JPH03100511A - Objective lens for endoscope - Google Patents

Abstract

PURPOSE:To obtain an endoscope objective lens being small-sized, short in overall length and having a wide angle, whose distortion is corrected satisfactorily by providing a specific aspherical surface in the vicinity of a field lens arranged so that a principal ray is made incident perpendicular to the image surface in the vicinity of the image forming surface of a lens group being in the rear of a diaphragm. CONSTITUTION:On the image side of an image forming lens provided with a brightness diaphragm, a field lens LF is provided, and also, on its outgoing side, a solid-state video element CCD is arranged. Also, in the vicinity of the field lens LF of the rear group, an aspherical surface for satisfying expressions I, II is provided. In expressions I, II, (f), fA, fB, and DELTAZmax denote a focal distance of the whole system, a focal distance of the aspherical lens provided in the vicinity of the field lens, a composite focal distance of the rear group, and the deviation quantity in the optical axis direction from the reference spherical surface in a point on the aspherical surface of a principal ray going to the maximum image height, respectively. In such a manner, the generation of distortion is suppressed, and also, other various aberrations are also corrected satisfactorily, and a lens system having a satisfactory performance, being short in overall length and small in size, and having a wide angle is obtained.

Description

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

[Prior Art] As an objective lens for an endoscope, a front group with a negative refractive power is provided on the object side of the aperture diaphragm S, and a front group with a positive refractive power is provided on the image side of the aperture diaphragm S, as shown in FIG. Many retrofocus type lens systems with a rear group are known. In addition, many endoscopes transmit images by installing an image fiber on the imaging plane of the objective lens (in this case, the light rays entering the fiber are required to be approximately perpendicular to the east end face of the fiber). This is because if the angle of incidence of the light ray that enters the image fiber is large, the light ray may not propagate inside the fiber and may pass through the fiber, or even if it does propagate, there will be a large number of total reflections inside the fiber, leading to a loss of light quantity. This is because you will be left alone.

Recently, many so-called electronic endoscopes that use solid-state imaging devices such as CCDs instead of image fibers have been released. When a so-called mosaic type image sensor is used as a solid-state image sensor, in which minute color filters are arranged in correspondence with each pixel, if the distance between the filter and the light-receiving surface of the solid-state image sensor is large, the element may On the other hand, light rays that enter at a large angle do not enter the pixel where they are supposed to enter after passing through the color filter, but instead enter the pixel adjacent to it, causing color unevenness (hereinafter referred to as color shading) in the resulting image. There is a problem called.

As a measure to prevent this, it is sufficient to make the light beam perpendicularly enter the solid-state image sensor. However, in the telecentric system used in conventional fiberscopes, the angle of incidence of the light beam onto the fiber is not necessarily constant, and varies by several degrees for each image height. Therefore, in the future, the picture elements of solid-state image sensors will become smaller and more dense. must be corrected to eliminate variations in

Furthermore, due to the unique structure of the endoscope objective lens, so-called barrel distortion occurs, in which the image collapses toward the periphery of the image. In particular, wide-angle lenses with an angle of view of more than 100° cause significant distortion.

[Problems to be Solved by the Invention] The present invention can prevent the occurrence of color shading even when it is combined with a mosaic solid-state image sensor that tends to occur, and can also satisfactorily correct various aberrations, especially distortion. The object of the present invention is to provide a compact, wide-angle endoscope objective lens with a short overall length.

[Means for Solving the Problems] In order to achieve the above object, the objective lens for an endoscope of the present invention has a negative refractive power group and a positive refractive power rear group with an aperture diaphragm in between. and a field lens arranged so that the chief ray is incident perpendicularly to the image plane near the image formation plane of the rear group, which is a lens group behind the aperture,
The present invention is characterized in that an aspherical surface is provided near the field lens of the rear group, and the following conditions (1) and (2) are satisfied.

(1) 0.5<fA/fa<10f2+ 0
．． 005f<IAZ,,,l <O, 15f but f
is the focal length of the entire system, fA is the focal length of the aspherical lens installed near the field lens, f8 is the combined focal length of the rear group, and ΔZ1.8 is the point on the aspherical surface of the chief ray heading toward the maximum image height. is the amount of deviation in the optical axis direction from the reference spherical surface.

The objective lens for an endoscope of the present invention has a field lens LF on the image side of an imaging lens equipped with an aperture diaphragm S, as shown in FIG. It is based on the optical system. In this way, by providing the field lens L so that the chief ray is incident perpendicularly to the image plane, it is possible to suppress the occurrence of color shading even when combined with a mosaic type solid-state image sensor. Note that M in the drawing is a color mosaic filter, which is placed at the CCD target.

However, since the angle of incidence of light rays on the image plane usually changes for each image height, it is necessary to provide an aspherical surface near the field lens to prevent the angle of incidence of light rays on the image plane from changing. I can do it. The shape of the aspherical surface provided here may include a portion where the refractive effect of the lens having the aspherical surface becomes gradually weaker as it moves from the optical axis to the periphery. In the case of a positive lens, "weakening" means that its converging action, ie, its positive power, becomes weaker, and in the case of a negative lens, it means that its diverging action, ie, its negative power, becomes weaker.

Next, it will be explained that by adopting the above configuration, it is possible to suppress a change in the angle of incidence of the light beam onto the image plane.

For example, assuming that the principal ray is perpendicularly incident on the image plane at each image height, when focusing on the rear group in the optical system, if the ray is traced backwards from the image side, it will emerge from each image height. All rays parallel to the optical axis pass through the center of the aperture stop. In other words, in a rear group that is a telecentric system with an infinite exit pupil, such as an endoscope objective lens, when the ray is traced back, the ray is parallel to the optical axis (the axial marginal ray with the object point at infinity). ), the spherical aberration of the pupil is considered to be 0, since all of them pass through the center of the aperture.

Therefore, the locations for providing the above aspherical surface are locations where spherical aberration is large when the light ray is traced back;
That is, it is preferable to provide it near the field lens where the height of the light beam is the highest.

In addition, objective lenses for endoscopes generally have a retrofocus type structure consisting of a front group with an overall negative refractive power across the aperture, and a rear group with an overall positive refractive power. Furthermore, normally, a positive lens has a larger refractive effect as it moves toward the periphery, and the light rays are bent more significantly, resulting in negative spherical aberration. Therefore, if the shape of the aspherical surface is such that the refractive effect of the lens gradually weakens from the optical axis toward the periphery, it is possible to suppress the occurrence of aberrations in the periphery.

However, when tracing back the light ray, the fact that the spherical aberration is 0 for the ray parallel to the optical axis means that it is for the entire lens group with positive refractive power on the image side of the aperture. Even if a lens is provided with an aspherical surface, this lens alone does not eliminate the spherical aberration of the pupil.

In the present invention, in order to achieve the above object, condition (1),
(It is also characterized by satisfying 21, and these conditions will be explained below.

As shown in Figure 1, when the lens group behind the diaphragm is LA, and the lens provided with an aspherical surface is LA, the combined focal length of the lens group is f@, and the aspherical lens L under condition (1).
The focal length of A is f, but if two or more aspherical surfaces are provided in the lens group behind the diaphragm and multiple lenses are provided, the main one of the lens surfaces provided with the aspherical surface is The lens with the highest ray height is considered to be LA.

In the above condition (1), the value of f, /fa is the upper limit of 10
If it is larger than , the focal length f of the aspherical lens L1 becomes large, the total length of the objective lens becomes long, and the outer diameter of the lens also becomes large, which is inconvenient for use in endoscopes. If it is smaller than the lower limit of 0.5, the overall length of the objective lens will become shorter, which is advantageous for compactness, but it will not be possible to secure a space for arranging an optical filter such as an infrared cut filter.

It is preferable to place the aspherical surface near the field lens where the ray height is highest as mentioned above, but considering that the spherical aberration of the pupil should be zero for the entire lens group behind the aperture, it is not necessary to place the aspherical surface near the field lens where the ray height is highest. It is not necessary to provide an aspherical surface on the lens.The location where an aspherical surface is provided is that the ray heading toward the maximum image height has a ray height of 0.5 times or more than the maximum ray height of that ray. desirable.

Next, condition (2) defines the shape of the aspherical surface.

Generally, the shape of an aspherical surface can be expressed by the following equation.

z = Cy”/ (1+ Frochi?l + By”
+ Ey'+py'+cy"+... Here, z and y are the directions perpendicular to the Z-axis with the optical axis as the two axes, the direction of the image in the positive direction, and the y-axis as the origin at the intersection of the surface and the optical axis. , C is the reciprocal of the radius of curvature of the circle that touches this aspherical surface near the optical axis, P is the shape of the aspherical surface, and parameters B, E, F, G, etc. are each quadratic. ,
These are 4th, 6th, 8th, etc. aspherical coefficients.

When P=1 and B, E, F, G, . . . are all 0, the above equation represents a spherical surface.

The amount of deviation in the optical axis direction between the aspherical surface and the reference spherical surface (the spherical surface that contacts the aspherical surface near the optical axis) is shown in Figure 18 (A1.tB1), where the solid line is the aspherical surface and the broken line is the reference spherical surface. Here, the amount of deviation ΔZ from the spherical surface at height I with respect to the two axes (optical axis) is positive if the deviation from the spherical surface is in the positive direction of the two axes, and conversely, if it is deviation in the negative direction , ΔZ assume negative values.

In other words, if the front surface of the positive lens is made into an aspherical surface as shown in Figure 18 (B1), the deviation amount will be negative and the power of the lens in the peripheral area will be weakened.Also, on the image side of the positive lens When an aspherical surface is provided as shown in Fig. 181B1, the amount of deviation is negative, but the power of the lens becomes stronger.The same goes for the case of a negative lens, with the aspherical surface being moved toward the object side. Depending on whether it is provided or provided on the image side, and whether the reference spherical surface is concave or convex facing the object side,
Even if the direction of deviation of the aspherical surface from the reference spherical surface is the same, the change in lens power is not necessarily the same. Therefore, when considering ΔZ including the sign in the above condition (2), the amount of deviation is the absolute value It will be expressed as

In the above condition (2), ΔZ wax is smaller than the lower limit value (when the deviation from the reference spherical surface is small, the effect of providing the aspherical surface is hardly obtained, and the desired aberration correction cannot be performed. On the other hand, if the upper limit is exceeded, the power at the lens periphery becomes too weak for the reason mentioned above, making it impossible to suppress changes in the angle of incidence of the rays on the imaging plane.In other words, the above condition (2) is satisfied near the field lens. This shows how much the aspherical surface provided in the spherical surface should be changed from the reference spherical surface.

The aspherical surface provided near the field lens is provided to correct changes in the angle of incidence of light rays on the imaging surface for each image height, and the degree of change in the angle of incidence for each image height is different. When considered by cutting along a meridional section that includes the optical axis, there are chief rays that enter from the periphery toward the optical axis and principal rays that enter from the optical axis toward the periphery. Therefore, the shape of the aspherical surface must correspond to the degree of incidence of the principal ray, so that the refractive power for light rays must be made stronger in certain regions than that of the reference surface and weaker in other regions. However, as already mentioned, basically, the higher the ray height, the greater the occurrence of spherical aberration.

In order to correct this, the refractive power can be weakened where the ray height is high.6 In other words, the effect of the aspheric surface is obtained near the maximum ray height, and it is important to specify the shape here. .

Also, when the rear group on the image side of the aperture is regarded as a single lens system, if the spherical aberration of this lens system is O, then when the ray is traced back, it will be parallel to the optical axis rather than the image plane, as shown in Figure 20. After passing through the lens, all the rays at each image height intersect at the center of the aperture. The shape of the aspheric surface at this time is generally close to a hyperboloid.

Next, the removal of distortion aberration in an objective lens for an endoscope will be described.

Generally, in order to correct distortion aberration in an optical system, it is good to provide an aspheric surface on the surface where the principal ray height is high. However, the area near the field lens of the rear group where the principal ray height is high is An aspherical surface is provided to make the incident angle of the principal ray constant, and the shape of the aspherical surface is also fixed.

Therefore, distortion can be corrected by providing an aspherical surface on a surface with a high principal ray height in front of the aperture. The aspherical shape provided here may include a portion where the refractive power of the lens gradually weakens as it goes from the optical axis to the peripheral portion.

In a normal endoscope objective lens, the height of the rays increases in front of this aperture because the object-side surface (first surface) of the first lens
It is.

This first surface causes a large negative distortion because the rays are bent outward to a large extent. Therefore, for example, by making this surface an aspherical surface, the degree of curvature of the rays is reduced and the distortion is Aberrations can be corrected.

In the case of a telecentric system with an almost infinite exit pupil, such as an objective lens for an endoscope, the focal length of the lens system behind the aperture stop is f2, and the optical axis direction of the principal ray entering the rear group is If the angle between is θ', then the image height I is I''
fzstnθ° is satisfied. Furthermore, the following equation is similarly satisfied for the entire system including the groups in front of the aperture.

I = f sinθ (1) where I
is the image height, θ is the angle between the principal ray incident on the first surface of the objective lens and the optical axis, and f is the focal length of the entire system.

Further, the following equation (11) holds true for an optical system without distortion.

I = f tan θ (ii) Furthermore, the distortion aberration DT is expressed by the following equation (ii).

DT (%) = ([-r.)/for X 100 (
il Here, I is the actual image height, and Io is the ideal image height without distortion.

Therefore, in the objective lens for an endoscope, formula (i).

(iil, (iil), the distortion aberration DT can be expressed by the following equation.

DT (%) = fcos θ-1)X100 In other words, the wider the angle of an endoscope objective lens, the more significant negative distortion, so-called barrel distortion, occurs.

By the way, in the case of an optical system in which the image height is expressed by f tan θ, the amount of peripheral light decreases at a rate of CO8'θ as θ increases. However, in the case of an optical system expressed by f sin θ, such as an objective lens for an endoscope, although the amount of peripheral light decreases at a rate of cos' θ, the peripheral image becomes smaller due to distortion, so the overall image becomes smaller due to both effects. It has the characteristic that the brightness of the surface is uniform. Therefore, if you try to remove distortion while keeping brightness uniform, 1
For example, the front group on the object side of the aperture is of the f tan θ type, and the rear group on the image side of the aperture is of the f sin θ type.

The entire system must satisfy the f tan θ type without distortion, and in order to achieve this configuration, it is preferable to use an aspherical surface.

When correcting distortion using an aspheric surface as described above,
The angle between the principal ray and the optical axis on the object side of the aspheric surface is 01. The angle between the principal ray and the light after being refracted by the aspherical surface is θ3. If the image height is I, then f tano type at the front side of the aperture and fs type at the rear side.
inθ type, and the entire system is f tinθ type, so the following formula (
) holds true.

1 = f tanθ1 (cypress) Also, since the rear side of the aspherical surface is of the fsinθ type, the relationship between ■ and 08 is expressed by the following formula fVl.

Iocsinθ2(v) Here, the front and back sides of this aspherical surface are respectively f' ta
I thought that it was a no type and an f sin θ type, but the same thing holds true even if you consider this with a lens with an aspherical surface as a boundary. In this case, f sin θ at the rear side of the aspherical lens
Since θ is satisfied, when fo is the focal length of the lens group behind the aspherical lens, and θ° is the angle between the principal ray incident on this lens group and the optical axis, the above formula (V) is It is expressed as the following equation (Vo).

I=f'sinθ'(V')Here, in order to remove the distortion aberration for each image height, the above equations by) and (V) must hold regardless of the image height, so these equations can be At the same time, you need to be satisfied. Therefore, the following equation (-) holds true.

sinew/lanθ+=k (@l where k
represents a constant.

Although the value of k is not necessarily constant over the entire image height,
The value may vary slightly for each image height, that is, each angle of view, as long as it does not cause any practical problems.It is possible to completely eliminate distortion.
This is because even if it is not done, there is no problem at all in practice.

Next, the shape of the aspherical surface will be specifically described. No. 19 (A
) Figure 19(B) shows the case when k is large, and Figure 19(B) shows the case when k is small, and the angle θ between the chief ray after refraction at the aspherical surface and the optical axis is the same in both cases.

If k increases from the center to the periphery, positive distortion will occur, and conversely, if k decreases, negative distortion will occur. Therefore, when negative distortion occurs, such as in the objective lens of an endoscope, it is preferable to use an aspherical shape as shown in FIG. 19(A), for example.

If an aspherical surface is provided on the first surface of the first lens (negative lens) of an objective lens for an endoscope, the refractive power of this surface will be stronger at the periphery of the lens, but the refractive power of the lens itself will be stronger at the periphery of the lens. It's getting weaker.

From the above, in the endoscope objective lens of the present invention, it is desirable that the value of k shown in the above formula (+W) satisfies the following condition (3).

+31 If the value of 0.1 < k < 1.5 is smaller than the lower limit value 0.1 of condition (3), distortion aberration cannot be corrected and the effect of using an aspheric surface cannot be obtained; When the value is greater than 1.5, distortion is removed, but other aberrations such as astigmatism become difficult to correct. In addition, the outer diameter of the first lunion becomes large, making it undesirable as an endoscope.
Furthermore, since the distortion does not necessarily have to be O, it is desirable from a practical standpoint that the above conditions be satisfied.

Furthermore, in the present invention, it is preferable that the following condition (4) is satisfied.

+41 0.0otf <IΔZ1゜l<0.4f but aZ=. is the amount of deviation in the optical axis direction from the reference spherical surface at the point where the principal ray for the maximum image height intersects with the aspheric surface provided for correction of the distortion aberration. Note that the reference spherical surface refers to a spherical surface that is in contact with an aspherical surface near the optical axis.

If ΔZ,0 becomes smaller than the lower limit value 0.001F of the above condition (4), the aspherical surface will hardly differ from the reference spherical surface, the effect of providing the aspherical surface will not be obtained, and distortion cannot be corrected. . On the other hand, when the upper limit value is greater than 0.4f, the effect of the aspherical surface is great, but it becomes difficult to correct aberrations other than distortion, and the outer diameter of the lens also becomes large, making it less compact. In order to remove distortion aberration, it is practically effective if the conditions are within the above range.

As mentioned above, astigmatism occurs when trying to correct distortion while maintaining the angle of incidence of rays on the image plane perpendicularly by providing one aspherical surface on the front and rear sides of the aperture diaphragm. do. Moreover, if an attempt is made to suppress this astigmatism, the angle of incidence of the light beam on the imaging surface may vary, making it impossible to correct the aberration satisfactorily. In such a case, an aspherical surface may be added to correct astigmatism and the like.

In an optical system, when the aperture or ray height is ρ and the half angle of view is ω, spherical aberration increases in proportion to β3, astigmatism,
The field curvature increases in proportion to ρω3. Therefore, it is a little difficult to suppress other aberrations by using only two aspherical surfaces after correcting the variation in the angle of incidence of light rays on the imaging surface and the distortion aberration.

Furthermore, it is even more desirable that the objective lens for an endoscope of the present invention satisfy the following conditions.

(5) f, <10f where f is the focal length of the field lens, and f is the focal length of the entire system.

By configuring the objective lens for an endoscope of the present invention as described above, the chief ray can be made to enter the image plane almost perpendicularly, and the occurrence of the color shading described above can be suppressed.

If the focal length of the field lens L1 is too large, not only will the total length of the lens system become long, but the outer diameter of the lens will also become large, which is inconvenient for use in endoscopes. Therefore, for compactness, it is desirable that the value of fr satisfies condition (5); in other words, if it deviates from condition (5), the overall length will become long and the lens diameter will become large, which is undesirable.

It is desirable that the objective lens for an endoscope of the present invention further satisfies the following condition (6).

f610. >0.2F However, Dl is the maximum air equivalent length between the aperture stop S and the field lens L.

Solid-state image sensors are also sensitive to infrared wavelengths, so leaving them as is will result in images with poor color reproducibility. In order to eliminate this drawback, it is usually necessary to provide an optical filter such as an infrared cut filter in the imaging optical path. The value in the above condition is the air equivalent length necessary for this purpose, and it is preferable that the above condition (6) is satisfied in order to provide an optical filter with a certain desired characteristic in the imaging optical path.
If this condition is not satisfied, it will be difficult to arrange the above-mentioned filter, etc.

In the objective lens for an endoscope of the present invention, the condition (51
, (61), it is more desirable to satisfy the following condition (7).

(710, 2f < D2 < 5f However, D2 is the air equivalent length from the field lens L to the imaging plane, and if the field lens L is integrated with the image sensor, the front side of the field lens L The air-equivalent length from the top of the surface to the imaging plane, if the field lens is separate from the image sensor, the field lens L
This is the air-equivalent length from the top of the rear surface of 2 to the imaging plane.

If the above value of glue is too small, it will not be possible to provide enough space to place an optical low-pass filter for moiré removal, and on the other hand, if it is too large, there will not be enough space to place an optical low-pass filter, etc. However, the overall length of the lens system becomes long, resulting in a problem that it cannot be made compact.

In the optical system of the present invention, if a parallel plane plate such as an optical filter is disposed in front of the field lens, that is, within the imaging lens or between the imaging lens and the field lens, this optical system It can be divided into a front group on the object side and a rear group on the image side with the parallel plane plate as the boundary. In addition, when two or more parallel plane plates are arranged,
Consider the parallel plane plate closest to the field lens as the boundary. The front group may be composed of a plurality of lenses including a positive lens and a negative lens in order to correct aberrations.

In that case, the first-order condition (81, +9).

(It is desirable to satisfy 101.

(8) fl > 0.3f +91 1f, I < 4f +101 0. :lf < f, < 5f but fl
is the focal length of the front group, ffi is the negative lens in the front group (
The focal length, f, of the independently existing negative lens (not including the negative lens in the cemented lens) is the focal length of the lens system excluding the negative lens in the front group.

Condition (8) defines the focal length f of the front group, and if the value of fI is too small, the air equivalent length between the front group and the rear group becomes short, and condition (8) is satisfied. Otherwise, it will not be possible to place the optical filter.

Condition (9) f at 0 condition (lO). If the value of and fp is too thick and exceeds the upper limit of the condition, the total length of the lens system and the outer diameter of the lens will become large, which is not preferable for use in endoscopes.

Further, in condition (10), if the value of fp deviates from the lower limit of the condition and becomes too small, there will be no air space for inserting the optical filter.

Further, Example 6, which will be described later, includes a portion where the rear group is almost afocal. Here, the afocal part in the rear group refers to a part where the incident chief ray is almost parallel to the optical axis, and when it exits, it is also almost parallel to the optical axis.
For example, in Example 6 (FIG. 6), the principal ray between the lenses L is approximately parallel to the optical axis (approximately 6°),
After exiting the field lens Lr, it becomes parallel to the optical axis again, and here the afocal optical system means that the lens L
.

and lens Lr. By doing this, even if an interference filter such as an infrared cut filter is inserted, the change in the angle of incidence of the light beam to the interference filter due to the image height becomes small, and color unevenness on one screen can be eliminated. I can do it.

Further, it is preferable that a lens system including a substantially afocal portion in the rear group as in the above-mentioned Example 6 be constructed so as to satisfy the following condition +(1).

(Ill f,,/fafl<-0,1 where f.,
fan is the focal length of the afocal system's positive power group and negative power group, respectively.

The condition (ill) defines what is generally called the afocal ratio; as this value approaches 0, the angle of incidence of the light ray to the rear group increases, and the angle of incidence of the light ray to the filter inserted between the front group and the rear group increases. The angle also becomes large.As a result, filters whose characteristics tend to change depending on the incident angle cannot be placed.On the other hand, when the absolute value of the afocal ratio mentioned above is large (
In this case, the incident light beam to the rear group decreases, which is convenient for reducing the diameter of the optical system, and conversely, the above afocal ratio becomes -0.
, when it approaches 0 rather than 1, the diameter of the lens becomes too large to fit into the tip of the endoscope.

Further, it is desirable that the following condition (12) be satisfied.

+121 -4Of < f,, <-0,2f This is,
With the rear group kept almost afocal, as lf,,l becomes large, the total length of the optical system tends to become longer, and -4O
When f > f, , the objective lens cannot enter the tip of the endoscope. On the other hand, the power of f0 is too strong f,...>-0
, 2f, it becomes difficult to correct aberrations.

[Example] Next, embodiments of the optical system for an image carrier according to the present invention will be described.

Example 1 f = 1.000, F/3.723, 2ω = 1
33.584″″I H= 1.0523 r1=■ M= 0.3189 Old= 1.88300
νt =40.78ra=0.6107 d2=0.2360 rs=3.6012 d3=0.3380 nt" 1.84666 "4=-1,1958 d4=0°0638 ",:CKI (aperture) ds" 0.0638 r6=-1,2107 d,=0.1913 n,=1.80518 rt=2.0604 d,=0.6696 r8=-o,8796 d,=0.0638 re=6.1125 d9 = o, 1658 rl. = 2.0098 dlo =0.8610 rz =-1,6842 d+ + = 0.1339 r1□ =■ lJ+z =0.2551 Q4= 1.51633 ns” 1.84666 1), = 1.51633 ny”1 .51633 Shi2=23.78 ν, , =25.43 ν, =64.15 νs ”23.78 Shiro -64,I5 ν, =64.15 rl, =■ d, , =0.4464 n, ”1.52000
v, =74.0Or14 =■ dz =0.255I n++=1.51633
1.19:64.15r16 = ■ d, 6 = 0.2572 r+s = 2.4259 d,, = 0.7334 n,,” 1.51633
v,, = 64.15rl? =-28,7961
(Aspherical surface) d+□ = 0.3079 r+a=c'' dlo =1.1926 r+z ''1.548
69 1/++=45.55r++=(fund) d,,” 0.2551 n,□=1-516
33 v, 2 = 64.15 rzo = l Aspheric coefficient P = 1.0000, E = 0.12395
x 10-'F = 0.58165 x 10-"f
,=4.368, D,=1.0213,
n2=1.2462f,=1.549, fn
=-0,692, fP=1.404f8=1.550
, 1A/fa =2.818, f, =4.
Z to 368,,,=0.02234,1. ,
, = 1.044809 Example 2 f = 1.000, F/3.955, 2ω =
I- ,8466G r,=-1,2209 d,=0.0642 rs=Flash (aperture) d,t=0.0642 rl,=-1,0589 ds"0.1926 rt" 1.8453 d,=0. 6739 ra=-0,8431 0, = 1.80518 n, = 1.51633 ν1 ν2 ν3 ν4 = 40.78 = 23.78 =25.43 =64.15 d, = 0.0642 re=7.6048 d-=0.1[169n-=1.84666
v, = 23.78 rho = 2.1084 dlo = 0.8665 n6 = 1.51633
v-=64.15r11 =-1,5072 dz=0.1348 ``1.=■ d, z = 0.2567 ny= 1.516
33 v-= 64.15r+z = flash dli = 0.4493 n1l= 1.52
00ro v, = 74.00[14=■ d,, =0.2567 n5=1.51633
v, =64.15r,, =c1°dls =0.2710r,, =2.56:3G (Aspherical surface) d16 = 0
．． 738I n,o = 1.51633
ν,. =64.15r+t =-117,1271 d,, =0.3087 r,a =OO dos =' 1.200:I nl 1 =
1.54869 1/l l = 45.551.
,=C+Q dle -0,25670,2=1.51633
ν1□=64.15r20 ” ■ Aspheric coefficient P = 1.0000, E = -0,81344
x 1O−2F = −0,46081x to−”f
F=4.869, D,=1.0400
, D2=1.253°f,=1.483
, fo=, -1,063, fP=1.257fs=
1.513, LA/f* =3.218,
fA=4.869ΔZ,,,=-0,01602,L
,,=1.049474 Example 3 f=1.000, F/3.936, 2ω=
119.436"I H= 1.0784 r, = 8.1850 (aspherical surface) d, = 0.3268 n, = 1.88300
v, =40.78ra : o, 5640 d, = 0.2418 ra"3.1632 ds" 0.3464 fi2 = 184666
1/a = 23.78r4 = -1,2492 d, = 0.0654 ``, =oo (aperture) d, = 0.0654 ra''-1,1727 d6: = o, 1961 ry = 1.9701 d, = 0.6863 rs = -0,8505 da = 0.0654 re" 6.8599 d, = 0.1699 rl0 = 1.9087 d,. = 0.8824 r++ = -1,6859 d++ = 0.1373 rI !: o.

dle = 0.2614 rth = 00 tLs = 0.4575 ns" 1.80518 vs = 25.43 j14 = 1.51633 ν4 = 64.15 n mini 1.84666 s" 23.78 na = 1.51633 ν, =64.15 n mini 1.51633 ν, =64.15 na= 1.52000 lea = 74.
00r14 =■ d+4 = 0.2614 no= 1.51633
ν, =64.15 rlS: ■ dls =0.2553 rls "2.3680 d,,"0.7516 nlo =1.51633
ν,. = 64.15r1a = -2:1.833
2 (Aspherical surface) d17 =0.3154 r,,==OO d,-=1.2222 n,1 =1.54869
V11=45.55ri11==QQ dle=0.2614 n,2=1.5163
3 C + a = 64.15r20 ” ω Aspheric coefficient (first surface) P = 1.0000, E = 0.27250
x 10-'F = 0.38296 x 10-2
．． G = -0,74369x 10-” (17th surface) P = 1.0000, E = 0.25928
xlO-'F = 0.32364 x lRO-'F, G = -0,83863x 10-'f
r”4.213, 0+=1.0384,
l1a=1.277Of,=1.605, f
n=-0,7, fp=1.446f,=1.531
, fA/fa =2.752, fA=4
．． 213ΔZ,,, =0.038713, 1
．． ,,=1.070526=0.2927,
Δ Zl+1=0.00206, IO=0.5
21822 Example 4 f = 1.000, F/3.821, 2ω=
119.978゜I H = 1.0949 rl = 7.7641 (non-I bundle surface) dI = 0.3
318 n+= 1.88300 v+ =
40.78r, = 0.5903 da"0.2455 ra = 3.2669 ds" 0.3517 nz = 1.84666
Va = 23.78r4 = -1,3331 d, = 0.0664 r5 = cx11 (aperture) d, = 0.0664 ra = -1,2398 d, "0.199I n, = 1.80518
v, =25.43r? = 1.7384 d, = 0.6967 n+=1 1633 ν4 = 64.15 renie o, 8023 d8 = 0.0664 re=7.1278 d, = 0.1725 n, = 1.84666r
+o = 1.7921 d+o = 0.8958 n6 = 1.5163
3r, = -1,6209 d+ 1 = 0.1393 r+z = ■ d12 = 0.2654 nt = 1.5+63
3r1. : ■ d, 3 = 0.4645 Q8 = 1.5200
0r14 = ■ d,, = 0.2654 j1g = 1.51
633r15 ” (Capital) d,, =0.2554 rla =2.5348 (Aspherical surface) d,, = 0.6172 n,, “1.
51633 5 =23.78 ν, =64. +5 ν, =64.15 ν, =74.00 ν, =64.15 ν,. =64.15 r+y =-35,5610 dl? =0.2346 rI8 :o.

d,, =1.2409 r+s = ■ (Lq =0.2654 n+ = 1.54869 ν+ + = 45.55I
2 = 1.51633 shi12 = 64.15rgo
= ■ Aspheric coefficient (first surface) P=1.01lOO, E=0.27612F = -0
,29431x 10-” (16th side) P = 1.0000, E = -0,1399
0xF = -0,37958x 10-”f, = 4
．． 608, D, = 1. []503f, =1.
461, f, = -0,740f, = 1.509
, fA/fa =3.054.

ΔZ,,, =-0,02779, L,, =1k =0
．． 2929, ΔZ 10: 0.00234 Example 5 4.847,
2 ω=97゜I H= 0.9810 r+=■ (aspherical surface) d, = 0.2973 n, = 1.88300 = 40.78 r2: 1.1731 da"0.3746 r3 = beauty r4 = ■ (Aperture) d4 = 0.1189 rs = 2.4507 d, = 0.4340 r6 = -4,4018 d, = 0.1189 rt = ■ d, = 0.8918 ra” (1) d, = 0. 8323 r, = 3.1928 d, = 0.7729 n, = 1.72916 n4 = 1.52000 jl, = 1.516341 ν, =54.68 ν, =74.00 ν5 = 64.15 r+o =- 1,0249 +Lo =0.2973 n6=1.84666
v6 =23.78= -1,9712 d,, =o,3iss r,, =4.2521 (Aspherical surface) d+a = 0.6421 ny= 1.7291
6 1) 7 = 54.68r13:CX:1 d+-= 0.8918 n-= 1.54869
va = 45.55'', 4 =OO d, 4:0.2378 ro, = 1.51633
ν, =64.15r16 = Flash aspheric coefficient (first surface) P = 1.0000. B=0.57318XlO-'
E=0.21885 xlO-', F=-0,3
4067xlO-2 (12th surface) P=-44,7174, E=0.26922 xlO-
'F=-0.43239xlO-', G=0
．． 23067 xlO-'f, = 5.832,
D,=1.538, D,=1.104f,=
2.325, f, = publication 564, fp=2
．． 21.8l f, = 2.431 fA/f8 = 2.399, fA = 5.83
2ΔZ,,, =-0,01688 1,,,=0.832708 k =0.4309, ΔZ 1°=0.
05164, l0=0.850596 Example 6 f=1.000, F/3.635.

I H = 1.2017 r, =oo (aspherical surface) d+ = 0.3277 r2 = 0.5828 d, = 0.7138 rs = -3,7267 d, = 0.3642 r, = -1,27: 14 d, = 0.0364 rS = oo (aperture) ds = 0.1092 rs = -1,8059 d, = 0.1821 r,: 1.5570 d, = 0.6336 n, = 1.51633 1/ 4 I64.15n
a=1.84666 i,=1.84666 n+=1.80610 2ω=113.602' ν, I40.95 νl I23.78 ν3 I23.78 ra=-1,2178 d,=0.0728 re=6 .2187ds”0.5462ns=1.6968Or
ho = -1,8999 d,. =0.0728 rth=00 d, =1.0925 na=1.52000r
l=OO d1□ = 0.2986 r+s =-2,2076 d+-=0.2185 nv=1.84666r,
, = 43.3086 d14 = 0.4224 nm = 1.51633r
+s = -2,5432 dos = 0.3038 rll = 2°3477 (aspherical surface) dts = 0.619I Q, = 1.772
5Or, 7 = flash d, t = 1.0925 n+o = 1.
54814 = 55.52 = 74.00 = 23.78 = 64.15 = 49.66 C1゜I45.78 r breath, I00 d,, =0.2913 n,, =1.51633
C,,=64.15r19” ■ Aspheric coefficient (first surface) P=1.0000, B=0.23517, E
=O, 19990F=-0,16297, G=0.43
056 xlO-' (16th surface) P=-4,3010, E=-0, I2093X10-'
F=0.66784 x 10-”fF=3.0
39, D,= 1.09, D,=
1.247f,=t,oat,fl,=-1
,1,fP=1.417f,p/fa,=-0,47
7,f,n=-6,365,f,,=3.039fm=
1.838, fA/fa = 1.653,
fa=3.039ΔZ,,, =-0,03698,1
,,,=0.935705k=0.4535,
ΔZ 1゜: o, 13826, Io
= Mouth, [182032 Example 7 f = 1.000, F/3.826,
2 (,1= 120'I H= 1.0963 r+ = 7.3216 (aspherical surface) d, = 0.3322 rz=0.5839 d2= 0.2458 rs=3.2317 da= 0.3522 r, =-1,3470 d4=0.0664 rs=oo (aperture) ds=0.0664 rs=-1,2449 da=0.1993 r, =1.6804 dy=0.6977 rs"-0,7957 d , = 0.0664 r, -= 7.0988 d, = 0.1728 "1° = 1.7664 d,, = 0.8970 rll = -1,619ti 1), = 1.88300 nm = 1.84666 nm=1.80518 n4=1.51633 ns=1.84666 nm=1.51633 = 40.78 I23.78 = 25.43 = 64.15 = 23.78 I64.15 d,, =0.1395 r Eyes = ■ d,, = 0.2658 n, = 1.516
33r13”00 d+-=0.4651 n-=1.5200Or,
4 = (capital) d, 4 = 0.2658 mouth, = 1.51633
r,, =o.

d,, =0.2543 r,, =2.5285 (aspherical surface) d,, =0.6264 n,, =1.51
&33r, y = -54,0626 (aspherical surface) d,,
=0.2414 rllll = ■ d,, =1.2425 n,, ”1.54
869th r = ■ d,, = 0.2658 n,, = 1.
51633ν, =64.15 νa”74.00 ν, =54.15 ν, .=64.15 ci,, =45.55 ν1□= 64.15 r2゜ = ■ Aspheric coefficient (first surface) P =1.0OOOO, E=0.33020 xlO-'
F = -0,78286X 10-" (16th side) P = 1.0000. E = -0,14437X10
F = -0,24025x 10-” (17th surface) P = 1.0000, E = 0.992
95 x 10-”F = -0,84124x 1
0-”fr=4.696, D,=1.05
04, D,=1.2190fl=1.
．． 458, fr,=-0,736,f,=
1.447L=1.512, fA/fa
=3.106, fA=4.696ΔZ,,
, =-0,02557, L, , =1.101719
k = 0.2961, ΔZ s. = 0.
00272, Io=0.545383 Example 8 f=1.000, F/4.03+, 2ω=
120.55゜I H= 1.1371 r, = 3.8935 (aspherical surface) d+ = 0.3446 n1= 1.88300
v+ = 40.78r2: 0.6525 d, = 0.3170 "3 = -13,5877 d 3 = 0, 3653 n 2 = 1, 8
4666r4 = -1,5462 d4 = 0.0689 r5 = cX3 (aperture) ds = 0.0689 r, = -1,3756 da = 0.2068 ns" 1.8051
8r, = 2.5197 d, = 0.7236 n, = 1.51633
rs=-0,8700 d, = 0.0689 r, = 5.4855 (aspherical surface) cL= 0.1792 n5= 1.84666
r+o = 1.8708 d, o = 0.9304 n, = 1.516
3:1r1+ =-1,7408 d,, = 0.1203 r+z=c'' ν2 ν5 = 23.78 = 25.4''( = 64.15 =64.15 rl, = ■ d, 3''0.4824 n,=1.52000
v, =74.00r14:QQ d,, =0.2757 n,”1.51633
v, =64. t5r+s = ■ dlg =0.2117 rla ”2-3721 (aspherical surface) d+s =0.8 (112neo =1.5163
3 si+o=64.15rlt=20.6589 d, 7 =0.3086 rllll=■ d,, =1.2888 n,, =1.548
69 νz=45.55r+* =■ d,, ”0.2757 n,2 =1.5163
:l si, z=64. l5r2G::QQ Aspheric coefficient (first surface) p = t, oooo.

E=0.10301 F=-0,76500X10-' G=0.1
2298xlO-'a+z = 0.2757 n
, = 1.51633 = 64.15 (9th surface) P = 1.0000, E = -0,149
62x 10-'F = O, 12839x 10-' (16th surface) P=1.0000. E=-〇, 14686x
IQ-'F = 0.10545 x 10-"fr
=5.114, D, =1.0130, D*
=1.3226f, =1.532, fn=
-0,934, fP=1.581fs=1536
, fA/fs =3.329, fA=
5.114ΔZ, ,, =-0,01943,1,
,,=1.097019k=0.3956,
ΔZ10=0.01318, Io=
0.652576 but rl+r7. ... is the radius of curvature of each lens surface, dl, d2. ... is the wall thickness and air spacing of each lens, nI.

nt,... is the refractive index of each lens, and 1. C2. ...
is the Atsube number of each lens.

Example 1 has a lens configuration shown in FIG.

By arranging a lens component having positive power in front of the diaphragm as in this embodiment, it is possible to satisfactorily correct comatic aberration and chromatic aberration of magnification. This is because there is only a negative lens in front of the diaphragm, which alleviates the optically asymmetrical configuration, and in particular allows correction of the lower coma. Furthermore, in order to correct chromatic aberration of magnification, it is advantageous to arrange a positive lens component in front of the diaphragm, and this positive lens component may be a cemented lens.

Embodiment 2 has a lens configuration shown in FIG.

In Examples 1 and 2, each field lens is provided with an aspherical surface to satisfactorily correct variations in the angle of incidence of light rays on the imaging plane. Note that Example 1 uses a field lens and a CC
Since D is a separate body, an aspherical surface is provided on the rear side of the field lens.

Further, in the second embodiment, an aspherical surface is provided on the front side of the field lens.

Examples 3 to 6 have the configurations shown in FIGS. 3 to 6, in which one aspherical surface is provided in each of the lens group on the front side and the lens group on the rear side of the aperture.

In the third embodiment, the field lens and the first surface of the lens system are each made into an aspherical surface to correct the incident ray angle to the imaging surface and distortion aberration.

Similarly, in the fourth embodiment, aspherical surfaces are provided in the lens groups before and after the aperture in order to correct the incident ray angle on the image-defining surface and the distortion aberration, but the locations of the aspherical surfaces are different from those in the third embodiment. Embodiment 6 Example 5 is an objective lens for an endoscope that can be used for side viewing or strabismus. In other words, instead of the flat f-square plate placed in front of the diaphragm, a field conversion prism such as a Taha prism having the same optical path length may be used.

Embodiment 6 is a lens system that includes an almost afocal part in the lens group after the aperture, and the workability of the lens is improved by making the concave lens in the lens group after the aperture a cemented lens. There is.

In addition, in Examples 5 and 6, the field lens using an aspherical surface is integrated with the photographing element to reduce the distance between the field lens and the imaging element and shorten the overall length, thereby reducing the height of the ray of the field lens and making it possible to reduce the diameter. . On the other hand, in other embodiments, the field lens and the image sensor are separate bodies with an air gap between them, so that this gap can be changed during focus adjustment during assembly. Moreover, due to this change in the interval, the angle of incidence of the principal ray on the photographing element does not change, and the angle of view does not change much.

Examples 7 and 8 use three aspherical surfaces in the configurations shown in FIGS. 7 and 8, respectively, and are able to correct the angle of incidence of the rays on the imaging surface and distortion, as well as astigmatism. It has been corrected.

In the seventh embodiment, since the field lens is separate from the image sensor, aspherical surfaces are provided before and after the field lens.

In Example 8, one side of the field lens is aspherical,
Another aspherical surface was provided in the lens group behind the aperture. This improved the workability of the field lens.

In these lens systems, the parallel plane plate installed in the lens system is used in order from the object side to the solid-state image sensor, in which an infrared cut filter and a mosaic type solid-state image sensor are used to cut light in the infrared wavelength range. This is an optical low-pass filter to prevent moiré. Here, the infrared cut filter may be an interference filter or an absorption filter, or may be an absorption filter coated with a coating.6 Furthermore, it may be a cut filter for cutting out light at wavelengths other than those for normal observation.

Further, the positions of the optical low-pass filter and the optical filter may be reversed, or a combination of each filter may be arranged.

It may also be a cut filter for blocking laser light during laser light therapy.

Of course, if these filters are not needed, there is no need to provide them, and it is sufficient to install filters whose characteristics match the needs.

Note that the present invention is fully applicable not only to mosaic-type solid-state imaging devices but also to one-plane sequential-type solid-state imaging devices, other imaging devices, ordinary fiberscopes, and the like.

In addition, it is possible to use materials such as plastic or optical glass for the aspherical lens, but considering cost efficiency and resistance such as chemical resistance required for an objective lens for an endoscope, glass may be molded. It is desirable to process and manufacture it.

[Effect of the invention 1] The endoscope objective lens of the present invention can sufficiently suppress the occurrence of color shading even when a mosaic type solid-state image sensor is combined, and further suppress the occurrence of distortion and other aberrations. It is a compact, wide-angle lens system with a short overall length and excellent performance, with various aberrations well corrected.

[Brief explanation of drawings]

1 to 8 are cross-sectional views of Examples 1 to 8 of the objective lens for an endoscope of the present invention, and FIGS. 9 to 16 are aberration curve diagrams of Examples 1 to 8, respectively. , Fig. 17 is a diagram showing the basic configuration of the present invention, Fig. 18 is a diagram explaining the shape of the aspherical surface, Fig. 19 is a diagram showing the relationship between the aspherical surface and the chief ray, and Fig. 20 is a diagram showing the shape of the aspherical surface. It is a figure which shows the light ray when reverse-tracing is carried out with the objective lens for.

Claims (1)

[Claims] It is composed of an entire group with negative refractive power and a rear group with positive refractive power, with an aperture diaphragm in between, and a principal ray is arranged perpendicularly to the image plane in the vicinity of the image formation plane of the rear group. An endoscope objective lens having a field lens arranged so that the field lens of the rear group is incident, an aspherical surface provided near the field lens of the rear group, and satisfying the following conditions (1) and (2). (1) 0.5<f_A/f_a<10 (2) 0.005f<|ΔZ_m_a_x|<0.15
f However, f is the focal length of the entire system, f_A is the focal length of the aspherical lens provided near the field lens, f_a
is the composite focal length of the rear group, and ΔZ_m_a_x is the amount of deviation in the optical axis direction from the reference spherical surface at a point on the aspherical surface of the principal ray heading toward the maximum image height.