image side surface of the lens closest to the object side of the front group Air equivalent distance to the object side surface of the lens located closest to the object side in the rear group. 2. The first lens unit on the object side of the front group according to claim 1.
The lens is a negative lens and is an objective optical system for an endoscope that satisfies the following conditional expression (4). (4) 1.70 <n _f1 where n _{f1 is the} refractive index of the negative lens with respect to the d-line. 3. The first lens unit on the object side of the rear group according to claim 1.
The lens is a positive lens, and is an objective optical system for an endoscope that satisfies the following conditional expression (5). (5) 0.00 <f / r _r1 <0.80 where r _{r1 is the} radius of curvature of the object-side surface of the positive lens. 4. The objective optical system for an endoscope according to claim 1, wherein the rear group includes at least one cemented lens of a positive lens and a negative lens, and satisfies the following conditional expression (6). (6) 0.08 <n _N −n _P where n _{N is the} refractive index of the negative lens in the cemented lens with respect to the d line, n _{P is the} refractive index of the positive lens with respect to the d line in the cemented lens. 5. The endoscope objective optical system according to claim 1, wherein a light beam direction changing optical element is arranged between the front group and the diaphragm.