JP5087265B2 - Long working distance objective lens - Google Patents

Description

  The present invention relates to a long working distance objective lens used in a microscope, and relates to a long working distance objective lens having a working distance of about 50 to 100 times and a working distance of 4 times or more of a focal length.

  In recent years, a long working distance is often required for an industrial microscope objective lens used for processing metals and semiconductors. For example, when observing an IC, a longer working distance is required in order to observe the pattern of the bottom surface of the recess. Further, in the observation on a substrate with unevenness, a long working distance is required for protecting the substrate. In addition, when used as a laser repair, the work piece is scattered from the specimen surface, and the working distance often includes a thin glass plate, lead wire, steps due to a fixture, etc., so a longer working distance There is a need for an objective lens having

  In order to extend the working distance while performing good aberration correction, it is effective to enlarge the entire length and width of the objective lens. However, the increase in the volume and weight of the objective lens accompanying the increase in the working distance is a serious detriment to the energy saving of the apparatus, the high accuracy of positioning, and the manufacturing cost.

In view of the above, there is a strong demand for an objective lens that maintains good optical performance, reduces the volume of the space in which the lens is accommodated, and increases the ratio of the working distance to the total length as compared with the prior art.
As for the objective lens having a long working distance with a high magnification, those shown in Patent Document 1 to Patent Document 7 listed below are known, but both have expanded the overall length and width of the objective lens, This is a major obstacle to energy saving of devices, high accuracy of positioning, and manufacturing cost.

Moreover, although the objective lens shown in the following Patent Document 8 is not enlarged in total length and width, it cannot be said that it has a sufficient working distance due to technological progress.
JP-A-6-1775034 JP-A-10-288740 JP 2000-206414 A JP 2003-167199 A JP 2001-208976 A JP 2005-258148 A Japanese Patent Laid-Open No. 7-20385 JP-A-9-90230

  The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to provide a long working distance that can increase the ratio of the working distance to the total length while having excellent imaging performance. It is to provide an objective lens.

  The long working distance objective lens of the present invention that achieves the above object includes a positive single lens and a cemented lens from the object side, and converges light rays from an object having a positive refractive power from the object side. A first lens group that converts light into a light beam and a second lens group that includes at least one cemented lens and has negative refractive power satisfy the following condition.

0.3 ≦ L _h / L ≦ 0.65 (1)
30 ≦ ν _2N -ν _2P ≦ 50 (2)
2.995 ≤ | f ₁ / f ₂ | ≤ 5 (3)
3.1 ≤ f ₁ / F ≤ 6 (4)
However, L is the distance from the object surface to the final lens surface on the image side, L _h is the distance from the object surface to the position where the light beam incident on and exits the lens is the highest, and the most image-side joint in the second lens group. The Abbe number of the negative lens of the lens is ν _2N , the Abbe number of the positive lens of the most image-side cemented lens in the second lens group is ν _2P , the focal length of the first lens group is f ₁ , and the focal point of the second lens group The distance is f ₂ and the focal length of the whole system is F.

The long working distance objective lens of the present invention that achieves the above object includes a positive single lens and a cemented lens from the object side when viewed as a three-group configuration, and has a positive refractive power and converges light rays from the object. A first lens group that converts light into a light beam, a second lens group that includes at least one cemented lens and has negative refractive power , and a single lens and a cemented lens or a cemented lens only, and third lens that has negative refractive power It is composed of lens groups and satisfies the following conditions.

0.3 ≦ L _h / L ≦ 0.65 (1)
30 ≦ ν _IIIN -ν _IIIP ≦ 50 (5)
2.995 ≤ | f _I / f _II-III | ≤ 5 (6)
3.1 ≦ f _I / F ≦ 6 (7)
Where L is the distance from the object surface to the final lens surface on the image side, L _h is the distance from the object surface to the position where the light beam incident on and exits the lens is the highest, and the Abbe number of the negative lens in the third lens group Ν _IIIN , the Abbe number of the positive lens in the III lens group is ν _IIIP , the focal length of the I lens group is f _I , and the combined focal length of the _II and III lens groups is f _II-III , Let F be the focal length of the system .

Moreover, it is desirable to satisfy the following conditions, regardless of whether it is regarded as a two-group configuration or a three-group configuration.
n _f > 1.8 (8)
However, the refractive index of the positive lens closest to the object side is n _f .

In addition, in the case of a three-group configuration, in order to apply the present invention to a long working distance objective lens of about 100 times, it is desirable that the following conditions are satisfied.
95 <| F _I / F | <105 ... (9)
n _IIN > 1.7 (10)
However, the focal length of the entire objective lens system is F, the focal length of the imaging lens combined with the long-acting objective lens is F _I , and the refractive index of the negative lens of the II lens group is n _IIN .

Further, in the long working distance objective lens, it is desirable that the following conditions are satisfied.
WD / L ≦ 0.25 (11)
However, WD is the working distance of the objective lens.

In order to apply the present invention to an objective lens having a long working distance of about 50 times, it is desirable to satisfy the following conditions.
45 <| F _I / F | <55 (12)
WD / L ≦ 0.55 (13)
Further, when the present invention is applied to an objective lens having a long working distance of about 50 times, when viewed as a two-group configuration from another viewpoint, it includes a positive single lens and a cemented lens from the object side, and has a positive refractive power. The first A1 lens group that converts light from an object into a convergent light beam and the second B2 lens group that has at least one cemented lens and has negative refractive power, satisfy the following conditions: .

45 <| F _I / F | <55 (12)
0.4 ≦ L _h / L ≦ 0.65 (13)
4.8 ≤ f _A1 / F ≤ 5.3 (14)
Where L is the distance from the object plane to the final lens surface on the image side, L _h is the distance from the object plane to the position where the light ray incident and exits the lens is the highest, and the focal length of the first lens group is f _A1 . the focal length of the entire system F, the focal length of the imaging lens to be combined with the objective lens and F _I.

Further, when the objective lens having a long working distance of about 50 times according to the present invention is regarded as a three-group configuration from another viewpoint, it includes a positive single lens and a cemented lens from the object side and has a positive refractive power from the object. Comprising a first AI lens group that converts the light beam into a convergent light beam, a second BII lens group having negative refractive power , and at least one cemented lens, and a first CIII lens group having negative refractive power, under the following conditions: It is characterized by satisfying.

45 <| F _I / F | <55 (12)
0.4 ≦ L _h / L ≦ 0.65 (13)
4.8 ≤ f _AI / F ≤ 5.3 (15)
However, L is the distance from the object surface to the final lens surface on the image side, L _h is the distance from the object surface to the position where the light ray incident on and exits the lens is the highest, and the focal length of the first lens group is f _AI , the focal length of the entire system F, the focal length of the imaging lens to be combined with the objective lens and F _I.

Below, the reason and effect | action which take the said structure in this invention are demonstrated.
In order to increase the working distance of an objective lens with a constant focal distance, it is necessary to place a lens group with positive refractive power on the object side and a lens group with strong negative refractive power on the image side There is. In general, as the working distance of the objective lens becomes longer, various aberrations rapidly deteriorate. For this reason, an objective lens having a long working distance needs to correct various aberrations while keeping the working distance as long as possible with this configuration.

The long working distance objective lens of the present invention is composed of one group having a positive refractive power and two groups having a negative refractive power in order from the object side. The first lens group includes a positive single lens and a cemented lens on the object side, and has a role of gently converting light rays from the object into a convergent light beam. When the working distance becomes long, the ray height becomes high and it becomes difficult to correct the spherical aberration. For this reason, it is necessary to dispose a positive lens that satisfies Equation (8) on the object side in order to suppress the height of light rays. Further, since it becomes difficult to correct chromatic aberration when the working distance becomes long, it is necessary to dispose a cemented lens in the first lens group in order to correct chromatic aberration.

  The second lens group has a strong negative refractive power, and plays a role of obtaining a large magnification of the convergent light beam after passing through the first lens group by the strong negative refractive power. In addition, the strong negative refractive power of the second lens group also serves to reduce the Petzval sum of the objective lens and to properly correct the field curvature. Further, since it becomes difficult to correct the chromatic aberration of magnification when the working distance becomes long, it is necessary to arrange a cemented lens in the second lens group in order to correct the chromatic aberration of magnification.

  The above equations (1) and (13) define the starting position of the convergent light beam of the objective lens. If the lower limit of 0.3 in equation (1) is not reached, the divergent light flux generated from the object point is forcibly made into a convergent light beam, so that the incident angle of the light beam on each lens surface near the object side of the first group becomes large, Spherical aberrations are greatly exacerbated and difficult to correct even in the back group that converges. If the upper limit of 0.65 in equation (1) is exceeded, the light beam will be forcibly converged at the rear, so that the incident angle of the light beam on each lens surface of the second lens group will be large, and it will be difficult to correct coma. Become. On the other hand, when it is about 50 times, the value within the value of equation (13) is desirable for correcting each aberration.

  The above equation (2) defines the relationship with the Abbe number of each lens of the cemented lens configured in the second lens group. If the lower limit 30 of the expression (2) is not reached, it is difficult to correct the chromatic aberration of magnification. If the upper limit of 50 in equation (2) is exceeded, it will be difficult to correct longitudinal chromatic aberration.

  Usually, in order to correct axial chromatic aberration, correction is performed using a cemented lens of a positive lens having a large Abbe number and a negative lens having a small Abbe number. However, with a long working distance objective, axial chromatic aberration can be corrected, but correction up to magnification chromatic aberration is difficult.

  This time, in order to correct both axial and magnification chromatic aberration, the axial chromatic aberration was corrected excessively in the first lens group, and as shown in the equation (2), the Abbe number is small as opposed to normal. By joining the positive lens and the negative lens having a large Abbe number, the overcorrected axial chromatic aberration is returned to an appropriate correction, and the lateral chromatic aberration is corrected.

  The above expression (3) defines the relationship between the refractive powers of the first lens group and the second lens group. If the lower limit of 2.9 in the expression (3) is not reached, the refractive power of the second lens group becomes weak, the Petzval sum of the objective lens becomes large, and correction of field curvature becomes difficult. Exceeding the upper limit of 5 in equation (3) increases the refractive power of the second lens group, which is advantageous for correcting curvature of field, but increases the ray height of the first lens group, and various aberrations occur. Correction becomes difficult. In addition, the lens outer diameter is increased, and the operability of the objective lens is deteriorated.

  The above equations (4) and (14) show the relationship of the focal length of the positive first lens group. Below 3.1 in the above formula, the positive refractive power is too large, the Petzval sum increases in the + direction, and the field curvature cannot be corrected. If the above formula 6 is exceeded, the positive refractive power that the positive first lens group bears will be reduced, and other lenses will bear that much, and it will be possible to correct short wavelength spherical aberration and coma aberration. It becomes difficult. By satisfying the above formula, it is possible to satisfactorily correct spherical aberration and coma. On the other hand, when it is about 50 times, it is desirable that the value is within the value of the equation (14) in order to correct each aberration.

  Equation (8) defines the refractive index of the positive lens closest to the object side in the first lens group. In order to make it difficult for spherical aberration to occur, it is necessary to make the incident angle of the light beam with respect to the lens surface as small as possible even for a high numerical aperture light beam. For this reason, it is desirable that the refractive power of the front sphere in the first lens group be as high as possible. Below 1.8 in the above formula, it becomes difficult to correct spherical aberration.

  The above formulas (9) and (12) show the relationship between the focal length of the objective lens and the imaging lens combined with the objective lens, and indicate the magnification to which the present invention is applied. In order to use it as about 100 × in practical use, the value is within the value of equation (9). Moreover, in order to use as about 50 ×, the value is within the value of the expression (12).

  The above expression (11) shows the relationship between the working distance and the distance from the object surface to the final lens surface on the image side for an objective lens with a magnification of about 100 ×. If 0.25 in the above formula is exceeded, the refractive power of the second lens group becomes weak, the Petzval sum of the objective lens becomes large, and it becomes difficult to correct curvature of field.

  The above expression (13) shows the relationship between the working distance and the distance from the object surface to the final lens surface on the image side with respect to an objective having a magnification of about 50 ×. If 0.55 in the above formula is exceeded, the refractive power of the second lens group becomes weak, the Petzval sum of the objective lens becomes large, and it becomes difficult to correct curvature of field.

In the present invention, the group configuration of the lens system can be regarded as a three-group configuration.
The I-th lens group includes a positive single lens and a cemented lens on the object side, and has a role of gently converting light rays from the object into a convergent light beam. When the working distance becomes long, the ray height becomes high and it becomes difficult to correct the spherical aberration. For this reason, it is necessary to dispose a positive lens that satisfies Equation (8) on the object side in order to suppress the height of light rays. Further, since it becomes difficult to correct chromatic aberration when the working distance becomes long, it is necessary to dispose a cemented lens in the first lens group in order to correct chromatic aberration.

  The II lens group is used to correct chromatic aberration, coma aberration, and spherical aberration that occur in the I lens group. By using a cemented lens, chromatic aberration and spherical aberration are strongly corrected. In addition, since the object-side surface of the joint is a convex surface, it is possible to suppress the occurrence of various aberrations when a light beam that has become a convergent light beam in the group I is incident.

  The third lens group has a strong negative refracting power, reduces the Petzval sum of the objective lens, and also plays a role in favorably correcting field curvature. Further, since it becomes difficult to correct the chromatic aberration of magnification when the working distance becomes long, it is necessary to arrange a cemented lens in the third lens group for correcting the chromatic aberration of magnification.

  The above equation (5) defines the relationship with the Abbe number of each lens of the cemented lens configured in the III lens group. If the lower limit 30 of the formula (5) is not reached, it is difficult to correct the chromatic aberration of magnification. If the upper limit of 50 in equation (5) is exceeded, it will be difficult to correct longitudinal chromatic aberration.

  Usually, in order to correct axial chromatic aberration, correction is performed using a cemented lens of a positive lens having a large Abbe number and a negative lens having a small Abbe number. However, with a long working distance objective, axial chromatic aberration can be corrected, but correction up to magnification chromatic aberration is difficult.

  The above formula (6) defines the refractive power relationship among the I lens group and the combined focal length of the II lens group and the III lens group. If the lower limit of 2.9 in equation (6) is not reached, the refractive power of the second lens group will be weakened, and the Petzval sum of the objective lens will increase, making it difficult to correct field curvature. If the upper limit of 5 in equation (6) is exceeded, the refracting power of the second lens group will increase, which is advantageous for correcting curvature of field, but the light height of the first lens group will increase, and various aberrations will occur. Correction becomes difficult. In addition, the lens outer diameter is increased, and the operability of the objective lens is deteriorated.

  The above expressions (7) and (15) show the relationship between the focal lengths of the positive first lens group. Below 3.1 in the above formula, the positive refractive power is too large, the Petzval sum increases in the + direction, and coma aberration cannot be corrected. If the above formula 6 is exceeded, the positive refractive power that the positive first lens group bears will be reduced, and other lenses will bear that much, and it will be possible to correct short wavelength spherical aberration and coma aberration. It becomes difficult. By satisfying the above formula, it is possible to satisfactorily correct spherical aberration and coma. On the other hand, when it is about 50 times, it is desirable that the value is within the value of equation (15) in order to correct each aberration.

  The above equation (10) defines the refractive index of the negative lens of the second lens group for an objective with a magnification of about 100 ×. Below 1.7 in the above formula, the incident angle of the light rays on the lens surfaces of the II lens group and the III lens group becomes large, and it becomes difficult to correct coma.

  According to the present invention, it is possible to provide a long working distance objective lens that has an excellent imaging performance but can increase the ratio of the working distance to the total length as compared with the conventional art.

  Examples 1 to 6 of the long working distance microscope objective lens of the present invention will be described below. Although lens data of each example will be described later, FIGS. 1 to 6 are cross-sectional views illustrating lens configurations of Examples 1 to 6, respectively. FIG. 13 is a cross-sectional view of the imaging lens described in Table 7 used in this embodiment.

  Example 1 is a design example of a 100 × objective lens. As shown in the cross-sectional view of FIG. 1, the first lens group (G1) includes two positive meniscus lenses having a concave surface facing the object side, and a biconvex lens. And a biconvex simplex positive lens. The second lens group (G2) includes a cemented lens of a meniscus lens having a convex surface facing the object side and a biconvex lens, a cemented lens of two pairs of biconvex lenses and a biconcave lens, a biconcave single negative lens, and a concave surface on the object side. Is composed of a cemented lens of a meniscus lens and a biconcave lens.

  Example 1 can also be regarded as a three-group lens. At this time, the I lens group is the same as the first lens group. The second lens group is composed of a meniscus lens having a convex surface facing the object side of the second lens group, a cemented lens of a biconvex lens, and a cemented lens of two pairs of biconvex lenses and a biconcave lens. , A biconcave single negative lens, a meniscus lens having a concave surface facing the object side, and a cemented lens of a biconcave lens.

  Example 2 is a design example of a 100 × objective lens. As shown in the sectional view of FIG. 2, the first lens group (G1) includes two positive meniscus lenses having a concave surface facing the object side, and a biconvex lens. And a biconvex lens, a biconcave lens, and a biconvex single positive lens. The second lens group (G2) includes a cemented lens composed of a meniscus lens having a convex surface facing the object, a biconvex lens and a biconcave lens, and a meniscus lens having both convex surfaces facing the object side. It is composed of a concave single negative lens and a cemented lens of a biconvex lens and a biconcave lens.

  Example 2 can also be regarded as a three-group lens. At this time, the I lens group is the same as the first lens group. The second lens group consists of a cemented lens composed of a combination of a meniscus lens having a convex surface facing the object side of the second lens group, a biconvex lens and a biconcave lens, and two meniscus lenses having a convex surface facing the object side. The third lens group includes a cemented lens of a biconvex lens and a biconcave lens.

  Example 3 is a design example of a 100 × objective lens. As shown in the cross-sectional view of FIG. 3, the first lens group (G1) includes two positive meniscus lenses having a concave surface facing the object side, and a biconvex lens. And a biconvex simplex positive lens. The second lens group (G2) includes a cemented lens of a meniscus lens having a convex surface facing the object side and a biconvex lens, a cemented lens having two pairs of biconvex lenses and a biconcave lens, and a negative single meniscus lens having a convex surface facing the object side. And a cemented lens of a meniscus lens having a concave surface facing the image side.

  Example 3 can also be regarded as a three-group lens. At this time, the I lens group is the same as the first lens group. The second lens group is composed of a meniscus lens having a convex surface facing the object side of the second lens group, a cemented lens of a biconvex lens, and a cemented lens of two pairs of biconvex lenses and a biconcave lens. And a negative single meniscus lens having a convex surface facing the object side, and a cemented lens of a biconcave lens and a meniscus lens having a concave surface facing the image side.

  Example 4 is a design example of a 50 × objective lens. As shown in the sectional view of FIG. 4, the first lens group (G1) has a biconvex single positive lens, a biconvex lens, and a convex surface facing the image side. Further, it is composed of a cemented lens of a meniscus lens and a biconvex single positive lens. The second lens group (G2) has a meniscus lens having a convex surface facing the object side, a three-piece cemented lens of a combination of a biconvex lens and a biconcave lens, a cemented lens of a biconvex lens and a biconcave lens, and a concave surface facing the object side. It is composed of a cemented lens of a meniscus lens and a biconcave lens.

  Example 4 can also be regarded as a two-group lens from different viewpoints. At this time, the A1 lens group includes a biconvex single positive lens, and a cemented lens of a biconvex lens and a meniscus lens having a convex surface facing the image side. The second B2 lens group consists of a biconvex single positive lens, a triplet cemented lens composed of a meniscus lens with a convex surface facing the object, a biconvex lens and a biconcave lens, a cemented lens of a biconvex lens and a biconcave lens, and a concave surface on the object side. Is composed of a cemented lens of a meniscus lens and a biconcave lens.

  Example 4 can also be regarded as a three-group lens. At this time, the I lens group is the same as the first lens group. The second lens group is composed of a meniscus lens having a convex surface facing the object side of the second lens group, a three-piece cemented lens of a combination of a biconvex lens and a biconcave lens, and a cemented lens of a biconvex lens and a biconcave lens. The III lens group includes a cemented lens of a meniscus lens having a concave surface facing the object side and a biconcave lens.

  Further, the fourth embodiment can be regarded as a three-group lens from different viewpoints. At this time, the AI lens group is the same as the A1 lens group. The BII lens group consists of a biconvex single positive lens of the B2 lens group, a three-piece cemented lens composed of a meniscus lens having a convex surface facing the object side, a biconvex lens and a biconcave lens, and a cemented lens of a biconvex lens and a biconcave lens. The CIII lens group includes a cemented lens of a meniscus lens having a concave surface facing the object side and a biconcave lens.

  Example 5 is a design example of a 50 × objective lens. As shown in the sectional view of FIG. 5, the first lens group (G1) has a biconvex single positive lens, a biconvex lens, and a convex surface facing the image side. Further, it is composed of a cemented lens of a meniscus lens and a biconvex single positive lens. The second lens group (G2) has a meniscus lens having a convex surface facing the object side, a three-piece cemented lens of a combination of a biconvex lens and a biconcave lens, a cemented lens of a biconvex lens and a biconcave lens, and a concave surface facing the object side. It is composed of a cemented lens of a meniscus lens and a biconcave lens.

  Example 5 can also be regarded as a two-group lens from different viewpoints. At this time, the A1 lens group includes a biconvex single positive lens, and a cemented lens of a biconvex lens and a meniscus lens having a convex surface facing the image side. The second B2 lens group consists of a biconvex single positive lens, a triplet cemented lens composed of a meniscus lens with a convex surface facing the object, a biconvex lens and a biconcave lens, a cemented lens of a biconvex lens and a biconcave lens, and a concave surface on the object side. Is composed of a cemented lens of a meniscus lens and a biconcave lens.

  Example 5 can also be regarded as a three-group lens. At this time, the I lens group is the same as the first lens group. The second lens group is composed of a meniscus lens having a convex surface facing the object side of the second lens group, a three-piece cemented lens of a combination of a biconvex lens and a biconcave lens, and a cemented lens of a biconvex lens and a biconcave lens. The III lens group includes a cemented lens of a meniscus lens having a concave surface facing the object side and a biconcave lens.

  Further, Example 5 can be regarded as a three-group lens from different viewpoints. At this time, the AI lens group is the same as the A1 lens group. The BII lens group consists of a biconvex single positive lens of the B2 lens group, a three-piece cemented lens composed of a meniscus lens having a convex surface facing the object side, a biconvex lens and a biconcave lens, and a cemented lens of a biconvex lens and a biconcave lens. The CIII lens group includes a cemented lens of a meniscus lens having a concave surface facing the object side and a biconcave lens.

  Example 6 is a design example of a 50 × objective lens. As shown in the sectional view of FIG. 6, the first lens group (G1) has a biconvex single positive lens, a biconvex lens, and a convex surface facing the image side. Further, it is composed of a cemented lens of a meniscus lens and a biconvex single positive lens. The second lens group (G2) has a meniscus lens having a convex surface facing the object side, a three-piece cemented lens of a combination of a biconvex lens and a biconcave lens, a cemented lens of a biconvex lens and a biconcave lens, and a concave surface facing the object side. It is composed of a cemented lens of a meniscus lens and a biconcave lens.

  Example 6 can also be regarded as a two-group lens from different viewpoints. At this time, the A1 lens group includes a biconvex single positive lens, and a cemented lens of a biconvex lens and a meniscus lens having a convex surface facing the image side. The second B2 lens group consists of a biconvex single positive lens, a triplet cemented lens composed of a meniscus lens with a convex surface facing the object, a biconvex lens and a biconcave lens, a cemented lens of a biconvex lens and a biconcave lens, and a concave surface on the object side. Is composed of a cemented lens of a meniscus lens and a biconcave lens.

  Example 6 can also be regarded as a three-group lens. At this time, the I lens group is the same as the first lens group. The second lens group is composed of a meniscus lens having a convex surface facing the object side of the second lens group, a three-piece cemented lens of a combination of a biconvex lens and a biconcave lens, and a cemented lens of a biconvex lens and a biconcave lens. The III lens group includes a cemented lens of a meniscus lens having a concave surface facing the object side and a biconcave lens.

  Further, Example 6 can be regarded as a three-group lens from different viewpoints. At this time, the AI lens group is the same as the A1 lens group. The BII lens group consists of a biconvex single positive lens of the B2 lens group, a three-piece cemented lens composed of a meniscus lens having a convex surface facing the object side, a biconvex lens and a biconcave lens, and a cemented lens of a biconvex lens and a biconcave lens. The CIII lens group includes a cemented lens of a meniscus lens having a concave surface facing the object side and a biconcave lens.

  The lens data for each example is shown below. In addition to the above, NA is the numerical aperture, WD is the working distance, β is the magnification, and f is the focal length. Each of Examples 1 to 6 is a correction type objective lens that is infinitely far away from which the light emitted from the objective lens becomes a parallel light beam, and these single lenses are not combined. Therefore, for example, the lens data shown in Table 7 is used and used in combination with an imaging lens whose lens cross-sectional view is shown in FIG. In Tables 1 to 7, r1, r2,... Are the curvature radii of the lens surfaces shown in order from the object side, d1, d2,... Are the refractive indices of the d-line of each lens, shown in order from the object side, νd1, νd2,. Is the Abbe number of each lens shown in order from the object side.

  Numerical values attached below the lens data correspond to the above-described conditional expressions (1) to (14) and are calculated from the lens data.

NA = 0.6, WD = 10.2, f = 1.8, β = −100

(1) L _h / L = 0.356
(2), (5) ν _2N -ν _2P = ν _IIIN -ν _IIIP = 42.24
(3), (6) | f ₁ / f ₂ | = f _I -f _II-III = 4.222
(4), (7) f ₁ / F = f _I /F=5.326
(8) n _f = 1.883
(9) | F _I / F | = 100
(10) n _IIN = 1.738
(11) WD / L = 0.21

NA = 0.7, WD = 7.9, f = 1.8, β = -100

(1) L _h / L = 0.417
(2), (5) ν _2N -ν _2P = ν _IIIN -ν _IIIP = 33.6
(3), (6) | f ₁ / f ₂ | = f _I -f _II-III = 3.065
(4), (7) f ₁ / F = f _I / F = 5.398
(8) n _f = 1.883
(9) | F _I / F | = 100
(10) n _IIN = 1.738
(11) WD / L = 0.162

NA = 0.6, WD = 8.9, f = 1.8, β = -100

(1) L _h / L = 0.339
(2), (5) ν _2N -ν _2P = ν _IIIN -ν _IIIP = 47.47
(3), (6) | f ₁ / f ₂ | = f _I -f _II-III = 3.543
(4), (7) f ₁ / F = f _I /F=5.518
(8) n _f = 1.883
(9) | F _I / F | = 100
(10) n _IIN = 1.72047
(11) WD / L = 0.182

NA = 0.35, WD = 18.1, f = 3.6, β = −50

(1) L _h / L = 0.448
(2), (5) ν _2N -ν _2P = ν _IIIN -ν _IIIP = 31.92
(3), (6) | f ₁ / f ₂ | = f _I -f _II-III = 2.995
(4), (7) f ₁ / F = f _I /F=3.177
(8) n _f = 1.834
(12) | F _I / F | = 50
(13) WD / L = 0.37
(14), (15) f _A1 / F = f _AI / F = 4.828

NA = 0.35, WD = 20, f = 3.6, β = −50

(1) L _h / L = 0.605
(2), (5) ν _2N -ν _2P = ν _IIIN -ν _IIIP = 31.92
(3), (6) | f ₁ / f ₂ | = f _I -f _II-III = 3.352
(4), (7) f ₁ / F = f _I /F=3.193
(8) n _f = 1.834
(12) | F _I / F | = 50
(13) WD / L = 0.408
(14), (15) f _A1 / F = f _AI / F = 5.077

NA = 0.25, WD = 24.1, f = 3.6, β = −50

(1) L _h / L = 0.559
(2), (5) ν _2N -ν _2P = ν _IIIN -ν _IIIP = 30.7
(3), (6) | f ₁ / f ₂ | = f _I -f _II-III = 4.523
(4), (7) f ₁ / F = f _I /F=3.143
(8) n _f = 1.834
(12) | F _I / F | = 50
(13) WD / L = 0.49
(14), (15) f _A1 / F = f _AI / F = 5.088
The interval between the objective lenses of Examples 1 to 6 and the imaging lens of FIG. 13 described below may be any position between 50 mm and 170 mm, but Examples 1 to 1 in the case where this interval is 120 mm. The aberration diagrams of Fig. 6 are shown in Figs. In these aberration diagrams, (a) shows spherical aberration, (b) shows astigmatism, (c) shows distortion, and (d) shows coma. IH in these aberration diagrams indicates the image height. In addition, the same aberration state is shown also in positions other than 120 mm between the intervals of 50 mm to 170 mm.

  In addition, the focal length of the imaging lens described below is 180 mm, and objective lenses having a magnification of 100 times in Examples 1 to 3 and a magnification of 50 in Examples 4 to 6 are realized.

As described above, the microscope objective lens according to any of the above-described embodiments is also a lens system suitable for an industrial microscope with a magnification of about 50 to 100 having excellent imaging performance while having a longer working distance than before. .

It is lens sectional drawing of Example 1 of the microscope objective lens of this invention. 6 is a lens cross-sectional view of Example 2. FIG. 5 is a lens cross-sectional view of Example 3. FIG. 6 is a lens cross-sectional view of Example 4. FIG. 6 is a lens cross-sectional view of Example 5. FIG. 10 is a lens cross-sectional view of Example 6. FIG. FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, distortion, and coma aberration in Example 1. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and coma aberration of Example 2. FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, distortion, and coma aberration in Example 3. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and coma aberration of Example 4. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and coma aberration of Example 5. FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, distortion, and coma aberration in Example 6. It is a lens sectional view of an example of an imaging lens used in combination with a microscope objective lens of each example.

Explanation of symbols

G1 ... 1st lens group
G2 ... Second lens group
I ... I lens group
II ... Second lens group
III ... III lens group
A1 ... A1 lens group
B2 ... B2 lens group
AI ... AI lens group
BII ... BII lens group
CIII ... CIII lens group

Claims (6)

A long working distance objective lens,
Consists of a first lens group and a second lens group in order from the object side,
The first lens group includes a positive single lens and a cemented lens, and is a lens group that converts a light beam from an object having a positive refractive power into a convergent light beam,
The second lens group includes at least one cemented lens, and is a lens group having a negative refractive power,
L is the distance from the object surface to the final lens surface on the image side, L _h is the distance from the object surface to the position where the light beam incident on and exits the lens is the highest, and the most image-side cemented lens in the second lens group The Abbe number of the negative lens is ν _2N , the Abbe number of the positive lens of the most image-side cemented lens in the second lens group is ν _2P , the focal length of the first lens group is f ₁ , and the second lens group Where f ₂ is the focal length of the lens, and F is the focal length of the entire system of the long working distance objective lens.
0.3 ≤ L _h / L ≤ 0.65
30 ≦ ν _2N -ν _2P ≦ 50
2.995 ≤ | f ₁ / f ₂ | ≤ 5
3.1 ≤ f ₁ / F ≤ 6
Long working distance objective lens characterized by satisfying A long working distance objective lens,
Consists of an I lens group, a II lens group, and a III lens group in order from the object side,
The first lens group includes a positive single lens and a cemented lens, and has a positive refractive power and converts a light beam from an object into a convergent light beam,
The second lens group includes at least one cemented lens and has a negative refractive power ,
The third lens group consists of only a single lens and a cemented lens or a cemented lens, and is a lens group having negative refractive power,
L is the distance from the object surface to the final lens surface on the image side, L _h is the distance from the object surface to the position where the light beam incident on and exits the lens is the highest, and the Abbe number of the negative lens in the third lens group is ν _IIIN , the Abbe number of the positive lens in the III lens group is ν _IIIP , the focal length of the I lens group is f _I , and the combined focal length of the II lens group and the III lens group is f _{II− III,} and when the focal length of the entire system of the long working distance objective lens is F , the following conditional expression
0.3 ≤ L _h / L ≤ 0.65
30 ≤ ν _IIIN -ν _IIIP ≤ 50
2.995 ≤ | f _I / f _II-III | ≤ 5
3.1 ≤ f _I / F ≤ 6
Long working distance objective lens characterized by satisfying The long working distance objective according to claim 1 or 2 ,
When the refractive index of the positive lens closest to the object side of the long working distance objective lens is n _f , the following conditional expression
n _f > 1.8
Long working distance objective lens characterized by satisfying In long working distance objective lens according to claim 2 in which the focal length is used in combination with the imaging lens of F _I,
When the focal length of the entire objective lens system is F and the refractive index of the negative lens of the second lens group is n _IIN , the following conditional expression
95 <| F _I / F | <105
n _IIN > 1.7
Long working distance objective lens characterized by satisfying The long working distance objective according to claim 4 ,
When the working distance of the long working objective lens is WD, the following conditional expression WD / L ≦ 0.25
Long working distance objective lens characterized by satisfying In long working distance objective lens according to claim 2 in which the focal length is used in combination with the imaging lens of F _I,
When the focal length of the whole objective lens system is F and the working distance of the long working objective lens is WD, the following conditional expression
45 <| F _I / F | <55
WD / L ≦ 0.55
Long working distance objective lens characterized by satisfying