Patent Publication Number: US-2021165201-A1

Title: Microscope objective lens and microscope

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of International Application PCT/JP2018/027952, with an international filing date of Jul. 25, 2018, which is hereby incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a microscope objective lens and a microscope. 
     BACKGROUND ART 
     There is a known objective lens for phase difference microscopy that has a phase plate arranged at the pupil position of the objective lens (for example, refer to PTL 1). 
     CITATION LIST 
     Patent Literature 
     {PTL 1} Japanese Unexamined Patent Application Publication No. Hei 9-197284 
     SUMMARY OF INVENTION 
     An aspect of the present invention is directed to a microscope objective lens including: in order from an object side, a first lens group having a negative refractive power; a second lens group having a positive refractive power; a third lens group having a negative refractive power; and a phase plate arranged nearer to an image side than a lens of the third lens group arranged nearest the image side is. A surface of the first lens group nearest the object side is a concave surface facing toward the object. The microscope objective lens satisfies the following conditional expression: 
       −3.8≤ f 1/ f≤− 2.0
 
     Here, f is the local length of the microscope objective lens, and f1 is the focal length of the first lens group. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram schematically illustrating a microscope according to an embodiment of the present invention. 
         FIG. 2  is a diagram illustrating a first example of an objective lens of the microscope in  FIG. 1 . 
         FIG. 3  is a diagram illustrating the shape of a coded aperture arranged at the pupil position of the objective lens in  FIG. 2 . 
         FIG. 4   FIG. 4  is a diagram illustrating spherical aberration of the objective lens in  FIG. 2 . 
         FIG. 5  is a diagram illustrating astigmatism of the objective lens in  FIG. 2 . 
         FIG. 6  is a diagram illustrating distortion of the objective lens in  FIG. 2 . 
         FIG. 7  is a diagram illustrating a second example of an objective lens of the microscope in  FIG. 1 . 
         FIG. 8  is a diagram illustrating spherical aberration of the objective lens in  FIG. 7 . 
         FIG. 9  is a diagram illustrating astigmatism of the objective lens in  FIG. 7 . 
         FIG. 10  is a diagram illustrating distortion of the objective lens in  FIG. 7 . 
         FIG. 11  is a diagram illustrating a third example of an objective lens of the microscope in  FIG. 1 . 
         FIG. 12  is a diagram illustrating spherical aberration of the objective lens in  FIG. 11 . 
         FIG. 13  is a diagram illustrating astigmatism of the objective lens in  FIG. 11 . 
         FIG. 14  is a diagram illustrating distortion of the objective lens in  FIG. 11 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An objective lens  4  and a microscope  1  according to an embodiment of the present invention will be described hereafter while referring to the drawings. 
     As illustrated in  FIG. 1 , the microscope  1  according to this embodiment includes: a stage  2  on which a sample (object) X is placed; the objective lens (microscope objective lens)  4  that irradiates the sample X placed on the stage  2  with excitation light from a light source  3  and collects fluorescence generated by the sample X; an image-forming lens  6  that images the fluorescence collected by the objective lens  4 ; and an image-capturing element  7  that subjects the formed image of the sample X to electro-optical conversion and captures a fluorescence image. 
     The light source  3  emits excitation light including ultraviolet light. 
     In the figure, symbol  8  denotes a dichroic mirror having transmittance characteristics such that the excitation light is deflected and fluorescence is transmitted therethrough and symbol  9  denotes a microlens array arranged on an image-capturing plane of the image-capturing element  7  between the image-forming lens  6  and the image-capturing element  7 . 
     As illustrated in  FIG. 2 , the objective lens  4  according to this embodiment includes, in order from the sample X side, a first lens group G 1  having a negative refractive power, a second lens group G 2  having a positive refractive power, a third lens group G 3  having a negative refractive power, and a phase plate  5 . 
     The phase plate  5  is a coded aperture and is formed of a glass material that satisfies the following conditional expressions: 
       1.43≤ nd≤ 1.61  (1)
 
       62≤ν d≤ 95  (2)
 
     Here, nd is the refractive index at the d-line, and νd is the Abbe number at the d-line. 
     The objective lens  4  of this embodiment satisfies the following conditional expressions: 
       −3.8≤ f 1/ f≤− 2.0  (3)
 
       −5.0≤ f 3/ f≤− 2.3  (4)
 
     Here, 
     f: focal length of objective lens  4 , 
     f1: focal length of first lens group G 1 , and 
     f3: focal length of third lens group G 3 . 
     The objective lens  4  is a telecentric lens on the sample X side and the phase plate  5  is arranged at a position where a principle light beam intersects the optical axis, i.e., at the pupil position of the objective lens  4 . 
     The operation of the thus-configured objective lens  4  and microscope  1  according to this embodiment will be described below. 
     To acquire a three-dimensional fluorescence image of the sample X using the microscope  1  according to this embodiment, the sample X is placed on the stage  2  and the objective lens  4  is arranged above the sample X. 
     When the excitation light is generated from the light source  3 , the excitation light is deflected at 90° by the dichroic mirror  8  and enters the objective lens  4 , and the objective lens  4  then collects and radiates the excitation light onto the sample X. A fluorescent material contained in the sample X is excited, and fluorescence is generated at the position at which the excitation light is radiated onto the sample X and part of the fluorescence is incident on the objective lens  4 . 
     The fluorescence incident on the objective lens  4  is converted into substantially parallel light by the objective lens  4 , and the fluorescence passes through the phase plate  5  arranged at the pupil position of the objective lens  4 . Then, the fluorescence, which has been converted into substantially parallel light by the objective lens  4 , passes through the dichroic mirror  8 , is collected by the image-forming lens  6 , passes through the microlens array  9 , and is captured as an image by the image-capturing element  7 . 
     Information regarding the direction of constraint of the fluorescence can be acquired at the same time as the fluorescence image by capturing the fluorescence as an image using the image-capturing element  7  after the fluorescence has passed through the microlens array  9 . This is a so-called light-field technique. The microscope  1  according to this embodiment has an advantage in that the microscope  1  can obtain three-dimensional information of the sample X in a short period of time using the light-field technique. 
     In addition, according to this embodiment, the depth of the fluorescence image is increased by the phase plate  5  arranged at the pupil position of the objective lens  4 , and therefore there is an advantage that the light-field technique can be complemented and three-dimensional information of the entire fluorescence image including focal position can be obtained by complementing the light field technique. 
     In this case, in this embodiment, since a glass material that satisfies conditional expressions (1) and (2) is used as the material of the coded aperture, i.e., the phase plate  5 , the generation of autofluorescence can be suppressed even when excitation light including ultraviolet light is radiated. Therefore, there is an advantage that autofluorescence can be prevented from being included as stray light in the fluorescence from the sample X, and a clear three-dimensional fluorescence image of the sample X can be acquired. 
     In addition, according to the objective lens  4  of this embodiment, since the phase plate  5  is arranged outside the objective lens  4 , i.e., nearer the image side than the lens L 12  is, which is the lens nearest the image side, a space in which to arrange an adjustment mechanism (not illustrated in the drawings) can be secured and there is an advantage that precise positional adjustment of the phase plate  5  can be readily performed. 
     In addition, the microscope  1  according to this embodiment has an advantage that it is possible to adjust shifting of the phase plate  5  in Z-axis directions along the optical axis, along X-axis directions perpendicular to the Z axis, and along Y-axis directions perpendicular to the Z axis and X axis and to adjust a rotational angle of the phase plate  5  around the Z axis by arranging an adjustment mechanism in the space secured for arrangement of the adjustment mechanism of the microscope  1 . 
     Therefore, the objective lens  4  according to this embodiment satisfies conditional expression (3). 
     In other words, below the lower limit of conditional expression (3), there is a problem that the refractive power of the first lens group G 1  is small, and the principal point cannot be sufficiently moved toward the image side, and above the upper limit of conditional expression (3), there is a problem that the refractive power of the first lens group G 1  is too high, aberration balance is degraded, and imaging performance deteriorates. 
     Therefore, by satisfying conditional expression (3), there is an advantage in that excellent imaging performance can be achieved while arranging the phase plate  5  at a pupil position located outside the objective lens  4  by sufficiently moving the principal point toward the image side. 
     Furthermore, the objective lens  4  according to this embodiment has an advantage that a sufficient working distance can be ensured by satisfying conditional expression (4). 
     In other words, below the lower limit of conditional expression (4), there is a problem that the refractive power of the third lens group G 3  is small and it becomes difficult to secure the operational distance, and above the upper limit of conditional expression (4), there is a problem that the refractive power of the third lens group G 3  is too high, aberration balance is degraded, and imaging performance deteriorates. 
     Therefore, there is an advantage that excellent imaging performance can be achieved while ensuring a sufficient working distance when conditional expression (4) is satisfied. 
     Example 1 
     Next, a first example of the objective lens  4  according to this embodiment will be described while referring to  FIGS. 2 to 6  and the lens data given below. 
     In the objective lens  4  of this example, the first lens group G 1  includes, in order from the sample X side, a meniscus lens L 1  having a concave surface facing toward the sample X and a meniscus lens L 2  having a concave surface facing toward the sample X. The second lens group G 2  includes, in order from the sample X side, a meniscus lens L 3  having a concave surface facing toward the sample X, a cemented lens including a meniscus lens L 4  and a biconvex lens L 5 , a meniscus lens L 6  having a concave surface facing toward the sample X, a cemented lens including a biconvex lens L 7  and a biconcave lens L 8 , and a cemented lens including a meniscus lens L 9  having a convex surface facing toward the sample X, a biconvex lens L 10 , and a meniscus lens L 11 . The third lens group G 3  includes a meniscus lens (lens) L 12  having a convex surface facing toward the sample X. The phase plate  5  is composed of flat plate glass. 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 Surface number 
                 r 
                 d 
                 nd 
                 νd 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 ∞ 
                 2.0000 
                 1.4585 
                 67.80 
               
               
                 2 
                 ∞ 
                 4.3717 
               
               
                 3 
                 −12.5000 
                 0.9500 
                 1.6541 
                 39.68 
               
               
                 4 
                 −19.4199 
                 0.1000 
               
               
                 5 
                 44.9912 
                 0.9500 
                 1.5710 
                 50.80 
               
               
                 6 
                 25.5554 
                 9.2504 
                 1.8414 
                 24.56 
               
               
                 7 
                 −13.8724 
                 0.9500 
                 1.7995 
                 42.22 
               
               
                 8 
                 −30.5511 
                 1.4287 
               
               
                 9 
                 −19.2131 
                 0.9500 
                 1.8081 
                 22.76 
               
               
                 10 
                 38.0112 
                 7.1402 
                 1.5952 
                 67.74 
               
               
                 11 
                 −18.7030 
                 0.1000 
               
               
                 12 
                 16.1275 
                 0.9500 
                 1.8052 
                 25.43 
               
               
                 13 
                 10.1159 
                 8.5916 
                 1.4970 
                 81.55 
               
               
                 14 
                 −18.1518 
                 0.9500 
                 1.8052 
                 25.43 
               
               
                 15 
                 −273.9537 
                 0.1000 
               
               
                 16 
                 10.0242 
                 4.3172 
                 1.6779 
                 55.34 
               
               
                 17 
                 27.9305 
                 0.1000 
               
               
                 18 
                 9.2598 
                 3.4750 
                 1.8040 
                 46.58 
               
               
                 19 
                 12.5716 
                 0.1000 
               
               
                 20 
                 5.2644 
                 2.7024 
                 1.8830 
                 40.77 
               
               
                 21 
                 1.5000 
                 0.8001 
                 1.3330 
                 55.72 
               
               
                   
               
            
           
         
       
     
     The focal length of the objective lens  4  is 12.0 mm, and the numerical aperture is 1.0. 
     In the above lens data, surface number  2  refers to a coded aperture, i.e., the phase plate  5 , and the radius of curvature r is given as ∞, but the actual shape would be: 
         z= 1.5×10 −11 ( x   3   +y   3 )  (3).
 
     Here, z is the optical axis direction, x and y are directions that are perpendicular to the optical axis and perpendicular to each other, and units of m are used. 
     The shape of the phase plate  5  is illustrated in  FIG. 3 . In the drawing, the area surrounded by a line is the effective diameter area. 
     The flat plate glass material is synthetic quartz or another glass material that exhibits low auto-fluorescence. 
     The objective lens  4  is telecentric lens located on the sample X side, and the phase plate  5  is arranged near the pupil position where a principal light beam intersects the optical axis. 
     According to the lens data, the focal length of the objective lens  4  is f=12.0, the focal length of the first lens group G 1  is f1=−32.90, the focal length of the second lens group G 2  is f2=−15.43, and the focal length of the third lens group G 3  is f3=−57.09. 
     Therefore, f1/f=−2.74 and f3/f=−4.76 and conditional expressions (3) and (4) are satisfied. 
       FIGS. 4 to 6  illustrate aberration diagrams. It is clear that aberrations are well corrected. 
     Second Example 
     Next, a second example of the objective lens  4  according to this embodiment will be described while referring to  FIGS. 7 to 10  and the lens data given below. 
     In the objective lens  4  of this example, the first lens group G 1  includes, from the sample X side, a meniscus lens L 1  having a concave surface facing toward sample X. The second lens group G 2  includes, in order from the sample X side, a meniscus lens L 2  having a concave surface facing toward the sample X, a biconvex lens L 3 , a cemented lens including a meniscus lens L 4  having a concave surface facing toward the sample X, a biconvex lens L 5 , and a meniscus lens L 6 , a meniscus lens L 7  having a convex surface facing toward the sample X, and a biconvex lens L 8 . The third lens group G 3  includes a meniscus lens (lens) L 9  having a convex surface facing toward the sample X. The phase plate  5  is composed of flat plate glass. 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 Surface number 
                 r 
                 d 
                 nd 
                 νd 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 ∞ 
                 2.0000 
                 1.5163 
                 64.14 
               
               
                 2 
                 ∞ 
                 2.0000 
               
               
                 3 
                 −8.5000 
                 0.4600 
                 1.5163 
                 64.14 
               
               
                 4 
                 −17.7969 
                 0.1000 
               
               
                 5 
                 25.9886 
                 2.1310 
                 1.7380 
                 32.26 
               
               
                 6 
                 −26.8723 
                 1.3536 
               
               
                 7 
                 −13.3818 
                 4.8626 
                 1.4970 
                 81.55 
               
               
                 8 
                 −11.6780 
                 0.1000 
               
               
                 9 
                 18.3631 
                 0.4600 
                 1.6730 
                 38.15 
               
               
                 10 
                 6.5862 
                 4.3664 
                 1.4970 
                 81.55 
               
               
                 11 
                 −7.0381 
                 1.9931 
                 1.6730 
                 38.15 
               
               
                 12 
                 57.3994 
                 0.1173 
               
               
                 13 
                 12.2679 
                 5.0000 
                 1.4388 
                 94.95 
               
               
                 14 
                 −14.8618 
                 0.1000 
               
               
                 15 
                 11.1001 
                 1.1271 
                 1.6779 
                 55.34 
               
               
                 16 
                 34.2081 
                 0.1000 
               
               
                 17 
                 6.1519 
                 3.5138 
                 1.8830 
                 40.77 
               
               
                 18 
                 3.5000 
                 2.5005 
               
               
                   
               
            
           
         
       
     
     The focal length of the objective lens  4  is 9.0 mm, and the numerical aperture is 0.5. 
     In the above lens data, surface number  2  refers to a coded aperture, i.e., the phase plate  5 , and the radius of curvature r is given as ∞, but the actual shape would be: 
         z= 2.29×10 −11 ( x   3   +y   3 )  (3).
 
     The flat plate glass material is S-BSL7 or another glass material that exhibits low auto-fluorescence. 
     According to the lens data, the focal length of the objective lens  4  is f=9.0, the focal length of the first lens group G 1  is f1=−24.27, the focal length of the second lens group G 2  is f2=11.58, and the focal length of the third lens group G 3  is f3=−31.94. 
     Therefore, f1/f=−2.70 and f3/f=−3.55, and conditional expressions (3) and (4) are satisfied. 
       FIGS. 8 to 10  illustrate aberration diagrams. It is clear that aberrations are well corrected. 
     Third Example 
     Next, a third example of the objective lens  4  according to this embodiment will be described while referring to  FIGS. 11 to 14  and the lens data given below. 
     In the objective lens  4  of this example, the first lens group G 1  includes, in order from the sample X side, a meniscus lens L 1  having a concave surface facing toward the sample X and a meniscus lens L 2  having a concave surface facing toward the sample X. The second lens group G 2  includes, in order from the sample X side, a meniscus lens L 3  having a concave surface facing toward the sample X, a cemented lens including a meniscus lens L 4  having a convex surface facing toward the sample X, a biconvex lens L 5 , and a meniscus lens L 6 , a 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 Surface number 
                 r 
                 d 
                 nd 
                 νd 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 ∞ 
                 2.0000 
                 1.4585 
                 67.80 
               
               
                 2 
                 ∞ 
                 2.0000 
               
               
                 3 
                 −4.2500 
                 0.4510 
                 1.6030 
                 65.44 
               
               
                 4 
                 −13.4696 
                 0.1020 
               
               
                 5 
                 79.6551 
                 1.3837 
                 1.7380 
                 32.26 
               
               
                 6 
                 −14.3032 
                 0.1000 
               
               
                 7 
                 19.6305 
                 1.8119 
                 1.6730 
                 38.15 
               
               
                 8 
                 7.7287 
                 3.6934 
                 1.4970 
                 81.55 
               
               
                 9 
                 −9.0783 
                 0.1000 
               
               
                 10 
                 8.5912 
                 0.3200 
                 1.6730 
                 38.15 
               
               
                 11 
                 4.7008 
                 3.8178 
                 1.4388 
                 94.95 
               
               
                 12 
                 −7.7520 
                 0.3200 
                 1.7380 
                 32.26 
               
               
                 13 
                 −20.0787 
                 0.1000 
               
               
                 14 
                 4.2464 
                 1.8881 
                 1.4970 
                 81.55 
               
               
                 15 
                 19.4995 
                 0.1000 
               
               
                 16 
                 4.4083 
                 0.7505 
                 1.6779 
                 55.34 
               
               
                 17 
                 6.1425 
                 0.1000 
               
               
                 18 
                 3.4366 
                 1.5381 
                 1.8830 
                 40.77 
               
               
                 19 
                 1.7500 
                 0.9998 
               
               
                   
               
            
           
         
       
     
     The focal length of the objective lens  4  is 4.5 mm, and the numerical aperture is 0.75. 
     In the above lens data, surface number  2  refers to a coded aperture, i.e., the phase plate  5 , and the radius of curvature r is given as ∞, but the actual shape would be: 
         z= 2.0×10 −11 ( x   3   +y   3 )  (3).
 
     The flat plate glass material is synthetic quartz or another glass material that exhibits low auto-fluorescence. 
     According to the lens data, the focal length of the objective lens  4  is f=4.5, the focal length of the first lens group G 1  is f1=−16.88, the focal length of the second lens group G 2  is f2=6.16, and the focal length of the third lens group G 3  is f3=−10.45. 
     Therefore, f1/f=−3.75 and f3/f=−2.32, and conditional expressions (3) and (4) are satisfied. 
       FIGS. 12 to 14  illustrate aberration diagrams. It is clear that aberrations are well corrected. 
     As a result, the above-described embodiment leads to the following aspect. 
     An aspect of the present invention is directed to a microscope objective lens including: in order from an object side, a first lens group having a negative refractive power; a second lens group having a positive refractive power; a third lens group having a negative refractive power; and a phase plate arranged nearer to an image side than a lens of the third lens group arranged nearest the image side is. A surface of the first lens group nearest the object side is a concave surface facing toward the object. The microscope objective lens satisfies the following conditional expression: 
       −3.8≤ f 1/ f≤− 2.0
 
     Here, f is the local length of the microscope objective lens, and f1 is the focal length of the first lens group. 
     According to this aspect, by satisfying the conditional formula, the principal point on the image side can be positioned on the image side, the exit pupil can be arranged nearer to the image side than the third lens group is, and the phase plate can be arranged at a position aligned with the exit pupil. This makes it possible to perform positional adjustment of the phase plate outside of precisely configured lens groups without affecting the lens groups. When the phase plate is a coded aperture, the position of the phase plate can be easily and precisely adjusted. 
     Below the lower limit of the conditional expression, the refractive power of the first lens group is small, and the principal point cannot be sufficiently moved toward the image side. In addition, above the upper limit of the conditional expression, the refractive power of the first lens group is too high, aberration balance is degraded, and imaging performance deteriorates. 
     In the above-described aspect, the following conditional expression may be satisfied: 
       −5.0≤ f 3/ f≤− 2.3
 
     Here, f3 is the focal length of the third lens group. 
     With this configuration, a sufficient operational distance can be secured. 
     Below the lower limit of the conditional expression, the refractive power of the third lens group is small, and it is difficult to ensure the working distance. In addition, above the upper limit of the conditional expression, the refractive power of the third lens group is too high, aberration balance is degraded, and imaging performance deteriorates. 
     In addition, in the above-described aspect, the phase plate may have a surface shape expressed by the following expression: 
         z=k ( x   3   +y   3 ) 
     Here, z is the coordinate in optical axis direction, x, y the coordinates in two directions perpendicular to the optical axis direction and perpendicular to each other, and k is an arbitrary rational number. 
     In addition, another aspect of the present invention provides a microscope including any of the above-described microscope objective lenses. 
     In the above-described aspect, the microscope may include the above-described microscope objective lens and an adjustment mechanism that adjusts shifting in Z-axis directions along an optical axis, shifting in X-axis directions perpendicular to the Z axis, and shifting in Y-axis directions perpendicular to the Z axis and the X axis, and adjusts a rotational angle around the Z axis. 
     In addition, in the above-described aspect, the microscope may further include: a light source that generates excitation light; an image-forming lens that images fluorescence that has passed through the microscope objective lens; an image-capturing element that subjects the image formed by the image-forming lens to electro-optical conversion; and a microlens array that is arranged between the image-forming lens and the image-capturing element. 
     The present invention affords the advantage that precise positional adjustment of a phase plate can be easily performed. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  microscope 
               3  light source 
               4  objective lens (microscope objective lens) 
               5  phase plate 
               6  image-forming lens 
               7  image-capturing element 
               9  microlens array 
             G 1  first lens group 
             G 2  second lens group 
             G 3  third lens group 
             L 9 , L 10 , L 12  meniscus lens (lens) 
             X sample (object)