JPH04218011A - Objective optical system of endoscope - Google Patents
Objective optical system of endoscopeInfo
- Publication number
- JPH04218011A JPH04218011A JP2269483A JP26948390A JPH04218011A JP H04218011 A JPH04218011 A JP H04218011A JP 2269483 A JP2269483 A JP 2269483A JP 26948390 A JP26948390 A JP 26948390A JP H04218011 A JPH04218011 A JP H04218011A
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- optical system
- positive
- distortion
- aberration
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- 230000003287 optical effect Effects 0.000 title claims abstract description 56
- 238000010030 laminating Methods 0.000 claims 1
- 230000004075 alteration Effects 0.000 abstract description 73
- 230000000694 effects Effects 0.000 abstract description 3
- 230000007423 decrease Effects 0.000 abstract 1
- 230000003247 decreasing effect Effects 0.000 abstract 1
- 210000001747 pupil Anatomy 0.000 description 36
- 206010010071 Coma Diseases 0.000 description 10
- 238000010586 diagram Methods 0.000 description 5
- 238000003384 imaging method Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 2
- 206010073261 Ovarian theca cell tumour Diseases 0.000 description 1
- 201000009310 astigmatism Diseases 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 210000000621 bronchi Anatomy 0.000 description 1
- 239000006059 cover glass Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000001839 endoscopy Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 210000002429 large intestine Anatomy 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000005304 optical glass Substances 0.000 description 1
- 210000000056 organ Anatomy 0.000 description 1
- 208000001644 thecoma Diseases 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Lenses (AREA)
- Endoscopes (AREA)
- Instruments For Viewing The Inside Of Hollow Bodies (AREA)
Abstract
Description
【発明の詳細な説明】 〔産業上の利用分野〕 本発明は、内視鏡対物光学系に関するものである。[Detailed description of the invention] [Industrial application field] The present invention relates to an endoscope objective optical system.
従来、内視鏡用対物レンズとしては、第１１図に示すよ
うなレトロフォーカスタイプのもの例えば特開昭４９−
１２１５４７号公報に記載されたものが知られている。Conventionally, as an objective lens for an endoscope, a retrofocus type objective lens as shown in FIG.
The one described in Japanese Patent No. 121547 is known.
このレトロフォーカスタイプの対物レンズは、絞りＳを
はさんで物体側に凹のレンズ群Ｉを、また像側に凸のレ
ンズ群ＩＩを配置したものである。この対物レンズは、
絞りＳより前に配置した凹のレンズ群Ｉで主光線Ｐを強
くまげて広角化を可能にし、更に絞りＳより後方の凸の
レンズ群ＩＩにより像面に入射する主光線Ｐが光軸に平
行になるようにしてイメージガイドＧに光束が入射する
ようなテレセントリックタイプとしている。This retrofocus type objective lens has a concave lens group I on the object side and a convex lens group II on the image side with an aperture S in between. This objective lens is
A concave lens group I placed in front of the aperture S strongly bends the principal ray P, making it possible to widen the angle of view, and a convex lens group II located behind the aperture S directs the principal ray P incident on the image plane to the optical axis. It is a telecentric type in which the light beam is incident on the image guide G in parallel.
このようにイメージガイドＧに垂直に光束を入射せしめ
ることによってイメージガイドＧ内での光の損失を少な
くすることが出来る。By making the light beam perpendicularly enter the image guide G in this manner, the loss of light within the image guide G can be reduced.
また単板カラー固体撮像素子を用いたビデオスコープで
は、色シェーディング等の問題を回避するため、テレセ
ントリックの条件を満たしていることが要求される。こ
のように内視鏡対物レンズは、テレセントリックの条件
を満たしていることが要求されるが、そのために内視鏡
対物光学系においては、大きな歪曲収差が発生する。Furthermore, a videoscope using a single-plate color solid-state image sensor is required to satisfy telecentric conditions in order to avoid problems such as color shading. As described above, the endoscope objective lens is required to satisfy the telecentric condition, but this causes large distortion aberration in the endoscope objective optical system.
歪曲収差は、入射瞳への主光線の入射角θ１に依存する
。又像高は、入射角θ１の関数である。Distortion depends on the angle of incidence θ1 of the chief ray on the entrance pupil. Further, the image height is a function of the incident angle θ1.
ここで歪曲収差をＤ（θ１）、像高をＨ（θ１）とする
と、歪曲収差Ｄ（θ１）は、次の式（ｉ）にて定義され
る。Here, assuming that the distortion aberration is D (θ1) and the image height is H (θ1), the distortion aberration D (θ1) is defined by the following equation (i).
ここでｆは対物光学系の焦点距離である。Here, f is the focal length of the objective optical system.
通常Ｈ（θ１）は、Ａ（θ１）をθ１の関数としてＨ（
θ１）＝ｆＡ（θ１）と云う形で表現されることが多い
。このＨ（θ１）＝ｆＡ（θ１）を式（ｉ）に代入する
と、次の式（ｉｉ）が導かれる。Normally, H(θ1) is calculated using A(θ1) as a function of θ1.
It is often expressed in the form θ1)=fA(θ1). By substituting this H(θ1)=fA(θ1) into equation (i), the following equation (ii) is derived.
このように、歪曲収差と主光線の入射角との関係は、像
高と主光線の入射角との関係を決める関数Ａ（θ１）の
みで定まり、この関数は、光学系の歪曲特性を示してい
る。In this way, the relationship between the distortion aberration and the angle of incidence of the principal ray is determined only by the function A (θ1) that determines the relationship between the image height and the angle of incidence of the principal ray, and this function indicates the distortion characteristics of the optical system. ing.
一般に、この関数Ａ（θ１）は、瞳の結像関係のみに依
存し、それは、近軸瞳倍率への依存と、瞳の結像におけ
る収差（瞳を物点として追跡した時の正弦条件不満足量
と球面収差）への依存の二つに分類される。瞳の収差が
ない場合は、つまり対物光学系の全像高にわたって瞳の
正弦条件が満足されていて、かつ入射瞳および射出瞳に
おける瞳の球面収差がないと仮定すると、Ａ（θ１）は
、全系の近軸瞳倍率のみをパラメーターとして一意に定
まる。つまり近軸瞳倍率をβＥとすると、下記の式（ｉ
ｉｉ）が得られる。In general, this function A(θ1) depends only on the pupil imaging relationship, and it is dependent on the paraxial pupil magnification and the aberration in the pupil imaging (dissatisfaction of the sine condition when tracking the pupil as an object point). It is classified into two types: dependence on the amount and spherical aberration). When there is no pupil aberration, that is, assuming that the pupil sine condition is satisfied over the entire image height of the objective optical system and there is no pupil spherical aberration at the entrance and exit pupils, A(θ1) is It is uniquely determined using only the paraxial pupil magnification of the entire system as a parameter. In other words, if the paraxial pupil magnification is βE, then the following formula (i
ii) is obtained.
テレセントリック条件を保つためには、内視鏡の対物光
学系は、近軸瞳倍率の絶対値｜βＥ｜を十分大きくする
必要がある。In order to maintain telecentric conditions, the objective optical system of the endoscope needs to have a sufficiently large absolute value |βE| of the paraxial pupil magnification.
｜βＥ｜が十分に大きいと、式（ｉｉｉ）よりＡ（θ１
）■ｓｉｎθ１と近似でき、歪曲収差は、次のようにな
る。If |βE| is sufficiently large, A(θ1
) ■ sin θ1, and the distortion aberration is as follows.
したがってθ１が増加するに伴って、負の歪曲収差が増
大する。Therefore, as θ1 increases, negative distortion increases.
このように、テレセントリック条件を満たすことを要求
される内視鏡の対物光学系では、瞳の近軸関係に起因す
る歪曲収差が支配的である。この歪曲収差を補正するた
めには、瞳の結像における正弦条件を、強制的に大きく
崩す必要がある。As described above, in the objective optical system of an endoscope that is required to satisfy the telecentric condition, distortion caused by the paraxial relationship of the pupils is dominant. In order to correct this distortion, it is necessary to forcibly break the sine condition for pupil imaging to a large extent.
内視鏡の光学系において、歪曲収差を補正する場合、瞳
の結像における正弦条件の不満足度を増大させるために
物体の結像における非対称性収差、つまり非点収差とコ
マ収差が直接影響を受けることになる。また対物光学系
をコンパクトにし、広角にする場合も、諸収差特に軸外
収差の補正が困難になる。そのため、内視鏡の対物光学
系においては、広角にし、歪曲収差を十分減少させかつ
光学系をコンパクトに（特に外径を小さく）した時に、
いかに歪曲収差以外の諸収差を良好に補正するかが設計
上のポイントである。これら要件を同時に満足させなけ
れば、内視鏡対物光学系を実現し得ない。In the optical system of an endoscope, when correcting distortion aberration, asymmetric aberrations in object imaging, that is, astigmatism and coma aberration, have a direct effect, increasing the degree of dissatisfaction with the sine condition in pupil imaging. I will receive it. Also, when the objective optical system is made compact and wide-angle, it becomes difficult to correct various aberrations, especially off-axis aberrations. Therefore, in the objective optical system of an endoscope, when the angle is made wide, distortion aberration is sufficiently reduced, and the optical system is made compact (particularly with a small outer diameter),
The key point in design is how to properly correct various aberrations other than distortion. Unless these requirements are simultaneously satisfied, an endoscope objective optical system cannot be realized.
非球面を用いて歪曲収差と他の収差を補正した対物レン
ズの例として特開昭５７−１７３８１０号公報に記載さ
れたものがある。しかしこの対物レンズは画角が５６°
とせまいにもかかわらず歪曲収差は完全には補正されて
いない。An example of an objective lens in which distortion and other aberrations are corrected using an aspheric surface is disclosed in Japanese Patent Laid-Open No. 173810/1983. However, this objective lens has an angle of view of 56°.
Despite its narrowness, distortion is not completely corrected.
また、第１２図に示す特開昭６０−１６９８１８号公報
に記載された光学系は、絞りを挟んで負のパワーを持つ
前群と正のパワーを持つ後群とにて構成され、前群に少
なくとも１面非球面を導入することにより、テレセント
リックな光学系で歪曲収差を補正したものである。しか
し上記公報に記載されている実施例の光学系は、コンパ
クトではなく、レンズ枚数も非常に多く好ましくない。Furthermore, the optical system described in Japanese Patent Application Laid-Open No. 169818/1983 shown in FIG. By introducing at least one aspherical surface into the lens, distortion is corrected using a telecentric optical system. However, the optical system of the embodiment described in the above publication is not compact and has a large number of lenses, which is not preferable.
また第１３図に示す特開昭６１−１６２０２１号公報に
記載されている光学系は、明るさ絞りの前後に少なくと
も１面以上の非球面を用いたテレセントリックで歪曲収
差が補正されているが、前記の特開昭６０−１６９８１
８号公報の光学系と同様に、光学系がコンパクトでなく
かつ用いている非球面は、球面からのずれ量が非常に大
きく製作が困難であり、実用的ではない。Furthermore, the optical system described in JP-A-61-162021 shown in FIG. 13 is telecentric and uses at least one aspherical surface before and after the aperture stop to correct distortion. The above-mentioned Japanese Patent Application Publication No. 60-16981
Similar to the optical system of Publication No. 8, the optical system is not compact and the aspherical surface used has a very large deviation from the spherical surface, making it difficult to manufacture and not practical.
本発明の目的は、広角で歪曲収差が良好に補正され同時
に他の諸収差も補正され非球面レンズの加工性がよくか
つレンズ枚数の少ないコンパクトな内視鏡対物光学系を
提供することにある。SUMMARY OF THE INVENTION An object of the present invention is to provide a compact endoscope objective optical system that has a wide angle, satisfactorily corrects distortion aberration, simultaneously corrects other aberrations, has good workability for aspherical lenses, and has a small number of lenses. .
本発明の内視鏡対物光学系は、物体側より順に、負の屈
折力を有する第１群と、正の屈折力を有する第２群と、
明るさ絞りと、その後方の正の屈折力のレンズと負の屈
折力を有するレンズとを貼合わせたレンズ群とを含み全
体として正の屈折力を有する後群とからなり、少なくと
も１面非球面を有するものである。The endoscope objective optical system of the present invention includes, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power,
It consists of an aperture diaphragm and a rear group having a positive refractive power as a whole, including a lens group behind the aperture diaphragm in which a lens with a positive refractive power and a lens with a negative refractive power are laminated together, and at least one surface is non-conductive. It has a spherical surface.
光学系の近軸瞳倍率βＥが無限大であり、入射瞳と射出
瞳に球面収差のない光学系について、歪曲収差と瞳の正
弦条件不満足量との関係について述べる。For an optical system in which the paraxial pupil magnification βE is infinite and there is no spherical aberration in the entrance pupil and the exit pupil, the relationship between distortion aberration and the amount of unsatisfactory sine condition of the pupil will be described.
第９図において、像高Ｈ（θ１）は、Ａ（θ１）をθ１
＝０°における微係数が１である任意の関数としてＨ（
θ１）＝ｆＡ（θ１）と表現される。この関係と無限遠
物点における正弦条件不満足量の定義式Ｈ（θ１）−ｆ
ｓｉｎθ１とから、像面から物体面へ向かっての主光線
の追跡により求められる瞳の正弦条件不満足量は、ｆ［
Ａ（θ１）−ｓｉｎθ］となる。In Fig. 9, the image height H(θ1) is calculated by dividing A(θ1) by θ1
H(
It is expressed as θ1)=fA(θ1). This relationship and the defining formula for the amount of dissatisfaction with the sine condition at an object point at infinity H(θ1)-f
From sin θ1, the amount of dissatisfaction with the sine condition of the pupil obtained by tracing the principal ray from the image plane to the object plane is f[
A(θ1)−sinθ].
これをｆｓｉｎθ１で割って規格化したものをＳ（θ１
）とおくと、Ｓ（θ１）は次の式（■）になる。This is divided by fsinθ1 and normalized to S(θ1
), S(θ1) becomes the following equation (■).
歪曲収差のない光学系では、Ａ（θ１）＝ｔａｎθ１で
あるから、βＥＴが無限大であるテレセントリックな光
学系では、歪曲収差を完全に除去するためには、Ｓ（θ
１）が次のようになるように瞳の正弦条件不満足量を発
生させれば良い。In an optical system without distortion, A(θ1) = tanθ1, so in a telecentric optical system where βET is infinite, S(θ
It is sufficient to generate the pupil sine condition dissatisfaction amount so that 1) becomes as follows.
進にＳ（θ１）がわかっていれば、Ａ（θ）が求められ
、歪曲収差Ｄ（θ１）を求めることが出来る。つまりＤ
（θ１）は次の式（■）のように表わされる。If S(θ1) is known in advance, A(θ) can be found and the distortion D(θ1) can be found. In other words, D
(θ1) is expressed as the following equation (■).
上述と同様にして、像面から物体面に向けての主光線追
跡によって求まる前群、後群単独での瞳の正弦条件不満
足量を規格化したものを求めることが出来る。その値を
夫々Ｓ１（θ１）、Ｓ２（θ１）とすると、Ｓ（θ１）
、Ｓ（θ１）、Ｓ２（θ１）の間には次の関係がある。In the same manner as described above, it is possible to obtain the normalized amount of unsatisfactory pupil sine condition for the front and rear groups alone, which is determined by principal ray tracing from the image plane to the object plane. If the values are respectively S1 (θ1) and S2 (θ1), then S(θ1)
, S(θ1), and S2(θ1) have the following relationship.
この関係からＳ１（θ１）、Ｓ２（θ１）がわかってい
ればＳ（θ１）を求めることが出来る。From this relationship, if S1 (θ1) and S2 (θ1) are known, S(θ1) can be found.
実際の光学系においては、入射瞳と射出瞳に球面収差が
存在するためその影響も考慮しなければならない。歪曲
収差が物点位置によって多少変動するのはこの影響であ
り、Ｓ１（θ１）、Ｓ２（θ１）も瞳の球面収差を考慮
した形にするのが望ましい。In an actual optical system, spherical aberration exists in the entrance pupil and the exit pupil, so its influence must also be taken into consideration. This is the reason why the distortion aberration varies somewhat depending on the object point position, and it is desirable that S1 (θ1) and S2 (θ1) also take into account the spherical aberration of the pupil.
入射瞳の球面収差を考慮したＳ１（θ１）を求めるため
には、明るさ絞りの中心を物点とし物体面を仮想絞りと
して明るさ絞りから前群に向かって第９図の矢印Ａ方向
に光線追跡すれば良い。この時のＳ１（θ１）は次の式
（■）のように定義出来る。In order to obtain S1 (θ1) that takes into account the spherical aberration of the entrance pupil, the center of the aperture diaphragm is the object point, the object plane is the virtual diaphragm, and the direction from the aperture diaphragm toward the front group is in the direction of arrow A in Fig. 9. Just do ray tracing. S1 (θ1) at this time can be defined as shown in the following equation (■).
ここでθ２は、絞り位置における主光線の光軸に対する
角度であり、絞りが硝材中にある場合は、空気中に換算
する。〓１は明るさ絞りから物体に向かって（矢印Ａ方
向）の前群の近軸瞳倍率である。ｌ１は物体面から近軸
入射瞳までの距離である。ｌ１（θ１）は物体面から軸
外の入射瞳までの距離である。■１、■１（θ１）は物
体面を基準にして矢印Ａ方向を正とする。Here, θ2 is the angle of the chief ray with respect to the optical axis at the aperture position, and when the aperture is in a glass material, it is converted into air. 〓1 is the paraxial pupil magnification of the front group from the aperture stop toward the object (in the direction of arrow A). l1 is the distance from the object plane to the paraxial entrance pupil. l1 (θ1) is the distance from the object plane to the off-axis entrance pupil. ■1, ■1 (θ1) assumes that the direction of arrow A is positive with respect to the object plane.
同様にしてＳ２（θ１）も、明るさ絞りの中心を物点と
し、像面を仮想絞りとして、明るさ絞りから後群に向か
って第９図の矢印Ｂの方向に光線追跡を行なえば求める
ことが出来る。この場合、前群の時と光線追跡方向が逆
になるため、Ｓ２（θ１）は次の（■）のように定義で
きる。Similarly, S2 (θ1) can be found by taking the center of the aperture diaphragm as the object point and the image plane as a virtual diaphragm, and tracing the rays from the aperture diaphragm toward the rear group in the direction of arrow B in Figure 9. I can do it. In this case, since the ray tracing direction is opposite to that in the front group, S2 (θ1) can be defined as (■) below.
ここでθ３は、像面から出射する主光線の光軸に対する
角度で、空気中の値に換算したものである。〓２は明る
さ絞りから像面に向かって（矢印Ｂ方向）の近軸瞳倍率
である。■２は像面から軸外の射出瞳までの距離である
。■２、ｌ２（θ１）の符号は、像面を基準にして矢印
Ｂ方向を正とする。Here, θ3 is the angle of the principal ray emitted from the image plane with respect to the optical axis, and is converted to a value in air. 〓2 is the paraxial pupil magnification from the aperture stop toward the image plane (in the direction of arrow B). (2) 2 is the distance from the image plane to the off-axis exit pupil. (2) The sign of 2, l2 (θ1) is positive in the direction of arrow B with the image plane as a reference.
尚、θ１、θ２、θ３の符号は、物体側から主光線を入
射させた時、絞りより前では進行方向が光軸に近くなる
方向の場合を負、絞りより後方では進行方向が光軸から
離れる方向の場合を負とする。The signs of θ1, θ2, and θ3 are negative when the principal ray is incident from the object side, if the direction of travel is close to the optical axis before the aperture, and negative if the direction of travel is close to the optical axis behind the aperture. In the case of moving away, the value is negative.
前群、後群共に負の歪曲収差を補正する方向に正弦条件
を崩す時は、Ｓ１（θ１）、Ｓ２（θ１）は共に正にな
り、式（■）により定まるＳ（θ１）も正になる。When breaking the sine condition in the direction of correcting negative distortion for both the front and rear groups, S1 (θ1) and S2 (θ1) both become positive, and S (θ1) determined by equation (■) also becomes positive. Become.
前記式（■）、（■）より瞳の正弦条件がほぼ満たされ
ている場合でも瞳の球面収差の発生量つまり式（■）、
（■）中の■１／ｌ１（θ１）又はｌ２（θ１）／■２
を変化させることによってＳ（θ１）を大きくすること
が出来る。絞りより後の後群の条件を一定にし前群に対
し絞りから物体側へ光線追跡を行なったとき、第１図に
示すような本発明のレンズ系では、明るさ絞りと第１群
との間に正の群を設けたことにより、第１群への光線の
入射角が小さくなり、θ１を一定に保つためには、第１
群のパワーを強くする必要がある。このように第１群の
パワーを強くすると、この群で発生する瞳の球面収差が
大きく式（■）のうちの■１／ｌ１（θ）を大にするこ
とが出来る。この値を大にすればＳ（θ１）が大になり
、歪曲収差を減少させることが出来る。From the above formulas (■) and (■), even when the pupil sine condition is almost satisfied, the amount of spherical aberration of the pupil, that is, the formula (■),
■1/l1(θ1) or l2(θ1)/■2 in (■)
By changing S(θ1), it is possible to increase S(θ1). When the conditions of the rear group behind the diaphragm are constant and rays are traced from the diaphragm to the object side for the front group, in the lens system of the present invention as shown in Fig. 1, the relationship between the aperture diaphragm and the first group is By providing a positive group in between, the angle of incidence of the light ray to the first group becomes small, and in order to keep θ1 constant, the first
We need to strengthen the power of the group. By increasing the power of the first group in this way, the spherical aberration of the pupil generated in this group becomes large, and it is possible to increase 1/l1(θ) in the equation (■). If this value is increased, S(θ1) becomes larger, and distortion can be reduced.
更に本発明の光学系で■１／ｌ１（θ１）を大きくする
ためには、次の条件（１）を満足することが望ましい。Furthermore, in order to increase 1/l1 (θ1) in the optical system of the present invention, it is desirable to satisfy the following condition (1).
（１）｜ｆ１／ｆ｜＜５
ただしｆ１は第１群の焦点距離、ｆは全系の焦点距離で
ある。(1) |f1/f|<5 where f1 is the focal length of the first group, and f is the focal length of the entire system.
条件（１）の上限を越えると式（■）の■１／ｌ１（θ
１）を大きくできないため歪曲収差の補正量が少なくな
る。If the upper limit of condition (1) is exceeded, ■1/l1(θ
1) cannot be increased, so the amount of distortion correction becomes small.
またθ１が等しい時は、第１群の入射角が小さい方が■
１／ｌ１（θ１）をより大きくできるので、第１群の入
射角を小さくする条件として次の条件（２）を満足する
ことが好ましい。Also, when θ1 is equal, the one with the smaller incident angle of the first group is
Since 1/l1 (θ1) can be made larger, it is preferable to satisfy the following condition (2) as a condition for reducing the incident angle of the first group.
（２）｜ｆ２／ｆ｜＜１０ ただしｆ２は第２群の焦点距離である。(2) |f2/f|<10 However, f2 is the focal length of the second group.
正の屈折力を持つ第２群において、第１群の瞳の球面収
差発生量と逆方向に発生させるためには、第２群は瞳を
物点とする時に球面収差の発生量が少ない形状にするこ
とが望ましい。そのためには球面収差の発生量とレンズ
のベンディングとの関係から、物点側に凸面を持ちその
反対側が平面である平凸レンズに近い形状が、最も球面
収差を小さく出来る形状である。したがって第２群の各
曲面は、絞りと反対側の面の曲率半径をｒａ、絞り側の
面の曲率半径をｒｂとすると、次の条件（３）を満足す
ることが望ましい。In order to generate spherical aberration in the opposite direction to the amount of spherical aberration generated in the pupil of the first group in the second group having positive refractive power, the second group must have a shape that generates less spherical aberration when the pupil is used as the object point. It is desirable to do so. To this end, in view of the relationship between the amount of spherical aberration generated and lens bending, a shape that is similar to a plano-convex lens with a convex surface on the object point side and a flat surface on the opposite side is the shape that can minimize spherical aberration the most. Therefore, each curved surface of the second group desirably satisfies the following condition (3), where ra is the radius of curvature of the surface opposite to the aperture, and rb is the radius of curvature of the surface on the aperture side.
（３）｜ｒｂ／ｒａ｜＜０．７
本発明の内視鏡対物光学系は、前記のように、負のパワ
ーの第１群と明るさ絞りとの間に正のパワーをもつ第２
群を配置してまた条件（１），（２），（３）を満足す
ることによって歪曲収差がある程度補正されているので
、非球面の数は少なくてすみ又非球面の形状も球面から
のずれ量が少なくてすむので加工性の良い形状にするこ
とができる。(3) |rb/ra|<0.7 As described above, the endoscope objective optical system of the present invention has a second group with positive power between the first group with negative power and the aperture stop.
Distortion aberration is corrected to some extent by arranging the groups and satisfying conditions (1), (2), and (3), so the number of aspherical surfaces is small, and the shape of the aspherical surface is also similar to that of the spherical surface. Since the amount of deviation is small, it is possible to form a shape with good workability.
更に負のパワーの群と明るさ絞りとの間に正のパワーの
群を配置した本発明のレンズ系は、次のようにして歪曲
収差以外の収差を補正することが出来る。Further, the lens system of the present invention in which a positive power group is arranged between a negative power group and an aperture stop can correct aberrations other than distortion as follows.
負のパワーの第１群と明るさ絞りの間に正のパワーを持
った第２群を配置すると、第１群の凹面で発生するマイ
ナス側のコマ収差とは反対のプラス側のコマ収差が第２
群の後面で発生するので、明るさ絞りの前側でコマ収差
をほぼ補正することが出来る。ここでコマ収差の符号は
、ガウス像面上で主光線より光軸側で結像させる方向を
マイナス、その逆をプラスとする。When a second group with positive power is placed between the first group with negative power and the aperture stop, coma on the positive side, which is opposite to the coma on the negative side that occurs on the concave surface of the first group, will be generated. Second
Since it occurs at the rear of the group, coma can be almost corrected in front of the aperture stop. Here, the sign of comatic aberration is negative in the direction in which the image is formed on the optical axis side of the principal ray on the Gaussian image plane, and positive in the opposite direction.
又球面収差に関しても、同時に、第１群で発生する強い
正の球面収差を第２群の凸の作用によって負の球面収差
を発生させることによって補正出来る。そのために第２
群はある程の球面収差を発生させる必要があり、前記の
第２群の球面収差の発生を少なくするための条件である
条件（３）に加え次の条件を満足することが好ましい。Regarding spherical aberration, at the same time, the strong positive spherical aberration generated in the first lens group can be corrected by generating negative spherical aberration through the action of the convexity of the second lens group. For that reason, the second
It is necessary for the group to generate a certain amount of spherical aberration, and in addition to condition (3), which is a condition for reducing the occurrence of spherical aberration in the second group, it is preferable to satisfy the following condition.
０．０１＜｜ｒａ／ｒｂ｜＜０．７
この条件の下限を越えると第１群で発生した正の球面収
差を十分補正できなくなる。0.01<|ra/rb|<0.7 If the lower limit of this condition is exceeded, the positive spherical aberration generated in the first group cannot be sufficiently corrected.
本発明の内視鏡対物光学系においては、明るさ絞りの後
ろ側では第３群の接合面でプラス側のコマ収差を発生さ
せて、正のパワーを持つ第４群で発生するマイナス側の
コマ収差と明るさ絞りの前側で僅かに残ったマイナス側
のコマ収差を補正している。このように本発明のレンズ
系では明るさ絞りの前と後ろでコマ収差を補正できるた
めコマ収差の曲りも少なく収差量も少なく出来る。In the endoscope objective optical system of the present invention, the positive side coma aberration is generated at the cemented surface of the third group behind the aperture stop, and the negative side coma aberration generated in the fourth group with positive power is generated. This corrects coma aberration and the slight coma aberration on the negative side that remains in front of the aperture stop. In this way, in the lens system of the present invention, coma aberration can be corrected before and after the aperture stop, so the amount of aberration can be reduced with less curvature of coma aberration.
また凹の群の直後に明るさ絞りを配置した従来のレンズ
系の場合、倍率の色収差を後群中の接合レンズのみで補
正しているので、凹レンズで発生した倍率の色収差を充
分に補正できなかった。本発明のレンズ系は、第１群と
明るさ絞りとの間に配置した第２群でも倍率の色収差を
補正できるので、充分に倍率の色収差を補正できる。Furthermore, in the case of conventional lens systems in which the aperture stop is placed immediately after the concave lens group, chromatic aberration of magnification is corrected only by the cemented lens in the rear group, so the chromatic aberration of magnification that occurs in the concave lens cannot be sufficiently corrected. There wasn't. In the lens system of the present invention, the chromatic aberration of magnification can be corrected even in the second group disposed between the first group and the aperture stop, so that the chromatic aberration of magnification can be sufficiently corrected.
このように、本発明のレンズ系は、明るさ絞りより前の
前群で収差が補正されているので少ないレンズ枚数で良
好な収差補正が可能である。In this way, in the lens system of the present invention, since aberrations are corrected in the front group before the aperture stop, good aberration correction can be achieved with a small number of lenses.
画角を広くしかつ第１群の外径を小さくするために第１
群の光線高を低くするには、第１群の負のパワーを非常
に強くする必要がある。In order to widen the angle of view and reduce the outer diameter of the first lens group,
In order to reduce the beam height of the group, it is necessary to make the negative power of the first group very strong.
第１１図のような従来の対物レンズは、第１群のパワー
を強くしたことによって発生する非常に大きなコマ収差
の非対称性を第２群以後のレンズで補正することができ
ない。また第１群のパワーを強くするためにその屈折率
を高くすると、一般に屈折率の高い光学用硝材は、分散
が大きいために第１群で発生する大きな色収差を第２群
以降のレンズで補正しきれなくなる。そのために第１群
のパワーをあまり強くできない。In the conventional objective lens as shown in FIG. 11, it is not possible to correct the very large asymmetry of comatic aberration caused by increasing the power of the first group using the lenses after the second group. In addition, when increasing the refractive index of the first group to increase its power, optical glass materials with high refractive index generally have large dispersion, so the large chromatic aberration that occurs in the first group is corrected by the second and subsequent lenses. I can't bear it anymore. Therefore, the power of the first group cannot be made very strong.
本発明のレンズ系は、前記のように第１群により発生す
るコマ収差や色収差を第２群によりキャンセルできるた
め、第１群のパワーを強くしても充分な収差の補正が可
能である。In the lens system of the present invention, comatic aberration and chromatic aberration caused by the first group can be canceled by the second group as described above, so that aberrations can be sufficiently corrected even if the power of the first group is increased.
このように本発明のレンズ系は、歪曲収差以外の収差も
良好に補正されコンパクトでレンズ枚数の少ない光学系
である。As described above, the lens system of the present invention is a compact optical system with a small number of lenses, in which aberrations other than distortion are well corrected.
またこのような光学系中に非球面を用いて歪曲収差を補
正するには軸外光線の光線高が高いレンズ面に非球面を
用いるのが効果的で、少ない非球面量で補正できる。そ
のため次の条件を満足することが望ましい。Furthermore, in order to correct distortion using an aspherical surface in such an optical system, it is effective to use the aspherical surface on the lens surface where the ray height of off-axis rays is high, and correction can be made with a small amount of aspherical surface. Therefore, it is desirable to satisfy the following conditions.
１．５＞｜ｈＡ／Ｉ｜＞０．４
ただしｈＡは非球面での光線高、Ｉは最大光線高である
。1.5>|hA/I|>0.4 where hA is the ray height on the aspherical surface, and I is the maximum ray height.
上記条件の下限を越えると歪曲収差を充分補正するため
には非球面量が大きくなり、非球面の加工性が悪くなる
。また上限を越えるとレンズ外径が大になり好ましくな
い。If the lower limit of the above conditions is exceeded, the amount of aspherical surface becomes large in order to sufficiently correct distortion aberration, and the workability of the aspherical surface deteriorates. Moreover, if the upper limit is exceeded, the outer diameter of the lens becomes large, which is not preferable.
歪曲収差を補正するための非球面の形状に関しては、特
開昭６０−１６９８１８号又は特開昭６１−１６２０２
１号公報に記載されているように、明るさ絞りの前側に
設ける場合は周辺になるほど正のパワーが強くなるか、
又は周辺になるほど負のパワーが弱くなる形状であれば
よい。例えば本発明のレンズ系において、第１群の第１
面を非球面にする場合は周辺ほど曲率が強くなる形状で
ある。更に明るさ絞りの後ろ側では周辺になる程正のパ
ワーが弱くなるか、周辺になる程負のパワーが強くなる
形状がよい。例えば本発明の光学系の第４群の最終面に
用いた場合は、周辺ほど曲率がゆるくなる非球面形状で
ある。上記のような非球面形状により歪曲収差を補正す
ることが出来る。Regarding the shape of an aspheric surface for correcting distortion aberration, see Japanese Patent Application Laid-open No. 60-169818 or No. 61-16202.
As stated in Publication No. 1, if it is installed in front of the aperture diaphragm, the positive power becomes stronger as it gets closer to the periphery.
Alternatively, it may be a shape in which the negative power becomes weaker toward the periphery. For example, in the lens system of the present invention, the first
When the surface is made aspherical, the curvature becomes stronger toward the periphery. Further, on the rear side of the aperture stop, it is preferable that the positive power becomes weaker toward the periphery, or that the negative power becomes stronger toward the periphery. For example, when used as the final surface of the fourth group of the optical system of the present invention, it has an aspherical shape in which the curvature becomes gentler toward the periphery. Distortion can be corrected by the aspherical shape as described above.
以上述べたように、本発明の光学系は、基準球面からの
ずれ量が少ない非球面で、また極力少ない数の非球面で
歪曲収差が良好に補正され、他の収差も良好に補正され
た光学系である。As described above, in the optical system of the present invention, distortion is well corrected using an aspheric surface with a small amount of deviation from the reference spherical surface, and the number of aspheric surfaces is as small as possible, and other aberrations are also well corrected. It is an optical system.
次に本発明の内視鏡対物光学系の各実施例を示す。 Next, embodiments of the endoscope objective optical system of the present invention will be described.
実施例１
ｆ＝１．０００、ＩＨ＝１．３１３７、２ω＝１２０゜
ｒ１＝２６．９５２８（非球面）
ｄ１＝０．３５８３ ｎ１＝１．５１６３３ ν１＝６
４．１５ｒ２＝０．８８１８
ｄ２＝０．９８４９
ｒ３＝−２０．９４８２
ｄ３＝１．１３５４ ｎ２＝１．８４６６６ ν２＝２
３．７８ｒ４＝−２．２１４９
ｄ４＝０．０６７１
ｒ５＝∽（絞り）
ｄ５＝１．４４９３
ｒ６＝３．９８２２
ｄ６＝０．２１５８ ｎ３＝１．８４６６６ ν３＝２
３．７８ｒ７＝２．０４６２
ｄ７＝１．１０９８ ｎ４＝１．５８９１３ ν４＝６
０．９７ｒ８＝−２６．５８０３（非球面）
ｄ８＝０．１０１３
ｒ９＝４．３３０９
ｄ９＝０．６５２９ ｎ５＝１．５１６３３ ν５＝６
４．１５ｒ１０＝∽
ｄ１０＝１．１９４３ ｎ６＝１．５４８１４ ν６＝
４５．７８ｒ１１＝∽
ｄ１１＝０．３１８５ ｎ７＝１．５２２８７ ν７＝
５９．８９ｒ１２＝∽
非球面係数
（第１面）
Ｐ＝１．００００、Ｂ＝０．２６３６４×１０−１Ｅ＝
０．２２９７２×１０−１、Ｆ＝−０．２４５８９×１
０−２Ｇ＝−０．１５７６７×１０−３
（第８面）
Ｐ＝１．００００、Ｂ＝−０．３１１６７Ｅ＝０．３１
９８４×１０−１、Ｆ＝０．３６９１３×１０−２Ｇ＝
−０．６７６２１×１０−３
｜ｆ１／ｆ｜＝１．８７７、｜ｆ２／ｆ｜＝１．４３｜
ｒｂ／ｒａ｜＝０．１０５７
実施例２
ｆ＝１．０００、ＩＨ＝１．４７０６、２ω＝１２０゜
ｒ１＝９０．９３０２（非球面）
ｄ１＝０．４０１１ ｎ１＝１．５１６３３ ν１＝６
４．１５ｒ２＝０．８９３８
ｄ２＝１．１０５４
ｒ３＝−９．７９４１
ｄ３＝１．２４７４ ｎ２＝１．８４６６６ ν２＝２
３．７８ｒ４＝−２．２５３４
ｄ４＝０．０７４７
ｒ５＝∽（絞り）
ｄ５＝１．６１４８
ｒ６＝３．８５５３
ｄ６＝０．２１６９ ｎ３＝１．８４６６６ ν３＝２
３．７８ｒ７＝２．１５７８
ｄ７＝１．２３９６ ｎ４＝１．５６８７３ ν４＝６
３．１６ｒ８＝−４２．２９７３（非球面）
ｄ８＝０．２０２３
ｒ９＝５．２０６４
ｄ９＝０．７３０８ ｎ５＝１．５１６３３ ν５＝６
４．１５ｒ１０＝∽
ｄ１０＝１．３３６９ ｎ６＝１．５４８１４ ν６＝
４５．７８ｒ１１＝∽
ｄ１１＝０．３５６５ ｎ７＝１．５２２８７ ν７＝
５９．８９ｒ１２＝∽
非球面係数
（第１面）
Ｐ＝１．００００、Ｂ＝０．１２６７７×１０−２Ｅ＝
０．１３６２６×１０−１、Ｆ＝−０．１０４６８×１
０−２Ｇ＝０．８２８０８×１０−６
（第８面）
Ｐ＝１．００００、Ｂ＝−０．２８６９８Ｅ＝０．２２
２７７×１０−１、Ｆ＝０．２０３３９×１０−２Ｇ＝
−０．３０９６８×１０−３
｜ｆ１／ｆ｜＝１．７４６、｜ｆ２／ｆ｜＝３．２１３
｜ｒｂ／ｒａ｜＝０．２３０
実施例３
ｆ＝１．０００、ＩＨ＝１．０５０３、２ω＝１２０゜
ｒ１＝∽
ｄ１＝０．２８６４ ｎ１＝１．５１６３３ ν１＝６
４．１５ｒ２＝０．７５５８
ｄ２＝０．７７６２
ｒ３＝１５．９７３６
ｄ３＝０．８８０８ ｎ２＝１．８４６６６ ν２＝２
３．７８ｒ４＝−１．７７４０
ｄ４＝０．０５５６
ｒ５＝∽（絞り）
ｄ５＝１．２０６５
ｒ６＝４．２６０３
ｄ６＝０．１９３４ ｎ３＝１．８４６６６ ν３＝２
３．７８ｒ７＝２．０２２３
ｄ７＝０．８３９１ ｎ４＝１．６０３１１ ν４＝６
０．７０ｒ８＝−２１．２５０７（非球面）
ｄ８＝０．２２３３
ｒ９＝２．７６２１
ｄ９＝０．５２２０ ｎ５＝１．５１６３３ ν５＝６
４．１５ｒ１０＝∽
ｄ１０＝０．９５４８ ｎ６＝１．５４８１４ ν６＝
４５．７８ｒ１１＝ω
ｄ１１＝０．２５４６ ｎ７＝１．５２２８７ ν７＝
５９．８９ｒ１２＝∽
非球面係数
Ｐ＝１．００００、Ｂ＝−０．２５９６５Ｅ＝０．３８
３３１×１０−１、Ｆ＝０．１３０６０×１０−１Ｇ＝
−０．３９４１４×１０−２
｜ｆ１／ｆ｜＝１．４６４、｜ｆ２／ｆ｜＝１．９３｜
ｒｂ／ｒａ｜＝０．０７３５
実施例４
ｆ＝１．０００、ＩＨ＝０．９９９４、２ω＝１２０゜
ｒ１＝５４．００２１（非球面）
ｄ１＝０．２７２６ ｎ１＝１．８８３００ ν１＝４
０．７８ｒ２＝０．６３５３
ｄ２＝０．６８４９
ｒ３＝２．７７１６
ｄ３＝０．７７８３ ｎ２＝１．７８５９０ ν２＝４
４．１８ｒ４＝−１．６５６７
ｄ４＝０．０８４１
ｒ５＝∽（絞り）
ｄ５＝１．１４３５
ｒ６＝５．９２５３
ｄ６＝０．７８９１ ｎ３＝１．６０３１１ ν３＝６
０．７０ｒ７＝−０．８４１１
ｄ７＝０．１９７９ ｎ４＝１．８４６６６ ν４＝２
３．７８ｒ８＝−１．７２６７
ｄ８＝０．９６１６
ｒ９＝３．６６５７
ｄ９＝０．４９６７ ｎ５＝１．７２９１６ ν５＝５
４．６８ｒ１０＝∽
ｄ１０＝０．９０８５ ｎ６＝１．５４８１４ ν６＝
４５．７８ｒ１１＝∽
ｄ１１＝０．２４２３ ｎ７＝１．５２２８７ ν７＝
５９．８９ｒ１２＝∽
非球面係数
Ｐ＝１．００００、Ｂ＝０．６９９６４×１０−２Ｅ＝
０．４５０５×１０−１、Ｆ＝０．１４５４２×１０−
１Ｇ＝−０．２２３１７×１０−１
｜ｆ１／ｆ｜＝０．７３８、｜ｆ２／ｆ｜＝２．８４｜
ｒｂ／ｒａ｜＝０．５９５
ただしｒ１，ｒ２，…は各レンズ面の曲率半径、ｄ１，
ｄ２，…は各レンズの肉厚およびレンズ間隔、ｎ１，ｎ
２，…は各レンズの屈折率、ν１，ν２，…は各レンズ
のアツベ数である。Example 1 f=1.000, IH=1.3137, 2ω=120°r1=26.9528 (aspherical surface) d1=0.3583 n1=1.51633 ν1=6
4.15r2=0.8818 d2=0.9849 r3=-20.9482 d3=1.1354 n2=1.84666 ν2=2
3.78r4=-2.2149 d4=0.0671 r5=∽(aperture) d5=1.4493 r6=3.9822 d6=0.2158 n3=1.84666 ν3=2
3.78r7=2.0462 d7=1.1098 n4=1.58913 ν4=6
0.97r8=-26.5803 (aspherical surface) d8=0.1013 r9=4.3309 d9=0.6529 n5=1.51633 ν5=6
4.15r10=∽ d10=1.1943 n6=1.54814 ν6=
45.78r11=∽ d11=0.3185 n7=1.52287 ν7=
59.89r12=∽ Aspheric coefficient (first surface) P=1.0000, B=0.26364×10-1E=
0.22972×10-1, F=-0.24589×1
0-2G=-0.15767×10-3 (8th surface) P=1.0000, B=-0.31167E=0.31
984×10-1, F=0.36913×10-2G=
-0.67621×10-3 |f1/f|=1.877, |f2/f|=1.43|
rb/ra | = 0.1057 Example 2 f = 1.000, IH = 1.4706, 2ω = 120° r1 = 90.9302 (aspherical surface) d1 = 0.4011 n1 = 1.51633 ν1 = 6
4.15r2=0.8938 d2=1.1054 r3=-9.7941 d3=1.2474 n2=1.84666 ν2=2
3.78r4=-2.2534 d4=0.0747 r5=∽(aperture) d5=1.6148 r6=3.8553 d6=0.2169 n3=1.84666 ν3=2
3.78r7=2.1578 d7=1.2396 n4=1.56873 ν4=6
3.16r8=-42.2973 (aspherical surface) d8=0.2023 r9=5.2064 d9=0.7308 n5=1.51633 ν5=6
4.15r10=∽ d10=1.3369 n6=1.54814 ν6=
45.78r11=∽ d11=0.3565 n7=1.52287 ν7=
59.89r12=∽ Aspheric coefficient (first surface) P=1.0000, B=0.12677×10-2E=
0.13626×10-1, F=-0.10468×1
0-2G=0.82808×10-6 (8th surface) P=1.0000, B=-0.28698E=0.22
277×10−1, F=0.20339×10−2G=
-0.30968×10-3 |f1/f|=1.746, |f2/f|=3.213
|rb/ra|=0.230 Example 3 f=1.000, IH=1.0503, 2ω=120°r1=∽ d1=0.2864 n1=1.51633 ν1=6
4.15r2=0.7558 d2=0.7762 r3=15.9736 d3=0.8808 n2=1.84666 ν2=2
3.78r4=-1.7740 d4=0.0556 r5=∽(aperture) d5=1.2065 r6=4.2603 d6=0.1934 n3=1.84666 ν3=2
3.78r7=2.0223 d7=0.8391 n4=1.60311 ν4=6
0.70r8=-21.2507 (aspherical surface) d8=0.2233 r9=2.7621 d9=0.5220 n5=1.51633 ν5=6
4.15r10=∽ d10=0.9548 n6=1.54814 ν6=
45.78r11=ω d11=0.2546 n7=1.52287 ν7=
59.89r12=∽ Aspheric coefficient P=1.0000, B=-0.25965E=0.38
331×10−1, F=0.13060×10−1G=
-0.39414×10-2 |f1/f|=1.464, |f2/f|=1.93|
rb/ra | = 0.0735 Example 4 f = 1.000, IH = 0.9994, 2ω = 120° r1 = 54.0021 (aspherical surface) d1 = 0.2726 n1 = 1.88300 ν1 = 4
0.78r2=0.6353 d2=0.6849 r3=2.7716 d3=0.7783 n2=1.78590 ν2=4
4.18r4=-1.6567 d4=0.0841 r5=∽(aperture) d5=1.1435 r6=5.9253 d6=0.7891 n3=1.60311 ν3=6
0.70r7=-0.8411 d7=0.1979 n4=1.84666 ν4=2
3.78r8=-1.7267 d8=0.9616 r9=3.6657 d9=0.4967 n5=1.72916 ν5=5
4.68r10=∽ d10=0.9085 n6=1.54814 ν6=
45.78r11=∽ d11=0.2423 n7=1.52287 ν7=
59.89r12=∽ Aspheric coefficient P=1.0000, B=0.69964×10-2E=
0.4505×10−1, F=0.14542×10−
1G=-0.22317×10-1 |f1/f|=0.738, |f2/f|=2.84|
rb/ra|=0.595 where r1, r2,... are the radius of curvature of each lens surface, d1,
d2,... are the thickness of each lens and the lens spacing, n1, n
2, . . . are refractive indexes of each lens, and ν1, ν2, . . . are Abbe numbers of each lens.
又非球面形状は、光軸をｘ軸、光軸と直交する方向をｙ
軸とする時次のように表わされる。In addition, for the aspherical shape, the optical axis is the x-axis, and the direction orthogonal to the optical axis is the y-axis.
When used as an axis, it is expressed as follows.
ここでＣは非球面頂点の曲率半径の逆数、Ｐは円錐定数
、Ｂ、Ｅ、Ｆ、Ｇ、……は非球面係数である。Here, C is the reciprocal of the radius of curvature of the apex of the aspherical surface, P is the conic constant, and B, E, F, G, . . . are the aspherical coefficients.
実施例１は、第１図に示す構成で、画角が１２０゜の固
体撮像素子と組合わせたものである。Embodiment 1 has the configuration shown in FIG. 1, which is combined with a solid-state image sensor having an angle of view of 120 degrees.
図中Ｆはモアレを除去するための光学的ローパスフィル
ター、Ｃは固体撮像素子のカバーガラスである。また実
際に使用する場合は、観察時に不用なレーザー光や赤外
光を遮断するＹＡＧカットフィルターと赤外カットフィ
ルターを明るさ絞りと第３群の間に挿入する。In the figure, F is an optical low-pass filter for removing moiré, and C is a cover glass of the solid-state image sensor. When actually used, a YAG cut filter and an infrared cut filter that block unnecessary laser light and infrared light during observation are inserted between the aperture diaphragm and the third group.
実施例２は、第２図に示すもので実施例１と同じように
固体撮像素子と組合わせたもので画角は１４０゜である
。Embodiment 2 is shown in FIG. 2, and like Embodiment 1, it is combined with a solid-state image sensor and has an angle of view of 140 degrees.
これら実施例１，２は、非球面を第１面と第８面に用い
ている。つまり絞りの前側では光線高の最も高い第１面
に用いて、球面からのずれ量が少なくても歪曲収差に対
する補正量を大に出来る。In Examples 1 and 2, aspherical surfaces are used for the first and eighth surfaces. In other words, on the front side of the diaphragm, by using the first surface with the highest ray height, the amount of correction for distortion can be increased even if the amount of deviation from the spherical surface is small.
また絞りより後ろ側では、コマ収差の発生量を少なくす
るため明るさ絞り側に曲率中心を持ち光線高の高い第８
面に非球面を用いている。In addition, behind the aperture, in order to reduce the amount of coma aberration, the 8th lens has a center of curvature on the brightness aperture side and has a high ray height.
The surface is aspherical.
次に実施例３、４は、夫々第３図、第４図に示す構成で
、いずれも画角が１２０゜である。又非球面は１面のみ
用いている。実施例３は、非球面を第８面のみに、実施
例４は非球面を第１面のみに用いている。Next, Examples 3 and 4 have the configurations shown in FIGS. 3 and 4, respectively, and both have an angle of view of 120 degrees. Also, only one aspherical surface is used. In Example 3, an aspherical surface is used only on the eighth surface, and in Example 4, an aspherical surface is used only on the first surface.
これら実施例３、４では、画角１２０゜で歪曲収差が夫
々２９％、３３％とやや残った状態になっている。これ
は以下述べるような理由による。In Examples 3 and 4, at an angle of view of 120 degrees, distortion remains at 29% and 33%, respectively. This is due to the reasons described below.
内視鏡においては、例えば医療用であれば気管支や大腸
などの管状の臓器を光軸を管の軸方向に向けて観察する
場合や、工業用でガス管、水道管等を観察することがあ
る。第９図は、このような観察状態を示す概念図である
。このような被写体の場合、視野周辺の管内表面にある
物体の形状が歪まないようにするのが望ましく、管内表
面で管の軸に平行な方向を管内観察のメリジオナル方向
、それに垂直な方向を管内観察のサジタル方向として対
物光学系で観察したときに視野の周辺でメリジオナル方
向の倍率とサジタル方向の倍率が等しくなるようにすれ
ば良い。For example, endoscopes can be used for medical purposes to observe tubular organs such as the bronchi and large intestine with the optical axis pointing in the direction of the axis of the tube, and for industrial purposes to observe gas pipes, water pipes, etc. be. FIG. 9 is a conceptual diagram showing such an observation state. In the case of such a subject, it is desirable to prevent the shape of the object on the inner surface of the tube around the field of view from being distorted. When observing with an objective optical system in the sagittal direction of observation, the magnification in the meridional direction and the magnification in the sagittal direction may be made equal to each other at the periphery of the field of view.
第１０図は、管内観察において、メリジオナル方向の倍
率βＭ（θ１）とサジタル方向の倍率βＳ（θ１）を求
めるための図である。Ａ（θ１）という特性をもつ対物
光学系では、βＭ（θ１）、βＳ（θ１）は次の式のよ
うになる。FIG. 10 is a diagram for determining the magnification βM (θ1) in the meridional direction and the magnification βS (θ1) in the sagittal direction in intratubal observation. In the objective optical system having the characteristic A(θ1), βM(θ1) and βS(θ1) are as shown in the following equations.
Ａ（θ１）＝Ｋｔａｎ（θ１／Ｋ）の時に、｜βＭ（θ
１）／βＳ（θ１）｜＝１となるθ１とＫとの組合わせ
は下記の式（ｘ）を満足する。When A(θ1)=Ktan(θ1/K), |βM(θ
1) The combination of θ1 and K such that /βS(θ1)|=1 satisfies the following formula (x).
上記式を満足するθ１とＫの関係は次の表の通りである
。The relationship between θ1 and K that satisfies the above equation is shown in the following table.
辺上の関係から、例えば画角１２０゜の光学系を管内観
察に適するようにするためには、歪曲収差を約３２％程
度にすればよいことがわかる。From the relationship on the sides, it can be seen that, for example, in order to make an optical system with an angle of view of 120° suitable for intraluminal observation, the distortion aberration should be about 32%.
このような理由から、実施例３、４は、歪曲収差が残る
ようにしている。このように歪曲収差の補正量が少い時
は、一つの非球面で充分である。For this reason, in Examples 3 and 4, distortion remains. When the amount of correction for distortion aberration is small like this, one aspherical surface is sufficient.
したがってこれら実施例のように、本発明の光学系は、
非球面１面で管内観察に適したものを実現し得る。この
場合実施例１、２で述べたと同じ理由で絞りの前に用い
る場合は第１面、絞りの後ろに用いる場合は第８面を非
球面にすることが好ましい。Therefore, as in these embodiments, the optical system of the present invention
It is possible to achieve something suitable for intra-tube observation with just one aspherical surface. In this case, for the same reason as stated in Examples 1 and 2, it is preferable that the first surface is aspherical when used before the aperture, and the eighth surface is preferably aspherical when used after the aperture.
また、本発明の各実施例および前記従来例の特開昭６０
−１６９８１８号の実施例１および特開昭６１−１６２
０２１号の実施例８の非球面の基準球面からのずれ量｜
Δｘ｜を示すと次の通りである。Further, each embodiment of the present invention and the conventional example disclosed in Japanese Patent Application Laid-open No. 60
Example 1 of No.-169818 and JP-A-61-162
Amount of deviation of the aspherical surface of Example 8 of No. 021 from the reference spherical surface |
Δx| is shown as follows.
（本発明）
実施例１ ０．０９２９１（第１面） ０．３４５３（
第８面）実施例２ ０．０７１７９（第１面） ０．４
２２９３第８面）実施例３ ０．１７７９８（第８面）
実施例４ ０．０１０１７（第１面）
（特開昭６０−１６９８１８）
実施例１ ０．３８６（第３面）
（特開昭６１−１６２０２１）
実施例８ ０．４０６２（第１面） ０．１４２９（第
１３面）上記の値からわかるように特開昭６０−１６９
８１８号の実施例１は、画角が９０゜で歪曲収差が約−
５％であるが、｜Δｘ｜は本発明の方が少ない。(This invention) Example 1 0.09291 (first side) 0.3453 (
8th side) Example 2 0.07179 (1st side) 0.4
2293 8th page) Example 3 0.17798 (8th page) Example 4 0.01017 (1st page) (JP-A-60-169818) Example 1 0.386 (3rd page) (JP-A-60-169818) 61-162021) Example 8 0.4062 (1st surface) 0.1429 (13th surface) As can be seen from the above values, JP-A-60-169
In Example 1 of No. 818, the angle of view is 90° and the distortion is about -
5%, but |Δx| is smaller in the present invention.
又特開昭６１−１６２０２１号の実施例８は、画角が１
２０゜で、歪曲収差が約４０％で本発明の実施例とほぼ
同じであるが、第１面、第１３面の｜Δｘ｜は大で、本
発明の光学系の方が｜Δｘ｜が小さい。Furthermore, in Example 8 of JP-A-61-162021, the angle of view is 1.
20°, the distortion is about 40%, which is almost the same as the embodiment of the present invention, but the |Δx| of the first and 13th surfaces are large, and the optical system of the present invention has a larger |Δx| small.
本発明の内視鏡対物光学系は、以上述べたような構成に
することによって、広角で歪曲収差が充分補正され同時
に他の諸収差も良好に補正され、又非球面レンズの加工
性が良くかつレンズ枚数の少ないコンパクトな光学系で
ある。By having the configuration described above, the endoscope objective optical system of the present invention sufficiently corrects distortion aberration at a wide angle, and at the same time, satisfactorily corrects other aberrations, and also allows for good workability of the aspherical lens. It is also a compact optical system with a small number of lenses.
第１図乃至第４図は夫々本発明の実施例１乃至実施例４
の断面図、第５図乃至第８図は実施例１乃至実施例４の
収差曲線図、第９図は、本発明の原理を説明する図、第
１０図は管内観察時のメリデイオナル・サジタル方向の
倍率を求めるための図、第１１図乃至第１３図は従来の
内視鏡学系の構成を示す図である。
出願人 オリンパス光学工業株式会社
代理人 向寛二1 to 4 are embodiments 1 to 4 of the present invention, respectively.
5 to 8 are aberration curve diagrams of Examples 1 to 4, FIG. 9 is a diagram explaining the principle of the present invention, and FIG. 10 is a meridional-sagittal direction during observation inside a tube. 11 to 13 are diagrams showing the configuration of a conventional endoscopy system. Applicant Olympus Optical Industry Co., Ltd. Agent Kanji Mukai
Claims (2)
と、正の屈折力を有する第２群と、明るさ絞りと、その
後方に配置された正の屈折力と負の屈折力を有するレン
ズを貼り合せてなるレンズを含み全体として正の屈折力
を有する後群とからなり、少なくとも一つの非球面を有
することを特徴とする内視鏡対物光学系。Claim 1: In order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, an aperture stop, and a positive refractive power and a negative refractive power disposed behind the aperture stop. 1. An objective optical system for an endoscope, comprising a rear group including a lens formed by laminating lenses having a power and having a positive refractive power as a whole, and having at least one aspherical surface.
項（１）の内視鏡対物光学系。 （１）｜ｆ１／ｆ｜＜５ （２）｜ｆ２／ｆ｜＜１０ （３）｜ｒｂ／ｒａ｜＜０．７ ただしｆ１は第１群の焦点距離、ｆ２は第２群の焦点距
離、ｆは全系の焦点距離、ｒａ、ｒｂは夫々第２群の物
体側の面及び絞り側の面の曲率半径である。2. The endoscope objective optical system according to claim 1, which satisfies the following conditions. (1) | f1/f | <5 (2) | f2/f | <10 (3) | rb/ra | <0.7 where f1 is the focal length of the first group, f2 is the focal length of the second group , f is the focal length of the entire system, and ra and rb are the radii of curvature of the object-side surface and the aperture-side surface of the second group, respectively.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2269483A JP2995491B2 (en) | 1990-10-09 | 1990-10-09 | Endoscope objective optical system |
| US07/683,018 US5208702A (en) | 1990-04-11 | 1991-04-10 | Objective lens system for endoscopes |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2269483A JP2995491B2 (en) | 1990-10-09 | 1990-10-09 | Endoscope objective optical system |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04218011A true JPH04218011A (en) | 1992-08-07 |
| JP2995491B2 JP2995491B2 (en) | 1999-12-27 |
Family
ID=17473073
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2269483A Expired - Fee Related JP2995491B2 (en) | 1990-04-11 | 1990-10-09 | Endoscope objective optical system |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2995491B2 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007292977A (en) * | 2006-04-25 | 2007-11-08 | Pentax Corp | Wide angle lens system |
| JP2009258659A (en) * | 2008-03-21 | 2009-11-05 | Olympus Medical Systems Corp | Objective lens for endoscope |
| JP2009300797A (en) * | 2008-06-13 | 2009-12-24 | Fujinon Corp | Imaging lens and capsule type endoscope |
| WO2018131264A1 (en) * | 2017-01-12 | 2018-07-19 | ソニーセミコンダクタソリューションズ株式会社 | Imaging unit and electronic device |
-
1990
- 1990-10-09 JP JP2269483A patent/JP2995491B2/en not_active Expired - Fee Related
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007292977A (en) * | 2006-04-25 | 2007-11-08 | Pentax Corp | Wide angle lens system |
| JP2009258659A (en) * | 2008-03-21 | 2009-11-05 | Olympus Medical Systems Corp | Objective lens for endoscope |
| US7885017B2 (en) | 2008-03-21 | 2011-02-08 | Olympus Medical Systems Corp. | Objective lens system for endoscope |
| JP2009300797A (en) * | 2008-06-13 | 2009-12-24 | Fujinon Corp | Imaging lens and capsule type endoscope |
| WO2018131264A1 (en) * | 2017-01-12 | 2018-07-19 | ソニーセミコンダクタソリューションズ株式会社 | Imaging unit and electronic device |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2995491B2 (en) | 1999-12-27 |
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