JPH0754373B2 - Objective lens for endoscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention provides an objective lens for an endoscope used in a small-diameter endoscope having a small outer diameter, and in particular, a CCD (Char
ge Coupled Device) for an objective lens for an endoscope.

[Conventional technology]

In recent years, with the increasing demand for thinning of small-diameter endoscopes such as bronchoscopes that perform observation and treatment by inserting them into bronchi with a narrow lumen, for endoscopes with a small outer diameter Various objective lenses have been developed. In this type of endoscope objective lens, as a lens system close to the endoscope objective lens according to the present invention, as shown in FIG. 7, in order from the object side, the object side is flat and the concave surface is the image side. Plano-concave negative first lens facing toward
L ₁ ′, a biconvex positive second lens L ₂ ′ with a surface having a large radius of curvature facing the object side, and a third cemented lens L ₃ ′ + L ₄ ′ having a positive refractive index as a whole and the convex surface are imaged An objective lens for an endoscope, which is composed of a fourth meniscus lens L ₅ ′ facing toward the side, and a diaphragm A is disposed between the second lens L ₂ ′ and the third cemented lens L ₃ ′ + L ₄ ′. Where m: surface number sequentially counted from the object side r ₁ , r ₂ , ... r ₈ , r ₉ : radius of curvature of each lens surface d ₁ , d ₂ , ... d ₈ : thickness of each lens or Air spacing n ₁ , n ₂ , n ₃ , n ₄ , n ₅ : Refractive index of each lens with respect to d-line ν ₁ , ν ₂ , ν ₃ ,, ν ₄ , ν ₅ : When the Abbe number of each lens is m, r d n ν 1 ∞ 2 0.502 0.281 1.88300 41.0 3 1.406 0.176 4 −0.879 0.949 1.72916 54.8 5 7.032 0.211 6 −0.586 1.020 1.72916 54.8 7 −1.082 0.281 1.80518 25.5 8 −0.582 0.295 9 −1.803 0.281 1.80518 25.5 and then the 8th Yield as shown There is an objective lens for an endoscope provided with a difference curve diagram.

[Problems to be Solved by the Invention]

However, in the lens system using the cemented lens as described above, the chromatic aberration is corrected by reducing the radius of curvature of the cemented surface of the cemented lens. Even if the radius of curvature is reduced, the chromatic aberration is corrected. In addition to the limitation, when the radius of curvature is reduced, it becomes extremely difficult to polish or process the lens, and there is a limit in terms of the processed surface.

If the chromatic aberration is not corrected sufficiently well, accurate observation and accurate diagnosis are hindered when observing and making a diagnosis in the lumen using the endoscope.

In view of the present situation, the present invention provides an objective lens for an endoscope, in which a convex lens made of a glass material having a large dispersion is arranged in front of a diaphragm, and the axial chromatic aberration and the lateral chromatic aberration are well corrected in a well-balanced manner. That is the purpose.

[Means for solving the problem and its action]

In order to achieve such an object, the present invention comprises, in order from the object side, a negative first lens L ₁ having a concave surface facing the image side, and a positive second lens L ₂ having a surface having a large radius of curvature facing the image side. It is composed of a positive third lens L ₃ with a surface having a large radius of curvature facing the object side, and a fourth cemented lens L ₄ + L ₅ having a positive refractive index as a whole,
In an endoscope objective lens in which a brightness diaphragm is arranged between the second lens L ₂ and the third lens L ₃ , (1) 0.60 <| f ₁ /f|<0.70 (2) n ₂ > 1.60 ν ₂ <45.0 (3) n ₃ > 1.60 ν ₃ > 50.0 (4) n ₄ > 1.60 ν ₄ > 50.0 (5) ν ₅ <40.0 where f _{1 is} the focal length of the first lens f: The combined focal length of the entire system n ₂ , n ₃ , n ₄ ,: _second lens L ₂ , third lens L ₃ , fourth cemented lens
Refractive index of the glass material used for the convex lens L ₄ of L ₄ + L ₅ with respect to d line ν ₂ , ν ₃ ,, ν ₄ , ν ₅ : second lens L ₂ , third lens L ₃ , fourth cemented lens L ₄ + L ₅ of the convex lens L _4, the fourth cemented lens L ₄ + objective lens for an endoscope, characterized by satisfying the Abbe's number becomes conditions of the glass material which L ₅ of being used for a concave lens L _5, and the like of the lens It is an objective lens for an endoscope in which only the expressions (4) and (5) are changed as follows.

(4) ν ₄ <40.0 (5) n ₅ > 1.60 ν ₅ > 50.0 where n ₅ ,: the refractive index of the glass material used for the convex lens L ₅ of the fourth cemented lens L ₄ + L ₅ with respect to d-line ν ₄ , [nu _5: fourth cemented lens L ₄ + L concave lens L ₄ of _5, Abbe's number of the fourth cemented lens L ₄ + L ₅ glass material used in the lens L ₅ below, illustrating the significance with the above conditions.

First, the condition (1) defines the power of the first lens L ₁ , and if the upper limit is exceeded, the focal length of the first lens L ₁ becomes long, so 90 ° which is necessary for the objective lens for an endoscope. 100
A wide angle of view of about ゜ cannot be obtained. On the other hand, if the lower limit is not satisfied, the radius of curvature of the concave surface of the first lens L ₁ becomes small, which makes polishing and processing of the lens difficult.

Conditions (2) to (5) are the first lens L ₁ , the second lens L ₂ , the third lens L ₃ and the fourth cemented lens L ₄ + L _{5 respectively.}
The glass material to be used for the convex lens and the concave lens is limited, and when the refractive index of the convex lens is less than this, Petzval sum deteriorates, the field curvature is insufficiently corrected, and further, this condition is satisfied. Without obtaining the same lens and power, the radius of curvature must be reduced, which makes polishing and processing of the lens difficult. If the Abbe number of each glass material deviates from this range, it becomes difficult to achieve well-balanced correction of axial chromatic aberration and lateral chromatic aberration, which is the original purpose of the present invention.

It is possible to make the outer diameter ratio of the first lens L ₁ and the lens L ₄ or L ₅ of the fourth cemented lenses approximately 1.0 by configuring the objective lens for an endoscope with the lens structure of the present invention. Therefore, it is possible to reduce the outer diameter of the entire endoscope objective lens.

In addition, since a CCD or the like is used as the image pickup element at the image forming position P of the lens configuration of the present invention, it is not necessary to configure the objective lens in a telecentric system.

〔Example〕

Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings.

However, in the following description, L ₁ to L ₅ : First lens to fifth lens X: Optical axis A: Aperture m: Surface numbers sequentially counted from the object side r ₁ , r ₂ , ... r ₉ : Each curvature of the lens surface radius d _1, d _2, · · · d _8: thickness or air space n ₁ of each _{lens, n 2, n 3, n} 4, n 5: refractive index [nu ₁ the d-line of each lens, ν ₂ , ν ₃ , ν ₄ , ν ₅ : Atbe number of each lens. In addition, the optical path in each lens configuration diagram represents the chief ray of an object height of 60 mm under the same conditions, and each aberration curve diagram shows the object distance of 5 mm and the object height of 20 mm and 40 m when the effective F number is 5.60.
The aberration amounts of m and 60 mm are shown.

The first embodiment is based on the basic configuration of the first lens shown in FIG. 1 and is as shown in the table below.

mr d n ν 1 ∞ 2 0.51 0.328 1.81550 44.4 3 1.125 0.131 4 ∞ 0.787 1.70154 41.1 5 ∞ 0.020 6 −0.846 0.656 1.62280 56.9 7 1.928 0.066 8 −0.794 0.852 1.62280 56.9 9 −11.705 0.328 1.80518 25.5 = f = 1 f ₁ −0.625 | f ₁ /f|=0.625 and h _F : the height of the chief ray of the maximum angle of view of the first surface of the first lens L ₁ h _R : the maximum angle of view of the final surface of the fourth cemented lens L ₄ + L ₅ In this example, h _F = 0.434 h _R = 0.424 and | h _F / h _R | = 1.024.

The aberration curve according to this specific configuration is as shown in FIG.

The second example is based on the basic configuration of the first lens shown in FIG. 1, and its specific configuration is as shown in the table below.

mr d n ν 1 ∞ 2 0.545 0.280 1.81550 44.4 3 1.275 0.140 4 ∞ 0.771 1.70154 41.1 5 ∞ 0.042 6 −0.904 0.631 1.72000 50.3 7 3.523 0.070 8 −0.701 0.841 1.72000 50.3 9 −12.541 0.280 1.80518 25.5 f = 1 f ₁ = −0.669 | f ₁ /f|=0.669 and h _F : the height of the chief ray of the maximum angle of view of the first surface of the first lens L ₁ h _R : the maximum angle of view of the final surface of the fourth cemented lens L ₄ + L ₅ In this example, h _F = 0.421 h _R = 0.408, and | h _F / h _R | = 1.032.

The aberration curve according to this specific configuration is as shown in FIG.

Further, the third example is based on the basic configuration of the first lens shown in FIG. 1, and its specific configuration is as shown in the table below.

m r d n ν 1 ∞ 2 0.545 0.280 1.81550 44.4 3 1.251 0.140 4 31.630 0.771 1.72342 38.0 5 -24.696 0.042 6 -0.875 0.631 1.72000 50.3 7 3.527 0.070 8 -0.701 0.841 1.72000 50.3 9 -12.533 0.280 1.80518 25.5 f = 1 f 1 = −0.668 | f ₁ /f|=0.668 and h _F : Height of the chief ray at the maximum angle of view of the first surface of the first lens L ₁ h _R : Maximum image of the final surface of the fourth cemented lens L ₄ + L ₅ Assuming the height of the chief ray of the angle, in this example, h _F = 0.421 h _R = 0.410 and | h _F / h _R | = 1.027.

The aberration curve according to this specific configuration is as shown in FIG.

Further, the fourth example is based on the basic configuration of the second lens shown in FIG. 2, and its specific configuration is as shown in the table below.

mr d n ν 1 8.000 2 0.500 0.280 1.81550 44.4 3 0.951 0.140 4 2.000 0.771 1.72825 28.3 5 1.429 0.042 6 −0.916 0.631 1.69680 55.6 7 −56.693 0.070 8 1.272 0.280 1.80518 25.5 9 −2.745 0.841 1.69680 55.6 = f = 1 f ₁ −0.665 | f ₁ /f|=0.665 and h _F : the height of the chief ray of the maximum angle of view of the first surface of the first lens L ₁ h _R : the maximum angle of view of the final surface of the fourth cemented lens L ₄ + L ₅ In this example, h _F = 0.451 h _R = 0.483 and | h _F / h _R | = 0.934.

The aberration curve according to this specific configuration is as shown in FIG.

FIG. 3 is an aberration curve diagram of each of the first to fourth examples,
The chromatic aberration of magnification in FIGS. 4, 5 and 6 is corrected to about half or less of the chromatic aberration of magnification in FIG. 8 which is an aberration curve diagram of the conventional example.

〔The invention's effect〕

As is clear from the above description, according to the present invention, the lens configuration and the conditions (1) to (5) are satisfied, so that a wide field angle characteristic can be obtained as an endoscope objective lens. In addition, it is possible to satisfactorily correct various aberrations due to monochromatic light and chromatic aberration of magnification to improve resolution, and it is possible to provide an objective lens for an endoscope with improved observation and diagnosis functions. .

Furthermore, it has become possible to provide an objective lens for an endoscope in which lens polishing and processing are easy.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first lens configuration basic type of the present invention, FIG. 2 is a lens configuration diagram of a second lens configuration basic type, FIG. 3 is an aberration curve diagram of the first embodiment, and FIG. 5 is an aberration curve diagram of Example 3, FIG. 5 is an aberration curve diagram of Example 3, FIG. 6 is an aberration curve diagram of Example 4, FIG. 7 is a conventional lens configuration diagram, and FIG. 8 is FIG. It is an aberration curve figure corresponding to. L ₁ to L ₅ : First lens to fifth lens X: Optical axis A: Aperture r ₁ , r ₂ ,… r ₉ : Radius of curvature of each lens surface d ₁ , d ₂ ,… d ₈ : Thickness of each lens Or air space P: Imaging position

Claims (2)

[Claims] 1. A negative first lens L ₁ having a concave surface facing the image side in order from the object side, a positive second lens L ₂ having a large radius of curvature facing the image side, and a surface having a large radius of curvature. the positive third lens L ₃ toward the object side, and a fourth cemented lens L ₄ + L ₅ having a positive refractive power as a whole, between the second lens L ₂ and third lens L ₃ In an endoscope objective lens with a brightness stop, (1) 0.60 <| f ₁ /f|<0.70 (2) n ₂ > 1.60 ν ₂ <45.0 (3) n ₃ > 1.60 ν ₃ > 50.0 ( 4) n ₄ ＞ 1.60 ν ₄ ＞ 50.0 (5) ν ₅ <40.0 where f _{1 is} the focal length of the first lens f is the combined focal length of the entire system n ₂ , n ₃ , n _{4 is} the second lens L ₂ , 3rd lens L ₃ , 4th cemented lens L
Refractive index of the glass material used for the convex lens L ₄ of ₄ + L ₅ with respect to d line ν ₂ , ν ₃ , ν ₄ , ν ₅ : second lens L ₂ , third lens L ₃ , fourth cemented lens L ₄ + L ₅ of the convex lens L _4, a fourth cemented lens L ₄ + endoscope objective lens satisfies the Abbe's number becomes conditions of the glass material which L ₅ is used in a concave lens L _5. 2. A negative first lens L ₁ having a concave surface facing the image side in order from the object side, a positive second lens L ₂ having a surface having a large radius of curvature facing the image side, and a surface having a large radius of curvature. the positive third lens L ₃ toward the object side, and a fourth cemented lens L ₄ + L ₅ having a positive refractive power as a whole, between the second lens L ₂ and third lens L ₃ In an endoscope objective lens with a brightness stop, (1) 0.60 <| f ₁ /f|<0.70 (2) n ₂ > 1.60 ν ₂ <45.0 (3) n ₃ > 1.60 ν ₃ > 50.0 ( 4) ν ₄ <40.0 (5) n ₅ > 1.60 ν ₅ > 50.0 where f _{1 is} the focal length of the first lens f is the combined focal length of the entire system n ₂ , n ₃ and n _{5 is} the second lens L ₂ , 3rd lens L ₃ , 4th cemented lens L
Refractive index of the glass material used for the convex lens L ₅ of ₄ + L ₅ with respect to d-line ν ₂ , ν ₃ ,, ν ₄ , ν ₅ : second lens L ₂ , third lens L ₃ , fourth cemented lens L ₄ + L ₅ of the concave lens L _4, a fourth cemented lens L ₄ + endoscope objective lens satisfies the Abbe's number becomes conditions of the glass material that the convex lens L ₅ L ₅ are used.