JP5462588B2 - Eyepiece lens system, finder optical system, electronic viewfinder, and imaging apparatus in imaging apparatus - Google Patents

Description

  The present invention is mounted on an imaging device such as a TV camera, a video camera, or a digital camera, and is an electronic viewfinder (EVF) that is a display device for observing a subject to focus on the subject or to determine a composition during photographing. ), An finder optical system including the eyepiece lens system, an electronic viewfinder including the finder optical system, and an imaging apparatus including the electronic viewfinder.

  The electronic viewfinder includes an LCD (Liquid Crystal Display) and a finder optical system. The LCD displays a subject image on a liquid crystal display surface in a finder in accordance with an image signal from an image sensor in the image pickup apparatus, and the LCD for displaying the image requires an illumination optical system for illuminating it. To do. In recent years, transmissive to reflective LCDs have been used in order to save space in installing the illumination optical system. This reflection type LCD is one in which illumination light is applied from the front of the liquid crystal display surface. Japanese Unexamined Patent Application Publication No. 2002-48985 is a conventional finder optical system. The publication discloses a positive refractive index on the optical axis from the liquid crystal display surface side to the observer's pupil position (eye point) and from the liquid crystal display surface side to the observer's pupil position (eye point) side. And a first lens having a negative refractive index, a second lens having a negative refractive index, and a third lens having a positive refractive index are disclosed. According to the description of this publication, this finder optical system has a high finder magnification, is compact, and can correct various aberrations at a low cost. As another conventional example of the finder optical system, for example, Japanese Patent Application Laid-Open No. 6-258582 also discloses a lens having an eyepiece lens in which the same first to third lenses are arranged. According to the description of the publication, a finder optical system having an eyepiece with good aberration correction and particularly small distortion is obtained.

  However, the reflective LCD has been increasingly required in recent years to be ultra-compact and high-definition. On the other hand, the subject image displayed on the liquid crystal display surface with the high-definition display secured is large and naturally, that is, Market orientation is high in that the entire image area is high resolution and no distortion, and those described in the above publication do not meet the requirements. For example, in the finder optical system described in Japanese Patent Application Laid-Open No. 2002-48985, when a reflective LCD having one pixel of about 12 μm × 12 μm is used for observation, the green e-line (546.1 nm) ), For example, 435.8nm, which is the blue with the shortest wavelength of visible light, is focused about 120μm before, and 656.3nm, which is the red with the longest wavelength of visible light, is about 70μm behind. Is in focus. Therefore, even though the RGB colors that are mixed within one dot are separated and the green color fits into one dot and looks blurless, the blue and red colors appear blurred and blurred. There is a problem in terms of observation. Further, the eyepiece system disclosed in Japanese Patent Application Laid-Open No. 6-258582 has a problem in that the magnification is only 4 times, and a very small LCD is greatly observed. Therefore, the viewfinder optical system proposed in the conventional literature has room for further improvement in terms of high definition and large observation.

JP 2002-48985 A JP-A-6-258582

  In order to solve the above-mentioned problems, an electronic viewfinder capable of observing a subject with high definition and an eyepiece system used for such an electronic viewfinder are provided.

  In a first aspect, an eyepiece system is provided that is disposed on an optical axis between an LCD for a viewfinder and a final optical surface of the viewfinder. In the eyepiece lens system, the first lens having a positive refractive index, the second lens having a negative refractive index, and the third lens having a positive refractive index are arranged from the LCD side toward the final optical surface side. They are arranged in order and satisfy the conditions of 18 mm <f1 <20 mm, -18 mm <f2 <-16 mm, 18 mm <f3 <20 mm, 19 mm <f <21 mm, 0 ≦ HH ′ / f <+0.13. Where f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f is the combined focal length of the first to third lenses, and HH ′ is the rear principal point H. And the distance in the optical axis direction from the front principal point H ′.

  In the second, third, and fourth aspects, a finder optical system, an electronic viewfinder, and an imaging device that include the eyepiece system of any of the first aspects are provided.

  According to the present invention, it is possible to provide an eyepiece lens system and an electronic viewfinder that enable high-definition observation of a subject.

FIG. 1 is a diagram showing a schematic internal block configuration of a circuit of an imaging apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an external configuration from the rear of the imaging apparatus. FIG. 3 is a diagram showing an exploded configuration of the electronic viewfinder. FIG. 4 is a diagram showing an assembled state of the electronic viewfinder. FIG. 5 is a diagram showing a schematic cross-sectional configuration of the electronic viewfinder. FIG. 6 is a diagram for explaining the diopter correction performed by the observer moving the finder optical system. FIG. 7 is a diagram showing the arrangement of lenses constituting the eyepiece lens system. FIG. 8 is an optical characteristic diagram (part 1) of the eyepiece lens system. FIG. 9 is an optical characteristic diagram (part 2) of the eyepiece lens system. FIG. 10 is a diagram illustrating both surfaces of the third lens.

  Hereinafter, with reference to the attached drawings, an eyepiece lens system according to an embodiment of the present invention, a finder optical system including the eyepiece lens system, an electronic viewfinder including the finder optical system, and an imaging including the electronic viewfinder The apparatus will be described.

  The embodiments described below exemplify an eyepiece system and the like for embodying the technical idea of the present invention, and the present invention specifies or limits the eyepiece system and the like to the following. It is not a thing. In particular, the specification does not limit the elements shown in the claims to the embodiments. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation.

  1 is a schematic internal block configuration of a circuit of an imaging apparatus, FIG. 2 is an external configuration from the rear of the imaging apparatus, FIG. 3 is an exploded configuration of an electronic viewfinder, and FIG. 4 is an external configuration of an assembled electronic viewfinder. FIG. 5 shows a cross-sectional configuration of the electronic viewfinder.

  First, referring to FIG. 1, an imaging apparatus 1 according to an embodiment includes a camera body 3 and an imaging lens unit 5. The imaging lens unit 5 has a cylindrical shape and is detachably mounted on the front surface of the camera body 3. The imaging lens unit 5 includes an imaging lens 5a, a diaphragm 5b, and the like. The camera body 3 includes an image sensor 7, a back LCD 9, an electronic viewfinder 11, a microcomputer 13, a card mounting unit 15, a power supply box 16, and the like.

  The image sensor 7 captures an optical image of a subject by the imaging lens 5 a in the imaging lens unit 5. The image sensor 7 is composed of an image sensor such as a CMOS or CCD. The image sensor 7 receives a subject optical image and generates analog image signals of RGB three primary colors from the received light.

  The microcomputer 13 drives and controls the image sensor 7. The microcomputer 13 digitally converts the image signal output from the image sensor 7 and performs various image processing such as YC conversion, electronic zoom processing, and compression processing on the digitally converted image signal to generate a digital image signal. , Etc. are performed.

  The microcomputer 13 further performs various drive controls such as zoom and autofocus on the imaging lens 5a, drive control of the diaphragm 5b, drive control of the card mounting unit 15, drive control of the electronic viewfinder 11, and display on the rear LCD 9. Control such as control.

  A memory card 17 can be attached to the card attachment unit 15. The memory card 17 stores image data. The microcomputer 13 reads the image data in the memory card 17 attached to the card attachment unit 15. The microcomputer 13 outputs the read image data to the electronic viewfinder 11.

  In the electronic viewfinder 11, a through image of the subject image and image data in the memory card 17 can be displayed on the reflective LCD 19. The microcomputer 13 can control the display of the through image of the subject image and the stored image data in the memory card 17 on the rear LCD 19. In addition, the imaging apparatus 1 is provided with various functions such as a still image, a moving image mode, flash photography, and a circuit for recording and reproduction, but illustration and description thereof are omitted.

  The electronic viewfinder 11 is installed integrally with the camera body 3 near the back of the upper surface of the camera body 3. The electronic viewfinder 11 may be detachably installed on the camera body 3. The electronic viewfinder 11 is connected to a board on which the microcomputer 13 and the like are provided by a flexible wiring board 28 (see FIG. 3). The flexible wiring board 28 has a signal line for image data and a signal line for power supply. Thereby, the electronic viewfinder 11 can receive image data from the microcomputer 13. The electronic viewfinder 11 receives power supply from a battery provided in the power supply box 16.

  The electronic viewfinder 11 includes a reflective LCD 19 and a finder optical system 22. The reflective LCD 19 processes the image signal input from the microcomputer 13 to reduce and display the subject image. The finder optical system 22 enlarges the subject image displayed on the liquid crystal display surface of the reflective LCD 19.

  The electronic viewfinder 11 will be described in more detail with reference to FIGS. The electronic viewfinder 11 includes the above-described reflective LCD 19, finder optical system 22, diopter adjustment mechanism 25, light transmissive plate 27, finder housing 29, and protective case 44. The reflective LCD 19 is positioned on one side of the finder housing 29 in the optical axis direction, and the finder optical system 22 is positioned on the other side of the finder housing 29 in the optical axis direction. A diopter adjustment mechanism 25 is provided on a side surface of the finder housing 29 along the optical axis direction. A protective case 44 is attached to one side of the finder housing 29 in the optical axis direction. A light transmissive plate 27 (final optical surface) is attached to the other side of the finder housing 29 in the optical axis direction.

  The reflective LCD 19 includes an RGB three-color LED light source 33, a diffusion sheet 35, a flat plate-shaped polarizing plate (polarizing beam splitter) 37, a dome-shaped polarizing plate 39, a liquid crystal unit 41, a reflective plate 42, a liquid crystal driver 48, and antireflection. It comprises a mask 46 and an LCD housing 43.

  Light emitted from the LED light source 33 is diffused by the diffusion sheet 35. Only the linearly polarized light of the diffused emitted light is transmitted through the polarizing plate 37. The linearly polarized light transmitted through the polarizing plate 37 is reflected on the inner surface of the dome-shaped polarizing plate 39. The linearly polarized light reflected by the inner surface of the dome-shaped polarizing plate 39 passes through the liquid crystal surface of the liquid crystal unit 41 to which no voltage is applied, and is reflected by the reflector 42 on the back of the liquid crystal unit 41.

  When linearly polarized light is transmitted through the liquid crystal surface, the polarization axis is twisted 45 degrees. Further, the linearly polarized light reflected by the reflecting plate 42 is also twisted by 45 degrees in the polarization axis. That is, the direction of the linearly polarized light reflected by the reflecting plate 42 is changed to a predetermined polarization state that can be transmitted through the dome-shaped polarizing plate 39.

  Thus, the linearly polarized light twisted on the liquid crystal surface passes through the dome-shaped polarizing plate 39 and is emitted as an optical image signal. The antireflection mask 46 is a member that can prevent reflection. The antireflection mask 46 is painted so that it can absorb light. As the paint, for example, an epoxy black paint or an acrylic black paint can be used. The liquid crystal driver 48 has a connector connected to the flexible wiring board 28 on the back surface, and drives the reflective LCD 19.

  The optical image signal emitted from the reflective LCD 19 is refracted by the finder optical system 22, is transmitted through the light transmissive plate 27, and enters the observer's pupil 45. Specifically, the viewfinder optical system 22 is placed at a position where the optical image signal emitted from the reflective LCD 19 is adapted to its own diopter, with the eyeglasses or the like that allows the observer to perform appropriate diopter correction, or with the naked eye. In the state where the lens is moved, its own eye is positioned on the optical axis, and it can be determined whether or not the entire area of the optical image signal emitted from the reflective LCD 19 can be observed.

  The viewfinder optical system 22 includes an eyepiece lens system 23 including three lenses. The eyepiece system 23 includes a first lens 23a having a positive refractive index, a second lens 23b having a negative refractive index, from the dome-shaped polarizing plate 39 of the reflective LCD 19 toward the pupil 45 (eye point side), and A configuration in which a third lens 23c having a positive refractive index is provided, and each of the lenses 23a to 23c is held by a lens holder 23d in a state where the positions of the lenses 23a to 23c constituting the eyepiece lens system 23 are held. It has become.

  The viewfinder optical system 22 enlarges the optical image output from the liquid crystal unit 41 of the reflective LCD 19. The finder optical system 22 is movable between the near vision side position and the far vision side position by the diopter adjustment mechanism 25 with respect to the finder housing 29. Diopter adjustment means that when the observer is a nearsighted person or a farsighted person, the viewfinder optical system 22 (specifically, the eyepiece lens system 23) of the electronic viewfinder 11 is moved forward and backward in both directions along the optical axis. It is an adjustment that helps the observation in the viewfinder by supplementing the refractive power of the eye.

  The diopter adjustment mechanism 25 includes a diopter adjustment dial 25 a and a drive gear 25 b that are rotatably supported by bosses 29 a and 29 b on the outer surface of the finder housing 29 and are engaged with each other. The pinion gear 25d is coaxially attached to the drive gear 25b, and the rack 25c is formed on the side surface of the lens holder 23d of the finder optical system 22 and engages with the pinion gear 25d.

  The rotation operation of the diopter adjustment dial 25a is transmitted from the drive gear 25b and the pinion gear 25d to the rack 25c. Accordingly, the eyepiece lens system 23 is converted into a linear motion in the finder housing 29 and moved in response to the rotation operation of the dial 25a. Thus, the observer can move the eyepiece system 23 to a position suitable for his or her diopter by rotating the diopter adjustment dial 25a according to whether his or her eyes are near or farsighted. In this case, the finder optical system 22 can be moved and controlled with high accuracy by controlling the number of teeth and the diameter ratio of the diopter adjustment dial 25a, the drive gear 25b, and the pinion gear 25d.

  The light transmissive plate 27 is made of glass, plastic, or the like, and is provided in the finder housing 29. The optically transparent plate 27 transmits a part of the optical image signal collected by the eyepiece lens system 23, and a part of the optical image signal is reflected by the transmission surface. The light transmissive plate 27 is provided such that the transmission surface is not perpendicular to the optical axis of the eyepiece lens system 23. As a result, the optical image signal reflected by the transmission surface of the light transmissive plate 27 does not enter the reflective LCD 19 via the eyepiece lens system 23. The optical image signal enlarged by the eyepiece lens system 23 is transmitted through the light transmissive plate 27. The light-transmitting plate 27 prevents dust from entering the housing together with the protective case 44 from the outside.

A specific example of the structure of the electronic viewfinder 11 is as follows. This data is obtained when the finder optical system 22 is at the -2.5 diopter position.
(Reflective LCD 19)
・ Diagonal length of LCD screen: 11.654mm
・ Distance between the LCD image surface and the first lens 23a: 12.587mm
(First lens 23a)
・ Core thickness: 6.5mm
LCD screen side curvature: aspherical surface 1
-Curvature on the observer side: aspherical surface 2
・ Material: Acrylic resin ・ Refractive index ne1: 1.494
・ Dispersion ratio ν1: 57.8
The distance between the opposing surfaces (G1) between the first lens 23a and the second lens 23b: 1.0 mm
(Second lens 23b)
・ Core thickness: 2.0mm
-Curvature on the LCD screen side: -21.372mm
-Observer side curvature: aspherical surface 3
・ Material: Polycarbonate resin ・ Refractive index ne1: 1.588
・ Dispersion ratio ν1: 29.8
The distance between the opposing surfaces (G2) between the second lens 23b and the third lens 23c: 0.5 mm
(Third lens 23c)
・ Core thickness: 6.5mm
-Curvature on the LCD screen side: 17.066mm
-Curvature on the observer side: Aspheric surface 4
・ Material: Acrylic resin ・ Refractive index ne1: 1.494
・ Dispersion ratio ν1: 57.8
The distance between the opposing surfaces between the third lens 23c and the light transmissive plate 27: 3.0 mm
(Light transmissive plate 27)
・ Shape: 1mm thick parallel plate ・ Material: Acrylic ・ Distance between the light transmissive plate 27 and the pupil of the observer (eye point): 15.0 mm
(Observer)
・ Pupil diameter: 4mm
(Aspherical equation)
Z = Ry ² / (1 + √ (1- (1 + K) R ² y ² )) + Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰
R: Basic curvature value
K: Conic coefficient
A, B, C, D: Higher order terms
y: Distance in the radial direction of the lens with the optical axis position at the base of y = 0mm
Z: Displacement of the shape in the cross-sectional direction of the lens with the optical axis position as Z = 0mm base point (aspherical surface 1)
In the above aspheric equation, the surface shape takes the following values.

R = -0.059 K = -0.779 A = -1.650E-04 B = 1.027E-06 C = 0 D = 0
(Aspherical surface 2)
In the above aspheric equation, the surface shape takes the following values.

R = 0.059 K = 0.625 A = -4.230E-04 B = 4.545E-07 C = 7.228E-08 D = -5.257E-10
(Aspherical surface 3)
In the above aspheric equation, the surface shape takes the following values.

R = -0.051 K = -11.801 A = -3.277E-05 B = 1.946E-06 C = -8.439E-08 D = 6.124E-10
(Aspherical surface 4)
In the above aspheric equation, the surface shape takes the following values.

R = 0.059 K = -1.988 A = 0 B = 0 C = 0 D = 0
FIG. 6 is a diagram for explaining that the observer moves the eyepiece lens system 23 and corrects the diopter. By adjusting the diopter adjustment dial 25a (see FIG. 4) of the diopter adjustment mechanism 25 (see FIG. 4) in the electronic viewfinder 11, the finder optical system 22 (specifically, the eyepiece) is operated with respect to the finder housing 29. The lens system 23) is moved in the optical axis direction. The finder optical system 22 has a closest viewing side position of −4 diopter (see FIG. 6A), an observation standard position of −2.5 diopter (see FIG. 6B), and a farthest viewing side position of +4 diopter (see FIG. 6). As shown in c), the eyepiece lens system 23 can be moved. Further, the light transmissive plate 27 is at a limit position (shortest position) where no physical contact is made even when the eyepiece lens system 23 is at a position of +4 diopter. The detailed data of the structure of the electronic viewfinder 11 described above is configuration data of the finder optical system 22 when the eyepiece lens system 23 is at the position of −2.5 diopter.

  Usually, when a human observes information on a plane, for example, a postcard placed on a table, the distance L from the observer's pupil to the object to be observed is known to be in the range of 250 mm to 1000 mm. .

This can be replaced with a diopter in the d = −1000 / L formula, and observation at a distance of 250 mm can be replaced with -4 diopter, and observation at a distance of 1000 mm can be replaced with −1 diopter. The finder optical system 22 of the present invention is designed so that the maximum performance and resolution can be exhibited when the eyepiece system 23 is located at the intermediate value of -2.5 diopter. Since 0 diopter corresponds to observing an object at an infinite distance from the d = −1000 / L equation, the light rays entering the observer's pupil 45 become parallel. That is, the time when the image plane of the reflective LCD 19 is located at the focal point of the eyepiece lens system 23 corresponds to 0 diopter. At this time, the separation distance between the image plane of the reflective LCD 19 and the first lens 23a is 13.582 mm. The distance L required to move the eyepiece system 23 so as to correspond to 1 diopter 'is L' calculated in = f ^2/1000 formula, the combined focal length f of the ocular lens system 23 is so 19.95mm 0.398mm. Therefore, when the eyepiece lens system 23 is at the position of -2.5 diopter, the distance d1 between the image plane of the reflective LCD 19 and the first lens 23a is 13.582-0.398 × 2.5 = 12.587 mm. When the eyepiece lens system 23 is located at the position of -2.5 diopter, the distance d2 between the third lens 23c and the observer's pupil 45 is 19.0 mm, and the light transmitting plate 27 and the pupil 45 are The distance d3 between the two becomes 15.0 mm, which is sufficiently longer than the distance between the glasses and the pupil 45. Therefore, the entire area of the optical image signal emitted from the reflective LCD 19 can be observed without being lost.

  When the eyepiece lens system 23 is at a position of −4 diopter, the distance d4 between the image plane of the reflective LCD 19 and the first lens 23a is 13.582−0.398 × 4 = 11.999 mm. Sufficient gaps that are not contacted can be ensured.

  Next, the configuration of the eyepiece lens system 23, which is a feature of the present embodiment, will be described with reference to FIGS. As shown in FIG. 7, as described above, the eyepiece lens system 23 includes a first lens 23a having a convex lens structure, a second lens 23b having a concave lens structure, and a convex lens from the reflective LCD 19 toward the viewer's pupil 45 side. The third lens 23c having the configuration is arranged in this order. These lenses are fabricated to satisfy the following conditions.

That is, this condition is
18mm <f1 <20mm,
-18mm <f2 <-16mm,
18mm <f3 <20mm,
19mm <f <21mm,
0 ≦ HH ′ / f <+0.13.

However,
f1 is the focal length of the first lens 23a,
f2 is the focal length of the second lens 23b,
f3 is the focal length of the third lens 23c,
f is the combined focal length of the first to third lenses 23a to 23c,
HH ′ is the distance between the rear principal point H and the front principal point H ′ in the optical axis direction.

  In defining the rear principal point H and the front principal point H ′, it is assumed that the lens group composed of the first lens 23a, the second lens 23b, and the third lens 23c is replaced with an extremely thin virtual lens. In addition, the rear principal point and the front principal point in the virtual lens are referred to as the rear principal point H when light is incident from the front of the lens and the principal point when light is incident from the rear of the lens. It is called the principal point H ′. Further, both surfaces of the first lens 23a are denoted by 23a1, 23a2, both surfaces 23b1, 23b2 of the second lens 23b, and both surfaces 23c1, 23c2 of the third lens 23c.

  As described above, in the present embodiment, the refractive power absolute values of the first, second, and third lenses 23a, 23b, and 23c are substantially evenly distributed. In the lens, the thickness ratio between the center thickness and the lens outer peripheral thickness can be suppressed to about 2: 1. This eliminates the problem of transferability in resin molding. The problem here is that when the difference between the thickness of the center of the lens and the thickness of the outer periphery of the lens is increased, the transferability at the time of injection molding is deteriorated and the lens performance is remarkably deteriorated.

  The distance G1 between the opposing surfaces on the optical axis of the first lens 23a and the second lens 23b and the distance G2 between the opposing surfaces on the optical axis of the second lens 23b and the third lens 23c are each 0.4 mm or more. 1.1mm or less. The inter-surface distance is the distance between the surfaces 23a2 and 23b1 (or surfaces 23b2 and 23c1) facing each other between the adjacent first lens 23a and second lens 23b (or the second lens 23b and the third lens 23c). This means distance, and the distance indicates each gap on the optical axis.

  As described above, in this embodiment, a sufficient clearance is ensured between adjacent lenses. For example, even if vibration occurs in the electronic viewfinder 11 in which the finder optical system 22 is incorporated, The lenses do not interfere with each other physically. In addition, it is possible to suppress the gap between the lenses so that the chromatic aberration is not optically enlarged, and at the same time, it is possible to suppress an increase in the total length of the finder optical system 22.

Further, the first, second, and third lenses 23a, 23b, and 23c are lenses that satisfy the following conditional expressions. That is,
57.5 <ν1 <58.0, 29.5 <ν2 <30.0,
57.5 <ν3 <58.0, 1.
48 <ne1 <1.50, 1.57 <ne2 <1.61,
1.48 <ne3 <1.50,
It is.

  Here, ν1, ν2, and ν3 are the dispersion rates of the first, second, and third lenses 23a, 23b, and 23c, respectively. Here, the dispersion ratio is a numerical value ν for evaluating the dispersion of the color of the transparent body, and is defined as follows.

ν = (ne-1) / (nF-nC)
However,
ne is the refractive index for Fraunhofer's e-line (546.1 nm),
nF is the refractive index with respect to Fraunhofer's F line (488.0 nm),
nC is the refractive index for Fraunhofer C line (643.9 nm),
ne1, ne2, and ne3 are refractive indexes of the first, second, and third lenses 23a, 23b, and 23c with respect to the Fraunhofer e-line (546.1 nm),
It is.

  Examples of materials suitable for the dispersion ratio include acrylic resins and polyolefin resins (first and third lenses 23a and 23c), and polycarbonate resins and polyester resins (second lenses 23b).

  In this embodiment, when each of the first, second, and third lenses 23a, 23b, and 23c is injection-molded, the position (gate position) at which the lens material resin is injected from the side surface of the mold is set to the adjacent lens. Because of this, the molecular orientation of adjacent lenses is different. As a result, the direction in which birefringence occurs differs between adjacent lenses. As a result, it is possible to suppress the deterioration of aberration caused by the fact that the directions in which birefringence occurs between adjacent lenses are equal.

  By designing as described above, the eyepiece lens system 23 of the present embodiment satisfies the aberration performances shown in FIGS. 8A to 8C and FIGS. 9A to 9H. The In particular, as shown in FIG. 8A, in the case of axial chromatic aberration, 486.1 nm, which is the blue color of visible light, is observed when focusing on the e-line (546.1 nm) of Fraunhofer which is green. The focus of 656.3 nm, which is the longest visible wavelength red, can be achieved with a focus of only about 10 μm behind. Furthermore, in the blue (435.8 nm), which is the shortest wavelength of visible light, a performance that is out of focus only about 5 μm ahead can be achieved. Therefore, each color of RGB does not appear to be separated, and the LCD image can be enlarged and observed with high definition. In addition, since a general optical resin that can be injection-molded can be used for the lens material, an inexpensive eyepiece lens system 23 can be manufactured.

  In the specific example of the present embodiment, the first, second, and third lenses 23a, 23b, and 23c have curved surface shapes of both lens surfaces (23a1, 23b1, 23c1) and (23a2, 23b2, 23c2). , Having the curved surface shape described above, or represented by the aspherical equation described above. Specifically, the surface 23a1 has the shape of the aspheric surface 1 described above. The surface 23a2 has the shape of the aspheric surface 2 described above. The surface 23b1 is a spherical surface having a radius of -21.372 mm. The surface 23b2 has the shape of the aspheric surface 3 described above. The surface 23c1 is a spherical surface having a radius of 17.066 mm. The surface 23c2 has the shape of the aspheric surface 4 described above.

  The above configuration means that the first, second, and third lenses 23a, 23b, and 23c do not have an inflection point that the direction of the curved surface of the lens is reversed or the curvature is remarkably changed. As shown in FIG. 10, when the observer moves his / her eyes, there is a case where the observer comes to a position where he / she radiates from the LCD image plane and passes through the inflection point. At that time, the light beam is distorted and refracted, and the observation image flows. Therefore, when a lens having no inflection point is used for the first, second, and third lenses 23a, 23b, and 23c, the light beam is not disturbed, and the observation image can be prevented from flowing.

  In the above embodiment, the case where the diagonal length of the LCD is 11.654 mm and the distance (eye point) from the light transmissive plate 27 (final optical surface) to the eyes of the observer is 15.0 mm has been described. The conditions regarding the first, second, and third lenses 23a, 23b, and 23c described above are that the diagonal length of the LCD is 12 mm or less (preferably 11.176 to 11.684 mm) and the eye point is 15.0 mm or less. The present invention can also be applied to an optical system used for a viewfinder.

  In the above-described embodiments, the present invention has been described on the assumption that the present invention is implemented in an electronic viewfinder incorporated in a single-lens reflex digital camera. However, the present invention is not limited to an electronic viewfinder mounted in such a digital camera. The present invention is not limited to this, and any electronic viewfinder that incorporates a reflective LCD as a viewfinder LCD can be used. For example, the present invention can also be implemented in an electronic viewfinder mounted on a stomach camera.

(Summary)
According to the configuration of the embodiment described above, the following problems can be dealt with. This will be specifically described below.

  Problem 1: The image display surface of the reflective LCD is a set of a plurality of display pixels (dots). When an image (dot image) displayed on these dots is viewed through the eyepiece lens system, the image display surface of the eyepiece lens system is displayed. A point image on an arbitrary dot can be seen across adjacent dots due to refraction, that is, a high-definition image display can be viewed over the entire image display surface at as high a magnification as possible without being blurred. To be able to do it.

  Problem 2: It is possible to manufacture by injection molding that satisfies the performance and the manufacturing cost is low, using optical resin that has low refractive index and low dispersion and generally low material cost. Realize an eyepiece system.

  Problem 3: When an observer moves an eye through an eyepiece lens system and observes an image on the image display surface of the reflective LCD, the observed image cannot be seen in a normal shape while the eye is moving. To lose.

  Problem 4: When the observer adjusts the position of the eyepiece lens system with respect to the image display surface of the reflective LCD and focuses the eyepiece lens system on the image display surface for observation, the position of the eyepiece lens system is determined by the observer. It is the limit that can be focused with the naked eye-Even if it is at the position of 4 diopters, the finder optical system including the eyepiece lens system should secure a sufficient distance from the reflective LCD to eliminate the possibility of contact.

  Problem 5: Even when an eyepiece lens system is adjusted to a myopic position (for example, -2.5 diopter position) by an observer wearing spectacles, the spectacles of the observer may hit the light transmissive plate of the electronic viewfinder. To ensure a long eye point (distance from the light-transmitting plate 27 (final optical surface) to the observer's eye) and to observe the entire image on the image display surface without any defects. .

  The eyepiece system 23 according to the above-described embodiment is an eyepiece system that is disposed on the optical axis between the reflective LCD 19 for the viewfinder 11 and the eyepoint of the observer of the viewfinder 11. In the eyepiece lens system 23, the first lens 23a having a positive refractive index, the second lens 23b having a negative refractive index, and the first lens having a positive refractive index from the reflective LCD 19 side toward the eye point side. 3 lenses 23c are arranged in this order, and 18mm <f1 <20mm, -18mm <f2 <-16mm, 18mm <f3 <20mm, 19mm <f <21mm, 0 ≦ HH´ / f <+0.1 3 Satisfied. Where f1 is the focal length of the first lens 23a, f2 is the focal length of the second lens 23b, f3 is the focal length of the third lens 23c, f is the combined focal length of the first to third lenses 23c, and HH ′ is the rear This is the distance in the optical axis direction between the side principal point H and the front principal point H ′.

In the eyepiece system 23 of the embodiment,
-It disappears that the dot image appears to spread across the dots,
-Eliminates the obstacles for viewing high-definition LCDs at as high a magnification as possible at every corner of the screen with high resolution.

  Thereby, the eyepiece lens system 23 of the embodiment can solve the problem 1.

  Further, according to the eyepiece lens system 23 of the embodiment, since the refractive power absolute values of the first, second, and third lenses 23a, 23b, and 23c are substantially evenly distributed, the refractive power of each lens is one. As a result, the difference between the center thickness of each lens and the thickness of the outer periphery of the lens is reduced. This solves the problem of transferability in resin molding and realizes a shape suitable for resin molding.

  That is, the eyepiece system 23 according to the embodiment can realize an eyepiece system that can be manufactured by injection molding, which can be manufactured at low cost, and can solve the problem 2.

  Further, in the eyepiece lens system 23 of the embodiment, even when the eyepiece lens system 23 is at the near vision side position, there is a sufficient distance from the image plane of the reflective LCD 19 and the reflective LCD 19 and the finder optical system 22 are in contact with each other. Therefore, the problem 4 can be solved.

  Furthermore, even when the eyepiece lens system 23 is in the nearsighted position, the eyepoint is long, so that the separation distance between the light transmissive plate 27 and the pupil of the observer is in the state where the observer is wearing glasses. The distance between the eyeglasses and the pupil is sufficiently longer than the distance between the eyeglasses and the pupils so that the eyeglasses do not physically interfere with the light transmissive plate 27. As a result, the finder image can be observed without any defects, and the above problem 5 can be solved. The light transmissive plate 27 is generally disposed between the electronic viewfinder eyepiece lens system 23 and the observer's pupil of the viewfinder 11.

  The focal length f1 of the first lens 23a is 18 mm or less, the focal length f2 of the second lens 23b is -16 mm or more, or the focal length f3 of the third lens 23c is 18 mm or less. The radius is reduced. This increases the difference between the center thickness of the lens and the thickness of the outer periphery of the lens, deteriorates transferability during injection molding, and significantly degrades lens performance. Further, although the vicinity of the center of the optical axis of the eyepiece lens system 23 is not so much affected, it also causes the resolution near the outer periphery to be significantly deteriorated, which is not preferable.

  Furthermore, since the combined focal length f is defined by the calculation formula 1 / f = 1 / f1 + 1 / f2 + 1 / f3, as a result, it is limited to 19 mm <f <21 mm. Therefore, the focal length f1 of the first lens 23a is 20 mm or more, the focal length f2 of the second lens 23b is 18 mm or less, or the focal distance f3 of the third lens 23c is 20 mm or more. As a result, the focal length f1 of the first lens 23a is 18 mm or less, the focal length f2 of the second lens 23b is -16 mm or more, and the focal length f3 of the third lens 23c is 18 mm or less. turn into. At these focal lengths, as described above, the radius of curvature of each lens decreases, and the difference between the lens center thickness and the lens outer peripheral thickness increases. Thereby, the transferability at the time of injection molding is deteriorated, and the lens performance is remarkably deteriorated. Further, although this does not affect the vicinity of the optical axis center of the eyepiece lens system 23, it is not preferable because the resolution near the lens outer periphery is remarkably deteriorated.

  The focal length f1 of the first lens 23a is preferably 18.44 to 18.46 mm, and optimally 18.45 mm. The focal length f2 of the second lens 23b is preferably -17.15 to -17.17 mm, and optimally -17.16 mm. Further, the focal length f3 of the third lens 23c is preferably 18.44 to 18.46 mm, and optimally 18.45 mm. HH ′ / f is preferably 0.02 to 0.04, and most preferably 0.03.

  In the eyepiece lens system 23 of the embodiment, the distance between the opposing surfaces of the first lens 23a and the second lens 23b and the distance between the opposing surfaces of the second lens 23b and the third lens 23c are each 0.4 mm. More than 1.1mm.

  In the eyepiece lens system 23 of such an embodiment, the clearance margin between adjacent lenses is physically sufficient, and therefore, for example, vibration is generated in the electronic viewfinder 11 in which the eyepiece lens system 23 having a resin lens is incorporated. Even if it occurs, adjacent lenses will not interfere and be damaged. Thereby, the said subject 2 can be solved. In addition, since the gap does not optically expand chromatic aberration, Problem 1 can be solved. Furthermore, since it can suppress that the full length of the finder optical system 22 becomes long, the problems 4 and 5 can be solved.

  The distance between the opposing surfaces on the optical axis between the first lens 23a and the second lens 23b is preferably 0.9 to 1.1 mm, and optimally 1.0 mm. The distance between the opposing surfaces on the optical axis between the second lens 23b and the third lens 23c is preferably 0.4 to 0.6 mm, and most preferably 0.5 mm.

  In the eyepiece lens system 23 of the embodiment, the first to third lenses 23c are 57.5 <ν1 <58.0, 29.5 <ν2 where the dispersion ratios of the first to third lenses 23c are ν1, ν2, and ν3, respectively. <30.0, 57.5 <ν3 <58.0 lens satisfying the formula. As a result, the effect that the point image does not appear blurred across the dots is exhibited, and the problem 1 can be solved. Furthermore, since the characteristics of a general and inexpensive optical resin are satisfied, the above problem 2 can be solved.

  When the dispersion ratio ν1 of the first lens 23a is 57.5 or less and 58.0 or more, it is not a general optical resin. When the dispersion ratio ν2 of the second lens 23b is 29.5 or less and 30.0 or more, it is not a general optical resin. When the dispersion ratio ν3 of the third lens 23c is 57.5 or less and 58.0 or more, it is not a general optical resin.

  Further, the dispersion ratio ν1 of the first lens 23a is preferably 57.75 to 57.85, and optimally 57.8. The dispersion ratio ν2 of the second lens 23b is preferably 29.75 to 29.85, and optimally 29.8. The dispersion ratio ν3 of the third lens 23c is preferably 57.75 to 57.85 and optimally 57.8.

  In the eyepiece system 23 of the embodiment, the refractive indexes of the first, second, and third lenses 23a, 23b, and 23c are set to ne1, ne2, and ne3, and the first to third lenses 23c have 1.48 <ne1 <. Since the lens is made of a material that satisfies the expressions 1.50, 1.57 <ne2 <1.61, and 1.48 <ne3 <1.50, it satisfies the characteristics of general optical resins. Therefore, the above problem 2 can be solved.

  When the refractive index ne1 of the first lens 23a is 1.48 or less and 1.50 or more, it is not a general optical resin. When the refractive index ne2 of the second lens 23b is 1.57 or less and 1.61 or more, it is not a general optical resin. When the refractive index ne3 of the third lens 23c is 1.48 or less and 1.50 or more, it is not a general optical resin.

  The refractive index ne1 of the first lens 23a is preferably 1.489 to 1.499, and optimally 1.494. The refractive index ne2 of the second lens 23b is preferably 1.583 to 1.593, and most preferably 1.588. The refractive index ne3 of the third lens 23c is preferably 1.489 to 1.499, and optimally 1.494.

  In the eyepiece lens system 23 of the embodiment, the material of the first and third lenses 23a and 23c is an acrylic resin, and the material of the second lens 23b is a polycarbonate resin. Examples of materials other than those described above include polyolefin resins for the first and third lenses 23a and 23c, and polyester resins for the second lens 23b.

  The resin material of the resin lens is, for example, an acrylic resin, polycarbonate resin, polyolefin resin, polyester resin, polyurethane resin, polysulfone resin, polystyrene resin, vinyl resin, or halogen resin. Examples thereof include thermosetting resins such as plastic resins, epoxy resins, polyimide resins, urea resins, phenol resins, and silicone resins. These resin groups are resins that can be molded by an injection molding method, and can also be employed as lens materials in the present invention.

  An example of the resin material for the resin lens is a light transmissive resin. Examples of the light transmissive resin include acrylic resins such as polymethyl methacrylate, polyhydroxyethyl methacrylate, and polycyclohexyl methacrylate, allyl resins such as polydiethylene glycol bisallyl carbonate, polycarbonate, methacrylic resins, polyurethane resins, polyester resins, and polyresins. Examples thereof include thermoplastic or thermosetting resins such as vinyl chloride resins, polyvinyl acetate resins, cellulose resins, polyamide resins, fluorine resins, polypropylene resins, and polystyrene resins. In the present embodiment, these resin materials can also be used as lens materials.

  Thus, in the eyepiece system 23 according to the embodiment, the first and third lenses 23a and 23c are made of acrylic resin, and the second lens 23b is made of polycarbonate resin. And 2 can be solved.

  When the first, second, and third lenses 23a, 23b, and 23c are injection-molded, the eyepiece lens system 23 of the embodiment has a resin injection position (gate position) when the resin is injected from the mold side surface. ) Between adjacent lenses. By doing so, it is possible to make the molecular orientation different between adjacent lenses, and as a result, the direction in which birefringence occurs can be made different. If the directions in which birefringence occurs between adjacent lenses are made equal, there is a risk of deteriorating aberrations that are difficult to predict. On the other hand, in the eyepiece lens system 23 of the embodiment, it is possible to prevent such aberration deterioration by changing the direction in which birefringence occurs between adjacent lenses. Solvable. At the same time, the present invention can be realized by the resin lens, so that the above problem 2 can be solved. The direction in which birefringence is different between adjacent lenses means a direction in which the direction in which birefringence occurs intersects with an angle of more than 0 degrees and less than 180 degrees. In this case, it preferably refers to a direction that intersects at an angle of 45 degrees to 135 degrees, and optimally refers to a direction that intersects at an angle of 90 degrees.

  In the eyepiece lens system 23 of the embodiment, both lens surfaces of the first, second, and third lenses 23a, 23b, and 23c have curved surfaces having no inflection points. This prevents the observation image from flowing when the observer moves his / her eyes. Therefore, claim 9 can solve the above-mentioned problem 3.

  The finder optical system 22, the electronic viewfinder 11, and the imaging device 1 are all provided with the eyepiece lens system 23, and can solve the above-described problems.

DESCRIPTION OF SYMBOLS 1 Imaging device 3 Camera body 5 Imaging lens unit 7 Imaging element 9 Rear LCD
11 Electronic Viewfinder 13 Microcomputer 19 Reflective LCD
22 finder optical system 23 eyepiece lens system 23a first lens 23b second lens 23c third lens

Claims (11)

An electronic viewfinder eyepiece system disposed on the optical axis between the viewfinder LCD and the final optical surface of the viewfinder,
A first lens having a positive refractive index, a second lens having a negative refractive index, and a third lens having a positive refractive index in this order from the LCD side toward the final optical surface side, and 18mm <f1 <20mm, -18mm <f2 <-16mm, 18mm <f3 <20mm, 19mm <f <21mm, 0 ≦ HH´ / f <+0.13 Eyepiece lens system.
Where f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f is the combined focal length of the first to third lenses, and HH ′ is the rear principal point H. And the distance in the optical axis direction from the front principal point H ′.   The distance between the opposing surfaces on the optical axis between the first lens and the second lens and the distance between the opposing surfaces on the optical axis between the second lens and the third lens are 0.4 mm or more and 1.1 mm, respectively. The eyepiece system according to claim 1, wherein:   The eyepiece system according to claim 1, wherein the diagonal length of the LCD is 12 mm or less, and the distance from the final optical surface to the observer's eye is 15.0 mm or less. 4. The eyepiece system according to claim 1, wherein the first, second, and third lenses are lenses made of a material that satisfies the following conditional expression.
57.5 <ν1 <58.0,
29.5 <ν2 <30.0,
57.5 <ν3 <58.0,
Here, ν1, ν2, and ν3 are the dispersion rates of the first, second, and third lenses, respectively. The eyepiece system according to any one of claims 1 to 4, wherein the first, second, and third lenses are lenses made of a material that satisfies the following conditional expression.
1.48 <ne1 <1.50,
1.57 <ne2 <1.61
1.48 <ne3 <1.50,
However, ne1, ne2, and ne3 are the refractive indexes with respect to the e-line (546.1 nm) of Fraunhofer of the first, second, and third lenses, respectively.   6. The eyepiece system according to claim 4, wherein the material of the first and third lenses is an acrylic resin, and the material of the second lens is a polycarbonate resin.   6. The eyepiece system according to claim 4, wherein the first, second, and third lenses are resin lenses, and the directions in which birefringence occurs in adjacent lenses are different.   The eyepiece system according to any one of claims 1 to 7, wherein both lens surfaces of the first, second, and third lenses have a curved surface shape having no inflection point.   9. A viewfinder optical system, wherein the eyepiece lens system according to claim 1 is housed in a lens holder, and the eyepiece lens system is movable together with the lens holder in the optical axis direction. With a finder housing,
The LCD is housed in the front part in the optical axis direction in the finder housing, and the finder optical system according to claim 9 is housed in the rear part in the optical axis direction,
The electronic viewfinder, wherein the finder housing includes a diopter adjustment mechanism for adjusting the diopter by moving the finder optical system back and forth in the optical axis direction. It has a camera body to which the taking lens unit can be attached and detached,
The said camera body is equipped with the image pick-up element which images the optical image from a photographic lens unit, and outputs the image signal by the image pick-up, and the electronic viewfinder of Claim 10 which monitors the image signal from the said image pick-up element. An imaging apparatus characterized by that.

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