JP6836466B2 - Endoscopic objective optical system - Google Patents

Description

The present invention relates to an endoscopic objective optical system.

In recent years, in observation with a medical endoscope, many magnified observations using a magnifying endoscope have come to be performed. Therefore, magnified observation has become a general observation rather than a special purpose observation.

With a magnifying endoscope, normal observation and magnified observation can be performed. In normal observation, a wider range can be observed than in magnified observation. Therefore, for example, normal observation is performed to confirm the presence or absence of a lesion. If a lesion is found under normal conditions, the lesion should be magnified. By doing so, it becomes possible to observe the pattern of the mucous membrane of the lesion and the pattern of the blood vessel in detail. Moreover, since detailed observation can be performed, a more accurate diagnosis can be made.

In the magnifying endoscope, the lens in the objective optical system is moved in order to perform normal observation and magnified observation. The object distance is different between normal observation and magnified observation. Therefore, the objective optical system has a focus function.

The objective optical system of the magnifying endoscope is disclosed in Patent Documents 1 to 4.

The objective optical system disclosed in Patent Document 1 is composed of a first group having a negative refractive power, a second group consisting of a positive meniscus lens, and a third group having a positive refractive power, and the second group. Moves in the optical axis direction.

The objective optical system disclosed in Patent Document 2 has a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a negative refractive power. It is composed of a fourth group having and the second group moves in the optical axis direction.

The objective optical system disclosed in Patent Documents 3 and 4 is composed of a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power. Then, the second group moves in the optical axis direction.

Japanese Patent No. 4934233 Japanese Patent No. 5767423 Japanese Unexamined Patent Publication No. 2012-32576 Japanese Unexamined Patent Publication No. 2010-32680

With the expansion of the use of magnifying endoscopes, it is desired to reduce the diameter of magnifying endoscopes. By using a small image sensor for a magnifying endoscope, the diameter of the magnifying endoscope can be reduced. In a small image sensor, the pixel pitch is reduced while keeping the size of the image sensor the same. In this case, since the number of pixels is not reduced, miniaturization can be performed without deteriorating the image quality.

If the F number of the optical system remains large even though the pixel pitch of the image sensor is reduced, the image quality of the image obtained by imaging is deteriorated due to the influence of diffraction. Therefore, the optical system used for the image sensor having a small pixel pitch must be an optical system having a small F number.

One of the manufacturing processes of an optical system is assembling the optical system. In assembling the optical system, adjustment (hereinafter referred to as "focus adjustment") is performed to match the position of the best image plane with the position of the imaging plane. In focus adjustment, for example, the position of the imaging surface is fixed and the position of the best image plane is changed. The position of the best image plane can be changed by moving at least one lens.

As the F number becomes smaller, the ratio of the movement amount of the best image plane to the movement amount of the lens (hereinafter, referred to as “focus adjustment sensitivity”) becomes higher, so that the focus adjustment becomes difficult. Therefore, the optical system used for the image sensor having a small pixel pitch is preferably an optical system having a low focus adjustment sensitivity.

The objective optical systems disclosed in Patent Documents 1 to 4 are all optical systems having a small F number. Therefore, it is difficult to use the objective optical system disclosed in Patent Documents 1 to 4 for an image sensor having a small pixel pitch.

In the objective optical system disclosed in Patent Document 1, Patent Document 3, and Patent Document 4, the lens located closest to the image side and the cover glass are arranged apart from each other. On the other hand, in the objective optical system disclosed in Patent Document 2, the lens located closest to the image side and the cover glass are joined. However, the lens located closest to the image side is a concave flat lens. Therefore, in the objective optical system disclosed in Patent Documents 1 to 4, the focus adjustment sensitivity becomes high.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an endoscopic objective optical system which is compact, has high imaging performance, and has low focus adjustment sensitivity. ..

In order to solve the above-mentioned problems and achieve the object, the endoscopic objective optical system according to at least some embodiments of the present invention is used.
In order from the object side, it has a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power.
For changes in object distance, at least the second group is scaled by moving it along the optical axis.
The first group has a plano-concave negative lens on the most object side,
The second group has a focus function and
The third group includes a biconvex positive lens, an image side junction lens, and a convex flat lens in order from the object side.
The image-side junction lens includes an image-side positive lens and a biconcave-shaped image-side negative lens.
The convex flat lens is characterized in that it is joined to the image pickup surface of the image pickup device or a cover glass formed on the image pickup surface.

According to the present invention, it is possible to provide an endoscopic objective optical system having high imaging performance and low focus adjustment sensitivity despite its small size.

It is a figure which shows the endoscope objective optical system of this embodiment. It is sectional drawing of the objective optical system of Example 1. FIG. It is an aberration diagram of the objective optical system of Example 1. FIG. It is sectional drawing of the objective optical system of Example 2. FIG. It is an aberration diagram of the objective optical system of Example 2. It is sectional drawing of the objective optical system of Example 3. FIG. It is an aberration diagram of the objective optical system of Example 3. It is sectional drawing of the objective optical system of Example 4. FIG. It is an aberration diagram of the objective optical system of Example 4. It is sectional drawing of the objective optical system of Example 5. FIG. It is an aberration diagram of the objective optical system of Example 5. It is sectional drawing of the objective optical system of Example 6. It is an aberration diagram of the objective optical system of Example 6.

Hereinafter, the reason and operation of the endoscopic objective optical system of the present embodiment will be described with reference to the drawings. The present invention is not limited to the endoscopic objective optical system of the following embodiments.

The endoscopic objective optical system of the present embodiment is an optical system capable of performing normal observation and magnified observation with one optical system in endoscopic observation. Therefore, the endoscope objective optical system is composed of a plurality of lens groups, and at least one lens group moves along the optical axis with respect to a change in the object distance. As a result, normal observation can be performed when the focus is on a long-distance object point, and magnified observation can be performed when the focus is on a short-distance object point.

The image magnification of the optical system in normal observation and the image magnification of the optical system in magnified observation are different. Therefore, in the following description, the change of the observation state from the normal observation to the magnified observation and the change of the observation state from the magnified observation to the normal observation are referred to as scaling.

The endoscopic objective optical system of the present embodiment includes a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side. The first group has a plano-concave negative lens on the most object side, and the second group has a plano-concave negative lens. Has a focus function, the third group has a biconvex positive lens, an image side junction lens, and a convex flatness lens in order from the object side, and the image side junction lens is an image side positive lens. It has a biconcave image-side negative lens, and the convex flat lens is bonded to an image pickup surface of an image pickup element or a cover glass formed on the image pickup surface.

The endoscopic objective optical system of the present embodiment will be described. FIG. 1 is a diagram showing an endoscope objective optical system of the present embodiment. FIG. 1A is a cross-sectional view of the lens during normal observation, and FIG. 1B is a cross-sectional view of the lens during magnified observation.

The endoscopic objective optical system of the present embodiment has a first group G1 having a positive refractive power, a second group G2 having a negative refractive power, and a third group having a positive refractive power in order from the object side. It has G3 and. As described above, in the endoscopic objective optical system of the present embodiment, the optical system is composed of three lens groups of the first group G1, the second group G2, and the third group G3, and the arrangement of the refractive powers is different. It is designed to have a positive refractive power, a negative refractive power, and a positive refractive power.

In the endoscopic objective optical system of the present embodiment, at least the second group G2 moves along the optical axis in response to a change in the object distance. By doing so, scaling can be performed.

The object distance during normal observation and the object distance during magnified observation are different. Therefore, for example, when scaling is performed, it is necessary to focus in the observed state after scaling. In the endoscopic objective optical system of the present embodiment, the second group G2 has a focus function. Therefore, by moving the second group G2 along the optical axis, focusing can be performed together with scaling. When the magnification is changed from the normal observation state to the magnified observation state, the second group G2 moves to the image side.

As described above, in the endoscope objective optical system of the present embodiment, the arrangement of the refractive powers is positive refractive power, negative refractive power, and positive refractive power. Therefore, by performing focusing in the second group G2, it is possible to suppress aberration fluctuations during focusing.

In the endoscopic objective optical system, a lens having a large negative refractive power is arranged closest to the object in order to widen the angle. If the lens placed closest to the object has a large negative refractive power, the principal point will be located closer to the image. This makes it possible to secure sufficient back focus.

In the first group G1, the negative lens L1 is arranged on the most object side. The negative lens L1 is a planing negative lens and has a large negative refractive power. The negative lens L1 makes it possible to sufficiently secure the back focus.

A positive lens L2 and a junction lens CL1 are arranged on the image side of the negative lens L1. In the bonded lens CL1, the positive lens L3 and the negative lens L4 are bonded. The bonding lens CL1 is an object-side bonding lens.

An optical filter F is arranged between the negative lens L1 and the positive lens L2. The optical filter F is, for example, an infrared cut filter, a color temperature conversion filter, or a laser cut filter.

An aperture diaphragm S is arranged between the first group G1 and the second group G2.

The second group G2 has a negative lens L5. By moving the negative lens L5 along the optical axis, normal observation and magnified observation can be performed. When the magnification is changed from normal observation to magnified observation, the negative lens L5 moves to the image side.

As described above, in the endoscope objective optical system of the present embodiment, since the negative lens L1 is arranged on the most object side, it is possible to sufficiently secure the back focus. However, if the back focus is too long, it becomes difficult to miniaturize the optical system.

Therefore, a positive lens L6, a junction lens CL2, and a positive lens L9 are arranged in the third group G3. In the bonded lens CL2, the positive lens L7 and the negative lens L8 are bonded. The junction lens CL2 is an image-side junction lens. The positive lens L6 is a biconvex positive lens, the positive lens L7 is an image-side positive lens, the negative lens L8 is an image-side negative lens, and the positive lens L9 is a convex flat positive lens.

As described above, the biconvex positive lens, the image side junction lens, and the convex normal lens are arranged in the third group G3. An image-side positive lens is arranged on the image-side junction lens. Therefore, the third group G3 can have an action of converging the luminous flux. As a result, the back focus can be shortened, so that the overall length of the optical system can be shortened.

However, if the positive refractive power in the third group G3 becomes excessive, the angle formed by the main ray on the image plane and the normal of the image plane (hereinafter, referred to as “oblique incident angle”) becomes larger. In this case, the oblique incident angle is tilted to the plus side. For this reason, it is desirable to arrange a negative lens as the image side junction lens. By arranging the negative lens on the image side junction lens, it is possible to suppress the excessive positive refractive power in the third group G3. In the endoscope objective optical system of the present embodiment, the image side negative lens is arranged in the image side junction lens.

The sign of the angle is negative when the main ray is tilted toward the optical axis with respect to the normal of the image plane, and positive when it is opposite. When the oblique angle of incidence is tilted to the plus side, the main ray travels toward the image plane so as to gradually approach the optical axis.

Further, if a convex flat lens is arranged between the image side junction lens and the image plane, the positive refractive power in the third group G3 becomes excessive. Therefore, the oblique incident angle is tilted to the plus side. Therefore, by using a biconcave lens for the negative image side lens, telecentricity can be ensured.

The endoscope objective optical system of the present embodiment can be combined with an image pickup device having a small pixel pitch. As described above, the optical system used for the image sensor having a small pixel pitch must be an optical system having a small F number. In an objective optical system having a small F-number, the permissible circle of confusion becomes small, so that the focus adjustment sensitivity tends to be high.

If the focus adjustment sensitivity is high, the error sensitivity at the time of focus adjustment becomes high. Therefore, in the endoscope objective optical system of the present embodiment, the positive lens L9 is joined to the cover glass CG. The cover glass CG is a cover glass of the image sensor. Therefore, the positive lens L9 and the image sensor are integrated.

When the positive lens L9 is joined to the cover glass CG, the positive lens L9 is located in the vicinity of the image sensor. In this case, the positive lens L9 bonded to the cover glass CG functions as a field lens. In this state, if the positive lens L9 and the image sensor are integrated, the vertical magnification of the optical system becomes small. As a result, the error sensitivity at the time of focus adjustment can be lowered.

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (1).
-0.53 <f62 / f7 <-0.15 (1)
here,
f62 is the focal length of the negative lens on the image side.
f7 is the focal length of the convex flat lens,
Is.

The conditional expression (1) is a conditional expression relating to the focus adjustment sensitivity.

If the upper limit of the conditional expression (1) is exceeded, the refractive power of the convex flat lens becomes too large. In this case, the error sensitivity at the time of focus adjustment is weakened too much, so that the image plane position cannot be adjusted.

If it falls below the lower limit of the conditional expression (1), the refractive power of the convex flat lens becomes too small. In this case, the error sensitivity at the time of focus adjustment cannot be weakened.

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (2).
-0.4 <(r62 + r63) / (r62-r63) <0.8 (2)
here,
r62 is the radius of curvature of the side surface of the object of the negative lens on the image side,
r63 is the radius of curvature of the image side of the negative lens on the image side.
Is.

The conditional expression (2) is a conditional expression regarding the oblique incident angle.

If the upper limit of the conditional expression (2) is exceeded, the radius of curvature of the object side surface of the image-side negative lens, that is, the radius of curvature of the junction surface of the image-side junction lens becomes too large. Therefore, the chromatic aberration of magnification cannot be corrected.

If it is less than the lower limit of the conditional expression (2), the curvature of the negative lens on the image side on the image plane side becomes small. In this case, the oblique incident angle is tilted to the plus side.

It is even better to satisfy the following conditional expression (2') instead of the conditional expression (2).
-0.3 <(r62 + r63) / (r62-r63) <0.3 (2')

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (3).
-9 <f7 / f1 <-4.7 (3)
here,
f7 is the focal length of the convex flat lens,
f1 is the focal length of the plano-concave negative lens,
Is.

By joining the convex flat lens to the image pickup surface of the image sensor, or by joining the convex flat lens to the cover glass of the image sensor, the adjustment sensitivity at the time of assembly can be relaxed. The conditional expression (3) is a conditional expression relating to the adjustment sensitivity at the time of assembly.

If the upper limit of the conditional expression (3) is exceeded, the focal length of the convex flat lens becomes too small. Therefore, the adjustment sensitivity at the time of assembly becomes tight.

If it is less than the lower limit of the conditional expression (3), the refractive power of the plano-concave negative lens becomes too large. Therefore, the variation in the imaging performance around the image due to the manufacturing error becomes large.

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (4).
1.3 <f5 / f61 <1.9 (4)
here,
f5 is the focal length of the biconvex positive lens,
f61 is the focal length of the positive lens on the image side.
Is.

The conditional expression (4) is a conditional expression relating to chromatic aberration of magnification. In the endoscopic objective optical system of the present embodiment, the appearance of chromatic aberration of magnification changes between normal observation and magnified observation. By satisfying the conditional expression (4), the chromatic aberration of magnification can be satisfactorily corrected.

If the upper limit of the conditional expression (4) is exceeded, the focal length of the image-side positive lens becomes large. In this case, the chromatic aberration of magnification tends to be negative during normal observation. Therefore, the chromatic aberration of magnification cannot be completely corrected.

If it is less than the lower limit of the conditional expression (4), the focal length of the image-side positive lens becomes small. In this case, the chromatic aberration of magnification tilts positively during magnified observation. Therefore, the chromatic aberration of magnification cannot be completely corrected.

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (5).
15 <L / dn <30 (5)
here,
L is the total length of the endoscopic objective optical system,
dn is the amount of movement of the second group,
Is.

Further, the conditional expression (5) is a conditional expression for miniaturizing the optical system.

If the upper limit of the conditional expression (5) is exceeded, the total length of the optical system becomes long. Therefore, the optical system cannot be miniaturized.

If it falls below the lower limit of the conditional expression (5), the amount of movement of the second group becomes too large. In this case, the ray height in the third group becomes high. Therefore, the diameter of the third group becomes large.

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (6).
1 ≦ z / a ≦ 1.25 (6)
here,
z is a predetermined outer diameter of the image-side positive lens,
a is the outer diameter of the positive lens on the image side,
The predetermined outer diameter is the diameter of a circle formed by the line of intersection of the extension surface of the object side surface of the image side positive lens and the extension surface of the image side surface of the image side positive lens.
Is.

In the third group, it is preferable that a sufficiently large positive refractive power is secured. Since the image-side positive lens has the function of converging the luminous flux, it is necessary to increase the refractive power of the image-side positive lens. If an attempt is made to increase the refractive power of the image-side positive lens, the radius of curvature of the lens surface becomes small. In this case, since the inner wall thickness of the lens becomes large, the total length of the third group becomes long.

The conditional expression (6) is a conditional expression for miniaturizing the third group. By satisfying the conditional expression (6), the medium wall thickness can be reduced while increasing the refractive power of the image-side positive lens.

If the upper limit of the conditional expression (6) is exceeded, the processing margin will be too large with respect to the outer diameter of the positive lens on the image side. Therefore, the image-side positive lens cannot be miniaturized. It does not fall below the lower limit of the conditional expression (6).

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (7).
here,
0.75 <f61 / fc <1.6 (7)
f61 is the focal length of the positive lens on the image side.
fc is the focal length of the third group,
Is.

The conditional expression (7) is a conditional expression for maintaining a positive refractive power having a sufficient magnitude in the third group. In the third group, it is necessary to maintain a sufficiently large positive refractive power. Therefore, at least one of the refractive power of the biconvex regular lens and the refractive power of the convex flat lens becomes large.

However, when the refractive power of the biconvex positive lens becomes large, the influence on coma aberration becomes large. If the refractive power of the convex flat lens becomes large, the adjustment sensitivity becomes too dull. Therefore, it is necessary to make the refractive power of the biconvex regular lens and the refractive power of the convex flat lens appropriate.

When the upper limit of the conditional expression (7) is exceeded, the focal length of the image-side positive lens becomes larger than the focal length of the third group. Therefore, the positive refractive power of the bonded lens becomes small.

If it is less than the lower limit of the conditional expression (7), the focal length of the third group becomes small, so that the refractive power of the third group becomes too large. Therefore, the negative power generated in the first group is overcorrected.

It is even better to satisfy the following conditional expression (7') instead of the conditional expression (7).
0.9 <f61 / fc <1.1 (7')

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (8).
-1.5 <f1 / fL <-1.1 (8)
here,
f1 is the focal length of the plano-concave negative lens,
fL is the focal length of the entire endoscope objective optical system during normal observation.
Is.

The conditional expression (8) is a conditional expression relating to the imaging performance around the image.

If the upper limit of the conditional expression (8) is exceeded, the focal length of the entire endoscope objective optical system becomes large. In this case, the total length of the optical system becomes long.

When it falls below the lower limit of the conditional expression (8), the focal length of the planing negative lens becomes smaller. In this case, since the radius of curvature of the planing negative lens becomes small, the refractive power of the planing negative lens becomes large. As a result, the variation in imaging performance around the image due to manufacturing error becomes large.

It is even better to satisfy the following conditional expression (8') instead of the conditional expression (8).
-1.46 <f1 / fL <-1.22 (8')

In the endoscopic objective optical system of the present embodiment, it is preferable that the first group has an object-side junction lens and satisfies the following conditional expression (9).
3.8 <f6 / f3 <10 (9)
here,
f6 is the focal length of the image side junction lens,
f3 is the focal length of the object-side junction lens,
Is.

The conditional expression (9) is a conditional expression relating to the correction of chromatic aberration. In order to satisfactorily correct chromatic aberration, it is necessary to satisfy the conditional expression (9).

If the upper limit of the conditional expression (9) is exceeded, the focal length of the object-side junction lens becomes too small. In this case, axial chromatic aberration appears positive during normal observation.

If it is less than the lower limit of the conditional expression (9), the chromatic aberration of magnification will be positive at the time of magnified observation.

It is even better to satisfy the following conditional expression (9') instead of the conditional expression (9).
4.5 <f6 / f3 <8 (9')

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (10).
0.15 <fL / f3 <0.35 (10)
here,
fL is the focal length of the entire endoscope objective optical system during normal observation.
f3 is the focal length of the object-side junction lens,
Is.

The conditional expression (10) is a conditional expression relating to the miniaturization of the objective optical system.

If the upper limit of the conditional expression (10) is exceeded, the focal length of the entire endoscope objective optical system becomes large. Therefore, the total length of the optical system becomes long.

If it is less than the lower limit of the conditional expression (10), the focal length of the entire endoscope objective optical system becomes too small. In this case, it is not possible to secure a sufficient space for arranging the lens. Therefore, the required number of lenses cannot be arranged. As a result, sufficient imaging performance cannot be ensured.

It is even better to satisfy the following conditional expression (10') instead of the conditional expression (10).
0.16 <fL / f3 <0.33 (10')

The endoscopic objective optical system of the present embodiment preferably satisfies the following conditional expression (11).
-9 <f6 / fb <-1 (11)
here,
f6 is the focal length of the image side junction lens,
fb is the focal length of the second group,
Is.

The conditional expression (11) is a conditional expression relating to deterioration of imaging performance due to movement of the lens. When the lens moves, the lens tends to be eccentric or tilted due to mechanical factors. Therefore, if the refractive power of the moving lens is too large, the imaging performance is likely to be deteriorated due to eccentricity and the imaging performance is likely to be deteriorated due to tilt. When the image is imaged by the image sensor, the image quality of the image obtained by the image pickup is deteriorated.

If the upper limit of the conditional expression (11) is exceeded, the focal length of the image-side junction lens becomes small. Therefore, the axial chromatic aberration cannot be completely corrected.

If it is less than the lower limit of the conditional expression (11), the refractive power of the focal length of the second group becomes large. Therefore, when the second group moves, the imaging performance is likely to be deteriorated due to eccentricity and the imaging performance is likely to be deteriorated due to tilt.

It is even better to satisfy the following conditional expression (11') instead of the conditional expression (11).
-6 <f6 / fb <-3 (11')

Hereinafter, examples of the endoscopic objective optical system will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.

The lens sectional view of each embodiment will be described. (A) is a cross-sectional view of the lens in the normal observation state, and (b) is a cross-sectional view of the lens in the magnified observation state.

The aberration diagram of each embodiment will be described. (A), (b), (c) and (d) are aberration diagrams of spherical aberration (SA), astigmatism (AS), distortion (DT), and chromatic aberration of magnification (CC) in the normal observation state, respectively. Is. (E), (f), (g) and (h) are aberration diagrams of spherical aberration (SA), astigmatism (AS), distortion (DT), and chromatic aberration of magnification (CC) in the magnified observation state, respectively. Is.

In each aberration diagram, the horizontal axis represents the amount of aberration. For spherical aberration, astigmatism, and Magnification aberration, the unit of aberration amount is mm. For distortion, the unit of aberration is%. FYI is the image height, the unit is mm, and Fno is the F number. The unit of wavelength of the aberration curve is nm.

The endoscopic objective optical system of the first embodiment has a first group G1 having a positive refractive power, a second group G2 having a negative refractive power, and a third group having a positive refractive power in order from the object side. It is composed of G3 and. The aperture diaphragm (aperture) S is arranged between the first group G1 and the second group G2.

The first group G1 is composed of a plano-concave negative lens L1, a positive meniscus lens L2 with a convex surface facing the image side, a biconvex positive lens L3, and a positive meniscus lens L4 with a convex surface facing the image side. There is. Here, the biconvex positive lens L3 and the positive meniscus lens L4 are joined.

The second group G2 is composed of a negative meniscus lens L5 having a convex surface facing the object side.

The third group G3 is composed of a biconvex positive lens L6, a biconvex positive lens L7, a biconcave negative lens L8, and a convex flat lens L9. Here, the biconvex positive lens L7 and the biconcave negative lens L8 are joined.

The infrared absorption filter F (hereinafter referred to as “filter F”) is arranged between the planing negative lens L1 and the positive meniscus lens L2. The cover glass CG is joined to the convex flat lens L9.

At the time of scaling, the second group G2 moves. More specifically, the second group G2 moves to the image side when the magnification is changed from the normal observation state to the magnified observation state. In addition, focusing is performed by the movement of the second group G2. In this way, scaling and focusing are performed at the same time.

In the endoscopic objective optical system of the second embodiment, the first group G1 having a positive refractive power, the second group G2 having a negative refractive power, and the third group having a positive refractive power are arranged in this order from the object side. It is composed of G3 and. The aperture diaphragm (aperture) S is arranged between the first group G1 and the second group G2.

The first group G1 is composed of a plano-concave negative lens L1, a positive meniscus lens L2 with a convex surface facing the image side, a biconvex positive lens L3, and a positive meniscus lens L4 with a convex surface facing the image side. There is. Here, the biconvex positive lens L3 and the positive meniscus lens L4 are joined.

The second group G2 is composed of a negative meniscus lens L5 having a convex surface facing the object side.

The third group G3 is composed of a biconvex positive lens L6, a biconvex positive lens L7, a biconcave negative lens L8, and a convex flat lens L9. Here, the biconvex positive lens L7 and the biconcave negative lens L8 are joined.

The filter F is arranged between the flat concave negative lens L1 and the positive meniscus lens L2. The cover glass CG is joined to the convex flat lens L9.

At the time of scaling, the second group G2 moves. More specifically, the second group G2 moves to the image side when the magnification is changed from the normal observation state to the magnified observation state. In addition, focusing is performed by the movement of the second group G2. In this way, scaling and focusing are performed at the same time.

The endoscopic objective optical system of Example 3 has a first group G1 having a positive refractive power, a second group G2 having a negative refractive power, and a third group having a positive refractive power in order from the object side. It is composed of G3 and. The aperture diaphragm (aperture) S is arranged between the first group G1 and the second group G2.

The first group G1 is composed of a plano-concave negative lens L1, a positive meniscus lens L2 with a convex surface facing the image side, a biconvex positive lens L3, and a positive meniscus lens L4 with a convex surface facing the image side. There is. Here, the biconvex positive lens L3 and the positive meniscus lens L4 are joined.

The second group G2 is composed of a negative meniscus lens L5 having a convex surface facing the object side.

The third group G3 is composed of a biconvex positive lens L6, a biconvex positive lens L7, a biconcave negative lens L8, and a convex flat lens L9. Here, the biconvex positive lens L7 and the biconcave negative lens L8 are joined.

The filter F is arranged between the flat concave negative lens L1 and the positive meniscus lens L2. The cover glass CG is joined to the convex flat lens L9.

At the time of scaling, the second group G2 moves. More specifically, the second group G2 moves to the image side when the magnification is changed from the normal observation state to the magnified observation state. In addition, focusing is performed by the movement of the second group G2. In this way, scaling and focusing are performed at the same time.

In the endoscopic objective optical system of the fourth embodiment, the first group G1 having a positive refractive power, the second group G2 having a negative refractive power, and the third group having a positive refractive power are arranged in this order from the object side. It is composed of G3 and. The aperture diaphragm (aperture) S is arranged between the first group G1 and the second group G2.

The first group G1 is composed of a plano-concave negative lens L1, a positive meniscus lens L2 with a convex surface facing the image side, a biconvex positive lens L3, and a positive meniscus lens L4 with a convex surface facing the image side. There is. Here, the biconvex positive lens L3 and the positive meniscus lens L4 are joined.

The second group G2 is composed of both concave and negative lenses L5.

The third group G3 is composed of a biconvex positive lens L6, a biconvex positive lens L7, a biconcave negative lens L8, and a convex flat lens L9. Here, the biconvex positive lens L7 and the biconcave negative lens L8 are joined.

The filter F is arranged between the flat concave negative lens L1 and the positive meniscus lens L2. The cover glass CG is joined to the convex flat lens L9.

At the time of scaling, the second group G2 moves. More specifically, the second group G2 moves to the image side when the magnification is changed from the normal observation state to the magnified observation state. In addition, focusing is performed by the movement of the second group G2. In this way, scaling and focusing are performed at the same time.

In the endoscopic objective optical system of Example 5, the first group G1 having a positive refractive power, the second group G2 having a negative refractive power, and the third group having a positive refractive power are arranged in this order from the object side. It is composed of G3 and. The aperture diaphragm (aperture) S is arranged between the first group G1 and the second group G2.

The first group G1 is composed of a plano-concave negative lens L1, a positive meniscus lens L2 with a convex surface facing the image side, a biconvex positive lens L3, and a positive meniscus lens L4 with a convex surface facing the image side. There is. Here, the biconvex positive lens L3 and the positive meniscus lens L4 are joined.

The second group G2 is composed of a negative meniscus lens L5 having a convex surface facing the object side.

The third group G3 is composed of a biconvex positive lens L6, a biconvex positive lens L7, a biconcave negative lens L8, and a convex flat lens L9. Here, the biconvex positive lens L7 and the biconcave negative lens L8 are joined.

The filter F is arranged between the flat concave negative lens L1 and the positive meniscus lens L2. The cover glass CG is joined to the convex flat lens L9.

At the time of scaling, the second group G2 moves. More specifically, the second group G2 moves to the image side when the magnification is changed from the normal observation state to the magnified observation state. In addition, focusing is performed by the movement of the second group G2. In this way, scaling and focusing are performed at the same time.

In the endoscopic objective optical system of Example 6, the first group G1 having a positive refractive power, the second group G2 having a negative refractive power, and the third group having a positive refractive power are arranged in this order from the object side. It is composed of G3 and. The aperture diaphragm (aperture) S is arranged between the first group G1 and the second group G2.

The first group G1 is composed of a plano-concave negative lens L1, a positive meniscus lens L2 with a convex surface facing the image side, a biconvex positive lens L3, and a positive meniscus lens L4 with a convex surface facing the image side. There is. Here, the biconvex positive lens L3 and the positive meniscus lens L4 are joined.

The second group G2 is composed of a negative meniscus lens L5 having a convex surface facing the object side.

The third group G3 is composed of a biconvex positive lens L6, a biconvex positive lens L7, a biconcave negative lens L8, and a convex flat lens L9. Here, the biconvex positive lens L7 and the biconcave negative lens L8 are joined.

The filter F is arranged between the flat concave negative lens L1 and the positive meniscus lens L2. The cover glass CG is joined to the convex flat lens L9.

At the time of scaling, the second group G2 moves. More specifically, the second group G2 moves to the image side when the magnification is changed from the normal observation state to the magnified observation state. In addition, focusing is performed by the movement of the second group G2. In this way, scaling and focusing are performed at the same time.

The numerical data of each of the above examples is shown below. In the surface data, r is the radius of curvature of each lens surface, d is the distance between each lens surface, ne is the refractive index of the e-line of each lens, and νd is the Abbe number of each lens.

In various data, OBJ is the object distance, Fno is the F number, ω is the half angle of view, IH is the image height, and a is the outer diameter of the positive lens on the image side. The unit of r, d, IH, and a is mm, and the unit of the half angle of view ω is °.

Numerical Example 1
Unit mm

Surface data Surface number rd ne νd
1 ∞ 0.4454 1.88815 40.76
2 1.2257 0.8549
3 ∞ 0.6682 1.52300 65.13
4 ∞ 0.3118
5 -4.1472 0.9321 1.79196 47.37
6 -3.2336 0.1559
7 24.8444 1.1143 1.59143 61.14
8-3.3345 0.7610 1.93429 18.90
9 -2.9504 0.1336
10 (Aperture) ∞ (Variable)
11 20.4959 0.5568 1.58482 40.75
12 3.2506 (variable)
13 4.0909 1.8263 1.48915 70.23
14 -4.8186 0.0891
15 3.0554 0.9577 1.65425 58.55
16 -6.3055 0.7795 1.93429 18.90
17 5.4605 0.8241
18 4.0089 1.0022 1.51825 64.14
19 ∞ 0.0156 1.51500 64.00
20 ∞ 0.7795 1.50700 63.26
21 (image plane) ∞

Various data Normal observation state Proximity observation state OBJ 31.18040 6.68151
Fno 3.27 3.62
ω 66.41 54.95
IH 1 1
d10 0.28952 1.01906
d12 1.14902 0.41948
a 3.18 3.18

Numerical Example 2
Unit mm

Surface data Surface number rd ne νd
1 ∞ 0.4454 1.88815 40.76
2 1.2472 0.8463
3 ∞ 0.6682 1.52300 65.13
4 ∞ 0.3118
5 -4.3936 1.1066 1.79196 47.37
6 -3.0414 0.1559
7 23.1535 1.3761 1.59143 61.14
8-3.2992 0.9307 1.93429 18.90
9 -3.2651 0.1336
10 (Aperture) ∞ (Variable)
11 19.7062 0.5568 1.58482 40.75
12 3.2506 (variable)
13 4.0005 1.8263 1.48915 70.23
14 -5.0949 0.0891
15 3.0198 0.9577 1.65425 58.55
16 -6.4564 0.7795 1.93429 18.90
17 5.6034 0.8241
18 5.7651 1.0022 1.51825 64.14
19 ∞ 0.0156 1.51500 64.00
20 ∞ 0.7795 1.50700 63.26
21 (image plane) ∞

Various data Normal observation state Proximity observation state OBJ 31.18040 6.68151
Fno 3.35 3.71
ω 66.41 54.96
IH 1 1
d10 0.28952 1.01906
d12 1.52437 0.79482
a 3.18 3.18

Numerical Example 3
Unit mm

Surface data Surface number rd ne νd
1 ∞ 0.4454 1.88815 40.76
2 1.2472 0.8463
3 ∞ 0.6682 1.52300 65.13
4 ∞ 0.3118
5 -4.2209 1.2267 1.79196 47.37
6 -3.0741 0.1559
7 26.9970 1.3669 1.59143 61.14
8-3.2917 0.9499 1.93429 18.90
9 -3.1757 0.1336
10 (Aperture) ∞ (Variable)
11 17.8376 0.5568 1.58482 40.75
12 3.2506 (variable)
13 4.0449 1.8263 1.48915 70.23
14 -6.8228 0.0891
15 2.9374 0.9577 1.65425 58.55
16 -6.8274 0.7795 1.93429 18.90
17 5.2324 0.8241
18 4.0089 1.0022 1.51825 64.14
19 ∞ 0.0156 1.51500 64.00
20 ∞ 0.7795 1.50700 63.26
21 (image plane) ∞

Various data Normal observation state Proximity observation state OBJ 31.18040 6.68151
Fno 3.42 3.89
ω 66.84 54.34
IH 1 1
d10 0.28952 1.01906
d12 1.33320 0.60366
a 3.18 3.18

Numerical Example 4
Unit mm

Surface data Surface number rd ne νd
1 ∞ 0.4454 1.88815 40.76
2 1.2472 0.8463
3 ∞ 0.6682 1.52300 65.13
4 ∞ 0.3118
5 -4.1451 2.2333 1.79196 47.37
6 -3.4316 0.1559
7 4.7603 0.6103 1.59143 61.14
8-2.8074 1.1481 1.93429 18.90
9 -3.0145 0.1336
10 (Aperture) ∞ (Variable)
11 -7.6012 0.5568 1.58482 40.75
12 3.2506 (variable)
13 8.2575 1.8263 1.48915 70.23
14 -3.8240 0.0891
15 3.0324 0.9577 1.65425 58.55
16 -5.6642 0.7795 1.93429 18.90
17 5.8981 0.8241
18 4.0089 1.0022 1.51825 64.14
19 ∞ 0.0156 1.51500 64.00
20 ∞ 0.7795 1.50700 63.26
21 (image plane) ∞

Various data Normal observation state Proximity observation state OBJ 31.18040 0.66815
Fno 3.41 3.78
ω 66.4 54.99
IH 1 1
d10 0.28952 0.84631
d12 1.11604 0.55925
a 3.18 3.18

Numerical Example 5
Unit mm

Surface data Surface number rd ne νd
1 ∞ 0.4454 1.88815 40.76
2 1.3855 0.8463
3 ∞ 0.6682 1.52300 65.13
4 ∞ 0.3118
5 -4.1473 1.2601 1.79196 47.37
6 -3.3458 0.1559
7 15.9321 1.4218 1.59143 61.14
8-2.8823 1.0428 1.93429 18.90
9 -3.1523 0.1336
10 (Aperture) ∞ (Variable)
11 22.2735 0.5568 1.58482 40.75
12 3.2506 (variable)
13 4.3199 1.8263 1.48915 70.23
14 -4.7719 0.0891
15 3.0381 0.9577 1.65425 58.55
16 -6.5499 0.7795 1.93429 18.90
17 5.6444 0.8241
18 4.0089 1.0022 1.51825 64.14
19 ∞ 0.0156 1.51500 64.00
20 ∞ 0.7795 1.50700 63.26
21 (image plane) ∞

Various data Normal observation state Proximity observation state OBJ 31.18040 6.68151
Fno 3.25 3.61
ω 66.4 54.99
IH 1 1
d10 0.28952 1.01906
d12 1.11600 0.38646
a 3.18 3.18

Numerical Example 6
Unit mm

Surface data Surface number rd ne νd
1 ∞ 0.4454 1.88815 40.76
2 1.2472 0.8463
3 ∞ 0.6682 1.52300 65.13
4 ∞ 0.3118
5 -4.1456 1.2341 1.79196 47.37
6 -2.9766 0.1559
7 44.0561 1.3219 1.59143 61.14
8-3.2782 0.9160 1.93429 18.90
9 -3.3638 0.1336
10 (Aperture) ∞ (Variable)
11 10.9540 0.5568 1.58482 40.75
12 3.2506 (variable)
13 3.9968 1.8263 1.48915 70.23
14 -5.9781 0.0891
15 3.0747 0.9577 1.65425 58.55
16 -6.4316 0.7795 1.93429 18.90
17 5.2860 0.8241
18 4.0089 1.0022 1.51825 64.14
19 ∞ 0.0156 1.51500 64.00
20 ∞ 0.7795 1.50700 63.26
21 (image plane) ∞

Various data Normal observation state Proximity observation state OBJ 31.18040 6.68151
Fno 3.41 3.78
ω 66.4 54.99
IH 1 1
d10 0.28952 1.18039
d12 1.36154 0.47067
a 3.18 3.18

Next, the values of the conditional expressions in each embodiment are listed below.

Conditional expression Example 1 Example 2 Example 3
(1) f62 / f7 -0.392 -0.280 -0.397
(2) (r62 + r63) / (r62-r63) 0.072 0.071 0.132
(3) f7 / f1 -5.61 -7.92 -5.51
(4) f5 / f61 1.48 1.50 1.68
(5) L / dn 18.70 20.03 19.95
(6) z / a 1.19 1.20 1.19
(7) f61 / fc 1.01 0.99 0.95
(8) f1 / fL -1.27 -1.27 -1.28
(9) f6 / f3 6.51 4.77 4.90
(10) fL / f3 0.27 0.24 0.24
(11) f6 / fb -4.00 -3.30 -3.23

Conditional expression Example 4 Example 5 Example 6
(1) f62 / f7 -0.387 -0.407 -0.389
(2) (r62 + r63) / (r62-r63) -0.020 0.074 0.098
(3) f7 / f1 -5.51 -4.96 -5.51
(4) f5 / f61 1.78 1.50 1.57
(5) L / dn 26.56 19.89 16.30
(6) z / a 1.17 1.20 1.20
(7) f61 / fc 0.94 1.02 0.98
(8) f1 / fL -1.32 -1.44 -1.29
(9) f6 / f3 6.72 4.92 6.13
(10) fL / f3 0.32 0.24 0.21
(11) f6 / fb -5.83 -3.39 -3.84

Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and the embodiments are configured by appropriately combining the configurations of these embodiments without departing from the spirit of the present invention. The form is also within the scope of the present invention.

(Additional note)
The inventions having the following configurations are derived from these examples.
(Appendix 1)
In order from the object side, it has a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power.
For changes in object distance, at least the second group is scaled by moving it along the optical axis.
The first group has a plano-concave negative lens on the most object side,
The second group has a focus function and
The third group includes a biconvex positive lens, an image side junction lens, and a convex flat lens in order from the object side.
The image-side junction lens includes an image-side positive lens and a biconcave-shaped image-side negative lens.
The convex flat lens is an endoscopic objective optical system characterized in that it is bonded to an image pickup surface of an image pickup element or a cover glass formed on the image pickup surface.

(Appendix 2)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (1).
-0.53 <f62 / f7 <-0.15 (1)
here,
f62 is the focal length of the negative lens on the image side.
f7 is the focal length of the convex flat lens,
Is.

(Appendix 3)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (2).
-0.4 <(r62 + r63) / (r62-r63) <0.8 (2)
here,
r62 is the radius of curvature of the side surface of the object of the negative lens on the image side,
r63 is the radius of curvature of the image side of the negative lens on the image side.
Is.

(Appendix 4)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (3).
-9 <f7 / f1 <-4.7 (3)
here,
f7 is the focal length of the convex flat lens,
f1 is the focal length of the planing negative lens,
Is.

(Appendix 5)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (4).
1.3 <f5 / f61 <1.9 (4)
here,
f5 is the focal length of the biconvex positive lens,
f61 is the focal length of the positive lens on the image side.
Is.

(Appendix 6)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (5).
15 <L / dn <30 (5)
here,
L is the total length of the endoscopic objective optical system,
dn is the amount of movement of the second group,
Is.

(Appendix 7)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (6).
1 ≦ z / a ≦ 1.25 (6)
here,
z is a predetermined outer diameter of the image-side positive lens.
a is the outer diameter of the positive lens on the image side,
The predetermined outer diameter is the diameter of a circle formed by the line of intersection of the extension surface of the object side surface of the image side positive lens and the extension surface of the image side surface of the image side positive lens.
Is.

(Appendix 8)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (7).
0.75 <f61 / fc <1.6 (7)
here,
f61 is the focal length of the positive lens on the image side.
fc is the focal length of the third group,
Is.

(Appendix 9)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (8).
-1.5 <f1 / fL <-1.1 (8)
here,
f1 is the focal length of the plano-concave negative lens,
fL is the focal length of the entire endoscope objective optical system during normal observation.
Is.

(Appendix 10)
The first group has an object-side junction lens and
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (9).
3.8 <f6 / f3 <10 (9)
here,
f6 is the focal length of the image side junction lens,
f3 is the focal length of the object-side junction lens,
Is.

(Appendix 11)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (10).
0.15 <fL / f3 <0.35 (10)
here,
fL is the focal length of the entire endoscope objective optical system during normal observation.
f3 is the focal length of the object-side junction lens,
Is.

(Appendix 12)
The endoscopic objective optical system according to Appendix 1, wherein the endoscopic objective optical system satisfies the following conditional expression (11).
-9 <f6 / fb <-1 (11)
here,
f6 is the focal length of the image side junction lens,
fb is the focal length of the second group,
Is.

As described above, the present invention is suitable for an endoscopic objective optical system having high imaging performance and low focus adjustment sensitivity despite its small size.

G1 1st group G2 2nd group G3 3rd group CL1, CL2 Junction lens L1 to L9 Lens F Optical filter, Infrared absorption filter S Aperture aperture I Image plane CG cover glass

Claims (7)

In order from the object side, it has a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power.
With respect to the change in the object distance, at least the second group is moved along the optical axis to change the magnification.
The first group has a plano-concave negative lens on the most object side.
The second group has a focus function and has a focus function.
The third group includes a biconvex positive lens, an image side junction lens, and a convex flat lens in order from the object side.
The image-side junction lens includes an image-side positive lens and a biconcave-shaped image-side negative lens.
The convex flat lens is an endoscopic objective optical system characterized in that it is joined to an image pickup surface of an image pickup device or a cover glass formed on the image pickup surface. The endoscopic objective optical system according to claim 1, wherein the following conditional expression (1) is satisfied.
-0.53 <f62 / f7 <-0.15 (1)
here,
f62 is the focal length of the image-side negative lens.
f7 is the focal length of the convex flat lens,
Is. The endoscopic objective optical system according to claim 1, wherein the endoscopic objective optical system satisfies the following conditional expression (2).
-0.4 <(r62 + r63) / (r62-r63) <0.8 (2)
here,
r62 is the radius of curvature of the side surface of the object of the negative lens on the image side.
r63 is the radius of curvature of the image side of the negative lens on the image side.
Is. The endoscopic objective optical system according to claim 1, wherein the following conditional expression (3) is satisfied.
-9 <f7 / f1 <-4.7 (3)
here,
f7 is the focal length of the convex flat lens,
f1 is the focal length of the planing negative lens.
Is. The endoscopic objective optical system according to claim 1, wherein the following conditional expression (4) is satisfied.
1.3 <f5 / f61 <1.9 (4)
here,
f5 is the focal length of the biconvex positive lens.
f61 is the focal length of the image-side positive lens.
Is. The endoscopic objective optical system according to claim 1, wherein the following conditional expression (5) is satisfied.
15 <L / dn <30 (5)
here,
L is the total length of the endoscope objective optical system.
dn is the amount of movement of the second group,
Is. The endoscopic objective optical system according to claim 1, wherein the following conditional expression (6) is satisfied.
1 ≦ z / a ≦ 1.25 (6)
here,
z is a predetermined outer diameter of the image-side positive lens.
a is the outer diameter of the image-side positive lens,
The predetermined outer diameter is the diameter of a circle formed by the line of intersection between the extension surface of the object side surface of the image side positive lens and the extension surface of the image side surface of the image side positive lens.
Is.

Images