Objective lens

Abstract

To provide an objective lens which satisfies specifications of a long WD (working distance) and a wide field of view and in which aberration performance down to the periphery of the field of view is well corrected.SOLUTION: An objective lens 1 is provided, comprised of a positive first lens group G1 and a negative second lens group G2. The first lens group G1 includes a positive meniscus lens with a concave object-side surface disposed on the most object side. The second lens goop G2 includes a pair of meniscus lens components with concave surfaces facing each other. The objective lens 1 has three or more cemented lenses located on the object side of the pair of meniscus lens components. The objective lens 1 satisfies the following conditional expressions: 2.6≤φL1 / DL1≤16 ...(1), 0.1≤|R212| / f≤3.5 ...(2), where φL1 represents an outer diameter of the positive meniscus lens, L1 represents an optical axial thickness of the positive meniscus lens, R212 represents a curvature radius of a most image-side surface of an object-side meniscus lens component of the pair of meniscus lens components, and f represents a focal length of the objective lens 1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The disclosure of this specification relates to an objective lens.

Background Art

[0002] For objective lenses used in industrial applications such as wafer inspection, a high numerical aperture (hereinafter referred to as NA) is required to achieve high resolution. Also, to achieve high throughput, a long working distance (hereinafter referred to as WD) is required to improve the conveyance speed while avoiding the risk of collision between the test object and the objective lens, along with a wide field of view.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For example, Patent Document 1 discloses an objective lens with a magnification of 100 times and an NA of 0.8 or more. However, such an objective lens has a too small actual field of view, making it difficult to obtain sufficient throughput. Also, when trying to achieve a wide field of view with the configuration of this objective lens, it is mainly difficult to correct the field curvature well. As a result, it is difficult to achieve good resolution up to the peripheral part of the wide field of view.

[0005] An object according to one aspect of the present invention is to provide an objective lens that satisfies the specifications of a long WD and a wide field of view, and has good aberration performance correction up to the peripheral part of the field of view.

Means for Solving the Problems

[0006] An objective lens according to one aspect of the present invention comprises a first lens group having positive refractive power that converts divergent light from an object point into convergent light, and a second lens group having negative refractive power that is positioned closer to the image than the first lens group. The first lens group includes a first lens, which is a meniscus lens having positive refractive power with its concave surface facing the object, located closest to the object. The second lens group includes a pair of meniscus lens components with their concave surfaces facing each other. The objective lens includes three or more cemented lenses located closer to the object than the pair of meniscus lens components. The objective lens satisfies the following condition. 2.6≦φ L1 / D L1 ≤16 ···(1) 0.1 ≤ |R 212 | / f≦3.5 ···(2) However, φ L1 D is the outer diameter of the first lens. L1 R is the thickness of the first lens along its optical axis. 212 f is the radius of curvature of the image-side surface of the first meniscus lens component, which is the object-side meniscus lens component of the pair of meniscus lens components. f is the focal length of the objective lens. [Effects of the Invention]

[0007] According to the above embodiment, it is possible to provide an objective lens that satisfies the specifications of long WD and wide field of view, and in which aberration performance is well corrected even at the edges of the field of view. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view of the objective lens 1 according to Embodiment 1 of the present invention. [Figure 2] This is a cross-sectional view of the imaging lens 10. [Figure 3] This is an aberration diagram of an optical system consisting of an objective lens 1 and an imaging lens 10. [Figure 4] This is a cross-sectional view of the objective lens 2 according to Embodiment 2 of the present invention. [Figure 5] This is an aberration diagram of an optical system consisting of an objective lens 2 and an imaging lens 10. [Figure 6] This is a cross-sectional view of the objective lens 3 according to Embodiment 3 of the present invention. [Figure 7] This is an aberration diagram of an optical system consisting of an objective lens 3 and an imaging lens 10. [Figure 8] This is a cross-sectional view of the objective lens 4 according to Embodiment 4 of the present invention. [Figure 9] This is an aberration diagram of an optical system consisting of an objective lens 4 and an imaging lens 10. [Modes for carrying out the invention]

[0009] An objective lens according to one embodiment of this application will now be described. The objective lens according to this embodiment (hereinafter simply referred to as the objective lens) is an infinity-corrected microscope objective lens used in combination with an imaging lens.

[0010] The objective lens consists of a first lens group having a positive refractive power that converts divergent light from an object point into convergent light, and a second lens group having a negative refractive power that is positioned closer to the image than the first lens group. The lens component closest to the image in the first lens group is the lens component closest to the object that converts divergent light from an object point into convergent light and acts to emit that convergent light. That is, if there are multiple lens surfaces in the objective lens that emit convergent light, the lens surface closest to the object among those lens surfaces is the lens surface closest to the image in the first lens group. The boundary between the first and second lens groups can be identified by the above characteristics.

[0011] In this specification, a lens component refers to a single lens block, whether a single lens or a cemented lens, where only two surfaces—the object-side surface and the image-side surface—through which light rays from an object point pass are in contact with the air. That is, one single lens is one lens component, and one cemented lens is also one lens component. On the other hand, multiple single lenses or multiple cemented lenses arranged with air between them are not considered a single lens component.

[0012] The first lens group converts divergent light from the object point into convergent light and directs it into the second lens group. The second lens group converts the convergent light from the first lens group into parallel light. By first converting the divergent light from the object point into convergent light in the first lens group before directing it into the second lens group, the marginal ray height within the second lens group can be made lower than the marginal ray height within the first lens group. This makes it possible to effectively correct the Petzval sum with the second lens group, which has negative refractive power, and as a result, it is possible to correct field curvature well over a wide field of view.

[0013] The first lens group includes a meniscus lens (hereinafter also referred to as the first lens) with positive refractive power and a concave surface facing the object, positioned closest to the object. In order to realize an objective lens with a high NA length and WD, the marginal ray height at the time of incidence to the objective lens is inevitably large due to the divergence of light before it enters the objective lens. For this reason, it is necessary to suppress the divergence of the ray beam by placing a lens with positive refractive power closest to the object. In this case, if the positive refractive power lens positioned closest to the object is a meniscus lens with a concave surface facing the object, the effect of mainly suppressing spherical aberration and coma aberration can be obtained. In the case of an objective lens with a particularly long WD, as shown in the embodiment described later, the marginal ray height at the time of incidence is very high, so unless the above-mentioned lens is placed, it will be difficult to correct aberrations in the entire optical system well. Therefore, a meniscus lens with positive refractive power and a concave surface facing the object is placed closest to the object in the objective lens.

[0014] The second lens group includes a pair of meniscus lens components with concave surfaces facing each other. By including a pair of meniscus lens components, which are Gaussian groups with convex surfaces facing outward and concave surfaces facing inward, within the second lens group into which the convergent light is incident, the marginal ray height can be reduced at the opposing concave surfaces. As a result, it becomes possible to effectively correct the Petzval sum at the concave surface with negative refractive power, and to sufficiently reduce field curvature.

[0015] The objective lens includes three or more cemented lenses on the object side of the pair of meniscus lens components described above. By including three or more cemented lenses that join lenses with different optical characteristics, chromatic aberration can be sufficiently corrected. In particular, a cemented lens composed of a low-dispersion positive lens and a high-dispersion negative lens generally has an effect of correcting axial chromatic aberration, which is generally called a color erasing effect. By arranging three or more cemented lenses having a color erasing effect in a region on the object side of the pair of meniscus lens components, which is a region with a large marginal ray height, a good axial chromatic aberration correction effect can be obtained.

[0016] Also, the objective lens is configured to satisfy the following conditional expressions (1) and (2). 2.6 ≦ φ L1 / D L1 ≦ 16 ···(1) 0.1 ≦ |R 212 | / f ≦ 3.5 ···(2) However, φ L1 is the outer diameter of the first lens. D L1 is the thickness of the first lens on the optical axis. R 212 is the radius of curvature of the most image-side surface of the meniscus lens component on the object side of the pair of meniscus lens components (hereinafter also referred to as the first meniscus lens component). f is the focal length of the objective lens. Note that the outer diameter of the first lens is usually an amount about 0.5 mm larger than the effective diameter (diameter) of the image-side surface of the first lens.

[0017] Conditional expression (1) is a conditional expression for preferably correcting spherical aberration and coma aberration in an objective lens with a long WD. Diverging light that enters with a large marginal ray height due to the influence of a long WD cannot significantly suppress its divergence on the concave surface on the object side of the first lens, but by satisfying conditional expression (1), spherical aberration and coma aberration can be preferably corrected.

[0018] φ L1 / D L1If φ falls below the lower limit (2.6), the thickness of the first lens becomes too large, causing the marginal ray height to become excessively large within the first lens. As a result, the marginal ray height incident on the image-side surface of the first lens and the subsequent optical system becomes too large, making it difficult to keep the amount of spherical aberration and coma aberration low. Consequently, good aberration correction for the entire optical system becomes difficult. On the other hand, φ L1 / D L1 If the value exceeds the upper limit (16), the thickness of the first lens becomes too thin relative to its outer diameter, making it difficult to ensure the rigidity of the first lens. As a result, the manufacturing error of the surface shape becomes large, making it difficult to achieve the desired aberration correction.

[0019] Condition (2) is primarily a condition for effectively correcting field curvature. By satisfying condition (2), the Petzval sum can be adequately corrected by the first meniscus lens component with its concave surface facing the image side, thus effectively correcting field curvature throughout the entire optical system.

[0020] |R 212 If | / f exceeds the upper limit (3.5), the radius of curvature of the concave surface of the first meniscus lens becomes too large, making it difficult to adequately correct the Petzval sum and thus difficult to properly correct the field curvature of the entire optical system. In particular, in optical systems with a long WD, the marginal ray height at the time of incidence is inevitably large, making it difficult to place a strong concave surface that acts in the direction of increasing the ray height in areas relatively close to the object, such as the first lens group included in the optical system, and thus difficult to correct the Petzval sum. For this reason, in order to have a long WD and achieve sufficient aberration correction over a wide field of view, sufficient correction of the Petzval sum is necessary in the first meniscus lens. On the other hand, |R 212 If | / f falls below the lower limit (0.1), the first meniscus lens overcorrects the Petzval sum. This makes it difficult to properly correct the field curvature of the entire optical system.

[0021] With the objective lens configured as described above, the specifications for long drive width and wide field of view are met, and aberrations can be corrected well even at the edges of the field of view.

[0022] The objective lens may be configured to satisfy either condition (1-1) or condition (1-2) below instead of condition (1). Furthermore, the objective lens may be configured to satisfy either condition (2-1) or condition (2-2) below instead of condition (2). 3.3≦φ L1 / D L1 ≤12 ···(1-1) 3.8≦φ L1 / D L1 ≤8 ···(1-2) 0.2 ≤ |R 212 | / f≦1.7 ···(2-1) 0.3 ≤ |R 212 f ≤ 1.2 ···(2-2)

[0023] The following describes the desirable configuration of the objective lens. The second lens group preferably includes a three-element cemented lens with positive-negative-positive configuration, where positive lenses are positioned on either side of a negative lens. Having an achromatic lens component consisting of three cemented lenses makes it possible to effectively correct axial chromatic aberration while making efficient use of the space within the objective lens. Furthermore, in order for the achromatic lens component to exert its full effect, it is desirable to place it in a region with a large marginal ray height, but in such a region the lens diameter will inevitably become larger. As described above, by using an achromatic lens component consisting of three cemented lenses, the rigidity of the lens component can be strongly maintained even if the lens diameter becomes large.

[0024] Each of the pair of meniscus lens components is preferably a cemented lens. As mentioned above, the pair of meniscus lens components primarily function to reduce the Petzval sum and correct field curvature, but by making them cemented lenses, they can be given the function of correcting chromatic aberration in addition to field curvature. For this reason, it becomes possible to correct axial chromatic aberration very well.

[0025] Furthermore, it is desirable that the objective lens satisfies at least one of the following conditions (3) to (5). 0.5 ≤ |R 211 | / f≦7 ···(3) 18 ≤ νdL ≤ 31 ···(4) 1.51 ≤ ndH ≤ 1.75 ···(5) However, R 211 νdL is the radius of curvature of the object-side surface of the first meniscus lens component. νdL is the minimum Abbe number of at least one positive lens positioned closer to the image than the image-side surface of the first meniscus lens component. ndH is the maximum refractive index of at least one negative lens included in the objective lens.

[0026] Conditional equation (3) is primarily a conditional equation for further correcting field curvature. As mentioned above, the first meniscus lens component with its convex side facing the object has a corrective effect on the Petzval sum, but in order to obtain a sufficient corrective effect, it is desirable to make the marginal ray height on the concave side of the first meniscus lens component sufficiently small.

[0027] |R 211 By ensuring that | / f does not exceed the upper limit (7), it is possible to avoid the radius of curvature of the object-side convex surface of the first meniscus lens component becoming too large. This allows the incident light to converge on the convex surface, keeping the marginal ray height on the image-side concave surface sufficiently small, thus effectively correcting field curvature. Also, |R 211 By ensuring that | / f does not fall below the lower limit (0.5), it is possible to avoid the radius of curvature of the object-side convex surface of the first meniscus lens component becoming too small. This prevents the occurrence of various aberrations, such as coma aberration, on that convex surface from becoming too large, enabling good aberration correction.

[0028] Conditional equation (4) is primarily a conditional equation for effectively correcting both axial and lateral chromatic aberration. The principal rays of off-axis light from the objective lens intersect the optical axis within the objective lens, so the sign of the height of the off-axis principal rays is reversed in the object-side region and the image-side region at the intersection. In such a configuration, by using a highly dispersed glass material for the positive lens positioned in the image-side region of the aforementioned intersection, it becomes possible to effectively correct lateral chromatic aberration that occurs in the object-side region.

[0029] By ensuring that νdL does not exceed the upper limit (31), the aforementioned effect makes it possible to effectively correct the chromatic aberration of the objective lens. Furthermore, by ensuring that νdL does not fall below the lower limit (18), it is possible to avoid excessive axial chromatic aberration and effectively correct axial chromatic aberration across the entire objective lens.

[0030] Conditional equation (5) is a conditional equation for effectively correcting wavefront aberrations such as spherical aberration. In order to give a lens negative refractive power, at least one surface must be concave, and generally the thickness of the lens is thinner in the center than in the periphery. Such a lens shape is prone to surface shape errors during manufacturing.

[0031] By keeping ndH below the upper limit (1.75), the refractive index of the negative lens does not become too large, minimizing the influence of lens surface shape errors on wavefront aberration. This allows for good correction of wavefront aberrations such as spherical aberration. Furthermore, glass materials with lower refractive indices generally tend to have low dispersion. Therefore, by keeping ndH below the lower limit (1.51), the dispersion of the negative lens does not become too small, enabling good correction of chromatic aberration.

[0032] Furthermore, the objective lens may be configured to satisfy condition (3-1) or condition (3-2) below instead of condition (3). Also, the objective lens may be configured to satisfy condition (4-1) or condition (4-2) below instead of condition (4). Also, the objective lens may be configured to satisfy condition (5-1) or condition (5-2) below instead of condition (5). 0.8 ≤ |R 211 | / f≦4 ···(3-1) 1.2 ≤ |R 211 | / f≦2.5 ···(3-2) 20 ≤ νdL ≤ 30 ···(4-1) 24 ≤ νdL ≤ 29 ···(4-2) 1.55 ≤ ndH ≤ 1.71 ···(5-1) 1.61 ≤ ndH ≤ 1.66 ···(5-2)

[0033] The objective lens with the above configuration has a medium magnification, more specifically, a magnification of 60x or less. That is, if the focal length of this objective lens is f, and the focal length of the imaging lens used in combination with this objective lens is ft, then the relationship ft / f ≤ 60 holds.

[0034] Furthermore, the objective lens with the above configuration achieves high numerical aperture (NA) and long working distance (WD) despite its compact size. More specifically, it satisfies the following conditions. 0.065 ≤ d0 / L ≤ 0.3 ···(6) NA≧0.75 ···(7) 40mm ≤ L ≤ 75mm ···(8) However, d0 is the distance along the optical axis from the specimen plane to the object-side surface of the objective lens. L is the distance along the optical axis from the specimen plane to the image-side surface of the objective lens. NA is the numerical aperture on the object side of the objective lens. That is, d0 is approximately equal to WD, and L is approximately equal to the sum of WD and the total length of the objective lens (more precisely, the total length of the optical system from the first lens group to the second lens group, as described later).

[0035] In particular, by satisfying condition (6), a long working distance (WD) and a compact configuration are achieved simultaneously. If d0 / L falls below the lower limit, the WD becomes too short or the objective lens becomes too large. On the other hand, if d0 / L exceeds the upper limit, the number and shape of the lenses become too restrictive, making aberration correction difficult.

[0036] The following describes in detail the embodiment of the objective lens mentioned above. [Example 1] Figure 1 is a cross-sectional view of the objective lens 1 according to this embodiment. The objective lens 1 is a microscope objective lens and consists of a first lens group G1 having positive refractive power that converts divergent light from an object point into convergent light, and a second lens group G2 having negative refractive power that is positioned closer to the image than the first lens group G1.

[0037] The first lens group G1 consists of, arranged in order from the object side, lens L1, which is a meniscus lens with a positive refractive power and a concave surface facing the object side; lens L2, which is a meniscus lens with a concave surface facing the object side; cemented lens CL1; and cemented lens CL2.

[0038] The cemented lens CL1 is a two-lens cemented lens consisting of a biconvex lens L3 and a meniscus lens L4 with its concave surface facing the object, arranged in order from the object side. The cemented lens CL2 is a two-lens cemented lens consisting of a meniscus lens L5 with its concave surface facing the image side and a biconvex lens L6, arranged in order from the object side.

[0039] The second lens group G2 consists of cemented lens CL3, cemented lens CL4, and cemented lens CL5, arranged in order from the object side. Cemented lenses CL4 and CL5 are a pair of meniscus lens components with their concave surfaces facing each other. Objective lens 1 includes three cemented lenses (ceilinged lens CL1, cemented lens CL2, and cemented lens CL3) on the object side of the pair of meniscus lens components.

[0040] The cemented lens CL3 is a three-element cemented lens consisting of a biconvex lens L7, a biconcave lens L8, and a biconvex lens L9, arranged in order from the object side. In other words, the cemented lens CL3 is a three-element cemented lens with positive-negative-positive configuration, where positive lenses (lenses L7 and L9) are placed on either side of a negative lens (lens L8).

[0041] The cemented lens CL4 is a two-lens cemented lens consisting of a biconvex lens L10 and a biconcave lens L11, arranged in order from the object side. The cemented lens CL5 is a two-lens cemented lens consisting of a biconcave lens L12 and a biconvex lens L13, arranged in order from the object side.

[0042] The various data for objective lens 1 are as follows. Note that β is the magnification when objective lens 1 is combined with imaging lens 10. NA ob is the numerical aperture on the object side of objective lens 1. f, f1, and f2 are the focal length of the objective lens, the focal length of the first lens group G1, and the focal length of the second lens group G2, respectively. The other parameters are as described above. NA ob =0.77, β=50, f=3.6mm, f1=8.461mm, f2=-17.921mm, L=48.7mm, d0=4.04mm, φ L1 =9.44mm, D L1 =2.262mm, R 211 =6.0569mm, R 212 =2.8444mm, νdL=28.43, ndH=1.65412

[0043] The lens data for objective lens 1 is as follows. Note that INF in the lens data indicates infinity (∞). Objective lens 1 srd nd νd 1 INF 4.040 2 -9.4060 2.262 1.88300 40.76 3 -5.4648 0.200 4 -27.1526 2.125 1.56907 71.30 5 -10.2529 0.150 6 44.3339 5.641 1.43875 94.66 7 -7.7306 1.550 1.61340 44.27 8 -20.8088 0.200 9 39.7597 2.398 1.65412 39.68 10 14.1869 5.904 1.43875 94.66 11 -12.1348 0.250 12 22.5186 4.207 1.43875 94.66 13 -10.2578 1.010 1.61340 44.27 14 6.4582 5.189 1.43875 94.66 15 -65.9501 0.200 16 6.0569 5.033 1.56907 71.30 17 -26.5773 2.570 1.65412 39.68 18 2.8444 2.437 19 -4.4665 1.210 1.48749 70.23 20 7.1260 2.122 1.78880 28.43 21 -13.6986 110.000

[0044] Here, s represents the surface number, r represents the radius of curvature (mm), d represents the interplanar spacing (mm), nd represents the refractive index with respect to line d, and νd represents the Abbe number. These symbols are the same in subsequent examples. The surface indicated by surface number s1 is the sample surface. The surfaces indicated by surface numbers s2 and s21 are the lens surface on the object side and the lens surface on the image side of objective lens 1, respectively. For example, the interplanar spacing d1 indicates the distance along the optical axis from the surface indicated by surface number s1 to the surface indicated by surface number s2. The interplanar spacing d21 indicates the distance along the optical axis from the surface indicated by surface number s21 to the imaging lens (110 mm).

[0045] Objective lens 1 satisfies conditions (1) to (8) as shown below. (1)φ L1 / D L1 =4.173 (2)|R 212 | / f=0.790 (3)|R 211 | / f=1.682 (4)νdL=28.430 (Lens L13) (5) ndH = 1.654 (Lens L5, Lens L11) (6) d0 / L = 0.083 (7) NA = 0.77 (8) L=48.7mm

[0046] Figure 2 is a cross-sectional view of the imaging lens 10 used in combination with the objective lens 1. The imaging lens 10 is a microscope imaging lens that forms a magnified image of an object in combination with an infinity-corrected objective lens. The imaging lens 10 is a cemented lens CTL1 consisting of a biconvex lens TL1 and a meniscus lens TL2 positioned on the image side of the biconvex lens with its concave surface facing the object side. The imaging lens 10 is positioned such that the distance along the optical axis from the lens surface closest to the image (surface number s21) of the objective lens 1 to the lens surface closest to the object (surface number s1) of the imaging lens 10 is 110 mm. The focal length of the imaging lens 10 is 180 mm.

[0047] The lens data for the imaging lens 10 is as follows: Imaging lens 10 srd nd νd 1 193.123 5.5 1.48749 70.23 2 -61.238 4.6 1.72047 34.71 3 -105.391

[0048] Figure 3 is an aberration diagram of an optical system consisting of an objective lens 1 and an imaging lens 10, showing the aberrations at the image plane where the objective lens 1 and the imaging lens 10 form an optical image. Figure 3(a) is a spherical aberration diagram. Figure 3(b) shows the amount of sinusoidal deviation. Figure 3(c) is an astigmatism diagram. Figure 3(d) is a coma aberration diagram at an image height ratio of 70% (image height 9.27 mm). In the figures, "M" represents the meridional component and "S" represents the sagittal component. As shown in Figure 3, in this embodiment, aberrations are well corrected over a wide field of view.

[0049] [Example 2] Figure 4 is a cross-sectional view of the objective lens 2 according to this embodiment. The objective lens 2 is a microscope objective lens and consists of a first lens group G1 having positive refractive power that converts divergent light from an object point into convergent light, and a second lens group G2 having negative refractive power that is positioned closer to the image than the first lens group G1.

[0050] The first lens group G1 consists of, arranged in order from the object side, lens L1, which is a meniscus lens with a positive refractive power and a concave surface facing the object side; lens L2, which is a meniscus lens with a concave surface facing the object side; cemented lens CL1; and cemented lens CL2.

[0051] The cemented lens CL1 is a two-lens cemented lens consisting of a biconvex lens L3 and a meniscus lens L4 with its concave surface facing the object, arranged in order from the object side. The cemented lens CL2 is a two-lens cemented lens consisting of a meniscus lens L5 with its concave surface facing the image side and a biconvex lens L6, arranged in order from the object side.

[0052] The second lens group G2 consists of cemented lenses CL3, CL4, and CL5, arranged in order from the object side. Cemented lenses CL4 and CL5 are a pair of meniscus lens components with their concave surfaces facing each other. The objective lens 2 includes three cemented lenses (ceilinged lenses CL1, CL2, and CL3) on the object side of the pair of meniscus lens components.

[0053] The cemented lens CL3 is a three-element cemented lens consisting of a biconvex lens L7, a biconcave lens L8, and a biconvex lens L9, arranged in order from the object side. In other words, the cemented lens CL3 is a three-element cemented lens with positive-negative-positive configuration, where positive lenses (lenses L7 and L9) are placed on either side of a negative lens (lens L8).

[0054] The cemented lens CL4 is a two-lens cemented lens consisting of a biconvex lens L10 and a biconcave lens L11, arranged in order from the object side. The cemented lens CL5 is a two-lens cemented lens consisting of a biconcave lens L12 and a biconvex lens L13, arranged in order from the object side.

[0055] The various data for objective lens 2 are as follows: NA ob =0.8, β=50, f=3.6mm, f1=8.529mm, f2=-17.839mm, L=48.699mm, d0=4.04mm, φ L1 =9.9mm, D L1 =2.306mm, R 211 =6.0577mm, R 212 =2.8933mm, νdL=28.43, ndH=1.65412

[0056] The lens data for objective lens 2 is as follows: Objective lens 2 srd nd νd 1 INF 4.040 2 -9.4059 2.306 1.88300 40.76 3 -5.5903 0.200 4 -28.3283 2.230 1.56907 71.30 5 -10.0330 0.150 6 39.2527 5.456 1.43875 94.66 7 -7.8854 1.587 1.61340 44.27 8 -21.2762 0.200 9 42.9739 2.616 1.65412 39.68 10 14.1151 6.128 1.43875 94.66 11 -12.1339 0.250 12 20.2765 4.284 1.43875 94.66 13 -10.3822 0.692 1.61340 44.27 14 6.2850 5.015 1.43875 94.66 15 -93.6689 0.200 16 6.0577 4.804 1.56907 71.30 17 -105.9012 2.570 1.65412 39.68 18 2.8933 2.585 19 -4.5205 1.191 1.48749 70.23 20 7.2372 2.194 1.78880 28.43 21 -14.3850 110.000

[0057] Objective lens 2 satisfies conditions (1) through (8) as shown below. (1)φ L1 / D L1 =4.293 (2)|R 212 | / f=0.804 (3)|R 211 | / f=1.683 (4)νdL=28.430 (Lens L13) (5) ndH = 1.654 (Lens L5, Lens L11) (6) d0 / L = 0.083 (7) NA = 0.80 (8) L=48.699mm

[0058] Figure 5 is an aberration diagram of an optical system consisting of an objective lens 2 and an imaging lens 10, showing aberrations in the image plane where the objective lens 2 and the imaging lens 10 form an optical image. Figure 5(a) is a spherical aberration diagram. Figure 5(b) shows the amount of sinusoidal deviation. Figure 5(c) is an astigmatism diagram. Figure 5(d) is a coma aberration diagram at an image height ratio of 70% (image height 9.27 mm). As shown in Figure 5, in this embodiment, aberrations are well corrected over a wide field of view.

[0059] [Example 3] Figure 6 is a cross-sectional view of the objective lens 3 according to this embodiment. The objective lens 3 is a microscope objective lens and consists of a first lens group G1 having positive refractive power that converts divergent light from an object point into convergent light, and a second lens group G2 having negative refractive power that is positioned closer to the image than the first lens group G1.

[0060] The first lens group G1 consists of, arranged in order from the object side, lens L1, which is a meniscus lens with a positive refractive power and a concave surface facing the object side; lens L2, which is a meniscus lens with a concave surface facing the object side; cemented lens CL1; and cemented lens CL2.

[0061] The cemented lens CL1 is a two-lens cemented lens consisting of a biconvex lens L3 and a meniscus lens L4 with its concave surface facing the object, arranged in order from the object side. The cemented lens CL2 is a two-lens cemented lens consisting of a meniscus lens L5 with its concave surface facing the image side and a biconvex lens L6, arranged in order from the object side.

[0062] The second lens group G2 consists of cemented lenses CL3, CL4, and CL5, arranged in order from the object side. Cemented lenses CL4 and CL5 are a pair of meniscus lens components with their concave surfaces facing each other. The objective lens 3 includes three cemented lenses (ceilinged lenses CL1, CL2, and CL3) on the object side of the pair of meniscus lens components.

[0063] The cemented lens CL3 is a three-element cemented lens consisting of a biconvex lens L7, a biconcave lens L8, and a biconvex lens L9, arranged in order from the object side. In other words, the cemented lens CL3 is a three-element cemented lens with positive-negative-positive configuration, where positive lenses (lenses L7 and L9) are placed on either side of a negative lens (lens L8).

[0064] The cemented lens CL4 is a two-lens cemented lens consisting of lens L10, a meniscus lens with its concave surface facing the image side, and lens L11, a meniscus lens with its concave surface facing the image side, arranged in order from the object side. The cemented lens CL5 is a two-lens cemented lens consisting of lens L12, a biconcave lens, and lens L13, a biconvex lens, arranged in order from the object side.

[0065] The various data for objective lens 3 are as follows: NA ob =0.82, β=50, f=3.6mm, f1=8.643mm, f2=-17.573mm, L=49.299mm, d0=3.733mm, φ L1 =9.76mm, D L1 =2.306mm, R 211 =6.337mm, R 212 =3.0206mm, νdL=29.84, ndH=1.65412

[0066] The lens data for objective lens 3 is as follows: Objective lens 3 srd nd νd 1 INF 3.733 2 -8.2556 2.306 1.88300 40.76 3 -5.5117 0.200 4 -23.7453 2.143 1.56907 71.30 5 -8.7229 0.150 6 38.6247 6.006 1.43875 94.66 7 -7.8819 2.525 1.61340 44.27 8 -17.7012 0.200 9 52.3455 1.560 1.65412 39.68 10 15.0020 6.140 1.43875 94.66 11 -12.6408 0.250 12 18.8709 4.205 1.43875 94.66 13 -10.6324 0.500 1.61340 44.27 14 6.4238 4.954 1.43875 94.66 15 -117.9018 0.200 16 6.3370 4.768 1.56907 71.30 17 9.8501 2.570 1.65412 39.68 18 3.0206 2.522 19 -4.7575 2.814 1.48749 70.23 20 8.9801 1.552 1.80000 29.84 21 -21.1397 110.000

[0067] The objective lens 3 satisfies conditions (1) through (8) as shown below. (1)φ L1 / D L1 =4.232 (2)|R 212 | / f=0.839 (3)|R 211 | / f=1.760 (4)νdL=29.840 (Lens L13) (5) ndH = 1.654 (Lens L5, Lens L11) (6) d0 / L = 0.076 (7) NA = 0.82 (8) L=49.299mm

[0068] Figure 7 is an aberration diagram of an optical system consisting of an objective lens 3 and an imaging lens 10, showing aberrations in the image plane where the objective lens 3 and the imaging lens 10 form an optical image. Figure 7(a) is a spherical aberration diagram. Figure 7(b) shows the amount of sinusoidal deviation. Figure 7(c) is an astigmatism diagram. Figure 7(d) is a coma aberration diagram at an image height ratio of 70% (image height 9.27 mm). As shown in Figure 7, in this embodiment, aberrations are well corrected over a wide field of view.

[0069] [Example 4] Figure 8 is a cross-sectional view of the objective lens 4 according to this embodiment. The objective lens 4 is a microscope objective lens and consists of a first lens group G1 having positive refractive power that converts divergent light from an object point into convergent light, and a second lens group G2 having negative refractive power that is positioned closer to the image than the first lens group G1.

[0070] The first lens group G1 consists of, arranged in order from the object side, lens L1, which is a meniscus lens with a positive refractive power and a concave surface facing the object side; lens L2, which is a meniscus lens with a concave surface facing the object side; cemented lens CL1; and cemented lens CL2.

[0071] The cemented lens CL1 is a two-lens cemented lens consisting of a biconvex lens L3 and a meniscus lens L4 with its concave surface facing the object, arranged in order from the object side. The cemented lens CL2 is a two-lens cemented lens consisting of a meniscus lens L5 with its concave surface facing the image side and a biconvex lens L6, arranged in order from the object side.

[0072] The second lens group G2 consists of cemented lens CL3, cemented lens CL4, cemented lens CL5, and a biconvex lens L14, arranged in order from the object side. Cemented lenses CL4 and CL5 are a pair of meniscus lens components with their concave surfaces facing each other. The objective lens 4 includes three cemented lenses (ceilinged lens CL1, cemented lens CL2, and cemented lens CL3) on the object side of the pair of meniscus lens components.

[0073] The cemented lens CL3 is a three-element cemented lens consisting of a biconvex lens L7, a biconcave lens L8, and a biconvex lens L9, arranged in order from the object side. In other words, the cemented lens CL3 is a three-element cemented lens with positive-negative-positive configuration, where positive lenses (lenses L7 and L9) are placed on either side of a negative lens (lens L8).

[0074] The cemented lens CL4 is a two-lens cemented lens consisting of lens L10, a meniscus lens with its concave surface facing the image side, and lens L11, a meniscus lens with its concave surface facing the image side, arranged in order from the object side. The cemented lens CL5 is a two-lens cemented lens consisting of lens L12, a biconcave lens, and lens L13, a biconvex lens, arranged in order from the object side.

[0075] The various data for objective lens 4 are as follows: NA ob =0.8, β=50, f=3.6mm, f1=8.824mm, f2=-17.901mm, L=53.001mm, d0=3.905mm, φ L1 =9.74mm, D L1 =2.359mm, R 211 =6.1484mm, R 212 =3.0222mm, νdL=25.42, ndH=1.673

[0076] The lens data for objective lens 4 is as follows: Objective lens 4 srd nd νd 1 INF 3.906 2 -8.3496 2.359 1.88300 40.76 3 -5.5048 0.200 4 -30.7266 2.031 1.56907 71.30 5 -9.4401 0.150 6 37.1063 5.361 1.43875 94.66 7 -8.0669 1.659 1.61340 44.27 8 -19.4171 2.208 9 49.6209 2.651 1.67300 38.26 10 14.6608 5.647 1.43875 94.66 11 -12.3950 0.250 12 16.9791 4.017 1.43875 94.66 13 -11.4067 1.000 1.61340 44.27 14 6.0053 4.506 1.43875 94.66 15 -241.4394 0.200 16 6.1484 4.711 1.56907 71.30 17 31.8644 2.570 1.65412 39.68 18 3.0222 2.290 19 -4.1357 1.000 1.48749 70.23 20 10.8194 0.941 1.76182 26.52 21 -39.7297 4.548 22 33.3089 0.796 1.80518 25.42 23 -73.8152 110.000

[0077] The objective lens 4 satisfies conditions (1) through (8) as shown below. (1)φ L1 / D L1 =4.129 (2)|R 212 | / f=0.840 (3)|R 211 | / f=1.708 (4)νdL=25.420 (Lens L14) (5) ndH = 1.673 (Lens L5) (6) d0 / L = 0.074 (7) NA = 0.80 (8) L=53.001mm

[0078] Figure 9 is an aberration diagram of an optical system consisting of an objective lens 4 and an imaging lens 10, showing aberrations in the image plane where the objective lens 4 and the imaging lens 10 form an optical image. Figure 9(a) is a spherical aberration diagram. Figure 9(b) shows the amount of sinusoidal deviation. Figure 9(c) is an astigmatism diagram. Figure 9(d) is a coma aberration diagram at an image height ratio of 70% (image height 9.27 mm). As shown in Figure 9, in this embodiment, aberrations are well corrected over a wide field of view. [Explanation of Symbols]

[0079] 1, 2, 3, 4... Objective lenses 10 ···Imaging lens G1 ···First lens group G2 ···Second lens group L1~L14, TL1~TL2... Lenses CL1~CL5, CTL1... Bonded lenses

Claims

1. An objective lens, a first lens group having a positive refractive power that converts divergent light from an object point into convergent light; a second lens group having negative refractive power, the second lens group being disposed closer to the image side than the first lens group; the first lens group includes a first lens, which is located closest to the object side and is a meniscus lens having positive refractive power and a concave surface facing the object side; the second lens group includes a pair of meniscus lens components with concave surfaces facing each other, the objective lens includes three or more cemented lenses located closer to the object than the pair of meniscus lens components, An objective lens characterized by satisfying the following conditional expression: 2.6≦φ Ｌ１ / D Ｌ１ ≦16 ・・・(1) 0.1≦|R ２１２ | / f≦3.5 ・・・(2) However, φ Ｌ１ is the outer diameter of the first lens. Ｌ１ is the thickness of the first lens on the optical axis. ２１２ is the radius of curvature of the surface closest to the image of the first meniscus lens component which is the meniscus lens component on the object side of the pair of meniscus lens components, and f is the focal length of the objective lens.

2. 2. The objective lens according to claim 1, The second lens group includes a positive-negative-positive triplet cemented lens in which positive lenses are disposed on both sides of one negative lens. An objective lens characterized by:

3. 3. The objective lens according to claim 1, An objective lens characterized by satisfying the following conditional expression: 0.5≦|R ２１１ | / f≦7 ・・・(3) However, R ２１１ is the radius of curvature of the surface of the first meniscus lens component closest to the object.

4. The objective lens according to any one of claims 1 to 3, Each of the pair of meniscus lens components is a cemented lens. An objective lens characterized by:

5. The objective lens according to any one of claims 1 to 4, An objective lens characterized by satisfying the following conditional expression: 18≦νdL≦31 (4) Here, νdL is the minimum value of the Abbe number of at least one positive lens arranged on the image side of the surface of the first meniscus lens component closest to the image side.

6. The objective lens according to any one of claims 1 to 5, An objective lens characterized by satisfying the following conditional expression: 1.51≦ndH≦1.75 (5) Here, ndH is the maximum value of the refractive index of at least one negative lens included in the objective lens.

7. An objective lens of 60x or less, a first lens group having a positive refractive power that converts divergent light from an object point into convergent light; a second lens group having negative refractive power, the second lens group being disposed closer to the image side than the first lens group; An objective lens characterized by satisfying the following conditional expression: 0.065≦d0 / L≦0.3 (6) NA≧0.75 (7) 40 mm≦L≦75 mm (8) where d0 is the distance on the optical axis from the specimen surface to the surface of the objective lens closest to the object, L is the distance on the optical axis from the specimen surface to the surface of the objective lens closest to the image, and NA is the numerical aperture of the objective lens on the object side.

8. An objective lens, a first lens group having a positive refractive power that converts divergent light from an object point into convergent light; a second lens group having negative refractive power, the second lens group being disposed closer to the image side than the first lens group; the first lens group includes a first lens, which is located closest to the object side and is a meniscus lens having positive refractive power and a concave surface facing the object side; the second lens group includes a pair of meniscus lens components with concave surfaces facing each other, the second lens group further includes a positive-negative-positive triplet cemented lens in which positive lenses are disposed on both sides of one negative lens, An objective lens characterized by satisfying the following conditional expression: 2.6≦φ L1 / D L1 ≦16 (1) 0.1≦|R212| / f≦3.5...(2) where φ L1 is the outer diameter of the first lens, D L1 is the thickness of the first lens on the optical axis, R 212 is the radius of curvature of the surface closest to the image of the first meniscus lens component which is the meniscus lens component on the object side of the pair of meniscus lens components, and f is the focal length of the objective lens.

9. The objective lens according to claim 8, An objective lens characterized by satisfying the following conditional expression: 0.5≦|R211| / f≦7...(3) Here, R 211 is the radius of curvature of the surface of the first meniscus lens component closest to the object side.

10. The objective lens according to claim 8 or claim 9, Each of the pair of meniscus lens components is a cemented lens. An objective lens characterized by:

11. The objective lens according to any one of claims 8 to 10, An objective lens characterized by satisfying the following conditional expression: 18≦νdL≦31 (4) Here, νdL is the minimum value of the Abbe number of at least one positive lens arranged on the image side of the surface of the first meniscus lens component closest to the image side.

12. The objective lens according to any one of claims 8 to 11, An objective lens characterized by satisfying the following conditional expression: 1.51≦ndH≦1.75 (5) Here, ndH is the maximum value of the refractive index of at least one negative lens included in the objective lens.

Images