Attachment optical system

Abstract

An attachment optical system (AL) for a microscope is detachably mounted between an objective lens (OL) that receives light from an object and converts the light into parallel light, and an imaging lens that forms an image with the light from the objective lens (OL). The attachment optical system has a first optical element (EL1) having negative refractive power and a second optical element (EL2) having positive refractive power.

Description

Attachment optical system

[0001] The present invention relates to an attachment optical system for a microscope.

[0002] Conventionally, various microscopes have been proposed that have an objective lens that receives light from an object and converts it into parallel light, and an imaging lens that forms an image from the light from the objective lens (see, for example, Patent Document 1). In such microscopes, it is required to effectively correct various aberrations.

[0003] Japanese Patent Application Laid-Open No. 2003-195175

[0004] The attachment optical system of the present invention is an attachment optical system for a microscope that is detachably attached between an objective lens that receives light from an object and converts it into parallel light, and an imaging lens that forms an image from the light from the objective lens, and has a first optical element having negative refractive power and a second optical element having positive refractive power.

[0005] FIG. 1 is a schematic diagram showing the configuration of a confocal fluorescence microscope. FIG. 2 is a schematic diagram showing the vicinity of a revolver in a confocal fluorescence microscope. FIG. 3 is a cross-sectional view showing the configuration of an attachment optical system and an objective lens according to a first example. FIG. 4 is a diagram showing various aberrations of the attachment optical system according to a first example when silicone is used as the immersion liquid. FIG. 5 is a diagram showing various aberrations of the attachment optical system according to a first example when glycerin is used as the immersion liquid. FIG. 6 is a diagram showing various aberrations of the attachment optical system according to a first example when oil is used as the immersion liquid. FIG. 7 is a diagram showing various aberrations of the attachment optical system according to a first example when water is used as the immersion liquid. FIG. 8 is a diagram showing coma aberration of the attachment optical system according to a first example when silicone is used as the immersion liquid. FIG. 9 is a diagram showing coma aberration of the attachment optical system according to a first example when glycerin is used as the immersion liquid. FIG. 10 is a diagram showing coma aberration of the attachment optical system according to a second example when water is used as the immersion liquid. 10A and 10B are diagrams showing various aberrations of the attachment optical system according to Example 2 when silicone is used as the immersion liquid. FIG. 10B are diagrams showing various aberrations of the attachment optical system according to Example 2 when glycerin is used as the immersion liquid. FIG. 10C are diagrams showing various aberrations of the attachment optical system according to Example 2 when oil is used as the immersion liquid. FIG. 10D are diagrams showing various aberrations of the attachment optical system according to Example 2 when water is used as the immersion liquid. FIG. 10E are diagrams showing coma aberrations of the attachment optical system according to Example 2 when silicone is used as the immersion liquid. FIG. 10F are diagrams showing coma aberrations of the attachment optical system according to Example 2 when glycerin is used as the immersion liquid. FIG. 10F are diagrams showing coma aberrations of the attachment optical system according to Example 2 when oil is used as the immersion liquid. FIG. 10H are diagrams showing coma aberrations of the attachment optical system according to Example 3 when observing an object at a water depth of 0.5 mm. 10A to 10C are diagrams showing various aberrations of the attachment optical system according to the third example when observing an object at a water depth of 2.5 mm.10A and 10B are diagrams showing various aberrations of the attachment optical system according to Example 3 when observing an object at a water depth of 3.5 mm. FIG. 11A is a diagram showing coma aberration of the attachment optical system according to Example 3 when observing an object at a water depth of 0.5 mm. FIG. 11B is a diagram showing coma aberration of the attachment optical system according to Example 3 when observing an object at a water depth of 2.5 mm. FIG. 11C is a diagram showing coma aberration of the attachment optical system according to Example 3 when observing an object at a water depth of 3.5 mm. FIG. 11D is a cross-sectional view showing the configuration of the attachment optical system and objective lens according to Example 4. FIG. 11E is a diagram showing various aberrations of the attachment optical system according to Example 4 when silicone is used as the immersion liquid. FIG. 11F is a diagram showing various aberrations of the attachment optical system according to Example 4 when glycerin is used as the immersion liquid. FIG. 11G is a diagram showing various aberrations of the attachment optical system according to Example 4 when oil is used as the immersion liquid. FIG. 11H is a diagram showing various aberrations of the attachment optical system according to Example 4 when water is used as the immersion liquid. FIG. 11H is a diagram showing coma aberration of the attachment optical system according to Example 4 when silicone is used as the immersion liquid. Fig. 10 is a diagram showing coma aberration of the attachment optical system according to Example 4 when glycerin is used as the immersion liquid, Fig. 11 is a diagram showing coma aberration of the attachment optical system according to Example 4 when oil is used as the immersion liquid, Fig. 12 is a diagram showing coma aberration of the attachment optical system according to Example 4 when water is used as the immersion liquid, Fig. 13 is a cross-sectional view showing the configuration of an imaging lens.

[0006] A preferred embodiment of the present invention will now be described. First, a confocal fluorescence microscope to which the attachment optical system according to this embodiment can be attached will be described. As shown in Fig. 1, the confocal fluorescence microscope 1 includes an excitation light introducing section 2 that guides illumination laser light from a light source unit 6 onto a sample SA, a scanning device 3 that deflects the laser light focused on the sample SA to scan the sample SA, a photodetector 5 that detects a light intensity signal from the sample SA, and a focusing optical system 4 that guides light from the sample SA to the photodetector 5.

[0007] The light source unit 6 may be provided in the confocal fluorescence microscope 1 or may be provided separately from the confocal fluorescence microscope 1. The light source unit 6 includes a laser light source (not shown), a beam diameter adjustment mechanism (not shown), etc. The light source unit 6 oscillates an illumination laser beam.

[0008] The excitation light introducing section 2 is composed of a collimator lens 21, a dichroic mirror 22, an imaging lens 23, and an objective lens 24. The collimator lens 21 and the dichroic mirror 22 are disposed inside the microscope housing 12, which is provided on top of the lens barrel 11 of the microscope main body 10. The light source unit 6 and the microscope housing 12 are connected by an optical fiber 69 using connectors C3 and C4. The collimator lens 21 converts the laser light (light beam) emitted from the light source unit 6 into parallel light. The dichroic mirror 22 reflects the laser light from the collimator lens 21 toward the sample SA. The laser light reflected by the dichroic mirror 22 is focused on the sample SA by the imaging lens 23 and the objective lens 24. The imaging lens 23 is disposed inside the lens barrel 11 of the microscope main body 10. The imaging lens 23 is also referred to as a second objective lens. The objective lens 24 is detachably attached to a revolver 15 provided at the bottom of the lens barrel 11 .

[0009] As shown in FIG. 2 , the objective lens 24 can be detachably attached to the revolver 15 together with the attachment optical system 25. This allows the attachment optical system 25 to be detachably attached between the objective lens 24 and the imaging lens 23. When the attachment optical system 25 is attached between the objective lens 24 and the imaging lens 23, the laser light reflected by the dichroic mirror 22 is focused onto the sample SA by the imaging lens 23, the attachment optical system 25, and the objective lens 24. The optical elements constituting the attachment optical system 25 are housed in a cylindrical optical element housing 26. A first thread 27a is formed on one end of the optical element housing 26 (on the objective lens 24 side), and a second thread 27b is formed on the other end of the optical element housing 26 (on the opposite side from the objective lens 24 side). The first thread 27a is a female thread that can be threaded onto the thread (not shown) of the objective lens 24. The second screw portion 27b is a male screw that can be threadedly engaged with a screw portion (not shown) of the revolver 15. In addition, a correction collar 28 that is rotated for aberration correction is provided on the side of the optical element housing 26.

[0010] As shown in FIG. 1 , the scanning device 3 includes a scanning mechanism (scanner) 31 and a scanning optical system 32. The scanning device 3 is disposed inside the microscope housing 12 between the dichroic mirror 22 and the imaging lens 23. The scanning mechanism (scanner) 31 includes, for example, a galvanometer mirror (not shown) or a resonant mirror (not shown). The scanning mechanism (scanner) 31 deflects the incident laser light. That is, the scanning mechanism (scanner) 31 deflects the laser light focused on the sample SA to scan the sample SA. The scanning optical system 32 is an optical system provided between the scanning mechanism (scanner) 31 and the imaging lens 23. The scanning optical system 32 is an optical system in which the focal position of the scanning optical system 32 is located on an image plane 13 (also referred to as a primary image plane) conjugate with the sample SA (the scanning plane of the sample SA).

[0011] The focusing optical system 4 includes an objective lens 24, an imaging lens 23, a total reflection mirror 41, and a condenser lens 42. The objective lens 24 receives fluorescence generated by the sample SA and converts it into parallel light. The imaging lens 23 focuses the fluorescence (parallel light) emitted from the objective lens 24 onto an imaging plane 13 (primary image plane) to form an image. Furthermore, when an attachment optical system 25 is attached between the objective lens 24 and the imaging lens 23, the imaging lens 23 focuses the fluorescence from the objective lens 24 that has passed through the attachment optical system 25 onto the imaging plane 13 to form an image. Thus, the fluorescence from the sample SA that has passed through the imaging lens 23 is focused onto the imaging plane 13, passes through the scanning device 3 and the dichroic mirror 22, and reaches the total reflection mirror 41. The total reflection mirror 41 and the condenser lens 42 are disposed above the dichroic mirror 22 inside the microscope housing 12. The total reflection mirror 41 reflects the fluorescence from the sample SA that has passed through the imaging lens 23. The condenser lens 42 condenses the fluorescence reflected by the total reflection mirror 41 onto a light-shielding plate 52 having a pinhole 51 (aperture).

[0012] The light detection device 5 is configured to include a light shielding plate 52 having a pinhole 51, an optical fiber 53, and a detection unit 55. The optical fiber 53 is connected to the microscope housing 12 and the detection unit 55 using connectors C1 and C2. Light (fluorescence) that has passed through the pinhole 51 is incident on the optical fiber 53. The detection unit 55 detects the light (fluorescence) that has passed through the pinhole 51 and the optical fiber 53. A processing unit 57 is electrically connected to the detection unit 55 via a cable 56. The processing unit 57 performs image processing (of the sample SA) based on the detection signal detected by the detection unit 55, and the observed image of the sample SA obtained by the image processing of the processing unit 57 is displayed on a monitor (not shown).

[0013] The laser light from the scanning device 3 is configured to be first focused on the image plane 13 (primary image plane) and then focused again on the sample SA by the imaging lens 23 and the objective lens 24. Furthermore, when the attachment optical system 25 is attached between the objective lens 24 and the imaging lens 23, the laser light from the scanning device 3 is configured to be first focused on the image plane 13 and then focused again on the sample SA by the imaging lens 23, the attachment optical system 25, and the objective lens 24. In other words, the scanning surface of the sample SA, the image plane 13, and the pinhole 51 are in a conjugate relationship with each other. Therefore, by configuring the light (fluorescence) from the sample SA to be focused by the imaging lens 23 and (the attachment optical system 25 and) the objective lens 24, it becomes possible for the fluorescence generated on the scanning surface of the sample SA to pass through the pinhole 51.

[0014] Although the confocal fluorescence microscope 1 has been described as an example of a microscope to which the attachment optical system according to this embodiment can be attached, the present invention is not limited to this. For example, the microscope to which the attachment optical system according to this embodiment can be attached may be a multiphoton excitation microscope, a super-resolution microscope, an observation microscope, etc. Furthermore, the confocal fluorescence microscope 1 may be an upright microscope or an inverted microscope.

[0015] An attachment optical system AL described below can be used as the attachment optical system 25 that can be attached between the objective lens 24 and the imaging lens 23 of such a confocal fluorescence microscope 1. Furthermore, an objective lens OL and an imaging lens IL described below can be used as the objective lens 24 and the imaging lens 23 of such a confocal fluorescence microscope 1.

[0016] Next, the attachment optical system AL according to this embodiment will be described. As an example of the attachment optical system AL according to this embodiment, the attachment optical system AL(1) shown in FIG. 3 has a first optical element EL1 having negative refractive power and a second optical element EL2 having positive refractive power. By detachably mounting the attachment optical system AL according to this embodiment between the objective lens OL and the imaging lens IL, when one type of objective lens is used for multiple types of immersion liquid, it is possible to effectively correct axial chromatic aberration and spherical aberration that occur depending on the type of immersion liquid. Furthermore, by detachably mounting the attachment optical system AL according to this embodiment between the objective lens OL and the imaging lens IL, it is possible to effectively correct aberrations (axial chromatic aberration and spherical aberration) that occur depending on the depth of the immersion liquid. The attachment optical system AL according to this embodiment may be the attachment optical system AL(2) shown in FIG. 12, the attachment optical system AL(3) shown in FIG. 21, or the attachment optical system AL(4) shown in FIG. 28.

[0017] In the attachment optical system AL according to this embodiment, at least one of the first optical element EL1 and the second optical element EL2 may be movable along the optical axis. This allows for excellent correction of axial chromatic aberration that occurs depending on the refractive index and Abbe number of the sample or immersion liquid. Note that either one of the first optical element EL1 and the second optical element EL2 may be movable along the optical axis. The first optical element EL1 and the second optical element EL2 may each be movable along the optical axis.

[0018] In the attachment optical system AL according to this embodiment, at least one of the first optical element EL1 and the second optical element EL2 may be movable in a direction perpendicular to the optical axis. This allows for excellent correction of aberrations due to decentering of the objective lens or the imaging lens (microscope). Note that either one of the first optical element EL1 and the second optical element EL2 may be movable in a direction perpendicular to the optical axis. The first optical element EL1 and the second optical element EL2 may each be movable in a direction perpendicular to the optical axis.

[0019] The attachment optical system AL according to this embodiment may satisfy the following conditional expression (1): 2<|fA| / TLA<10000 (1) where fA: focal length of the attachment optical system AL, and TLA: total length of the attachment optical system AL.

[0020] Conditional expression (1) defines an appropriate relationship between the focal length of the attachment optical system AL and the overall length of the attachment optical system AL. By satisfying conditional expression (1), the overall magnification of the microscope does not change significantly even when the attachment optical system AL is attached, thereby suppressing fluctuations in the field of view range of the microscope due to the attachment optical system AL being attached. Note that by setting the lower limit of conditional expression (1) to 25, or even 100, the effects of this embodiment can be made more certain. By setting the upper limit of conditional expression (1) to 7000, 5000, 3000, or even 1500, the effects of this embodiment can be made more certain.

[0021] In the attachment optical system AL according to this embodiment, a first optical element EL1 and a second optical element EL2 may be arranged along the optical axis in this order from the objective lens OL side. This causes light rays passing through the attachment optical system AL to deviate from the optical axis, thereby enabling good correction of spherical aberration. Furthermore, it is possible to correct aberrations (axial chromatic aberration and spherical aberration) that occur depending on the type of sample and immersion liquid.

[0022] In the attachment optical system AL according to this embodiment, the second optical element EL2 is one positive lens or one cemented lens having at least a positive lens, and may satisfy the following conditional expression (2): 35<νdP<101 (2), where νdP is the Abbe number of the positive lens.

[0023] Conditional expression (2) defines an appropriate range for the Abbe number of the positive lens. By satisfying conditional expression (2), axial chromatic aberration and spherical aberration can be corrected well. Note that by setting the lower limit of conditional expression (2) to 40, or even 45, the effect of this embodiment can be made more certain. By setting the upper limit of conditional expression (2) to 96, 90, or even 80, the effect of this embodiment can be made more certain. Furthermore, the second optical element EL2 may be a single positive lens.

[0024] In the attachment optical system AL according to this embodiment, the first optical element EL1 is one negative lens or one cemented lens having at least a negative lens, and the second optical element EL2 is one positive lens or one cemented lens having at least a positive lens, and may satisfy the following conditional expression (3): 0≦νdP−νdN<30 (3), where νdP is the Abbe number of the positive lens, and νdN is the Abbe number of the negative lens.

[0025] Conditional expression (3) defines an appropriate relationship between the Abbe number of the positive lens and the Abbe number of the negative lens. By satisfying conditional expression (3), axial chromatic aberration can be effectively corrected. If the value corresponding to conditional expression (3) falls outside the above range, the difference in Abbe number between the positive lens and the negative lens becomes too large, resulting in excessive aberration correction by the attachment optical system AL and making it difficult to effectively correct axial chromatic aberration. The effects of this embodiment can be further ensured by setting the upper limit of conditional expression (3) to 25, 20, or even 15. The second optical element EL2 may also be a single positive lens.

[0026] In the attachment optical system AL according to this embodiment, the first optical element EL1 may be a diffractive optical element having negative refractive power, and the second optical element EL2 may be a diffractive optical element having positive refractive power, and a diffractive optical element having negative refractive power may be arranged in this order from the objective lens OL along the optical axis. This makes it possible to effectively correct axial chromatic aberration that occurs depending on the refractive index and Abbe number of the sample or immersion liquid by utilizing the diffraction phenomenon.

[0027] The attachment optical system AL according to this embodiment may satisfy the following conditional expression (4): 0.1<δA / TLA<4.5 (4) where δA is the distance on the optical axis from the optical surface of the attachment optical system AL that is closest to the objective lens OL to the back focal position FP of the objective lens OL, and TLA is the total length of the attachment optical system AL.

[0028] Conditional expression (4) defines an appropriate relationship between the optical axial distance from the optical surface in the attachment optical system AL closest to the objective lens OL to the back focal position FP of the objective lens OL and the overall length of the attachment optical system AL. The back focal position FP of the objective lens OL may be located closer to the imaging lens IL than the optical surface in the attachment optical system AL closest to the objective lens OL. The back focal position FP of the objective lens OL may be located closer to the objective lens OL than the optical surface in the attachment optical system AL closest to the objective lens OL. The optical axial distance from the optical surface in the attachment optical system AL closest to the objective lens OL to the back focal position FP of the objective lens OL indicates the absolute value of the optical axial distance from the optical surface in the attachment optical system AL closest to the objective lens OL to the back focal position FP of the objective lens OL. By satisfying conditional expression (4), lateral chromatic aberration can be suppressed to a small value, while axial chromatic aberration occurring depending on the refractive index and Abbe number of the sample or immersion liquid can be effectively corrected. Setting the lower limit of conditional expression (4) to 0.2, 0.3, or even 0.5 can further enhance the effects of this embodiment. Setting the upper limit of conditional expression (4) to 4, 3.5, or even 3 can further enhance the effects of this embodiment.

[0029] The attachment optical system AL according to this embodiment may satisfy the following conditional expression (5): 0.05<TLA / TLB<0.75 (5) where TLA is the total length of the attachment optical system AL, and TLB is the total length of the objective lens OL.

[0030] Conditional expression (5) defines an appropriate relationship between the overall length of the attachment optical system AL and the overall length of the objective lens OL. By satisfying conditional expression (5), the overall length of the attachment optical system AL is shortened, thereby minimizing the change in the distance between the objective lens OL and the sample due to the attachment optical system AL being attached. Therefore, an existing microscope can be used as a microscope to which the objective lens OL can be attached together with the attachment optical system AL. Note that the effects of this embodiment can be further ensured by setting the lower limit of conditional expression (5) to 0.1, or even 0.15. The effects of this embodiment can be further ensured by setting the upper limit of conditional expression (5) to 0.6, or even 0.5.

[0031] Furthermore, in this embodiment, the attachment optical system AL may be designed so that the total length of the objective lens OL is an integer multiple (e.g., 2x, 3x, 4x, 5x, 6x, etc.) of the total length of the attachment optical system AL. Note that, in actual objective lenses and attachment optical systems, it is extremely difficult to strictly set the ratio between the total length of the objective lens and the total length of the attachment optical system to an integer multiple in terms of manufacturing technology or measurement technology. Therefore, within the spirit of this embodiment, the ratio between the total length of the objective lens and the total length of the attachment optical system may be approximately an integer multiple. That is, in this embodiment, the term "integral multiple" is a concept that includes approximately an integer multiple and includes at least a range within which the range of precision in manufacturing technology can be obtained. For example, the ratio between the total length of the objective lens and the total length of the attachment optical system may be a (mathematical) integer multiple ±10% magnification, an integer multiple ±5% magnification, an integer multiple ±3% magnification, an integer multiple ±1% magnification, or the like, which are considered to be approximately integer multiples and are included in the range of integer multiples in this embodiment.

[0032] Examples of the attachment optical system AL according to this embodiment will be described below with reference to the drawings. FIGS. 3, 12, 21, and 28 are optical path diagrams showing the configurations of the attachment optical systems AL {AL(1) to AL(4)} and the objective lenses OL {OL(1) to OL(4)} according to Examples 1 to 4. In FIGS. 3, 12, 21, and 28, the optical elements are each represented by a combination of the symbol L and a number (or alphabet). In this case, to prevent the number and types of symbols and numbers from becoming too large and cumbersome, lenses, etc., are represented by a separate combination of symbols and numbers for each Example. Therefore, even if the same combination of symbols and numbers is used between Examples, this does not necessarily mean that the structures are identical.

[0033] Tables 1 to 4 are shown below, with Table 1 showing data on various specifications for Example 1, Table 2 for Example 2, Table 3 for Example 3, and Table 4 for Example 4. In each example, the d-line (wavelength λ=587.6 nm), C-line (wavelength λ=656.3 nm), F-line (wavelength λ=486.1 nm), and g-line (wavelength λ=435.8 nm) were selected as the targets for calculating aberration characteristics.

[0034] In the table of [Overall Specifications], NA indicates the numerical aperture of the objective lens when the attachment optical system is attached. β indicates the magnification of the objective lens when the attachment optical system is attached. f indicates the focal length of the attachment optical system. φ indicates the pupil diameter of the attachment optical system. TLA indicates the total length of the attachment optical system (the distance on the optical axis from the optical surface in the attachment optical system closest to the objective lens to the optical surface closest to the imaging lens). TLB indicates the total length of the objective lens (the distance on the optical axis from the lens surface in the objective lens closest to the object side to the lens surface in the objective lens closest to the image side). δA indicates the distance on the optical axis from the optical surface in the attachment optical system closest to the objective lens to the back focal position of the objective lens.

[0035] In the "Lens Data" table, the surface numbers indicate the order of the lens surfaces from the object side, R indicates the radius of curvature corresponding to each surface number (positive values ​​are given for lens surfaces convex toward the object side), D indicates the lens thickness or air gap on the optical axis corresponding to each surface number, nd indicates the refractive index of the optical material corresponding to each surface number with respect to the d-line (wavelength λ=587.6 nm), and νd indicates the Abbe number of the optical material corresponding to each surface number with respect to the d-line. The "∞" next to the radius of curvature indicates a flat surface or an aperture. The refractive index of air, nd=1.00000, is omitted. If the optical surface is a diffractive optical surface, an * is added to the surface number, and the paraxial radius of curvature is shown in the "Ratio of Curvature" column.

[0036] If the attachment optical system has a diffractive optical element, the phase coefficient of the diffractive optical surface calculated using the phase function method is shown in [Diffractive Optical Surface Data]. The reference wavelength for the phase coefficient is 587.6 nm. The phase coefficient "E-n" is calculated as "×10 -n For example, 1.234E-05 = 1.234 x 10 -5 The phase polynomial that determines the shape of the diffractive optical surface is expressed by the following equation (A).

[0037]

[0038] The [Variable Distance Data] table shows the surface spacing for surface number i, where the surface spacing in the [Lens Data] table is (Di). The [Variable Distance Data] table also shows surface spacing according to the type or depth of immersion liquid. In the [Variable Distance Data] table, ndM indicates the refractive index of the corresponding immersion liquid at the d-line (wavelength λ=587.6 nm). νdM indicates the Abbe number based on the d-line of the corresponding immersion liquid.

[0039] In the following, for all specifications, the focal length f, radius of curvature R, surface spacing D, and other lengths are generally expressed in "mm" unless otherwise specified, but this is not limited to this because the same optical performance can be obtained even when the optical system is proportionally enlarged or reduced.

[0040] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0041] First Example The first example will be described with reference to FIGS. 3 to 11 and Table 1. FIG. 3 is a cross-sectional view showing the configuration of the attachment optical system and objective lens according to the first example. The attachment optical system AL(1) according to the first example is detachably mounted between the objective lens OL(1) according to the first example and an imaging lens (not shown in FIG. 3). The objective lens OL(1) according to the first example receives light from an object (sample SA) and converts it into parallel light. Light (parallel light) from the objective lens OL(1) according to the first example is incident on the attachment optical system AL(1) according to the first example. Air is filled between the tip of the objective lens OL(1) according to the first example and the cover glass CV that covers the object. Furthermore, an immersion liquid M is filled between the cover glass CV and the object. The immersion liquid M may be, for example, silicone, glycerin, oil, or water.

[0042] The objective lens OL(1) according to the first example is composed of first to eighth lenses L1 to L8 arranged in order from the object side along the optical axis. The first lens L1, second lens L2, fifth lens L5, and eighth lens L8 are biconvex positive lenses. The third lens L3, fourth lens L4, and seventh lens L7 are biconcave negative lenses. The sixth lens L6 is a meniscus positive lens with its concave surface facing the object side. The second lens L2 and the third lens L3 are cemented together. The fourth lens L4 and the fifth lens L5 are cemented together. The seventh lens L7 and the eighth lens L8 are cemented together.

[0043] The attachment optical system AL(1) according to the first example is composed of a negative meniscus lens L11 with its concave surface facing the object side and a positive meniscus lens L12 with its concave surface facing the object side, arranged in order from the object side (the objective lens OL(1) side) along the optical axis. In the first example, the negative lens L11 corresponds to the first optical element EL1 described above, and the positive lens L12 corresponds to the second optical element EL2 described above. The back focal position FP of the objective lens OL(1) according to the first example is located near the image side (the imaging lens side) of the positive lens L12. In addition, the negative lens L11 can be moved along the optical axis by rotating a correction collar 28 (see FIG. 2 ) around the optical axis depending on the type and depth of the immersion liquid M, the thickness of the cover glass CV, etc.

[0044] In the first example, the refractive index of silicone to the d-line (wavelength λ=587.6 nm) is 1.4041. The refractive index of glycerin to the d-line (wavelength λ=587.6 nm) is 1.4738. The refractive index of oil to the d-line (wavelength λ=587.6 nm) is 1.5150. The refractive index of water to the d-line (wavelength λ=587.6 nm) is 1.3326. The refractive index of cover glass CV to the d-line (wavelength λ=587.6 nm) is 1.5244.

[0045] The following Table 1 shows the specifications of the attachment optical system and the objective lens according to Example 1. Note that the first surface is the object surface, and the second and eighteenth surfaces are virtual surfaces.

[0046] (Table 1) [Overall specifications] NA = 0.200 β = 4.731 f = -6999.947 φ = 16.911 TLA = 5.843 TLB = 32.00 δA = 7.064 [Lens data] Surface number R D nd νd 1 ∞ (D1) (ndM) (νdM) 2 ∞ 10.800 (ndM) (νdM) 3 ∞ 2.000 1.5244 54.3 4 ∞ 19.000 5 81.180 2.762 1.8040 46.6 6 -28.510 0.200 7 19.709 6.427 1.5932 67.9 8 -11.033 2.258 1.5481 45.8 9 12.498 4.417 10 -7.790 1.000 1.7380 32.3 11 42.222 6.661 1.4978 82.6 12 -13.523 0.200 13 -71.317 3.500 1.7408 27.7 14 -15.666 0.200 15 -23.138 1.000 1.6127 44.5 16 52.277 3.376 1.4978 82.6 17 -29.535 0.200 18 ∞ (D18) 19 -43.191 1.000 1.5168 64.1 20 -1610.538 (D20) 21 -584.564 2.360 1.5168 64.1 22 -43.970 100.000 [Variable interval data] D1 D18 D20 ndM νdM Silicone 1.200 4.457 2.483 1.4041 52.0 Glycerin 1.743 4.287 2.652 1.4738 60.6 Oil 1.502 2.486 4.454 1.5150 43.1 Water 0.952 5.766 1.174 1.3326 55.9.

[0047] FIG. 4 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the attachment optical system according to Example 1 when silicone is used as the immersion liquid. FIG. 5 is a diagram showing various aberrations of the attachment optical system according to Example 1 when glycerin is used as the immersion liquid. FIG. 6 is a diagram showing various aberrations of the attachment optical system according to Example 1 when oil is used as the immersion liquid. FIG. 7 is a diagram showing various aberrations of the attachment optical system according to Example 1 when water is used as the immersion liquid. FIG. 8 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the attachment optical system according to Example 1 when silicone is used as the immersion liquid. FIG. 9 is a diagram showing coma aberrations of the attachment optical system according to Example 1 when glycerin is used as the immersion liquid. FIG. 10 is a diagram showing coma aberrations of the attachment optical system according to Example 1 when oil is used as the immersion liquid. FIG. 11 is a diagram showing coma aberrations of the attachment optical system according to Example 1 when water is used as the immersion liquid.

[0048] Each aberration diagram shows various aberrations when the objective lens and imaging lens are combined with the attachment optical system. In each of the aberration diagrams in Figures 4 to 11, d indicates aberrations for the d-line (wavelength λ = 587.6 nm), C indicates aberrations for the C-line (wavelength λ = 656.3 nm), F indicates aberrations for the F-line (wavelength λ = 486.1 nm), and g indicates aberrations for the g-line (wavelength λ = 435.8 nm). In spherical aberration diagrams, the vertical axis indicates values ​​normalized with the maximum value of the entrance pupil radius set to 1, and the horizontal axis indicates the aberration value [mm] for each light ray. In aberration diagrams showing field curvature, the solid line indicates the sagittal image plane for each wavelength, and the dashed line indicates the meridional image plane for each wavelength. In addition, in aberration diagrams showing field curvature, the vertical axis indicates the image height [mm] and the horizontal axis indicates the aberration value [mm]. In the distortion diagrams, the vertical axis represents the image height [mm], and the horizontal axis represents the aberration ratio as a percentage (% value). Each coma aberration diagram shows the aberration value when the image height ratio RFH (Relative Field Height) is 0.00 to 1.00. Note that the same symbols as in this embodiment are used in the aberration diagrams of each embodiment shown below, and redundant explanations will be omitted.

[0049] From each aberration diagram, it can be seen that the attachment optical system according to Example 1 has excellent imaging performance, with various aberrations being well corrected depending on the type of immersion liquid.

[0050] Second Example The second example will be described with reference to FIGS. 12 to 20 and Table 2. FIG. 12 is a cross-sectional view showing the configuration of the attachment optical system and objective lens according to the second example. The attachment optical system AL(2) according to the second example is detachably attached between the objective lens OL(2) according to the second example and an imaging lens (not shown in FIG. 12). The objective lens OL(2) according to the second example receives light from the object (sample SA) and converts it into parallel light. Light (parallel light) from the objective lens OL(2) according to the second example is incident on the attachment optical system AL(2) according to the second example. Air is filled between the tip of the objective lens OL(2) according to the second example and the cover glass CV that covers the object. Furthermore, an immersion liquid M is filled between the cover glass CV and the object. The immersion liquid M may be, for example, silicone, glycerin, oil, or water.

[0051] The objective lens OL(2) according to Example 2 is composed of first to eighth lenses L1 to L8, which have the same configuration as the first to eighth lenses L1 to L8 of the objective lens OL(1) according to Example 1, and detailed description thereof will be omitted.

[0052] The attachment optical system AL(2) according to the second example is composed of, arranged in order from the object side (the objective lens OL(2) side) along the optical axis, a cemented lens CL11 formed by cementing together a biconcave negative lens L11 and a meniscus positive lens L12 with a convex surface facing the object side, and a biconvex positive lens L13. In the second example, the cemented lens CL11 having negative refractive power corresponds to the first optical element EL1 described above, and the positive lens L13 corresponds to the second optical element EL2 described above. The cemented lens CL11 can be moved along the optical axis by rotating a correction collar 28 (see FIG. 2 ) around the optical axis depending on the type and depth of the immersion liquid M, the thickness of the cover glass CV, etc.

[0053] In the second example, the refractive index of silicone to the d-line (wavelength λ=587.6 nm) is 1.4041. The refractive index of glycerin to the d-line (wavelength λ=587.6 nm) is 1.4738. The refractive index of oil to the d-line (wavelength λ=587.6 nm) is 1.5150. The refractive index of water to the d-line (wavelength λ=587.6 nm) is 1.3326. The refractive index of cover glass CV to the d-line (wavelength λ=587.6 nm) is 1.5244. In addition, the back focal position FP of the objective lens OL(2) in the second example is located near the image side (imaging lens side) of the positive lens L13.

[0054] The values ​​of the specifications of the attachment optical system and the objective lens according to Example 2 are listed in Table 2. Note that the first surface is the object surface, and the second and eighteenth surfaces are virtual surfaces.

[0055] (Table 2) [Overall specifications] NA = 0.200 β = 4.857 f = 2704.038 φ = 16.470 TLA = 6.987 TLB = 32.00 δA = 9.404 [Lens data] Surface number R D nd νd 1 ∞ (D1) (ndM) (νdM) 2 ∞ 10.800 (ndM) (νdM) 3 ∞ 2.000 1.5244 54.3 4 ∞ 19.000 5 81.180 2.762 1.8040 46.6 6 -28.510 0.200 7 19.709 6.427 1.5932 67.9 8 -11.033 2.258 1.5481 45.8 9 12.498 4.417 10 -7.790 1.000 1.7380 32.3 11 42.222 6.661 1.4978 82.6 12 -13.523 0.200 13 -71.317 3.500 1.7408 27.7 14 -15.666 0.200 15 -23.138 1.000 1.6127 44.5 16 52.277 3.376 1.4978 82.6 17 -29.535 0.200 18 ∞ (D18) 19 -146.966 1.016 1.6584 50.8 20 74.971 1.402 1.6180 63.3 21 92.777 (D21) 22 93.046 3.082 1.7340 51.5 23 -188.384 100.000 [Variable interval data] D1 D18 D21 ndM νdM Silicone 0.004 3.313 1.487 1.4041 52.0 Glycerin 0.507 3.215 1.584 1.4738 60.6 Oil 0.311 1.790 3.009 1.5150 43.1 Water -0.334 4.001 0.800 1.3326 55.9.

[0056] Fig. 13 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the attachment optical system according to the second example when silicone is used as the immersion liquid. Fig. 14 is a diagram showing various aberrations of the attachment optical system according to the second example when glycerin is used as the immersion liquid. Fig. 15 is a diagram showing various aberrations of the attachment optical system according to the second example when oil is used as the immersion liquid. Fig. 16 is a diagram showing various aberrations of the attachment optical system according to the second example when water is used as the immersion liquid. Fig. 17 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the attachment optical system according to the second example when silicone is used as the immersion liquid. Fig. 18 is a diagram showing coma aberrations of the attachment optical system according to the second example when glycerin is used as the immersion liquid. Fig. 19 is a diagram showing coma aberrations of the attachment optical system according to the second example when oil is used as the immersion liquid. FIG. 20 is a diagram showing coma aberration of the attachment optical system according to the second example when water is used as the immersion liquid.

[0057] From the aberration diagrams, it can be seen that the attachment optical system according to Example 2 has excellent imaging performance, with various aberrations being well corrected depending on the type of immersion liquid.

[0058] Third Example The third example will be described with reference to FIGS. 21 to 27 and Table 3. FIG. 21 is a cross-sectional view showing the configuration of the attachment optical system and objective lens according to the third example. The attachment optical system AL(3) according to the third example is detachably attached between the objective lens OL(3) according to the third example and an imaging lens (not shown in FIG. 21). The objective lens OL(3) according to the third example receives light from the object (sample SA) and converts it into parallel light. Light (parallel light) from the objective lens OL(3) according to the third example is incident on the attachment optical system AL(3) according to the third example. Air is filled between the tip of the objective lens OL(3) according to the third example and the cover glass CV that covers the object. Furthermore, an immersion liquid M is filled between the cover glass CV and the object. Water is used as the immersion liquid M.

[0059] The objective lens OL(3) according to the third example is composed of first to eighth lenses L1 to L8 arranged in order from the object side along the optical axis. The first lens L1, second lens L2, fifth lens L5, and eighth lens L8 are biconvex positive lenses. The third lens L3, fourth lens L4, and seventh lens L7 are biconcave negative lenses. The sixth lens L6 is a meniscus positive lens with its concave surface facing the object side. The second lens L2 and the third lens L3 are cemented together. The fourth lens L4 and the fifth lens L5 are cemented together.

[0060] The attachment optical system AL(3) according to the third example has the same configuration as the attachment optical system AL(2) according to the second example, and a detailed description thereof will be omitted. In the third example, the cemented lens CL11 having negative refractive power corresponds to the first optical element EL1, and the positive lens L13 corresponds to the second optical element EL2. Furthermore, the cemented lens CL11 is moved along the optical axis by rotating the correction collar 28 (see FIG. 2 ) around the optical axis in accordance with the depth of the immersion liquid M. Specifically, as the depth of the immersion liquid M becomes deeper, the cemented lens CL11 is moved along the optical axis toward the object (toward the objective lens OL(3)) by rotating the correction collar 28 around the optical axis.

[0061] In the third example, the refractive index of water at the d-line (wavelength λ=587.6 nm) is 1.3326. The refractive index of the cover glass CV at the d-line (wavelength λ=587.6 nm) is 1.5244. The back focal position FP of the objective lens OL(3) in the third example is located near the image side (tube lens side) of the positive lens L13.

[0062] The values ​​of the specifications of the attachment optical system and the objective lens according to Example 3 are listed in Table 3. Note that the first surface is the object surface, and the eighteenth surface is a virtual surface.

[0063] (Table 3) [Overall specifications] NA = 0.200 β = 3.911 f = 3140.5 φ = 20.455 TLA = 6.614 TLB = 33.86 δA = 17.251 [Lens data] Surface number R D nd νd 1 ∞ (D1) 1.3326 55.9 2 ∞ 1.000 1.5244 54.3 3 ∞ (D3) 4 3353.400 2.701 1.8040 46.6 5 -20.954 2.252 6 17.610 4.043 1.6030 65.4 7 -145.072 1.000 1.5481 45.5 8 12.312 4.848 9 -7.474 2.119 1.7380 32.3 10 37.508 5.134 1.4978 82.6 11 -12.221 0.200 12 -37.834 3.969 1.7408 27.7 13 -13.138 0.401 14 -15.898 1.000 1.6127 44.5 15 53.834 1.001 16 57.265 5.189 1.4978 82.6 17 -20.426 2.000 18 ∞ (D18) 19 -146.966 1.016 1.6584 50.8 20 74.971 1.402 1.6180 63.3 21 92.777 (D21) 22 93.046 3.082 1.7340 51.5 23 -188.384 100.000 [Variable interval data] D1 D3 D18 D21 Depth 0.5 0.500 28.500 7.386 1.114 Depth 2.5 2.500 26.500 6.015 2.484 Depth 3.5 3.500 25.500 5.342 3.158.

[0064] Fig. 22 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the attachment optical system according to Example 3 when observing an object at a water depth of 0.5 mm. Fig. 23 is a diagram showing various aberrations of the attachment optical system according to Example 3 when observing an object at a water depth of 2.5 mm. Fig. 24 is a diagram showing various aberrations of the attachment optical system according to Example 3 when observing an object at a water depth of 3.5 mm. Fig. 25 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the attachment optical system according to Example 3 when observing an object at a water depth of 0.5 mm. Fig. 26 is a diagram showing coma aberrations of the attachment optical system according to Example 3 when observing an object at a water depth of 2.5 mm. Fig. 27 is a diagram showing coma aberrations of the attachment optical system according to Example 3 when observing an object at a water depth of 3.5 mm.

[0065] In Example 3, in the aberration diagrams showing field curvature, the vertical axis represents object height [mm] and the horizontal axis represents aberration value [mm]. In the distortion diagrams, the vertical axis represents object height [mm] and the horizontal axis represents the proportion of aberration as a percentage (% value). From each aberration diagram, it can be seen that the attachment optical system according to Example 3 has excellent imaging performance, with various aberrations being well corrected according to the depth of the immersion liquid.

[0066] Fourth Example The fourth example will be described using FIGS. 28 to 36 and Table 4. FIG. 28 is a cross-sectional view showing the configuration of the attachment optical system and objective lens according to the fourth example. The attachment optical system AL(4) according to the fourth example is detachably attached between the objective lens OL(4) according to the fourth example and the imaging lens (not shown in FIG. 28). The objective lens OL(4) according to the fourth example receives light from the object (sample SA) and converts it into parallel light. Light (parallel light) from the objective lens OL(4) according to the fourth example is incident on the attachment optical system AL(4) according to the fourth example. Air is filled between the tip of the objective lens OL(4) according to the fourth example and the cover glass CV that covers the object. Furthermore, an immersion liquid M is filled between the cover glass CV and the object. The immersion liquid M may be, for example, silicone, glycerin, oil, or water.

[0067] The objective lens OL(4) according to Example 4 is composed of first to eighth lenses L1 to L8, which have the same configuration as the first to eighth lenses L1 to L8 of the objective lens OL(1) according to Example 1, and detailed description thereof will be omitted.

[0068] The attachment optical system AL(4) according to the fourth embodiment is composed of a diffractive optical element DL1 having positive refractive power and a diffractive optical element DL2 having negative refractive power, arranged in this order from the object side (the side of the objective lens OL(4)) along the optical axis. In the fourth embodiment, the diffractive optical element DL2 having negative refractive power corresponds to the first optical element EL1 described above, and the diffractive optical element DL1 having positive refractive power corresponds to the second optical element EL2 described above. In addition, the attachment optical system AL(4) is configured so that the diffractive optical element DL1 having positive refractive power can be moved along the optical axis by rotating a correction collar 28 (see FIG. 2 ) around the optical axis depending on the type and depth of the immersion liquid M, the thickness of the cover glass CV, etc.

[0069] The diffractive optical element DL1 having positive refractive power is configured to include, arranged in order from the object side (the objective lens OL (4) side) along the optical axis, a first parallel plate PP1, a first optical element element DE1 cemented to the first parallel plate PP1, a second optical element element DE2 cemented to the first optical element element DE1, and a second parallel plate PP2 cemented to the second optical element element DE2. The first optical element element DE1 and the second optical element element DE2 have different refractive indices, etc. A ring-shaped diffractive optical surface (not shown) constituting a diffraction grating is formed at the interface between the first optical element element DE1 and the second optical element element DE2. In this way, the diffractive optical element DL1 having positive refractive power is a contact multi-layer diffractive optical element.

[0070] The diffractive optical element DL2 having negative refractive power is configured to include, arranged in order from the object side (the objective lens OL(4) side) along the optical axis, a third parallel plate PP3, a third optical element element DE3 cemented to the third parallel plate PP3, a fourth optical element element DE4 cemented to the third optical element element DE3, and a fourth parallel plate PP4 cemented to the fourth optical element element DE4. The third optical element element DE3 and the fourth optical element element DE4 have different refractive indices, etc. A ring-shaped diffractive optical surface (not shown) constituting a diffraction grating is formed at the interface between the third optical element element DE3 and the fourth optical element element DE4. In this way, the diffractive optical element DL2 having negative refractive power is also a contact multi-layer type diffractive optical element.

[0071] In the fourth embodiment, the refractive index of silicone to the d-line (wavelength λ=587.6 nm) is 1.4041. The refractive index of glycerin to the d-line (wavelength λ=587.6 nm) is 1.4738. The refractive index of oil to the d-line (wavelength λ=587.6 nm) is 1.5150. The refractive index of water to the d-line (wavelength λ=587.6 nm) is 1.3326. The refractive index of cover glass CV to the d-line (wavelength λ=587.6 nm) is 1.5244. In addition, the back focal position FP of the objective lens OL(4) according to the fourth embodiment is disposed between the diffractive optical element DL1 having positive refractive power and the diffractive optical element DL2 having negative refractive power.

[0072] Table 4 below lists the specifications of the attachment optical system and objective lens according to Example 4. Note that surface 1 is the object surface, surface 2 is a virtual surface, and surfaces 20 and 25 are diffractive optical surfaces.

[0073] (Table 4) [Overall specifications] NA = 0.200 β = 5.016 f = -39566.881 φ = 16.746 TLA = 14.900 TLB = 32.00 δA = 9.731 [Lens data] Surface number R D nd νd 1 ∞ (D1) (ndM) (νdM) 2 ∞ 1.870 (ndM) (νdM) 3 ∞ 2.000 1.5244 54.3 4 ∞ (D4) 5 81.180 2.762 1.8040 46.6 6 -28.510 0.200 7 19.709 6.427 1.5932 67.9 8 -11.033 2.258 1.5481 45.8 9 12.498 4.417 10 -7.790 1.000 1.7380 32.3 11 42.222 6.661 1.4978 82.6 12 -13.523 0.200 13 -71.317 3.500 1.7408 27.7 14 -15.666 0.200 15 -23.138 1.000 1.6127 44.5 16 52.277 3.376 1.4978 82.6 17 -29.535 (D17) 18 ∞ 1.000 1.5168 64.1 19 ∞ 0.100 1.5571 49.7 20* ∞ 0.100 1.5278 33.4 21 ∞ 1.000 1.5168 64.1 22 ∞ (D22) 23 ∞ 1.000 1.5168 64.1 24 ∞ 0.100 1.5571 49.7 25* ∞ 0.100 1.5278 33.4 26 ∞ 1.000 1.5168 64.1 27 ∞ 100.000 [Diffractive optical surface data] Surface 20 Diffraction order = -1 term Surface 20 coefficient C2 1.0513E-04 C4 4.1567E-07 C6 -2.7587E-09 Surface 25 Diffraction order = -1 term Surface 25 coefficient C2 -1.1806E-04 C4 -3.6187E-07 C6 2.4757E-09 [Variable spacing data] D1 D4 D17 D22 ndM νdM Silicone 0.790 17.070 2.400 10.600 1.4041 52.0 Glycerin 1.290 17.130 2.680 10.320 1.4738 60.6 Oil -2.070 19.570 2.670 10.330 1.5150 43.1 Water 1.870 15.820 2.500 10.500 1.3326 55.9.

[0074] Fig. 29 is a diagram showing various aberrations (spherical aberration, field curvature, and distortion) of the attachment optical system according to Example 4 when silicone is used as the immersion liquid. Fig. 30 is a diagram showing various aberrations of the attachment optical system according to Example 4 when glycerin is used as the immersion liquid. Fig. 31 is a diagram showing various aberrations of the attachment optical system according to Example 4 when oil is used as the immersion liquid. Fig. 32 is a diagram showing various aberrations of the attachment optical system according to Example 4 when water is used as the immersion liquid. Fig. 33 is a diagram showing coma aberrations (meridional coma aberration and sagittal coma aberration) of the attachment optical system according to Example 4 when silicone is used as the immersion liquid. Fig. 34 is a diagram showing coma aberrations of the attachment optical system according to Example 4 when glycerin is used as the immersion liquid. Fig. 35 is a diagram showing coma aberrations of the attachment optical system according to Example 4 when oil is used as the immersion liquid. FIG. 36 is a diagram showing coma aberration of the attachment optical system according to the fourth example when water is used as the immersion liquid.

[0075] In Example 4, in the aberration diagrams showing field curvature, the vertical axis represents object height [mm] and the horizontal axis represents aberration value [mm]. In the distortion diagrams, the vertical axis represents object height [mm] and the horizontal axis represents the proportion of aberration as a percentage (% value). From each aberration diagram, it can be seen that the attachment optical system of Example 4 effectively corrects various aberrations depending on the type of immersion liquid, and has excellent imaging performance.

[0076] The objective lens according to each example is an infinity-corrected lens. Therefore, the attachment optical system according to each example is used in combination with an imaging lens that forms an image from the objective lens. An example of an imaging lens used in combination with the attachment optical system will be described with reference to FIG. 37 and Table 5. FIG. 37 is a cross-sectional view showing the configuration of the imaging lens used in combination with the attachment optical system according to each example. The aberration diagrams for the attachment optical system according to each example are for when the objective lens according to each example and this imaging lens are used in combination with the objective lens according to each example. The imaging lens IL shown in FIG. 37 is composed of, arranged in order from the object side, a cemented lens formed by cementing a biconvex positive lens L51 and a biconcave negative lens L52, and a cemented lens formed by cementing a biconvex positive lens L53 and a biconcave negative lens L54. The imaging lens IL is positioned on the image side of the objective lens according to each example. FIG. 37 also shows the entrance pupil plane Pu of the imaging lens IL.

[0077] The specifications of the imaging lens are listed in Table 5 below. In the [Overall Specifications] table, f' indicates the focal length of the imaging lens. In the [Lens Data] table, the surface numbers R, D, nd, and vd are the same as those shown in the explanations of Tables 1 to 4 above.

[0078] (Table 5) [Overall specifications] f' = 200 [Lens data] Surface number R D nd νd 1 75.043 5.100 1.6228 57.03 2 -75.043 2.000 1.7495 35.19 3 1600.580 7.500 4 50.256 5.100 1.6676 41.96 5 -84.541 1.800 1.6127 44.40 6 36.911 168.438

[0079] Next, the table of [Values ​​Corresponding to Conditional Expressions] is shown below. This table summarizes the values ​​corresponding to each of the conditional expressions (1) to (5) for all examples (first to fourth examples). Conditional Expression (1) 2<|fA| / TLA<10000 Conditional Expression (2) 35<νdP<101 Conditional Expression (3) 0≦νdP−νdN<30 Conditional Expression (4) 0.1<δA / TLA<4.5 Conditional Expression (5) 0.05<TLA / TLB<0.75

[0080] [Values ​​corresponding to conditional expressions] (Examples 1 to 4) Conditional Expression Example 1 Example 2 Example 3 Example 4 (1) 1197.993 386.994 474.851 2655.495 (2) 64.1 51.5 51.5 - (3) 0.0 0.7 0.7 - (4) 1.209 1.346 2.608 0.653 (5) 0.183 0.218 0.195 0.466

[0081] According to each of the above embodiments, it is possible to realize an attachment optical system that can correct the axial chromatic aberration and spherical aberration that occur depending on the type of immersion liquid.

[0082] Here, the above examples show specific examples of this embodiment, and this embodiment is not limited to these.

[0083] In the first to third embodiments described above, the second optical element EL2 is a single positive lens, but is not limited to this. For example, the second optical element EL2 may be a cemented lens having positive refractive power in which a positive lens and a negative lens are cemented together, or may be a cemented lens having at least a positive lens.

[0084] In the first embodiment described above, the negative lens L11 is configured to be movable along the optical axis, but this is not limitative. For example, the positive lens L12 may be configured to be movable along the optical axis, and the negative lens L11 and the positive lens L12 may each be configured to be movable along the optical axis. Note that the negative lens L11 may be configured to be movable not only in a direction along the optical axis, but also in a direction perpendicular to the optical axis. Furthermore, the positive lens L12 may be configured to be movable in a direction perpendicular to the optical axis, and the negative lens L11 and the positive lens L12 may each be configured to be movable in a direction perpendicular to the optical axis.

[0085] In the second and third embodiments described above, the cemented lens CL11 is configured to be movable along the optical axis, but this is not limitative. For example, the positive lens L13 may be configured to be movable along the optical axis, or the cemented lens CL11 and the positive lens L13 may each be configured to be movable along the optical axis. The cemented lens CL11 may be configured to be movable not only in the direction along the optical axis, but also in a direction perpendicular to the optical axis. Furthermore, the positive lens L13 may be configured to be movable in the direction perpendicular to the optical axis, or the cemented lens CL11 and the positive lens L13 may each be configured to be movable in the direction perpendicular to the optical axis.

[0086] In the fourth embodiment described above, the diffractive optical element DL1 having positive refractive power is configured to be movable along the optical axis, but this is not limited to this. For example, the diffractive optical element DL2 having negative refractive power may be configured to be movable along the optical axis, or the diffractive optical element DL1 having positive refractive power and the diffractive optical element DL2 having negative refractive power may each be configured to be movable along the optical axis. Note that the diffractive optical element DL1 having positive refractive power may be configured to be movable not only in the direction along the optical axis, but also in a direction perpendicular to the optical axis. Furthermore, the diffractive optical element DL2 having negative refractive power may be configured to be movable in the direction perpendicular to the optical axis, or the diffractive optical element DL1 having positive refractive power and the diffractive optical element DL2 having negative refractive power may each be configured to be movable in the direction perpendicular to the optical axis.

[0087] AL Attachment optical system OL Objective lens IL Imaging lens

Claims

1. 1. An attachment optical system for a microscope that is detachably attached between an objective lens that receives light from an object and converts it into parallel light, and an imaging lens that forms an image using the light from the objective lens, An attachment optical system having a first optical element having a negative refractive power and a second optical element having a positive refractive power.

2. The attachment optical system according to claim 1 , wherein at least one of the first optical element and the second optical element is movable along an optical axis.

3. 2. The attachment optical system according to claim 1, wherein at least one of the first optical element and the second optical element is movable in a direction perpendicular to the optical axis.

4. 2. The attachment optical system according to claim 1, which satisfies the following condition: 1.0<f< .... 2<|fA| / TLA<10000 where fA is the focal length of the attachment optical system TLA: total length of the attachment optical system

5. The attachment optical system according to claim 1 , wherein the first optical element and the second optical element are arranged in order from the objective lens side along the optical axis.

6. the second optical element is one positive lens or one cemented lens having at least one positive lens, 6. The attachment optical system according to claim 5, which satisfies the following condition: 1.0<1.0<1.0<2 ... 35<νdP<101 where νdP is the Abbe number of the positive lens.

7. the first optical element is one negative lens or one cemented lens having at least one negative lens, the second optical element is one positive lens or one cemented lens having at least one positive lens, 6. The attachment optical system according to claim 5, which satisfies the following condition: 1.0<1.0<1.0<2 ... 0≦νdP−νdN<30 where νdP is the Abbe number of the positive lens. νdN: Abbe number of the negative lens

8. the first optical element is a diffractive optical element having negative refractive power, the second optical element is a diffractive optical element having a positive refractive power, 2. The attachment optical system according to claim 1, wherein the diffractive optical element having positive refractive power and the diffractive optical element having negative refractive power are arranged in this order from the objective lens side along the optical axis.

9. 2. The attachment optical system according to claim 1, which satisfies the following condition: 1.0<f< .... 0.1<δA / TLA<4.5 where δA is the distance on the optical axis from the optical surface in the attachment optical system that is closest to the objective lens to the rear focal position of the objective lens. TLA: total length of the attachment optical system

10. 2. The attachment optical system according to claim 1, which satisfies the following condition: 1.0<f< .... 0.05<TLA / TLB<0.75 However, TLA: total length of the attachment optical system TLB: total length of the objective lens