JP2007093891A - Eyepiece optical system and optical equipment mounted therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an eyepiece optical system having excellent optical performance by securing high finder magnification and long eye relief while achieving the upsizing of an optical system, and optical equipment in which the eyepiece optical system is mounted. <P>SOLUTION: In the eyepiece optical system 1, a subject image formed on a focusing screen 14 (predetermined image-formation surface) by an objective 11 is turned into an erect image by a pentagonal prism (erect optical system) 16, and the erect image is observed through an eyepiece 18. The eyepiece 18 comprises a first lens group L1 having negative refractive power and a second lens group L2 having positive refractive power along an optical axis in order from an object side, and an optical prism (optical path dividing means) 17 is arranged between the pentagonal prism 16 and the first lens group L1 of the eyepiece 18. When the thickness of the optical prism 17 in the optical axis direction is denoted as PL, and the entire length from the emitting surface of the pentagonal prism 16 to the third lens group (lens nearest to the eye point EP side) of the eyepiece 18 is denoted as TL, the eyepiece optical system 1 satisfies a following expression; 0.10<PL/TL<0.75. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides an eyepiece optical system for observing an erect image through an eyepiece lens by using an erecting optical system as a subject image formed on a predetermined imaging plane by an objective lens, and an optical system equipped with the eyepiece optical system. Regarding equipment.

2. Description of the Related Art Conventionally, an eyepiece that is mounted on a camera or the like and that observes a real image (subject image) formed on a predetermined image plane (focus plate) by an objective lens as an erect image by an erecting optical system through an eyepiece. Various types of optical systems have been proposed in which an optical path dividing means is provided in the vicinity of the eyepiece lens and an additional function is achieved by the light beam divided by the optical path dividing means. For example, one of the functions is to detect an observer's line of sight (see, for example, Patent Document 1).
JP-A-7-218985

  Recently, the performance of cameras (optical devices) equipped with an eyepiece optical system has been improved, and as in Patent Document 1, an external display member such as a liquid crystal plate or an operation member is arranged near the eyepiece lens. Therefore, the camera tends to increase in size. For this reason, in the eyepiece optical system, it is required that the distance between the image plane on which the subject image is formed by the objective lens and the eye point is larger than that in the conventional optical system. In addition, the eyepiece optical system is required to secure a high finder magnification in order to cope with an image sensor that is more downsized than before. Further, in an eyepiece optical system, a long eye relief (distance from an eyepiece lens to an eye point) is required to cope with the visual acuity of each observer.

  However, since the eyepiece optical system of Patent Document 1 requires a large air space inside, it is advantageous for increasing the overall length of the optical system, but ensures a high viewfinder magnification and a long eye relief. There was a problem that it was difficult to balance these.

  The present invention has been made in view of such a problem, and an eyepiece optical system having good optical performance by securing a high finder magnification and a long eye relief while increasing the size of the optical system, and the same. An object is to provide an optical device to be mounted.

  In order to achieve such an object, according to the present invention, an object image formed on a predetermined imaging surface by an objective lens is converted into an erect image by an erecting optical system, and the erect image is observed through an eyepiece. In the eyepiece optical system, the eyepiece lens includes a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side along the optical axis. An optical path splitting means is arranged at any air distance between the system and the lens closest to the eye point of the eyepiece lens, and the thickness of the optical path splitting means in the optical axis direction is PL, and the erecting optical system When the total length from the exit surface to the lens closest to the eye point of the eyepiece is TL, the following expression 0.10 <PL / TL <0.75 is satisfied.

  As described above, according to the present invention, an eyepiece optical system having excellent optical performance and an optical apparatus equipped with the eyepiece optical system can be obtained while ensuring a high viewfinder magnification and a long eye relief while increasing the size of the optical system. Can be realized.

  Embodiments according to the present invention will be described below with reference to the drawings.

  In the eyepiece optical system of the present invention, an objective lens, a mirror, a focusing screen, a condenser lens, an erecting optical system (penta prism), an optical path dividing unit (optical prism), and an eyepiece are arranged in order from the object side. Has been.

  The objective lens forms an object image on the focusing screen. The mirror deflects the optical axis of the objective lens at a right angle. The condenser lens guides the subject image on the focusing screen (predetermined imaging plane) formed by the objective lens to the pentaprism. The pentaprism (upright optical system) inverts the subject image (inverted image) on the focusing screen imaged by the objective lens to form an upright image. The optical prism (optical path dividing means) transmits a part of the light beam incident from the pentaprism (upright optical system) and reflects a part thereof. The eyepiece guides the subject image that has passed through the optical prism and has become an erect image by the pentaprism to the viewer's eyes.

  In the eyepiece optical system according to the present invention having the above-described configuration, the light from the subject passes through the objective lens, is reflected by the mirror, forms an image on the focusing screen, and then enters the pentaprism via the condenser lens. It becomes an erect image, passes through an optical prism, and is observed by an observer through an eyepiece.

  In such an eyepiece optical system according to the present invention, the eyepiece lens includes a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side along the optical axis. Therefore, it is desirable that the optical prism (optical path dividing means) is arranged at any air distance between the pentaprism and the lens closest to the eye point of the eyepiece. Since the light from the object converges in the vicinity of the eyepiece, the optical prism can be miniaturized with the above arrangement.

  The eyepiece according to the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. And an optical prism (optical path dividing means) is preferably arranged in the air space between the pentaprism (upright optical system) and the first lens group. .

  Alternatively, the eyepiece according to the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. It is desirable that the optical path dividing means is disposed in the air gap between the second lens group and the third lens group.

  A long eye relief can be ensured by adopting any of the above-described configurations of the eyepiece. Further, as will be described later, diopter adjustment can be effectively performed (with a small amount of movement by moving the second lens group having positive refractive power).

  In the present invention, it is desirable that the eyepiece is configured to adjust the diopter by moving the second lens group on the optical axis of the eyepiece. With such a configuration, it is possible to effectively adjust the diopter with a small amount of movement by moving the (second) lens group having positive refractive power. In the present invention, it is possible to obtain the same effect by moving a lens group having a positive refractive power other than the second lens group, or by moving a plurality of lens groups. .

  The optical prism (optical path dividing means) is an optical prism (specifically, a half-beam) having a light splitting surface that transmits part of the light beam incident from the pentaprism (upright optical system) and reflects part of it. An optical prism having a structure in which a mirror film or the like is sealed is desirable. With this configuration, the durability of the optical path dividing means can be improved.

  The optical prism (optical path splitting means) is preferably an optical prism having a plane of incidence and exit (in other words, no refractive power with respect to an erecting optical system). With such a configuration, it is possible to easily manufacture the optical prism and arrange the optical path dividing means in the eyepiece optical system. In addition, the optical prism can be configured to be easily removable from the eyepiece optical system.

  In the present invention, in order to reduce irregular reflections, ghosts, etc. occurring in the present optical system without being affected by light rays in the screen field of view, the entrance surface and exit surface of the optical prism (optical path dividing means) It is desirable to tilt several degrees rather than perpendicular to the axis. This is because if there is a plane in the finder optical system, the incident surface of the optical path splitting means may be reflected and become a ghost when illuminated by a light source stronger than the eyepoint side of the eyepiece. It is.

  The eyepiece optical system according to the present invention desirably satisfies conditional expressions (1) and (2).

  In the eyepiece optical system of the present invention, the thickness in the optical axis direction of the optical prism (optical path dividing means) is PL, and the total length from the exit surface of the pentaprism (upright optical system) to the lens closest to the eyepoint of the eyepiece. Is preferably TL, it is desirable to satisfy the following equation (1).

          0.10 <PL / TL <0.75 (1)

  The above conditional expression (1) represents an appropriate ratio of the total length TL from the exit surface of the erecting optical system to the lens closest to the eye point of the eyepiece with respect to the center thickness PL in the optical axis direction of the eyepiece optical system of the optical prism. It stipulates. When the upper limit of conditional expression (1) is exceeded, the optical prism has a thick center thickness PL in the optical axis direction, which exceeds the size and weight of an appropriate eyepiece optical system. Further, it is not preferable because curvature of field is deteriorated and it becomes difficult to obtain good optical performance. On the other hand, if the lower limit of conditional expression (1) is not reached, the optical prism will be too small and thin, and the object of the present invention will not be achieved. The upper limit is desirably 0.6. The lower limit is preferably 0.15. More desirably, the lower limit is desirably 0.20. These values have been found as a result of extensive research by the inventors.

  In the eyepiece optical system of the present invention, it is desirable that the following expression (2) is satisfied when the refractive index for the d-line of the optical prism (optical path dividing means) is ndp.

          1.55 <ndp (2)

  Conditional expression (2) defines an appropriate range of the refractive index ndp for the d-line of the optical prism so that the light beam reflected by the light splitting surface is totally reflected at least once inside the optical prism. . Here, the light guided to the reduction optical system includes a light beam on the optical axis of the eyepiece optical system, that is, a light beam perpendicularly incident on the optical prism (hereinafter referred to as an axial beam), and an off-axis having an angle of view. There is a ray. In order to totally reflect the light beam guided to all these reduction optical systems inside the optical prism, the critical angle on the total reflection surface must be reduced. If the lower limit value of the conditional expression (2) is not reached, a necessary refractive index cannot be obtained, and part (or all) of the light beam traveling toward the reduction optical system is not totally reflected, and part of the solid-state image sensor or the like. This is not preferable because the light beam is blocked. The lower limit is more preferably about 1.59.

  In the present invention, the lens system is composed of a plurality of lens groups. However, other lens groups are added between the lens groups, or other lens groups are provided adjacent to the image side or object side of the lens system. It is also possible to add a lens group.

  Embodiments according to the present invention will be described below with reference to the drawings.

In each of the embodiments, the height of the aspheric surface in the direction perpendicular to the optical axis is y, and the distance (sag amount) along the optical axis from the tangential plane at the apex of the aspheric surface to the position on the aspheric surface at the height y. was the S (y), of the reference spherical surface radius of curvature (paraxial radius of curvature) and R, a cone coefficient is kappa, when the n-th order aspherical coefficient was C _n, expressed by the following equation (3). In the table of specifications in each embodiment, an aspherical surface is marked with * on the left side of the surface number.

S (y) = (y ² / R) / {1+ (1−κ × y ² / R ² ) ^1/2 }
+ C ₄ y ⁴ + C ₆ y ⁶ + C ₈ y ⁸ + C ₁₀ y ¹⁰ (3)

  In all the following specification values, “mm” is used as the unit of length described unless otherwise specified. However, since the optical system can obtain the same optical performance even when proportionally enlarged or proportionally reduced, the unit is not limited to “mm”, and other appropriate units can be used. The radius of curvature of 0.0000 indicates a plane, and the refractive index of air of 1.0000 is omitted.

The diopter unit [m ⁻¹ ], which is described in all the specification values, will be described below. The diopter X [m ⁻¹ ] is the diopter X [m ⁻¹ ] on the optical axis from the eye point EP. This shows a state where the position can be set to the position of 1 / X [m]. The sign is positive when the image is closer to the viewer than the eyepiece.

(First embodiment)
An eyepiece optical system according to a first example of the present invention will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram of a single-lens reflex camera (optical apparatus) equipped with an eyepiece optical system 1 according to a first embodiment of the present invention. As shown in FIG. 1, in this camera, a reduction optical system 2 is mounted in addition to the eyepiece optical system 1 according to the present invention.

  As shown in FIG. 2, the eyepiece optical system 1 according to the present invention includes an objective lens 11, a mirror 12, an imaging element 13 for imaging, a focusing plate 14, a condenser lens 15, and a pentaprism (upright) in order from the object side. An optical system) 16, an optical prism 17, and an eyepiece 18 are disposed.

  In FIG. 2, a pentaprism (upright optical system) is shown expanded on the optical axis. In FIG. 2, the objective lens 11, the mirror 12, and the image pickup device 13 for photographing are omitted, and surface numbers to be described later are shown in parentheses.

  Note that the imaging element 13 and the focusing screen 14 for photographing are arranged at optically conjugate positions. The mirror 12 is inserted at an angle of 45 degrees with respect to the optical axis of the observation optical system 1, and light from a subject (not shown) that has passed through the objective lens 11 in a normal state (in a shooting standby state). Is reflected to form an image on the focusing screen 13, and in the shutter release, the mirror is raised and jumps up so that light from a subject (not shown) passing through the objective lens 11 forms an image on the imaging element 13 for photographing. It has become.

  As shown in FIG. 2, the eyepiece 18 includes, in order from the object side, a first lens unit L1 including a negative meniscus lens having a convex surface facing the object side, and a second lens including a positive lens having a convex surface facing the object side. The lens unit L2 includes a third lens unit L3 including a positive lens having a convex surface facing the object side, and a fourth lens unit L4 including a negative meniscus lens having a concave surface facing the object side. In the present embodiment, the eyepiece 18 moves the second lens unit L2 in the optical axis direction to adjust the diopter.

  Here, the optical prism 17 is installed between the pentaprism 16 and the first lens group L1 of the lens closest to the object side of the eyepiece lens 18. In this embodiment, the optical prism 17 is an observation optical system. 1 has a half mirror film HM (light splitting surface; see FIG. 1) that transmits and reflects a light beam incident thereon, and the light transmitted through the half mirror film HM is guided to the eyepiece lens 18 and the reflected light is reduced. It leads to the optical system 2.

  In the observation optical system 1 configured as described above, light from a subject (not shown) passes through the objective lens 11, is reflected by the mirror 12, is reflected toward the focusing screen 14, and a subject image is formed on the focusing screen 14. . The light beam from the subject image on the focusing screen 14 enters the optical prism 17 through the condenser lens 15 and the pentaprism 16. Of the light incident on the optical prism 17, the light transmitted through the half mirror film HM (light splitting surface) passes through the eyepiece 18 and is guided to the eye point EP. An observer can observe a real image of a subject (not shown) at an eye point EP.

  At the time of shutter release, the light from the subject (not shown) that has passed through the objective lens 11 is focused on the imaging element 13 for photographing with the mirror 12 in the mirror-up state.

  In the reduction optical system 2, a photographing lens 21, a filter group 22 (for example, a low-pass filter and an infrared cut filter), and a solid-state imaging device 23 (for example, a CCD, a CMOS, and the like) are disposed in order from the object side (for example, a CCD or a CMOS). (See FIG. 1).

  Note that the reduction optical system 2 supports the photographing of a single-lens reflex camera user. For example, a face recognition function that focuses on the subject's face, and the focus position changes following the movement of the main subject in the image. It is installed to develop new functions that were not available in single-lens reflex cameras, such as an automatic tracking function that makes it easy to focus on the main subject, and a real-time display function that displays images in real time on the rear LCD screen of the camera body. It is what.

  In the reduction optical system 2 having such a configuration, the light beam from the subject image formed on the focusing screen 14 enters the optical prism 17 through the condenser lens 15 and the pentaprism 16, and is reflected by the half mirror film HM. After that, the light is totally reflected once inside the prism 17 and emitted, and enters the photographing lens 21. Then, the light incident on the photographing lens 21 is converged and re-imaged on the imaging surface of the solid-state imaging device 23 through the filter group 22 so that information as an electronic image can be obtained. .

Table 1 shows the specifications of each lens of the eyepiece optical system 1 according to the present example. As shown in Table 1, in the specification table, the first column m is the number of each optical surface from the object side (hereinafter referred to as surface number), the second column r is the radius of curvature of each optical surface, and the third Column d is the distance on the optical axis from each optical surface to the next optical surface (or image surface) (hereinafter referred to as the surface interval), column 4 nd is the refractive index for the d-line (wavelength 587.6 nm), fifth A column νd represents the Abbe number with respect to the d-line (wavelength 587.6 nm). In the table, the diopter indicates the diopter of the eyepiece according to the present invention, fe indicates the focal length of the eyepiece when -1 [m ^-1 ], and EP indicates the eye point.

In Table 1, the surface interval indicated by surface number 9 (namely, the surface interval between surface number 9 and surface number 10) d9 and the surface interval indicated by surface number 11 (namely, the surface interval between surface number 11 and surface number 12) d11. Since the eye point EP changes when diopter adjustment is performed, the minus end (−2.0 [m ⁻¹ ]) state, the −1.0 [m ⁻¹ ] state, and the plus end (+1.0). The variable interval data in each diopter state in the [m ⁻¹ ]) state are shown. The values corresponding to the above conditional expressions (1) and (2), that is, the condition corresponding values are also shown below.

  As can be seen from the table of specifications shown in Table 1, it can be seen that the eyepiece optical system 1 according to the present example satisfies all the conditional expressions (1) and (2).

3 to 5 are diagrams illustrating various aberrations (spherical aberration, astigmatism, distortion aberration, and coma aberration) with respect to the d-line (wavelength λ = 587.6 nm) in the eyepiece optical system 1 according to the present example. Specifically, FIG. 3 is an aberration diagram in the minus end (−2.0 [m ⁻¹ ]) state, and FIG. 4 is an aberration diagram in the −1.0 [m ⁻¹ ] state. 5 shows various aberrations in the plus end (+1.0 [m ⁻¹ ]) state. In each aberration diagram, Y1 represents the incident height of the light beam to the erect system, Y0 represents the object height on the focusing screen, and min represents “minute”, which is an angular unit. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the dotted line indicates the meridional image plane. The description of the aberration diagrams is the same in the other examples.

As is apparent from the aberration diagrams shown in FIGS. 3 to 5, in the first embodiment according to the present invention, the minus end (−2.0 [m ⁻¹ ]) state is changed to the plus end (+1.0 [m]. ^-1 ])) In each diopter adjustment state up to the state, it can be seen that various aberrations are well corrected and excellent imaging performance is secured.

(Second embodiment)
An eyepiece optical system according to a second example of the present invention will be described with reference to FIGS. 1 and 6 to 9. FIG. 1 is a schematic configuration diagram of a single-lens reflex camera (optical apparatus) equipped with an eyepiece optical system 1 according to the present embodiment. As shown in FIG. 1, in this camera, a reduction optical system 2 is mounted in addition to the eyepiece optical system 1 according to the present invention.

  As shown in FIG. 6, the eyepiece optical system 1 according to the present invention includes an objective lens 11, a mirror 12, an imaging device 13 for imaging, a focusing plate 14, a condenser lens 15, and a pentaprism (upright) in order from the object side. An optical system) 16, an optical prism 17, and an eyepiece 18 are disposed.

  In FIG. 6, a pentaprism (upright optical system) is shown developed on the optical axis. Further, in FIG. 6, the objective lens 11, the mirror 12, and the imaging element 13 for photographing are omitted, and surface numbers described later are shown in parentheses.

  The imaging element 13 and the focusing screen 14 for photographing are disposed at optically conjugate positions. The mirror 12 is inserted at an angle of 45 degrees with respect to the optical axis of the eyepiece optical system 1, and reflects light from a subject (not shown) that has passed through the objective lens 11 to the focusing screen 13 when down. At the time of shuttering, the shutter is in an up state and jumps up, and light from a subject (not shown) passing through the objective lens 11 forms an image on the imaging element 13 for photographing.

  Specifically, as shown in FIG. 6, the eyepiece 18 is, in order from the object side, a first lens unit L1 including a negative meniscus lens having a convex surface facing the object side, and a first lens including a positive lens having a convex surface facing the object side. The second lens unit L2 includes a second lens unit L2 and a third lens unit L3 including a negative meniscus lens having a convex surface facing the object side. In the present embodiment, the eyepiece 18 moves the second lens unit L2 in the optical axis direction to adjust the diopter.

  Here, the optical prism 17 is disposed between the pentaprism 16 and the first lens unit L1 of the most object side lens of the eyepiece 18. In this embodiment, the optical prism 17 has a half mirror film HM (light splitting surface; see FIG. 1) that transmits and reflects the light beam incident from the observation optical system 1, and the light transmitted through the half mirror film HM. Leads to the eyepiece 18, and the reflected light guides to the reduction optical system 2.

  In the observation optical system 1 configured as described above, light from a subject (not shown) passes through the objective lens 11, is reflected by the mirror 12, is reflected toward the focusing screen 14, and a subject image is formed on the focusing screen 14. . The light beam from the subject image on the focusing screen 14 enters the optical prism 17 through the condenser lens 15 and the pentaprism 16. Of the light incident on the optical prism 17, the light transmitted through the half mirror film HM (light splitting surface) passes through the eyepiece 18 and is guided to the eye point EP. An observer can observe a real image of a subject (not shown) at an eye point EP.

  At the time of shutter release, the light from the subject (not shown) that has passed through the objective lens 11 is focused on the imaging element 13 for photographing with the mirror 12 in the mirror-up state.

  In the reduction optical system 2, a photographing lens 21, a filter group 22 (for example, a low-pass filter and an infrared cut filter), and a solid-state imaging device 23 (for example, a CCD, a CMOS, and the like) are disposed in order from the object side (for example, a CCD or a CMOS). (See FIG. 1).

  Note that the reduction optical system 2 supports the photographing of a single-lens reflex camera user. For example, a face recognition function that focuses on the subject's face, and the focus position changes following the movement of the main subject in the image. It is installed to develop new functions that were not available in single-lens reflex cameras, such as an automatic tracking function that makes it easy to focus on the main subject, and a real-time display function that displays images in real time on the rear LCD screen of the camera body. It is what.

  In the reduction optical system 2 having such a configuration, the light beam from the subject image formed on the focusing screen 14 enters the optical prism 17 through the condenser lens 15 and the pentaprism 16, and is reflected by the half mirror film HM. After that, the light is totally reflected once inside the prism 17 and emitted, and enters the photographing lens 21. Then, the light incident on the photographing lens 21 is converged and re-imaged on the imaging surface of the solid-state imaging device 23 through the filter group 22 so that information as an electronic image can be obtained. .

Table 2 shows the specifications of each lens of the eyepiece optical system 1 according to the present example. In Table 2, the surface interval indicated by surface number 9 (namely, the surface interval between surface number 9 and surface number 10) d9 and the surface interval indicated by surface number 11 (namely, the surface interval between surface number 11 and surface number 12) d11. Since the eye point EP changes when diopter adjustment is performed, the minus end (−2.0 [m ⁻¹ ]) state, the −1.0 [m ⁻¹ ] state, and the plus end (+1.0). The variable interval data in each diopter state in the [m ⁻¹ ]) state are shown. The values corresponding to the above conditional expressions (1) and (2), that is, the condition corresponding values are also shown below.

  As can be seen from the table of specifications shown in Table 2, it can be seen that the eyepiece optical system 1 according to the present example satisfies all the conditional expressions (1) and (2).

7 to 9 are diagrams showing various aberrations (spherical aberration, astigmatism, distortion aberration and coma aberration) for the d-line (wavelength λ = 587.6 nm) in the eyepiece optical system 1 according to the present example. 7 is an aberration diagram in the minus end (−2.0 [m ⁻¹ ]) state, FIG. 8 is an aberration diagram in the −1.0 [m ⁻¹ ] state, and FIG. It is an aberration diagram of the end (+1.0 [m ⁻¹ ]) state.

As is apparent from the aberration diagrams shown in FIGS. 7 to 9, in the second embodiment according to the present invention, from the minus end (−2.0 [m ⁻¹ ]) state to the plus end (+1.0 [m]. ^-1 ])) In each diopter adjustment state up to the state, it can be seen that various aberrations are well corrected and excellent imaging performance is secured.

(Third embodiment)
An eyepiece optical system according to a third example of the present invention will be described with reference to FIGS. FIG. 10 is a schematic configuration diagram of a single-lens reflex camera (optical apparatus) equipped with the eyepiece optical system 1 according to the third embodiment of the present invention. As shown in FIG. 10, this camera is equipped with a reduction optical system 2 in addition to the eyepiece optical system 1 according to the present invention.

  As shown in FIG. 11, the eyepiece optical system 1 according to the present invention includes, in order from the object side, an objective lens 11, a mirror 12, an imaging element 13 for imaging, a focusing plate 14, a condenser lens 15, and a pentaprism (upright). Optical system) 16, an eyepiece lens 18, and an optical prism 17 are disposed.

  In FIG. 11, a pentaprism (upright optical system) is developed on the optical axis. In FIG. 11, the objective lens 11, the mirror 12, and the imaging element 13 for photographing are omitted, and surface numbers to be described later are shown in parentheses.

  The imaging element 13 and the focusing screen 14 for photographing are disposed at optically conjugate positions. The mirror 12 is inserted at an angle of 45 degrees with respect to the optical axis of the eyepiece optical system 1, and reflects light from a subject (not shown) that has passed through the objective lens 11 to the focusing screen 13 when down. At the time of shuttering, the shutter is in an up state and jumps up, and light from a subject (not shown) passing through the objective lens 11 forms an image on the imaging element 13 for photographing.

  As shown in FIG. 11, the eyepiece 18 includes, in order from the object side, a first lens unit L1 including a negative meniscus lens having a convex surface facing the object side, and a second lens including a positive lens having a convex surface facing the object side. The lens unit L2 includes a group L2 and a third lens unit L3 including a negative meniscus lens having a convex surface facing the object side. In the present embodiment, the eyepiece 18 moves the second lens unit L2 in the optical axis direction to adjust the diopter.

  Here, the optical prism 17 is installed between the second lens group L2 and the third lens group L3 of the eyepiece lens 18. In this embodiment, the optical prism 17 is incident from the observation optical system 1. The eyepiece 18 has a half mirror film HM (light splitting surface, see FIG. 10) that transmits and reflects the light beam that has passed through the first lens unit L1. The light that has passed through the half mirror film HM passes through the eyepiece 18. The light guided to the second lens unit L2 and reflected is guided to the reduction optical system 2.

  In the observation optical system 1 configured as described above, light from a subject (not shown) passes through the objective lens 11, is reflected by the mirror 12, is reflected toward the focusing screen 14, and a subject image is formed on the focusing screen 14. . Then, the light beam from the subject image on the focusing screen 14 enters the optical prism 17 via the condenser lens 15, the pentaprism 16, and the first lens group L 1 of the eyepiece lens 18. Of the light incident on the optical prism 17, the light transmitted through the half mirror film HM (light splitting surface) passes through the second lens group L2 and the third lens group L3 of the eyepiece 18 and is guided to the eye point EP. It is burned. An observer can observe a real image of a subject (not shown) at an eye point EP.

  At the time of shutter release, the light from the subject (not shown) that has passed through the objective lens 11 is focused on the imaging element 13 for photographing with the mirror 12 in the mirror-up state.

  In the reduction optical system 2, a photographing lens 21, a filter group 22 (for example, a low-pass filter and an infrared cut filter), and a solid-state imaging device 23 (for example, a CCD, a CMOS, and the like) are disposed in order from the object side (for example, a CCD or a CMOS). (See FIG. 10).

  Note that the reduction optical system 2 supports the photographing of a single-lens reflex camera user. For example, a face recognition function that focuses on the face of the subject, and the focus position changes following the movement of the main subject in the image. It is installed to develop new functions that were not available in single-lens reflex cameras, such as an automatic tracking function that makes it easy to focus on the main subject, and a real-time display function that displays images in real time on the rear LCD screen of the camera body. It is what.

  In the reduction optical system 2 having such a configuration, the light beam from the subject image formed on the focusing screen 14 enters the optical prism 17 through the condenser lens 15 and the pentaprism 16, and is reflected by the half mirror film HM. After that, the light is totally reflected once inside the prism 17 and emitted, and enters the photographing lens 21. Then, the light incident on the photographing lens 21 is converged and re-imaged on the imaging surface of the solid-state imaging device 23 through the filter group 22 so that information as an electronic image can be obtained. .

Table 3 shows the specifications of each lens of the eyepiece optical system 1 according to the present example. In Table 3, surface number 8 is formed in an aspherical shape, and aspherical data relating to this is shown. Further, the surface interval indicated by the surface number 7 (namely, the surface interval between the surface number 7 and the surface number 8) d7 and the surface interval indicated by the surface number 9 (namely, the surface interval between the surface number 9 and the surface number 10) d9 and the eye point. Since EP changes when diopter adjustment is performed, the minus end (−2.0 [m ⁻¹ ]) state, the −1.0 [m ⁻¹ ] state, the plus end (+1.0 [m ^{−). 1} ]) Variable interval data in each diopter state. The values corresponding to the above conditional expressions (1) and (2), that is, the condition corresponding values are also shown below.

  As can be seen from the table of specifications shown in Table 3, it can be seen that the eyepiece optical system 1 according to the present example satisfies all the conditional expressions (1) and (2).

12 to 14 are diagrams showing various aberrations (spherical aberration, astigmatism, distortion aberration and coma aberration) for the d-line (wavelength λ = 587.6 nm) in the eyepiece optical system 1 according to the present example. That is, FIG. 12 is an aberration diagram in the minus end (−2.0 [m ⁻¹ ]) state, FIG. 13 is an aberration diagram in the −1.0 [m ⁻¹ ] state, and FIG. It is an aberration diagram of the end (+1.0 [m ⁻¹ ]) state.

As is apparent from the aberration diagrams shown in FIGS. 12 to 14, in the third embodiment according to the present invention, from the minus end (−2.0 [m ⁻¹ ]) state to the plus end (+1.0 [m]. ^-1 ])) In each diopter adjustment state up to the state, it can be seen that various aberrations are well corrected and excellent imaging performance is secured.

  The present invention as described above is not limited to the above embodiment, and can be improved as appropriate without departing from the gist of the present invention.

It is a schematic block diagram of the finder optical system of the single-lens reflex camera provided with the eyepiece lens system which concerns on this invention. 1 is a schematic configuration diagram of an eyepiece lens system according to a first example of the present invention. FIG. 6 is a diagram illustrating various aberrations in a minus end (−2.0 [m ⁻¹ ]) state according to the first example. FIG. 6 is a diagram illustrating various aberrations in a −1.0 [m ⁻¹ ] state according to the first example. FIG. 6 is a diagram illustrating various aberrations in a plus end (+1.0 [m ⁻¹ ]) state according to the first example. It is a schematic block diagram of the eyepiece lens system which concerns on 2nd Example of this invention. FIG. 6 is a diagram illustrating various aberrations in a minus end (−2.0 [m ⁻¹ ]) state according to the second example. FIG. 12 is a diagram illustrating various aberrations in a −1.0 [m ⁻¹ ] state according to the second example. FIG. 6 is a diagram illustrating various aberrations in a plus end (+1.0 [m ⁻¹ ]) state according to the second example. It is a schematic block diagram of the finder optical system of the single-lens reflex camera provided with the eyepiece system which concerns on 3rd Example of this invention. It is a schematic block diagram of the eyepiece lens system which concerns on the said 3rd Example. FIG. 12 is a diagram illustrating various aberrations in the minus end (−2.0 [m ⁻¹ ]) state according to the third example. FIG. 10 is a diagram illustrating all aberrations in the −1.0 [m ⁻¹ ] state according to the third example. FIG. 12 is a diagram illustrating various aberrations in a plus end (+1.0 [m ⁻¹ ]) state according to the third example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Observation optical system 11 Objective lens 12 Mirror 13 Image pick-up element 14 for imaging | photography 14 Focus plate 15 Condenser lens 16 Penta prism (upright optical system) 17 Optical prism (optical path dividing means)
18 Eyepiece
2 Reduction optical system 21 Shooting lens 22 Filter group
23 Solid-state imaging devices (imaging devices)
HM half mirror film (light splitting surface) EP eye point

Claims (8)

In an eyepiece optical system in which an object image formed on a predetermined imaging surface by an objective lens is an erect image by an erecting optical system, and this erect image is observed through an eyepiece lens,
The eyepiece includes a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side along the optical axis.
An optical path dividing means is disposed in any air gap between the erecting optical system and the most eye point side lens of the eyepiece,
When the thickness in the optical axis direction of the optical path dividing means is PL, and the total length from the exit surface of the erecting optical system to the lens closest to the eye point of the eyepiece lens is TL,
0.10 <PL / TL <0.75
An eyepiece optical system characterized by satisfying the above requirements. The eyepiece lens includes, in order from the 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 positive refractive power, and a negative refractive power. A fourth lens group having
The eyepiece optical system according to claim 1, wherein the optical path dividing unit is disposed in an air gap between the erecting optical system and the first lens group. The eyepiece includes, in order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power,
2. The eyepiece optical system according to claim 1, wherein the optical path splitting unit is disposed in an air gap between the second lens group and the third lens group.   The eyepiece optical system according to any one of claims 1 to 3, wherein the eyepiece lens performs diopter adjustment by moving the second lens group on an optical axis of the eyepiece lens. When the refractive index for the d-line of the optical path dividing means is ndp,
1.55 <ndp
The eyepiece optical system according to any one of claims 1 to 4, wherein:   The eyepiece optical according to any one of claims 1 to 5, wherein the optical path dividing means is an optical prism that transmits a part of a light beam incident from the erecting optical system and reflects a part thereof. system.   The eyepiece optical system according to any one of claims 1 to 6, wherein the optical path splitting unit has a plane of incidence and exit surfaces with respect to the erecting optical system.   An optical apparatus comprising the eyepiece optical system according to claim 1.

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