Patent Publication Number: US-2022211265-A1

Title: Ophthalmic optical system and ophthalmic device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of International Application No. PCT/JP2020/035560, filed Sep. 18, 2020, the disclosure of which is incorporated herein by reference in its entirety. Further, this application claims priority from Japanese Patent Application No. 2019-174572, filed Sep. 25, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an ophthalmic optical system and an ophthalmic device. 
     BACKGROUND ART 
     U.S. Patent Application Publication No. 2016/0150953 discloses a device that images an subject eye by using a scanning-type laser ophthalmoscope and optical coherence tomography. 
     SUMMARY 
     A first aspect of the technique of the present disclosure is an ophthalmic optical system for observing an subject eye, including: 
     an objective optical system that forms a pupil that has a conjugate relationship with a pupil of the subject eye, 
     wherein, given that a distance from a pupil position that has a conjugate relationship with the pupil of the subject eye to the pupil of the subject eye is L, and a sum of central thicknesses of lenses included in the objective optical system is D, a conditional expression expressed by 
       0.1≤ D/L≤ 0.25
 
     is satisfied. 
     A second aspect of the technique of the present disclosure is an ophthalmic device including: 
     a scanning section that scans light from a light source; and 
     an objective optical system having lens groups that form a pupil, which has a conjugate relationship with a pupil of an subject eye, at the scanning section, 
     wherein, given that a distance from the scanning section to the pupil of the subject eye is L, and a sum of central thicknesses of the lens groups is D, the objective optical system satisfies a conditional expression expressed by 
       0.1≤ D/L≤ 0.25.
 
     Note that the pupil of the subject eye means the position at which the pupil of the subject eye is disposed so as to coincide with the device, i.e., “the position corresponding to the pupil position of the subject eye” with respect to the device, at the time when the device scans/images the subject eye, and, it goes without saying that the subject eye is not included as a portion of the device. In the following description, there are cases in which this position is called the “pupil position of the subject eye” or simply the “pupil of the subject eye”. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic structural drawing of an ophthalmic device of a first embodiment. 
         FIG. 2  is a schematic structural drawing of an imaging optical system of the first embodiment. 
         FIG. 3  is a schematic structural drawing illustrating an example of specific structures of a first lens group and a second lens group that are included in an objective lens structuring the imaging optical system. 
         FIG. 4  is a schematic structural drawing illustrating an example of the lens structure of an objective lens relating to Example 1. 
         FIG. 5  is an aberration graph illustrating pupil aberration of the objective lens relating to Example 1. 
         FIG. 6  is a schematic structural drawing illustrating an example of the lens structure of an objective lens relating to Example 2. 
         FIG. 7  is an aberration graph illustrating pupil aberration of the objective lens relating to Example 2. 
         FIG. 8  is a schematic structural drawing illustrating an example of the lens structure of an objective lens relating to Example 3. 
         FIG. 9  is an aberration graph illustrating pupil aberration of the objective lens relating to Example 3. 
         FIG. 10  is a schematic structural drawing illustrating an example of the lens structure of an objective lens relating to Example 4. 
         FIG. 11  is an aberration graph illustrating pupil aberration of the objective lens relating to Example 4. 
         FIG. 12  is a schematic structural drawing illustrating a structure in which an attached optical system relating to a second embodiment can be attached to and removed from a portable terminal. 
         FIG. 13  is a schematic structural drawing illustrating an example of the structure of the attached optical system relating to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention are described in detail hereinafter with reference to the drawings. 
     First Embodiment 
     An ophthalmic device  110  relating to a first embodiment of the present invention is described hereinafter with reference to the drawings. 
     The schematic structure of the ophthalmic device  110  is illustrated in  FIG. 1 . 
     For convenience of explanation, a scanning laser ophthalmoscope is called “SLO”. Further, optical coherence tomography is called “OCT”. 
     Note that the horizontal direction, in a case in which the ophthalmic device  110  is set on a horizontal surface, is the “X direction”, the direction orthogonal to the horizontal surface is the “Y direction”, and the optical axis direction of an imaging optical system  116 A is the “Z direction”. The device is placed, with respect to an subject eye  12 , such that pupil center  27  of the subject eye is positioned on the optical axis that is the Z direction. Further, the X direction, the Y direction and the Z direction are orthogonal to one another. 
     The ophthalmic device  110  includes an imaging device  14  and a control device  16 . The imaging device  14  has a SLO unit  18  that acquires an image of fundus  12 A of the subject eye  12 , and an OCT unit  20  that acquires a tomographic image of the subject eye  12 . Hereinafter, the fundus image that is generated on the basis of the SLO data acquired by the SLO unit  18  is called a SLO image. Further, the tomographic image that is generated on the basis of the OCT data acquired by the OCT unit  20  is called an OCT image. Note that the SLO image is also referred to as a two-dimensional fundus image. Further, the OCT image is also referred to as a fundus tomographic image and an anterior eye portion tomographic image, in accordance with the imaged region of the subject eye  12 . 
     The ophthalmic device  110  is an example of the “ophthalmic device” of the technique of the present disclosure. 
     The control device  16  has a computer having a CPU (Central Processing Unit)  16 A, a RAM (Random Access Memory)  16 B, a ROM (Read Only Memory)  16 C, and an input/output port (I/O)  16 D. 
     The control device  16  has an input/display device  16 E that is connected to the CPU  16 A via the I/O port  16 D. The input/display device  16 E has a graphic user interface that displays the image of the subject eye  12  and receives various instructions from the user. A touch panel display can be used as the input/display device  16 E. The control device  16  also has a communication I/F  16 F that is connected to the I/O port  16 D. 
     Further, the control device  16  has an image processing device  17  that is connected to the I/O port  16 D. The image processing device  17  generates an image of the subject eye  12  on the basis of data obtained by the imaging device  14 . 
     As described above, in  FIG. 1 , the control device  16  of the ophthalmic device  110  has the input/display device  16 E, but the technique of the present disclosure is not limited to this. For example, the control device  16  of the ophthalmic device  110  may not have the input/display device  16 E, and may have a separate input/display device that is physically independent of the ophthalmic device  110 . In this case, the display device has an image processing processor unit that operates under the control of the CPU  16 A of the control device  16 . The image processing processor unit may display the SLO image and the like on the basis of image signals that are outputted and instructed from the CPU  16 A. 
     The imaging device  14  operates under the control of the control device  16 . The imaging device  14  includes the SLO unit  18 , the imaging optical system  116 A and the OCT unit  20 . The imaging optical system  116 A is moved in the X, Y, Z directions by an imaging optical system driving section (not illustrated), under the control of the CPU  16 A. The aligning (positioning) of the imaging device  14  and the subject eye  12  may be carried out, for example, by moving not merely the imaging device  14 , but the entire ophthalmic device  110  in the X, Y, Z directions. 
     A SLO system is realized by the control device  16 , the SLO unit  18  and the imaging optical system  116 A that are illustrated in  FIG. 1 . 
     The SLO unit  18  has plural light sources. For example, as illustrated in  FIG. 1 , the SLO unit  18  has a light source  40  of B light (blue color light), a light source  42  of G light (green color light), a light source  44  of R light (red color light), and a light source  46  of IR light (infrared light (e.g., near infrared light)). The lights that exit from the respective light sources  40 ,  42 ,  44 ,  46  are directed toward the same optical path via respective optical members  48 ,  50 ,  52 ,  54 ,  56 . The optical members  48 ,  56  are mirrors, and the optical members  50 ,  52 ,  54  are beam splitters. The B light is guided via the optical members  48 ,  50 ,  54  to the optical path of the imaging optical system  116 A. The G light is guided via the optical members  50 ,  54  to the optical path of the imaging optical system  116 A. The R light is guided via the optical members  52 ,  54  to the optical path of the imaging optical system  116 A. The IR light is guided via the optical members  56 ,  52  to the optical path of the imaging optical system  116 A. Note that LED light sources or laser light sources can be used as the light sources  40 ,  42 ,  44 ,  46 . Note that an example using laser light sources is described hereinafter. Total reflection mirrors can be used as the optical members  48 ,  56 . Further, dichroic mirrors, half mirrors or the like can be used as the optical members  50 ,  52 ,  54 . 
     The light sources  40 ,  42 ,  44 ,  46  are examples of the “light source” of the technique of the present disclosure. 
     The SLO unit  18  is structured so as to be able to be switched between various light-emitting modes such as a light-emitting mode in which G light, R light, B light and IR light are respectively emitted independently, a light-emitting mode in which these lights are all emitted simultaneously or some thereof are emitted simultaneously, and the like. In the example illustrated in  FIG. 1 , the four light sources that are the light source  40  of B light (blue color light), the light source  42  of G light, the light source  44  of R light, and the light source  46  of IR light are provided, but the technique of the present disclosure is not limited to this. For example, the SLO unit  18  may further have a light source of white light. In this case, in addition to the above-described various light-emitting modes, a light-emitting mode in which only white light is emitted, or the like, may be set. 
     The laser light that is incident on the imaging optical system  116 A from the SLO unit  18  is scanned in the X direction and the Y direction by scanning sections ( 120 ,  142 ) that are described later in  FIG. 2 . The scanning light is illuminated, via the pupil  27 , onto the posterior eye portion (e.g., the fundus  12 A) of the subject eye  12 . The reflected light that is reflected by the fundus  12 A is incident, via the imaging optical system  116 A, onto the SLO unit  18 . 
     The scanning sections ( 120 ,  142 ) are examples of the “scanning sections” of the technique of the present disclosure. 
     The reflected light that is reflected at the fundus  12 A is detected by light detecting elements  70 ,  72 ,  74 ,  76  that are provided at the SLO unit  18 . In the present embodiment, the SLO unit  18  has the B light detecting element  70 , the G light detecting element  72 , the R light detecting element  74  and the IR light detecting element  76 , in correspondence with the plural light sources, i.e., the B light source  40 , the G light source  42 , the R light source  44  and the IR light source  46 . The B light detecting element  70  detects the B light that is reflected at the beam splitter  64 . The G light detecting element  72  detects the G light that is transmitted through the beam splitter  64  and reflected at the beam splitter  58 . The R light detecting element  74  detects the R light that is transmitted through the beam splitters  64 ,  58  and is reflected at the beam splitter  60 . The IR light detecting element  76  detects the G light that is transmitted through the beam splitters  64 ,  58 ,  60  and is reflected at the beam splitter  62 . APDs (avalanche photodiodes) are examples of the light detecting elements  70 ,  72 ,  74 ,  76 . 
     Under the control of the CPU  16 A, the image processing device  17  generates SLO images corresponding to the respective colors, by using the signals detected by the B light detecting element  70 , the G light detecting element  72 , the R light detecting element  74  and the IR light detecting element  76 , respectively. The SLO images corresponding to the respective colors are a B-SLO image generated by using the signals detected by the B light detecting element  70 , a G-SLO image generated by using the signals detected by the G light detecting element  72 , an R-SLO image generated by using the signals detected by the R light detecting element  74 , and an IR-SLO image generated by using the signals detected by the IR light detecting element  76 . Further, in the case of the light-emitting mode in which the B light source  40 , the G light source  42  and the R light source  44  emit light simultaneously, an RGB-SLO image may be synthesized from the B-SLO image, the G-SLO image and the R-SLO image that are generated by using the respective signals detected by the R light detecting element  74 , the G light detecting element  72  and the B light detecting element  70 . Further, in the case of the light-emitting mode in which the G light source  42  and the R light source  44  emit light simultaneously, an RG-SLO image may be synthesized from the G-SLO image and the R-SLO image that are generated by using the respective signals detected by the R light detecting element  74  and the G light detecting element  72 . Although an RG-SLO image is used as the SLO image in the first embodiment, the technique of the present disclosure is not limited to this, and another SLO image can be used. 
     Dichroic mirrors, half mirrors or the like can be used for the beam splitters  58 ,  60 ,  62 ,  64 . 
     The OCT system is a three-dimensional image acquiring device that is realized by the control device  16 , the OCT unit  20  and the imaging optical system  116 A that are illustrated in  FIG. 1 . The OCT unit  20  includes a light source  20 A, a sensor (detecting element)  20 B, a first optical coupler  20 C, a reference optical system  20 D, a collimator lens  20 E and a second optical coupler  20 F. 
     The light source  20 A emits light for optical coherence tomography. For example, a super luminescent diode (SLD) can be used as the light source  20 A. The light source  20 A generates low interference light of a broadband light source that has a wide spectral width. The light that exits from the light source  20 A is split at the first optical coupler  20 C. One divisional light is made into parallel light at the collimator lens  20 E as measurement light, and thereafter, is made incident on the imaging optical system  116 A. The measurement light is scanned in the X direction and the Y direction by scanning sections ( 148 ,  142 ) that are described later. The scanning light is illuminated onto the anterior eye portion of the subject eye, or onto the posterior eye portion via the pupil  27 . The measurement light that is reflected by the anterior eye portion or the posterior eye portion goes through the imaging optical system  116 A and is made incident on the OCT unit  20 , and, via the collimator lens  20 E and the first optical coupler  20 C, is incident on the second optical coupler  20 F. Note that, in the present embodiment, an SD-OCT using an SLD is given as an example of the light source  20 A, but the technique of the present disclosure is not limited to this, and an SS-OCT that uses a wavelength sweeping light source may be employed instead of an SLD. 
     The other light, which exits from the light source  20 A and is branched-off at the first optical coupler  20 C, is incident on the reference optical system  20 D as reference light, and goes through the reference optical system  20 D and is incident on the second optical coupler  20 F. 
     The measurement light (returned light) that is reflected and scattered at the subject eye  12 , and the reference light, are combined at the second optical coupler  20 F, and interference light is generated. The interference light is detected at the sensor  20 B. On the basis of a detection signal (OCT data) from the sensor  20 B, the image processing device  17  generates a tomographic image of the subject eye  12 . 
     In the first embodiment, the OCT system generates a tomographic image of the anterior eye portion or the posterior eye portion of the subject eye  12 . 
     The anterior eye portion of the subject eye  12  is the portion that includes, for example, the cornea, the iris, the corner angle, the lens, the ciliary body and a portion of the vitreous body, as the anterior eye segment. The posterior eye portion of the subject eye  12  is the portion that includes, for example, the remaining portion of the vitreous body, the retina, the choroid and the sclera, as the posterior eye segment. Note that the vitreous body that belongs to the anterior eye portion is the portion of the vitreous body that is at the cornea side, with the border being the X-Y plane that passes through the point of the lens that is nearest to the center of the eyeball. The vitreous body that belongs to the posterior eye portion is the portion of the vitreous body that is other than the vitreous body belonging to the anterior eye portion. 
     In a case in which the anterior eye portion of the subject eye  12  is the region that is the object of imaging, the OCT system generates a tomographic image of the cornea for example. Further, in a case in which the posterior eye portion of the subject eye  12  is the region that is the object of imaging, the OCT system generates a tomographic image of the retina for example. 
     The schematic structure of the imaging optical system  116 A is illustrated in  FIG. 2 . The imaging optical system  116 A has an objective lens  130 , the horizontal scanning section  142 , a relay lens device  140 , a beam splitter  147 , the vertical scanning sections  120 ,  148 , a focus adjusting device  150  and the collimator lens  20 E that are disposed in that order from the subject eye  12  side. 
     For example, dichroic mirrors, half mirrors or the like can be used as beam splitters  178 ,  147 . 
     The horizontal scanning section  142  is an optical scanner that scans, in the horizontal direction, the laser light of SLO and the measurement light of OCT that are incident via the relay lens device  140 . In the present embodiment, the horizontal scanning section  142  is shared by the SLO optical system and the OCT optical system, but the technique of the present disclosure is not limited to this. A horizontal scanning section may be provided for each of the SLO optical system and the OCT optical system. 
     The collimator lens  20 E makes, into parallel light, the measurement light that exits from end portion  158  of a fiber through which the light exiting from the OCT unit  20  advances. 
     The focus adjusting device  150  has plural lenses  152 ,  154 . The focus adjusting device  150  adjusts the focus position of the measurement light at the subject eye  12  by moving the plural lenses  152 ,  154  respectively in the optical axis direction appropriately in accordance with the region to be imaged at the subject eye  12 . Note that, although not illustrated, in a case in which a focus detecting device is provided, an autofocus device can be realized by driving the lenses  152 ,  154  by the focus adjusting device in accordance with the state of focal point detection, and carrying out focusing automatically. 
     The vertical scanning section  148  is an optical scanner that scans, in the vertical direction, the measurement light that is incident thereon via the focus adjusting device  150 . 
     The vertical scanning section  120  is an optical scanner that scans, in the vertical direction, the laser light that is incident thereon from the SLO unit  18 . 
     The relay lens device  140  has plural lenses  144 ,  146  that have positive power. The relay lens device  140  is structured by the plural lenses  144 ,  146  such that the positions of the vertical scanning sections  148 ,  120  and the position of the horizontal scanning section  142  are conjugate. More specifically, the relay lens device  140  is structured such that the central positions of the angular scanning of the both scanning sections are conjugate. 
     The beam splitter  147  is disposed between the relay lens device  140  and the vertical scanning section  148 . The beam splitter  147  is an optical member that combines the SLO optical system and the OCT optical system, and reflects the SLO light, which exits from the SLO unit  18 , toward the relay lens device  140 , and transmits the measurement light, which exits from the OCT unit  20 , toward the relay lens device  140 . The measurement light that exits from the OCT unit  20  is two-dimensionally scanned by the vertical scanning section  148  and the horizontal scanning section  142 . Further, the light that exits from the SLO unit  18  is two-dimensionally scanned by the vertical scanning section  120  and the horizontal scanning section  142  that structure the SLO optical system. The OCT measurement light and the SLO laser light that are scanned two-dimensionally are respectively made incident onto the subject eye  12  via the objective lens  130  that structures a shared optical system. The SLO laser light that is reflected at the subject eye  12  goes through the objective lens  130 , the horizontal scanning section  142 , the relay lens device  140 , the beam splitter  147  and the vertical scanning section  120 , and is made incident on the SLO unit  18 . Further, the OCT measurement light that has gone through the subject eye  12  goes through the objective lens  130 , the horizontal scanning section  142 , the relay lens device  140 , the beam splitter  147 , the vertical scanning section  148 , the focus adjusting device  150  and the collimator lens  20 E, and is made incident on the OCT unit  20 . 
     For example, resonant scanners, galvano mirrors, polygon mirrors, rotating mirrors, dove prisms, double dove prisms, rotation prisms, MEMS mirror scanners, acousto-optic elements (AOMs) and the like are suitably used as the horizontal scanning section  142  and the vertical scanning sections  120 ,  148 . In the present embodiment, a galvano mirror is used as the vertical scanning section  148 , and further, a polygon mirror is used as the vertical scanning section  120 . Note that, in a case in which a two-dimensional optical scanner such as a MEMS mirror scanner or the like is used instead of an optical scanner such as a polygon mirror or a galvano mirror or the like, the incident light can be angle-scanned two-dimensionally by that reflecting element, and therefore, the relay lens device  140  may be eliminated. 
     The objective lens  130  has, in order from the horizontal scanning section  142  side, a first lens group  134  and a second lens group  132 . At least the second lens group  132  is, overall, a positive lens group having positive power. In the first embodiment, the first lens group  134  as well is, overall, a positive lens group having positive power. Each of the first lens group  134  and the second lens group  132  has at least one positive lens. In a case in which each of the first lens group  134  and the second lens group  132  has plural lenses, the first lens group  134  and the second lens group  132  may include a negative lens, provided that each of the first lens group  134  and the second lens group  132  has positive power overall. 
     The first lens group  134  is an example of the “first lens group” of the technique of the present disclosure, and the second lens group  132  is an example of the “second lens group” of the technique of the present disclosure. 
     The first lens group  134  and the second lens group  132  that structure the objective lens  130  are separated by the longest air gap on optical axis AX between lens surfaces at the objective lens  130 . Note that, even if there is a glass plate that does not have power at a position between the first lens group  134  and the second lens group  132 , the glass plate is not considered to be a lens that belongs to either the first lens group  134  or the second lens group  132 , and it is considered that the first lens group  134  and the second lens group  132  are separated by the longest air gap. This longest air gap is convenient for providing a combining section that has light combining and light dividing functions such as a dichroic mirror or the like. 
     Note that, with regard to the first lens group  134  and the second lens group  132 , the lenses that are disposed further toward a pupil conjugate position Ps side than a fundus conjugate position, which is in a conjugate relationship with the fundus of the subject eye  12 , may be classified as the first lens group  134 , and the lenses that are disposed further toward the subject eye  12  side than the fundus conjugate position may be classified as the second lens group. Further, at the first lens group  134  and the second lens group  132 , with the region between adjacent lenses, which is a predetermined gap that is set in advance, being considered to be a boundary, the lenses that are disposed further toward the pupil conjugate position Ps side than this boundary may be classified as the first lens group, and the lenses that are disposed further toward the subject eye  12  side than this boundary may be classified as the second lens group. 
     Note that, although not illustrated, the imaging optical system  116 A can have an optical module that includes a fixation lamp that provides a fixation target, a camera and an illumination device, and the optical module, i.e., the fixation lamp, the camera, and the optical path of the illumination device, can be disposed so as to be combined into the optical path of the imaging optical system  116 A by a beam splitter or the like. 
     The imaging optical system  116 A has the objective lens  130  that functions as a posterior eye portion observing optical system that observes at least the posterior eye portion of the subject eye  12 . Due to the imaging optical system  116 A having an optical module for anterior eye portion observation that can be inserted onto and removed from the optical path of the objective lens  130 , and the optical module for anterior eye portion observation being placed on the optical path of the objective lens  130 , the imaging optical system  116 A can be switched from the posterior eye portion observing optical system to the anterior eye portion observing optical system. In the first embodiment, the imaging optical system  116 A is described with the focus being on the posterior eye portion observing optical system, and description of the imaging optical system  116 A, which functions as an anterior eye portion observing optical system in which an optical module for anterior eye portion observation is placed on the optical path of the objective lens  130 , is omitted. 
     An example of specific structures of the first lens group  134  (G 1 ) and the second lens group  132  (G 2 ), which are included in the objective lens  130  structuring the imaging optical system  116 A that functions as a posterior eye portion observing optical system that observes the posterior eye portion of the subject eye  12 , is illustrated in  FIG. 3 . 
     As illustrated in  FIG. 3 , the objective lens  130  is disposed such that the scanning center position (the position marked Ps in  FIG. 3 ) of the horizontal scanning section  142  and the vertical scanning section  148  is conjugate with pupil position Pp of the subject eye  12 . Namely, the scanning center position of the scanning sections is pupil position (hereinafter called pupil conjugate position) Ps that has a conjugate relationship with the pupil position Pp of the subject eye  12 . In a SLO optical system, the SLO laser light that is scanned by the vertical scanning section  120  and the horizontal scanning section  142  goes through the objective lens  130  and is angle-scanned two-dimensionally with the pupil position Pp of the subject eye  12  being the center. As a result, the collected point of the SLO laser light is scanned two-dimensionally at the fundus  12 A. Further, at the OCT optical system as well, similarly, the measurement light that is scanned by the vertical scanning section  148  and the horizontal scanning section  142  goes through the objective lens  130  and is angle-scanned two-dimensionally with the pupil position Pp of the subject eye  12  being the center. As a result, the collected point of the measurement light is scanned two-dimensionally at the fundus  12 A. In a case of observing the posterior eye portion, a fundus two-dimensional image is acquired by the SLO unit  18 , and a fundus tomographic image is acquired by the OCT unit  20 . 
     The objective lens  130  has plural lens groups, i.e., the first lens group  134  (G 1 ) that is positive and the second lens group  132  (G 2 ) that is positive, and the positive first lens group  134  and the positive second lens group  132  form an afocal system. As illustrated as an example, the first lens group  134  includes, in order from the pupil conjugate position Ps side, i.e., the side of the horizontal scanning section  142  that is nearest (hereinafter called scanning section side) toward the subject eye side, a lens component (a cemented lens of lens L 11  and lens L 12 ) that is shaped as a meniscus whose convex surface faces the scanning section side, and a positive lens L 13  having a convex surface at the scanning section side. Note that “lens component” in the present specification means a lens in which there are two interfaces that contact air on the optical axis. One lens component means one single lens, or one cemented lens that is structured by plural lenses being cemented together. A case in which the meniscus-shaped lens component of the first lens group  134  is a cemented lens as illustrated is effective for chromatic aberration correction, but the lens component of the first lens group  134  can be made to be a single lens in a case in which the wavelength region of the lights that are used is relatively narrow. 
     As an example, the second lens group  132  (G 2 ) includes, in order from the scanning section side toward the subject eye side, a biconvex, positive lens component (a cemented lens of positive lens L 21  and negative lens L 22 ), a positive lens L 23  whose convex surface faces the scanning section side, and a positive meniscus lens L 24  whose convex surface faces the scanning section side. A case in which the biconvex, positive lens component of the second lens group  132  is a cemented lens as illustrated is effective for chromatic aberration correction, but the lens component of the second lens group  132  can be made to be a single lens in a case in which the wavelength region of the lights that are used is relatively narrow. 
     Here, due to the imaging optical system  116 A forming a wide angle optical system, observation in a wide field of view FOV at the fundus  12 A is realized. The field of view FOV means the range that can be imaged by the imaging device  14 . The field of view FOV can be expressed as the viewing angle. In the first embodiment, the viewing angle can be prescribed by the internal illumination angle and the external illumination angle. The external illumination angle is the illumination angle in which the illumination angle of the light bundle, which is illuminated from the ophthalmic device  110  toward the subject eye  12 , is prescribed by using the pupil  27  as the reference. Further, the internal illumination angle is the illumination angle in which the illumination angle of the light bundle, which is illuminated toward the fundus  12 A, is prescribed by using eyeball center O as the reference. The external illumination angle and the internal illumination angle are in a corresponding relationship. For example, in a case in which the external illumination angle is 120°, the internal illumination angle corresponds to approximately 160°. 
     Among conventional fundus scanning devices, for example, there are fundus scanning devices of a narrow field angle whose field of view FOV is from 30° to 45°, and there are fundus scanning devices of a wide field angle whose field of view FOV exceeds 100°. With a fundus scanning device of a narrow field angle, there is the problem that the range that can be observed all at once is limited, and there are cases in which imaging of plural times (e.g., 7 times) is needed in order to broaden the observation range. With a fundus scanning device of a wide field angle, there is the problem that the optical structure is complex and large, and, as a result, the cost is high. Thus, the first embodiment provides an optical system that enables observation over a wide range, and can reduce the number of times for imaging the entire fundus, and that can suppress an increase in costs. Specifically, in the first embodiment, there is provided an objective lens that serves as an example of an ophthalmic optical system that makes it possible to obtain an ophthalmic device of a medium field angle of a field of view FOV of around 70°. 
     In a case of forming the objective lens  130  that has a medium-angle field of view, a range that encompasses the observation range that doctors and the like require for fundus observation can be formed as the field of view FOV. For example, a range, which is covered in cases of carrying out observation a predetermined number of times (e.g., 7 times) in an observation range for a single instance of observation in ETDRS (Early Treatment Diabetic Retinopathy Study), is made to be the field of view FOV. In this case, the system can be structured such that the field of view FOV by the objective lens  130  that has a medium-angle field of view satisfies following conditional expression (1). 
       60°≤ FOV≤ 80°  (1)
 
     By structuring the system in this way, by making 60°≤FOV, fundus observation in a medium-angle field of view, which is a range encompassing the seven times of observation in accordance with ETDRS, is possible. Further, by making FOV≤80°, an increase in cost, which is due to at least one of an increase in the lens diameter of the objective lens  130  and an increase in the number of lenses, can be suppressed. 
     Note that, in conditional expression (1), the field of view FOV may be prescribed as being a field of view that exceeds 60°. Further, in conditional expression (1), the field of view FOV may be prescribed as being less than 80°. 60° that is the lower limit of the field of view FOV is a value that is preferable in order to prescribe a range that encompasses the seven times of observation in accordance with ETDRS. 80° that is the upper limit of the field of view FOV is a value that is preferable in order to suppress an increase in cost due to at least one of an increase in the lens diameter of the objective lens  130  and an increase in the number of lenses. There are cases in which these upper limit and lower limit vary in accordance with the set conditions, and further, the system may be structured such that at least one of the upper limit and the lower limit is satisfied. 
     Incidentally, optimization of pupil aberration is necessary in order to obtain an ophthalmic device with a medium field angle (a field of view (FOV) of around 70°). In the first embodiment, the pupil aberration is defined as the lateral aberration in the image surface in a case in which light beam tracking is carried out using the scanning center position of the scanning section (the pupil conjugate position Ps) as the object point, and the pupil position (the exit pupil position) as the image point. In a case in which this pupil aberration is greater than the pupil diameter of a human eye (e.g., around 2 mm to 4 mm in non-mydriatic imaging), at the time of scanning the scanning light, the scanning light at the field of view perimeter is vignetted at the pupil. The pupil aberration increases as the FOV becomes larger. Accordingly, correction (optimization) of pupil aberration is needed in order to avoid vignetting of the scanning light at the pupil. 
     Here, in the structural example illustrated in  FIG. 3 , in a case of forming the objective lens  130  that has a medium-angle field of view, given that the distance from the pupil conjugate position Ps that is in a conjugate relationship with the pupil of the subject eye  12  to the pupil position Pp of the subject eye  12  is L, and that the sum of the central thicknesses of the lenses included in the objective lens  130  is D, the system is structured so as to satisfy following conditional expression (2). 
       0.1≤ D/L≤ 0.25  (2)
 
     Due to such a structure, SLO imaging at a medium-angle field of view is possible, and OCT imaging in all regions of medium field angles is possible. 
     In conditional expression (2), 0.1 that is the lower limit and 0.25 that is the upper limit are values that are preferable in order to reduce the total weight of the objective lens  130  and improve the transmittance rate of the objective lens  130 . There are cases in which these upper limit and lower limit vary in accordance with the set conditions, and further, the system may be structured such that at least one of the upper limit and the lower limit is satisfied. Note that, in order to reduce the total weight of the objective lens  130  and improve the transmittance rate of the objective lens  130 , it is even more preferable that the system be structured so as to satisfy following conditional expression (3). 
       0.15≤ D/L≤ 0.25  (3)
 
     Further, optimization of the angular magnification at the objective lens  130  is required in order to obtain a fundus scanning device of a medium field angle. Specifically, if the angular magnification is low, the field angle is large, and the cost of the objective lens  130  increases. On the other hand, if the angular magnification is high, the requisite accuracy relating to scanning is high accuracy, and the cost increases. Therefore, optimization of the angular magnification is required. 
     In the structural example illustrated in  FIG. 3 , in a case of forming the objective lens  130  that has a medium-angle field of view, the system is structured so as to satisfy following conditional expression (4), where the field angle from the pupil that has a conjugate relationship with the pupil of the subject eye  12 , i.e., from the pupil conjugate position Ps, is θs, and the field angle from the pupil of the subject eye  12  is θp. 
       1.6≤θ p/θs≤ 4.0  (4)
 
     Due to such a structure, by making 1.6≤θp/θs, enlarging of the aperture of the lens that accompanies an increase in the scanning angle of the scanning section can be suppressed, and increased cost of the objective lens  130  in an imaging optical system of a medium-angle field of view can be suppressed. Further, by making θp/θs≤4.0, the difference between the field angle θs (the scanning angle) and the field angle θp is suppressed, and effects of errors of the scanning element at the scanning section can be suppressed. Further, with θp/θs being angular magnification β, conditional expression (4) can be expressed as 1.6≤β≤4.0. In conditional expression (4), 1.6 that is the lower limit is a value that is preferable in order to suppress an increase in cost due to enlarging of the aperture of the objective lens  130  that accompanies an increase in the field angle from the pupil conjugate position Ps (the maximum scanning angle of the scanning section). 4.0 that is the upper limit is a value that is preferable in order to enable suppression of effects due to errors of the scanning element (e.g., a galvano mirror) at the scanning section. It is preferable to structure the objective lens  130  in the range of these upper limit and lower limit. Further, the objective lens  130  may be structured so as to satisfy at least one of these upper limit and lower limit. Note that, in consideration of an increase in the scanning angle of the scanning section and the effects due to errors of the scanning element, the system can also be structured so as to satisfy following conditional expression (5). 
       0.15≤θ p/θs≤ 4.0  (5)
 
     In conditional expression (4), the angular magnification β is prescribed as θp/θs, but similar effects can be obtained even with only the field angle from the pupil conjugate position Ps (the scanning angle of the scanning section). Namely, in the structural example illustrated in  FIG. 3 , in a case of forming the objective lens  130  of a medium-angle field of view, the system can be structured so as to satisfy following conditional expression (6), where the field angle from the pupil that has a conjugate relationship with the pupil of the subject eye  12 , i.e., from the pupil conjugate position Ps (the maximum scanning angle of the scanning section), is θs. 
       30°≤θ s≤ 45°  (6)
 
     Due to this structure, by making 30°≤θs, effects due to errors of the scanning element (e.g., a galvano mirror) can be suppressed. By making θs≤45°, increased cost due to an enlarged aperture of the objective lens  130  can be suppressed. 
     In conditional expression (6), 30° that is the lower limit is a value that is preferable in order to suppress effects due to errors of the scanning element (e.g., a galvano mirror) at the scanning section. Further, 45° that is the upper limit is a value that is preferable in order to suppress an increase in cost due to enlarging of the aperture of the objective lens  130  that accompanies an increase in the field angle from the pupil conjugate position Ps (the maximum scanning angle of the scanning section). There are cases in which these upper limit and lower limit vary in accordance with the set conditions, and further, the system may be structured such that at least one of the upper limit and the lower limit is satisfied. 
     By the way, the focal distance of the first lens group and the focal distance of the second lens group at the objective lens  130  affect the obtaining of a fundus scanning device of a medium field angle. Specifically, due to the relationship between the focal distance of the first lens group and the focal distance of the second lens group, the system is affected by errors in the scanning element at the scanning section, and increased cost due to enlarging of the aperture of the lens is brought about. Therefore, optimization of the relationship between the focal distance of the first lens group and the focal distance of the second lens group is required. 
     In the structural example illustrated in  FIG. 3 , the system is structured so as to satisfy following conditional expression (7), where the focal distance of the first lens group of the objective lens  130  is f 1 , and the focal distance of the second lens group is f 2 . 
       0.3≤ f 2/ f 1≤0.6  (7)
 
     Due to this structure, by making 0.3≤f 2 /f 1 , effects of errors of the scanning element at the scanning section can be suppressed. Further, by making f 2 /f 1 ≤0.6, increased cost of the objective lens  130  at the imaging optical system of a medium-angle field of view can be suppressed. 
     In conditional expression (7), 0.3 that is the lower limit is a value that is preferable in order to suppress effects due to errors of the scanning element (e.g., a galvano mirror) at the scanning section. Further, 0.6 that is the upper limit is a value that is preferable in order to suppress an increase in cost due to enlarging of the aperture of the objective lens  130  that accompanies an increase in the field angle from the pupil conjugate position Ps (the maximum scanning angle of the scanning section). There are cases in which these upper limit and lower limit vary in accordance with the set conditions, and further, the system may be structured such that at least one of the upper limit and the lower limit is satisfied. 
     In order to obtain a fundus scanning device of a medium field angle (field of view FOV around 70°), optimization of the working distance of the objective lens  130  is required. Specifically, with regard to the working distance, there is the concern that, if the working distance is short, the lens will interfere with the subject eye  12  or the face of the person being subjected. On the other hand, if the working distance is long, the lens diameter must be made large, and costs increase. Therefore, optimization of the working distance is needed. 
     In the structural example illustrated in  FIG. 3 , the objective lens  130  is structured so as to satisfy following conditional expression (8), where the distance (working distance) from the subject eye  12  side end portion of the objective lens  130  to the pupil position of the subject eye  12  is WD. 
       20 mm≤ WD≤ 40 mm  (8)
 
     In this structure, by structuring the objective lens  130  such that WD≤40 mm, enlarging of the aperture of the objective lens  130  and an increase in the number of lenses are suppressed, and an increase in costs can be suppressed. By structuring the objective lens  130  such that 20 mm≤WD, interference between the objective lens  130  and the face of the person being subjected can be avoided. 
     Note that WD may be the distance from the end portion on the optical axis AX at the subject eye  12  side of the objective lens  130 , to the pupil position of the subject eye  12 . Or, WD may be the distance from the end portion on the optical axis AX at the subject eye  12  side of the objective lens  130 , to the end portion at the subject eye  12  side. 
     In conditional expression (8), 20 mm that is the lower limit is a value that is preferable in order to suppress enlarging of the aperture of the objective lens  130  and an increase in the number of lenses. 4.0 mm that is the upper limit is a value that is preferable in order to suppress interference between the objective lens  130  and the face of the person being subjected. There are cases in which these upper limit and lower limit vary in accordance with the set conditions, and further, the system may be structured such that at least one of the upper limit and the lower limit is satisfied. 
     In above conditional expression (7), the ratio (f 2 /f 1 ) of the focal distance f 1  of the first lens group of the objective lens  130  and the focal distance f 2  of the second lens group is prescribed, but effects at the objective lens  130  can be obtained even by prescribing only the focal distance f 2  of the second lens group. Namely, given that the focal distance of the second lens group is f 2 , the objective lens  130  can be structured so as to satisfy following conditional expression (9). 
       40 mm≤ f 2≤60 mm  (9)
 
     Due thereto, by making f 2 ≤60 mm, the working distance WD of the objective lens  130  can be ensured. Further, by making 40 mm≤f 2 , enlarging of the aperture of the objective lens  130  and an increase in the number of lenses are suppressed, and an increase in cost can be suppressed. 40 mm that is the lower limit value is a value that is preferable in order to ensure a predetermined distance, which is set in advance, as the working distance WD of the objective lens  130 . 60 mm that is the upper limit is a value that is preferable in order to suppress enlarging of the aperture of the objective lens  130  and an increase in the number of lenses. 
     By the way, in a case in which an optical element, for example, the optical element (e.g., a galvano mirror) of the scanning section, is placed at the pupil conjugate position Ps, it is preferable to ensure the distance between the pupil conjugate position Ps and the scanning element so that the outer shape of the scanning element (including the range of operation when accompanied by operation) does not interfere with the objective lens  130 . Therefore, optimization of the distance between the pupil conjugate position Ps and the element (e.g., the scanning element) that is disposed at that pupil conjugate position Ps is required. 
     In the structural example illustrated in  FIG. 3 , given that the distance from the scanning section side end portion of the objective lens  130  to the pupil conjugate position Ps that has a conjugate relationship with the pupil of the subject eye is d 0 , the objective lens  130  is structured so as to satisfy following conditional expression (10). 
       15 mm≤ d 0  (10)
 
     By structuring the objective lens  130  in this way, interference between the objective lens  130  and the element (e.g., the scanning element) that is disposed at the pupil conjugate position Ps can be suppressed. 
     In conditional expression (10), 15 mm that is the lower limit is a condition that is suitable in order to suppress interference between the objective lens  130  and the element (e.g., the scanning element) that is disposed at the pupil conjugate position Ps. 
     By structuring the objective lens  130  in accordance with the above-described first embodiment, there can be provided an ophthalmic device in which the number of times of imaging that makes at least wide-range observation possible is reduced, and in which an increase in cost is suppressed, and that makes observation of a medium field angle of a field of view FOV of around 70° possible. 
     Note that, in the first embodiment, a case is described in which light is scanned by the horizontal scanning section  142  and the vertical scanning section  148 , and polygon mirrors and galvano mirrors are given as examples of the horizontal scanning section  142  and the vertical scanning section  148 . However, the technique of the present disclosure is not limited to this. For example, another optical element that can scan scanning light in the Y direction may be used, and examples thereof are a MEMS (Micro-electromechanical system) mirror, a rotating mirror, a prism, and a resonant mirror. 
     Further, with regard to the scanning of the scanning light in the first embodiment, similar scanning can, of course, be carried out even if the X direction and the Y direction are switched. 
     Suitable Examples 
     Examples of the objective lens  130  of the technique of the present disclosure are described next. 
     Example 1 
     An example of the lens structure of the objective lens  130  relating to Example 1 is illustrated in  FIG. 4 . Objective lens  1360  is a refractive optical system that includes the lenses L 11 ˜L 24 . 
       FIG. 4  illustrates the pupil conjugate position Ps that is common to the scanning center position of the scanning section, and the pupil position Pp of the subject eye  12 . Note that Ps and Pp in the drawing are illustrated in order to illustrate positions in the optical axis direction, and the drawing is not intended to illustrate the shapes and sizes thereof. The objective lens  130  includes, in order from the scanning section side, the first lens group  134  (G 1 ) and the second lens group  132  (G 2 ). 
     In the following description, the first lens group  134  is called the first lens group G 1 , and the second lens group  132  is called the second lens group G 2 . The first lens group G 1  and the second lens group G 2  are separated by the longest air gap within the objective lens  130 . 
     The first lens group G 1  includes, in order from the pupil conjugate position Ps side that is the scanning section side toward the subject eye side, the negative meniscus lens L 11  whose convex surface faces the scanning section side, the positive lens L 12  having a convex surface at the scanning section side, and the positive lens L 13  having a convex surface at the scanning section side. The lens L 11  and the lens L 12  are cemented together, and form a lens component that is shaped as a positive lens whose convex surface faces the scanning section side. 
     The second lens group G 2  includes, in order from the scanning section side toward the subject eye side, the positive lens L 21  having a convex surface at the scanning section side, the negative meniscus lens L 22  whose concave surface faces the scanning section side, the positive lens L 23 , and the positive meniscus lens L 24  whose convex surface faces the scanning section side. The lens L 21  and the lens L 22  are cemented together, and form a lens component that is shaped as a positive lens. 
     Lens data of Example 1 is illustrated in Table 1. The lens data illustrates, in order from the left column, the surface number (No.), the radius of curvature (R), the surface gap (D) on the optical axis, the refractive index (nd) based on the d line (wavelength 587.56 nm), and the Abbe number (vd) based on the d line. The 1st surface of the lens data is the pupil conjugate position Ps that is common to the scanning center position of the scanning section. The value in the final row of the D column expresses the distance, on the optical axis, from the lens surface that is furthest toward the subject eye side in the table to the pupil position Pp. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 No. 
                 R 
                 D 
                 nd 
                 vd 
               
               
                   
               
             
            
               
                  0 
                   
                 128.74 
                   
                   
               
               
                  1 
                  569.129 
                  10.00 
                 1.860740 
                 23.07 
               
               
                  2 
                  151.885 
                  17.00 
                 1.617720 
                 49.81 
               
               
                  3 
                 −123.798 
                  37.16 
                   
                   
               
               
                  4 
                  170.662 
                  13.00 
                 1.497820 
                 82.57 
               
               
                  5 
                 −460.407 
                 117.10 
                   
                   
               
               
                  6 
                  167.100 
                  17.00 
                 1.497820 
                 82.57 
               
               
                  7 
                  −58.441 
                   4.00 
                 1.860740 
                 23.07 
               
               
                  8 
                 −318.269 
                   0.50 
                   
                   
               
               
                  9 
                  104.135 
                  12.00 
                 1.497820 
                 82.57 
               
               
                 10 
                 −147.471 
                   0.50 
                   
                   
               
               
                 11 
                   33.000 
                  10.00 
                 1.801000 
                 34.92 
               
               
                 12 
                   56.338 
                  33.00 
               
               
                   
               
            
           
         
       
     
       FIG. 5  is a graph of pupil aberration (lateral aberration at the exit pupil) of the objective lens that is structured by the various items of Table 1. In the pupil aberration graph of  FIG. 5 , image height is on the vertical axis, the solid line illustrates a central wavelength of 850.0 nm, the dashed line illustrates 633.0 nm, the one-dot chain line illustrates 532.0 nm, and the two-dot chain line illustrates 488.0 nm. 
     As is clear from the pupil aberration graph illustrated in  FIG. 5 , it is clear that the objective lens of Example 1 has excellent performances as an objective lens suited for use in an ophthalmic device of a medium field angle of a field of view FOV of around 70°. Note that, although not illustrated, it is confirmed that various aberrations such as spherical aberration, astigmatism, distortion aberration and the like also are corrected well. 
     Example 2 
     An example of the lens structure of the objective lens  130  relating to Example 2 is illustrated in  FIG. 6 . Note that, because Example 2 has a structure that is similar to Example 1, the same portions are denoted by the same reference numerals, and detailed description thereof is omitted. 
     The first lens group G 1  includes, in order from the pupil conjugate position Ps side that is the scanning section side toward the subject eye side, the negative meniscus lens L 11  whose convex surface faces the scanning section side, the positive lens L 12  having a convex surface at the scanning section side, and the positive meniscus lens L 13  having a concave surface at the scanning section side. The lens L 11  and the lens L 12  are cemented together, and form a lens component that is shaped as a positive lens. 
     The second lens group G 2  includes, in order from the scanning section side toward the subject eye side, the positive lens L 21  having a convex surface at the scanning section side, the positive lens L 22  having a convex surface at the scanning section side, the negative meniscus lens L 23  whose concave surface faces the scanning section side, and the positive meniscus lens L 24  whose convex surface faces the scanning section side. The lens L 22  and the lens L 23  are cemented together, and form a lens component that is shaped as a positive lens. 
     Lens data of Example 1 is illustrated in Table 2. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 No. 
                 R 
                 D 
                 nd 
                 vd 
               
               
                   
               
             
            
               
                  0 
                   
                  80.08 
                   
                   
               
               
                  1 
                 3545.072 
                  10.00 
                 1.805180 
                 25.44 
               
               
                  2 
                  120.964 
                  17.00 
                 1.563840 
                 60.70 
               
               
                  3 
                 −126.620 
                  33.65 
                   
                   
               
               
                  4 
                 −450.302 
                  13.00 
                 1.518600 
                 69.89 
               
               
                  5 
                  −84.218 
                 156.84 
                   
                   
               
               
                  6 
                 1651.717 
                  15.00 
                 1.518600 
                 69.89 
               
               
                  7 
                  −71.505 
                   0.50 
                   
                   
               
               
                  8 
                  110.291 
                  20.00 
                 1.563840 
                 60.70 
               
               
                  9 
                  −45.069 
                   4.00 
                 1.860740 
                 23.07 
               
               
                 10 
                 2389.739 
                   0.50 
                   
                   
               
               
                 11 
                   45.190 
                  10.00 
                 1.850260 
                 32.35 
               
               
                 12 
                  172.145 
                  38.00 
               
               
                   
               
            
           
         
       
     
       FIG. 7  is a graph of pupil aberration (lateral aberration at the exit pupil) of the objective lens that is structured by the various items of Table 2. 
     As is clear from the pupil aberration graph illustrated in  FIG. 7 , it is clear that the objective lens of Example 2 has excellent performances as an objective lens suited for use in an ophthalmic device of a medium field angle of a field of view FOV of around 70°. Note that, although not illustrated, it is confirmed that various aberrations such as spherical aberration, astigmatism, distortion aberration and the like also are corrected well. 
     Example 3 
     An example of the lens structure of the objective lens  130  relating to Example 3 is illustrated in  FIG. 8 . Note that, because Example 3 has a structure that is similar to Example 1, the same portions are denoted by the same reference numerals, and detailed description thereof is omitted. 
     The first lens group G 1  includes, in order from the pupil conjugate position Ps side that is the scanning section side toward the subject eye side, the negative meniscus lens L 11  whose convex surface faces the scanning section side, the positive lens L 12  having a convex surface at the scanning section side, and the positive meniscus lens L 13  having a concave surface at the scanning section side. The lens L 11  and the lens L 12  are cemented together, and form a lens component that is shaped as a positive lens. 
     The second lens group G 2  includes, in order from the scanning section side toward the subject eye side, the positive lens L 21  having a convex surface at the scanning section side, the negative meniscus lens L 22  whose concave surface faces the scanning section side, and the positive lens L 23 . The lens L 21  and the lens L 22  are cemented together, and form a lens component that is shaped as a positive lens. Further, the lens surface, which is furthest toward the subject eye  12  side of the lens L 23 , is an aspherical surface. 
     Lens data of Example 3 is illustrated in Table 3. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 No. 
                 R 
                 D 
                 nd 
                 vd 
               
               
                   
               
             
            
               
                  0 
                   
                  77.30 
                   
                   
               
               
                  1 
                 −7928.234 
                  10.00 
                 1.795040 
                 28.69 
               
               
                  2 
                    50.000 
                  17.00 
                 1.623740 
                 47.00 
               
               
                  3 
                   −75.474 
                  80.55 
                   
                   
               
               
                  4 
                  −110.685 
                  13.00 
                 1.572500 
                 57.29 
               
               
                  5 
                   −63.363 
                 117.10 
                   
                   
               
               
                  6 
                    62.316 
                  27.76 
                 1.497820 
                 82.57 
               
               
                  7 
                   −44.247 
                   4.00 
                 1.860740 
                 23.07 
               
               
                  8 
                  −138.182 
                   0.50 
                   
                   
               
               
                  9 
                    61.061 
                  10.00 
                 1.851080 
                 40.12 
               
               
                 10 
                 aspherical 
                  38.00 
                   
                   
               
               
                   
                 surface 
               
               
                   
               
            
           
         
       
     
     At the aspherical surface listed in Table 3, when h represents the height in the direction orthogonal to the optical axis, zs represents the distance (sag amount) along the optical axis from the tangent plane at the apex of the aspherical surface to the position on the aspherical surface at height h, c represents the inverse of the radius of curvature of the near axis, k represents the constant of the cone, A represents the 4th-order aspherical coefficient, B represents the 6th-order aspherical coefficient, C represents the 8th-order aspherical coefficient, D represents the 10th-order aspherical coefficient and E represents the 12th-order aspherical coefficient, zs is expressed by the following formula. 
         zs =( c·h   2 )/[1+{1−(1+ k )· h   2   ·c   2 } 1/2 ]+ A·h   4   +B·+h   6   +C·h   8   +D·h   10   +E·h   12  
 
     The aspherical coefficients of the aspherical surfaces in Example 3 are listed in Table 4. In Table 4, the aspherical coefficient A is listed as C4, B as C6, and C as C8. Further, listing of the aspherical coefficients D, E is omitted. “E−n” (n is an integer) in Table 4 means “×10 −n ”. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 aspherical coefficient 
                 surface 10 
               
               
                   
                   
               
             
            
               
                   
                 R 
                 −726.009 
               
               
                   
                 K 
                 0 
               
               
                   
                 C4 
                  3.30E−06 
               
               
                   
                 C6 
                 −5.27E−09 
               
               
                   
                 C8 
                  2.69E−12 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 9  is a graph of pupil aberration (lateral aberration at the exit pupil) of the objective lens that is structured by the various items of Table 3 and Table 4. 
     As is clear from the pupil aberration graph illustrated in  FIG. 9 , it is clear that the objective lens of Example 3 has excellent performances as an objective lens suited for use in an ophthalmic device of a medium field angle of a field of view FOV of around 70°. Note that, although not illustrated, it is confirmed that various aberrations such as spherical aberration, astigmatism, distortion aberration and the like also are corrected well. 
     Example 4 
     An example of the lens structure of the objective lens  130  relating to Example 4 is illustrated in  FIG. 10 . Note that, because Example 4 has a structure that is similar to Example 1, the same portions are denoted by the same reference numerals, and detailed description thereof is omitted. 
     The first lens group G 1  includes, in order from the pupil conjugate position Ps side that is the scanning section side toward the subject eye side, the negative meniscus lens L 11  whose concave surface faces the scanning section side, the positive lens L 12  having a convex surface at the scanning section side, and the positive lens L 13 . The lens L 11  and the lens L 12  are cemented together, and form a lens component that is shaped as a positive lens. 
     The second lens group G 2  includes, in order from the scanning section side toward the subject eye side, the positive lens L 21  having a convex surface at the scanning section side, the negative meniscus lens L 22  having a concave surface at the scanning section side, the positive meniscus lens L 23  whose convex surface faces the scanning section side, and the positive meniscus lens L 24  whose convex surface faces the scanning section side. The lens L 21  and the lens L 22  are cemented together, and form a lens component that is shaped as a positive lens. 
     Lens data of Example 4 is illustrated in Table 5. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 No. 
                 R 
                 D 
                 nd 
                 vd 
               
               
                   
               
             
            
               
                  0 
                   
                  64.44 
                   
                   
               
               
                  1 
                 −150.364 
                   3.90 
                 1.801000 
                 34.92 
               
               
                  2 
                   74.627 
                  15.30 
                 1.603110 
                 60.59 
               
               
                  3 
                  −57.127 
                   0.50 
                   
                   
               
               
                  4 
                  310.877 
                  10.00 
                 1.804000 
                 46.59 
               
               
                  5 
                 −171.831 
                 129.64 
                   
                   
               
               
                  6 
                  234.391 
                  17.00 
                 1.754998 
                 52.32 
               
               
                  7 
                  −54.790 
                   4.00 
                 1.805180 
                 25.44 
               
               
                  8 
                 −449.748 
                   0.50 
                   
                   
               
               
                  9 
                   67.299 
                  11.70 
                 1.713000 
                 53.95 
               
               
                 10 
                 1197.919 
                   0.50 
                   
                   
               
               
                 11 
                   33.345 
                   8.20 
                 1.754998 
                 52.32 
               
               
                 12 
                   46.636 
                  33.42 
               
               
                   
               
            
           
         
       
     
       FIG. 11  is a graph of pupil aberration (lateral aberration at the exit pupil) of the objective lens that is structured by the various items of Table 5. 
     As is clear from the pupil aberration graph illustrated in  FIG. 11 , it is clear that the objective lens of Example 4 has excellent performances as an objective lens suited for use in an ophthalmic device of a medium field angle of a field of view FOV of around 70°. Note that, although not illustrated, it is confirmed that various aberrations such as spherical aberration, astigmatism, distortion aberration and the like also are corrected well. 
     Next, the conformance of the above conditional expressions with the objective lenses in the respective Examples of above-described Example 1 through Example 4 is described. Values relating to the above conditional expressions for Example 1 through Example 4 respectively are listed in Table 6. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                   
                 lower limit 
                 upper limit 
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 FOV 
                 60 
                 80 
                 80 
                 70 
                 70 
                 80 
               
               
                 WD 
                 20 
                 40 
                 20 
                 25 
                 25 
                 20 
               
               
                 D0 
                 25 
                 50 
                 33 
                 38 
                 38 
                 33.42 
               
               
                 f2 
                 40 
                 60 
                 51.9 
                 53.4 
                 52.7 
                 45.9 
               
               
                 f1 
                 80 
                 200 
                 123.9 
                 136.8 
                 136 
                 89.2 
               
               
                 β(θp/θs) 
                 1.5 
                 4 
                 2.5 
                 2.6 
                 2.6 
                 1.9 
               
               
                 pupil aberration 
                 — 
                 2 
                 0.12 
                 0.2 
                 0.13 
                 0.28 
               
               
                 BF 
                 15 
                 128.7 
                 80.1 
                 77.3 
                 50 
                   
               
               
                 scanning angle 
                 30 
                 45 
                 32 
                 32 
                 32 
                 37.7 
               
               
                 FOV/scanning angle 
                 2 
                 4 
                 2.50 
                 2.19 
                 2.19 
                 2.12 
               
               
                 total length 
                   
                   
                 400.0 
                 398.6 
                 395.2 
                 299.1 
               
               
                 sum of lens thicknesses 
                   
                   
                 83.0 
                 89.0 
                 81.8 
                 70.1 
               
               
                 ratio (D/L) 
                 0.15 
                 0.25 
                 0.21 
                 0.22 
                 0.21 
                 0.23 
               
               
                 f2/f1 
                   
                   
                 0.419 
                 0.390 
                 0.388 
                 0.515 
               
               
                   
               
            
           
         
       
     
     As is clear from Table 6, it is clear that the objective lenses of Example 1 through Example 4 are in conformance with the above conditional expressions. 
     Second Embodiment 
     A second embodiment is described next. In the second embodiment, the objective lens  130 , which is the main portion of the imaging optical system  116 A relating to the first embodiment, is formed as an attached optical system, and can be attached to and removed from a portable terminal that has an imaging function. Because the structures of the second embodiment are substantially similar to the first embodiment, the same portions are denoted by the same reference numerals, and description thereof is omitted, and mainly the portions that are different are described. 
       FIG. 12  illustrates an example of a structure in which an attached optical system  300  relating to the second embodiment can be attached to and removed from a portable terminal  400  that has an imaging function. 
     As illustrated in  FIG. 12 , the portable terminal  400  has an imaging section  402  for realizing the imaging function. The imaging section  402  operates in a usual imaging mode, in which the imaging section  402  captures an image of a subject at infinity such as a landscape or the like, by user operation of an unillustrated operation portion that the portable terminal  400  has. Namely, the imaging section  402  of the portable terminal  400  has a lens  404  for a portable terminal ( FIG. 13 ), and is structured so as to, by operation in the usual imaging mode, form an image on an imaging element  406  ( FIG. 13 ) when parallel light is incident. 
       FIG. 13  illustrates an example of the structure of the attached optical system  300  relating to the second embodiment. A state in which the attached optical system  300  is attached to the portable terminal  400  is illustrated in  FIG. 13 . The attached optical system  300  has the first lens group G 1  and the second lens group G 2  that structure the above-described objective lens  130 . Because the structures of these first lens group G 1  and second lens group G 2  are similar to the first embodiment, detailed description thereof is omitted. 
     At the attached optical system  300  relating to the second embodiment, the point that an illuminating portion  304  that emits illumination light, and a half mirror  302  that guides the illumination light that is from the illuminating portion to the optical path that runs along the optical axis AX, are provided at the objective lens  130  relating to the first embodiment, is different. The illuminating portion  304  emits the illumination light that illuminates the subject eye  12 . The half mirror  302  guides the illumination light that is from the illuminating portion  304  to the optical path that runs along the optical axis AX. 
     Note that, in a case in which the portable terminal  400  has a subject illuminating portion that illuminates the subject, it suffices for the attached optical system  300  to, instead of the illuminating portion  304  and the half mirror  302 , employ the illumination light that is emitted from the subject illuminating portion, and have an optical system that guides the illumination light that is from the subject illuminating portion to the optical path that runs along the optical axis AX. Further, the illuminating portion  304  may be an independent structure, and not be provided at the attached optical system  300 . 
     The attachment optical system  300  has an attaching portion  306  that attaches the attachment optical system  300  to the portable terminal  400 , in order to configure the attachment optical system  300  and the portable terminal  400  attachably and removably. Owing to the attachment optical system  300  having this attaching portion  306 , a configuration in which the attachment optical system  300  can be attached to and removed from the portable terminal  400  is enabled. 
     The first lens group G 1  and the second lens group G 2  that are included in the attached optical system  300  function as an objective optical system  301  that forms a pupil that has a conjugate relationship with the pupil of the subject eye  12 . The attached optical system  300  and the portable terminal  400  are fixed by the attaching portion  306  such that the incident pupil of the imaging section  402  of the portable terminal  400  is positioned at the position (the pupil conjugate position Ps) of the pupil that is in a conjugate relationship with the pupil of the subject eye  12  formed by the objective optical system  301 . By structuring the system in this way, a fundus image of the subject eye  12  can be imaged by the simple structure of merely attaching the attached optical system  300  to the portable terminal  400 . 
     Although the technique of the present disclosure has been described by using embodiments, the technical scope of the present disclosure is not limited to the scope put forth in the above-described embodiments. Various modifications and improvements can be added to the above-described embodiments within a scope that does not depart from the gist of the invention, and forms to which such modifications and improvements have been added also are included in the technical scope of the present disclosure. Further, all publications, patent applications, and technical standards mentioned in the present specification are incorporated by reference into the present specification to the same extent as if such individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference. 
     EXPLANATION OF REFERENCE NUMERALS