JP2009210656A - Eyepiece lens for finder and electronic viewfinder using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an eyepiece lens for finder, which can extend an eye relief and a back focus appropriately even with a compact configuration and high magnification, has satisfactory imaging performance and distortion aberration characteristic, ensures a color aberration correction sufficient for use, and is composed of two lenses for a cost reduction which is high in priority. <P>SOLUTION: The finer eyepiece lens includes, in order from the eyepiece side, a positive first lens and a negative second lens and satisfies conditional formulae described the followings: (1) 1.0<TL/f<1.3 and (2) 1.9<f/(D1+D2+D3)<2.9, wherein TL is a distance on an optical axis from the first face of the lens to the face of an image element (a parallel planar portion is converted into an air length), f is the focal distance of the entire lens system, D1 is the thickness of the first lens on the optical axis, D2 is a distance between the second and third faces on the optical axis, and D3 is the thickness of the second lens on the optical axis. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an eyepiece used in an electronic viewfinder such as a video camera or a digital camera, and an electronic viewfinder using the eyepiece.

  In recent years, video cameras and digital cameras, which have been remarkably popular, use many electronic viewfinders that allow a user to view a photographed video.

  Various electronic devices installed therein are rapidly becoming higher in performance and smaller in size, and the optical performance of an eyepiece for a finder is becoming increasingly demanding.

  One feature of video cameras and digital cameras is their small size. Therefore, the electronic viewfinders mounted on them are inevitably required to be small.

  That is, an image element such as an LCD that greatly affects the miniaturization of the electronic viewfinder and an optical lens for observing the image element with the eyes are also required to be small first.

  Furthermore, due to the miniaturization of the image element, it is essential to increase the magnification as an eyepiece for a finder.

  In addition, electronic devices such as video cameras and digital cameras are highly cost-competitive, and low cost is a natural requirement and a priority issue for electronic viewfinders.

  In addition, eyepieces for viewfinders are required to have an eye relief and back focus that are reasonably long, have good imaging performance and distortion characteristics, and have sufficient chromatic aberration correction for use.

A large number of eyepiece lenses having a small size and excellent optical performance having a two-lens structure have been disclosed. (For example, see Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4) An electronic viewfinder using an eyepiece is also disclosed. (For example, see Patent Document 5)
Japanese Patent No. 2588505 JP-A-6-222264 JP-A-6-235870 JP 2000-131624 A JP 2006-108882 A

  However, the speed of miniaturization of video cameras and digital cameras is extremely fast, and the sizes of various electronic devices and video elements such as LCDs are becoming smaller than expected.

  In addition, the required performance of electronic viewfinders has been further improved with the increase in image quality and resolution of video elements.

  Therefore, it is necessary to increase the magnification of the eyepiece in proportion. Maintaining optical performance with higher magnification becomes much more difficult, and inevitably, how far the increase in the number of lens components and cost increase can be suppressed has become a recent issue.

  The present invention has been made in view of such problems, and particularly relates to an electronic viewfinder used for a video camera, a digital camera, etc. and an eyepiece used therefor, which has a small configuration and a high magnification. However, the eye relief and back focus can be extended to an appropriate length, have good imaging performance and distortion characteristics, and have sufficient chromatic aberration correction for use. An object of the present invention is to provide a viewfinder eyepiece and a small and high-performance electronic viewfinder using the eyepiece.

An eyepiece for a finder comprising a positive first lens and a negative second lens in order from the pupil side and satisfying the following conditional expression.
(1) 1.0 <TL / f <1.3
(2) 1.9 <f / (D1 + D2 + D3) <2.9
However,
TL: Distance on the optical axis from the first lens surface to the image element surface (parallel plane portion is air length converted)
f: focal length of all lens system D1: thickness on optical axis of first lens D2: distance on optical axis of second and third surfaces D3: thickness on optical axis of second lens

In the finder eyepiece, the first lens is a double-sided convex lens, and satisfies the following conditional expression.
(3) 1.5 <f / f1 <2.0
(4) -1.5 <R1 / R2 <-1.1
However,
f1: Focal length R1 of the first lens R1: Paraxial radius of curvature of the pupil side surface of the first lens R2: Paraxial radius of curvature of the image element side surface of the first lens

In the finder eyepiece, the second lens is a concave lens having a concave surface facing the pupil side, and satisfies the following conditional expression.
(5) -1.25 <f / f2 <-0.75
(6) -2.65 <f / R3 <−1.85
However,
f2: focal length of the second lens R3: paraxial radius of curvature of the pupil side surface of the second lens

In the finder eyepiece, the second lens and the third lens may further satisfy the following conditional expression, and may be a finder eyepiece.
(7) 0.9 <R2 / R3 <1.2
(8) -17.1 <f2 / D3 <-6.5
(9) 2.6 <(ν1 + ν2) / ν2
However,
R2: paraxial radius of curvature of image element side surface of first lens R3: paraxial radius of curvature of pupil side surface of second lens f2: focal length of second lens D3: thickness on optical axis of second lens ν1: first Abbe number of lens material ν2: Abbe number of second lens material

  In the finder eyepiece, both the side surfaces of the first lens and the both surfaces of the second lens are aspherical.

  In the finder eyepiece, each of the lenses is made of a resin material.

  In the finder eyepiece, when the length in the optical axis direction from the top of each surface in the curvature shape on each surface is a sag amount, the aspherical shape on the side of the image element of the second lens is from the center. A viewfinder eyepiece having a region in which the sag amount to the peripheral end portion increases and decreases at least once.

  In addition, an electronic view finder is characterized in that a liquid crystal display element is arranged at the image element surface position using the finder eyepiece.

  The liquid crystal display element is a reflection type liquid crystal display device having a front light unit.

  According to the present invention, although the configuration is small and the magnification is high, the eye relief and the back focus can be appropriately lengthened, have good imaging performance and distortion characteristics, and have sufficient chromatic aberration correction for use. In addition, it is possible to obtain an eyepiece for a finder having a two-lens configuration that realizes low cost with priority.

  A small and high-performance electronic viewfinder using the eyepiece can be obtained.

  One embodiment of the present invention will be described below.

Examples of eyepieces for viewfinders according to the present invention will be described below. However, symbols used in the description of the embodiments are as follows.
EP: Eye point L1: First lens L2: Second lens CG: Cover glass I: Image element surface f: Focal length 2ω of all lens systems: Apparent field of view (unit: degree) (field angle)
D *: Distance on the optical axis between each surface and the next surface (* has a number corresponding to each surface)
TL: Distance on the optical axis from the first lens surface to the image element surface (the parallel plane portion is converted to air length)
R *: Paraxial radius of curvature of each surface (* has a number corresponding to each surface)
Nd *: Refractive index of each lens material at d-line (* has a number corresponding to each lens)
νd *: Abbe number of each lens at the d-line (* has a number corresponding to each lens)

ただし、ｋ＝α１＋１ とし、
Ｃ ：非球面頂点の曲率
α１ ：円錐係数
α２〜α１０ ：非球面係数
ρ ：光軸からの高さ
Ｚ ：レンズ面頂点における接平面から光軸方向への距離
である。 The aspherical expression when the lens is aspherical is described as follows.

Where k = α1 + 1 and
C: Curvature α1 of aspherical vertex: Conical coefficient α2 to α10: Aspherical coefficient ρ: Height from optical axis Z: Distance from the tangential plane at the lens surface vertex to the optical axis direction.

  FIG. 1 is a lens configuration diagram of the best mode according to the present invention (Example 1). The left side is shown as the pupil side, and the right side is shown as the image element side.

  2A and 2B are aberration diagrams of this example, in which (A) shows spherical aberration, (B) shows astigmatism, (C) shows distortion, and (D) shows chromatic aberration of magnification. In the spherical aberration diagram, as shown, spherical aberrations at the wavelengths of g-line 1, F-line 2, e-line 3, d-line 4 and C-line 5 when the pupil diameter is 4 mm are shown. Yes. The astigmatism diagram shows astigmatism on the sagittal surface S and the tangential surface T as shown. In the chromatic aberration diagram of magnification, as shown, the chromatic aberration of magnification at the wavelengths of g-line 1a, F-line 2a, e-line 3a, d-line 4a, and C-line 5a are shown. Y = 2.53 indicates the distance (image height) from the center of the image element to the diagonal length.

Table 1-1 shows numbers from the pupil side of this embodiment to the eye point EP, the surface of the first lens L1, the surface of the second lens L2, the surface of the cover glass CG, and the image element surface I (S0 to S7 shown in FIG. 1). ), And a table summarizing each surface by entering the radius of curvature, distance (interval), refractive index, Abbe number, and the like. The symbols R, D, Nd, and νd are as described above. Table 1-1 also shows the focal length f and the apparent field of view 2ω of all the lens systems when the diopter is adjusted to 0 diopter. Table 1-2 describes the aspherical coefficient when the surface of Table 1-1 is described by the above-described Equation 1.

Table 4 is a table summarizing the results calculated by substituting specific numerical values corresponding to the conditional expressions (1) to (9) described in the claims. In Table 4, calculation results in Example 2 and Example 3 in addition to Example 1 are also described. Further, the description of the calculation part that is not directly related to the present invention in the items of Table 4 will be omitted.

  In Example 1 shown in FIG. 1, an eyepiece for a finder having a configuration in which a positive first lens L1 and a negative second lens L2 are placed in order from the pupil side. A distance D0 from the first surface S1 of the first lens L1 to the pupil (eye point EP) S0 is an eye relief, and an appropriate length is secured. If this is too short, the eyes and eyelashes directly hit the lens, and if it is too long, it will be contrary to miniaturization, which is a problem. The distance D2 from the second surface S2 of the first lens L1 to the first surface S3 of the second lens L2 is a major factor for determining the optical length TL along with the thicknesses D1 and D3 of each lens. The length from the second surface S4 of the second lens L2 to the image element surface I (S7) (the distance D4 from the second surface S4 of the second lens L2 to the first surface S1 of the cover glass CG, and the cover glass The thickness D5 of the CG and the sum of the distance D6 from the second surface S6 of the cover glass CG to the image element surface I (S7) are back focus, and an appropriate length is secured. In particular, a front light type image device requires a space because there is an obstructing structure on the front surface.

Table 4 shows that TL / f is 1.178 and f / (D1 + D2 + D3) is 1.938, which satisfies the following conditional expression defined in claim 1.
(1) 1.0 <TL / f <1.3
(2) 1.9 <f / (D1 + D2 + D3) <2.9

  Conditional expression (1) represents the relationship between the magnification and size reduction of the eyepiece lens. When the magnification is the same, size reduction is not achieved when the upper limit is exceeded, and size reduction is possible when the lower limit is exceeded. A large back focus cannot be secured, and the power of each lens becomes excessive, and good performance cannot be maintained. When the optical length is the same, if the upper limit is exceeded, the magnification becomes too high and the performance deteriorates. If the lower limit is exceeded, the balance between the required magnification and performance is greatly deteriorated. Conditional expression (2) is a condition for lens thickness and size reduction. If the upper limit is exceeded, downsizing is possible, but the lens thickness is reduced and performance is degraded. In particular, chromatic aberration of magnification cannot be corrected. If the lower limit is exceeded, the thickness of the lens becomes thick, the distance becomes too large, and miniaturization cannot be achieved. The lens shape also has a sharp curvature at the periphery, and the chromatic aberration of magnification in particular deteriorates. By satisfying the conditional expressions (1) and (2) at the same time, it is possible to obtain a two-piece finder eyepiece having a high magnification and reduced size without impairing lens performance.

  In Example 1, the first lens L1 is a double-sided convex lens.

Similarly, it can be seen from Table 4 that f / f1 is 1.661 and R1 / R2 is −1.167, which satisfies the following conditional expression defined in claim 2.
(3) 1.5 <f / f1 <2.0
(4) -1.5 <R1 / R2 <-1.1

  Conditional expression (3) defines the power of the entire lens system and the power ratio of the first lens L1 to define the positive power of the first lens L1. If the upper limit is exceeded, the positive power increases, and the negative power of the second lens L2 cannot be balanced, resulting in overcorrection. Since the lens thickness is also increased, the moldability is deteriorated. If the lower limit is exceeded, the positive power becomes small, and aberration correction is insufficient, so that performance cannot be ensured. Since the entire lens length is long, it is impossible to reduce the size. Conditional expression (4) is also related to the first lens L1, and the shape is defined by the ratio of the first surface S1 and the second surface S2 of the positive double-sided convex lens. The paraxial radius of curvature R2 of the second surface S2 is smaller in absolute value than the paraxial radius of curvature R1 of the first surface S1, and represents the degree. When the upper limit is exceeded, the symmetry between the first surface S1 and the second surface S2 becomes strong, and axial chromatic aberration increases. When the lower limit is exceeded, the balance of aberration correction is lost and spherical aberration increases. In either case, correction becomes difficult. By satisfying the conditional expressions (3) and (4) at the same time, a more balanced two-lens eyepiece for a finder can be obtained without impairing lens performance.

  In Example 1, the second lens L2 is a concave lens having a concave surface facing the pupil side.

Similarly, Table 4 shows that f / f2 is −0.831 and f / R3 is −1.926, which satisfies the following conditional expression defined in claim 3.
(5) -1.25 <f / f2 <-0.75
(6) -2.65 <f / R3 <−1.85

  Conditional expression (5) defines the power of the entire lens system and the power ratio of the second lens L2, and defines the negative power of the second lens L2. If the upper limit is exceeded, the negative power becomes small and advantageous for aberration correction, but both axial chromatic aberration and lateral chromatic aberration increase. Since the entire lens length is long, it is impossible to reduce the size. If the lower limit is exceeded, the negative power becomes excessive, the shape of the lens peripheral portion becomes worse, and it becomes difficult to correct the spherical aberration and coma aberration caused thereby. Conditional expression (6) also relates to the second lens L2, and is an expression that defines the shape of the second lens L2 by defining the size of the paraxial radius of curvature of the first surface S3. When the upper limit is exceeded, the depth of the concave surface becomes shallow, the negative power becomes too small, and various aberrations cannot be corrected. Chromatic aberration also increases, making correction difficult. When the lower limit is exceeded, the depth of the concave surface increases and the negative power becomes excessive. The power balance of the entire lens system is lost, making it difficult to correct aberrations. By satisfying the conditional expressions (5) and (6) simultaneously, it is possible to obtain a well-balanced two-piece compact finder eyepiece having better imaging performance and distortion characteristics.

Similarly, from Table 4, R2 / R3 is 0.958, f2 / D3 is −7.682, (ν1 + ν2) / ν2 is 2.907, and the following conditional expression defined in claim 4 It turns out that is satisfied.
(7) 0.9 <R2 / R3 <1.2
(8) -17.1 <f2 / D3 <-6.5
(9) 2.6 <(ν1 + ν2) / ν2

  Conditional expression (7) represents the relationship between the first surface S1 and second surface S2 of the first lens L1 and the first surface S3 of the second lens L2. The spherical aberration, coma aberration, and chromatic aberration of magnification generated on the first surface S1 of the first lens L1 are corrected by balancing the second surface S2 of the first lens L1 and the first surface S3 of the second lens L2. Yes. If the upper and lower limits are exceeded, the balance between the two surfaces is lost, and aberration correction becomes difficult. Conditional expression (8) is a condition for downsizing the thickness D3 of the second lens L2. If the upper limit is exceeded, the thickness D3 of the second lens L2 becomes thick, and miniaturization cannot be achieved. The lens shape also has a sharp curvature at the periphery, and spherical aberration and chromatic aberration of magnification deteriorate and cannot be corrected. If the lower limit is exceeded, the thickness D3 of the second lens L2 becomes too thin, and downsizing is achieved, but performance deteriorates. In particular, chromatic aberration of magnification cannot be corrected. Conditional expression (9) is a color correction condition. Because of the positive and negative two-lens configuration, the positive lens of the first lens L1 is an achromatic type with a low dispersion material and the negative lens of the second lens L2 is a high dispersion material. If the lower limit is exceeded, chromatic aberration increases and correction cannot be made. By satisfying the conditional expressions (7), (8), and (9) at the same time, two balanced configurations having better imaging performance and distortion characteristics and sufficient chromatic aberration correction for use. A finder eyepiece with reduced size can be obtained.

  Further, from Table 1-1 and Table 1-2, it is desirable that both side surfaces S1, S2 of the first lens L1 and both side surfaces S3, S4 of the second lens L2 are aspherical. The content of claim 5 is satisfied.

  This is because the first surface S1 and the second surface S2 of the first lens L1 are made aspherical in order to correct the spherical aberration that occurs on the first surface S1 of the first lens L1 that is a positive double convex lens. It is very effective. Further, in order to correct distortion aberration and chromatic aberration of magnification that are increased by the negative second lens L2, it is effective to make the first surface S3 and the second surface S4 of the second lens L2 aspherical.

  Further, from Table 1-1, it is desirable that each of the first lens L1 and the second lens L2 is formed of a resin material. The content of Claim 6 is satisfied.

  This makes it possible to manufacture lenses by injection molding and to mass-produce uniform and high-quality eyepieces at low cost. This is also an indispensable element for cost reduction.

  Further, from FIG. 1, Table 1-1, and Table 1-2, when the length in the optical axis direction from the top of each surface in the curvature shape on each surface is defined as the sag amount, the second surface of the second lens L2. The aspherical shape of S4 desirably has a region where the sag amount from the center to the peripheral edge portion increases and decreases at least once. The content of Claim 7 is satisfy | filled.

  This is because, as mentioned above, the structure is small and the magnification is high, but the eye relief and back focus can be appropriately lengthened, with good imaging performance and distortion characteristics, and sufficient chromatic aberration correction for use. Furthermore, in order to obtain a two-view finder eyepiece that realizes low cost with priority, the results are derived by satisfying the conditions of claims 1 to 6.

  FIG. 3 is a lens configuration diagram of another embodiment according to the present invention (Example 2). The left side is shown as the pupil side, and the right side is shown as the image element side.

  4A and 4B are aberration diagrams of this example, where FIG. 4A shows spherical aberration, FIG. 4B shows astigmatism, FIG. 4C shows distortion, and FIG. 4D shows lateral chromatic aberration. In the spherical aberration diagram, as shown, spherical aberrations at the wavelengths of g-line 1, F-line 2, e-line 3, d-line 4 and C-line 5 when the pupil diameter is 4 mm are shown. Yes. The astigmatism diagram shows astigmatism on the sagittal surface S and the tangential surface T as shown. In the chromatic aberration diagram of magnification, as shown, the chromatic aberration of magnification at the wavelengths of g-line 1a, F-line 2a, e-line 3a, d-line 4a, and C-line 5a are shown. Y = 2.53 indicates the distance (image height) from the center of the image element to the diagonal length.

In Table 2-1, the eye point EP, the surface of the first lens L1, the surface of the second lens L2, the surface of the cover glass CG, and the image element surface I from the pupil side of this embodiment are numbered (S0 to S7 shown in FIG. 3). ), And a table summarizing each surface by entering the radius of curvature, distance (interval), refractive index, Abbe number, and the like. The symbols R, D, Nd, and νd are as described above. Table 2-1 also shows the focal length f and the apparent field of view 2ω of all the lens systems when the diopter is adjusted to 0 diopter. Table 2-2 describes the aspherical coefficients when the surface of Table 2-1 is described by the above-described Equation 1. As can be seen from Table 2-1, the first lens L1 in Example 1 was replaced with another low dispersion material.

  Table 4 is a table summarizing the results calculated by substituting specific numerical values corresponding to the conditional expressions (1) to (9) described in the claims. The column of Example 2 in Table 4 is the calculation result in this example.

  From Table 2-1, Table 2-2, and Table 4, as in Example 1, all conditions are satisfied.

  FIG. 5 is a lens configuration diagram of another embodiment according to the present invention (Example 3). The left side is shown as the pupil side, and the right side is shown as the image element side.

  6A and 6B are aberration diagrams of this example, where FIG. 6A shows spherical aberration, FIG. 6B shows astigmatism, FIG. 6C shows distortion, and FIG. 6D shows lateral chromatic aberration. In the spherical aberration diagram, as shown, spherical aberrations at the wavelengths of g-line 1, F-line 2, e-line 3, d-line 4 and C-line 5 when the pupil diameter is 4 mm are shown. Yes. The astigmatism diagram shows astigmatism on the sagittal surface S and the tangential surface T as shown. In the chromatic aberration diagram of magnification, as shown, the chromatic aberration of magnification at the wavelengths of g-line 1a, F-line 2a, e-line 3a, d-line 4a, and C-line 5a are shown. Y = 2.53 indicates the distance (image height) from the center of the image element to the diagonal length.

Table 3-1 shows the eye point EP, the surface of the first lens L1, the surface of the second lens L2, the surface of the cover glass CG, and the image element surface I from the pupil side of this embodiment with numbers (S0 to S7 shown in FIG. 5). ), And a table summarizing each surface by entering the radius of curvature, distance (interval), refractive index, Abbe number, and the like. The symbols R, D, Nd, and νd are as described above. Table 3-1 also shows the focal length f and the apparent field of view 2ω of all the lens systems when the diopter is adjusted to 0 diopter. Table 3-2 shows the aspherical coefficients when the surface of Table 3-1 is described by the above-described Equation 1. As can be seen from Table 3-1, the second lens L2 in Example 1 was replaced with another high dispersion material.

  Table 4 is a table summarizing the results calculated by substituting specific numerical values corresponding to the conditional expressions (1) to (9) described in the claims. The column of Example 3 in Table 4 is the calculation result in this example.

  From Table 3-1, Table 3-2, and Table 4, all the conditions are satisfied as in Examples 1 and 2.

  FIG. 7 is a sectional view of an electronic viewfinder using the lens (Example 1) of the best mode according to the present invention (Example 4). The left side is shown as the pupil side, and the right side is shown as the image element side.

  The first lens 11 and the second lens 12 are arranged with the eye point position 10 as a reference, and the outer periphery of the first lens 11 and the second lens 12 is covered with a lens holder 13. The first lens 11 is inserted from the left side of the lens holder 13 (the eye point position 10 side), and the second lens 12 is inserted from the right side of the lens holder 13 (opposite side of the first lens 11). The positioning is fixed.

  A reflective liquid crystal display device 14 is disposed at an appropriate position of the image element from the position of the first lens 11 and the second lens 12. The reflective liquid crystal display device 14 is a unit including a front light unit 15 and a drive circuit board 16. An FPC (Flexible Printed Circuit) 17 is attached to the outside of the drive circuit board for coupling electric signals to the camera body. A cover plate 18 is disposed at an appropriate position between the eye point 10 and the first lens 11. The cover plate 18, the first lens 11, the second lens 12, the lens holder 13, and the reflective liquid crystal display device 14 are each positioned and fixed by a case 19.

  The lens holder 13 into which the first lens 11 and the second lens 12 are inserted is connected to the direction of the eye point position 10 and the reflection type via a knob (not shown) arranged outside the case 19. An appropriate amount of movement can be moved in the direction of the liquid crystal display device 14, and diopter adjustment can be performed.

  This is obtained by satisfying the conditions of claims 1 to 7 as described above, the structure is small, and the eye relief and back focus can be appropriately lengthened while being high magnification, Compact and high-performance electronic view using a two-piece finder eyepiece with good imaging performance and distortion characteristics, sufficient chromatic aberration correction for use, and low-cost priority. Can be a viewfinder.

The lens block diagram which shows the best embodiment of this invention. Example 1 FIG. 3A is an aberration diagram in the best embodiment of the present invention, FIG. 3A is an aberration diagram showing spherical aberration, FIG. 3B is an aberration diagram showing astigmatism, FIG. 3C is an aberration diagram showing distortion, and FIG. An aberration diagram showing chromatic aberration of magnification. Example 1 The lens block diagram which shows another embodiment of this invention. (Example 2) FIG. 5A is an aberration diagram according to another embodiment of the present invention, FIG. 3A is an aberration diagram illustrating spherical aberration, FIG. 3B is an aberration diagram illustrating astigmatism, FIG. 3C is an aberration diagram illustrating distortion, and FIG. Is an aberration diagram showing chromatic aberration of magnification. (Example 2) The lens block diagram which shows another embodiment of this invention. (Example 3) FIG. 5A is an aberration diagram according to another embodiment of the present invention, FIG. 3A is an aberration diagram illustrating spherical aberration, FIG. 3B is an aberration diagram illustrating astigmatism, FIG. 3C is an aberration diagram illustrating distortion, and FIG. Is an aberration diagram showing chromatic aberration of magnification. (Example 3) The electronic viewfinder sectional drawing using the lens which shows the best embodiment of this invention. (Example 4)

Explanation of symbols

1 spherical aberration at g-line wavelength 2 spherical aberration at F-line wavelength 3 spherical aberration at e-line wavelength 4 spherical aberration at d-line wavelength 5 spherical aberration at C-line wavelength 1a g-line wavelength Chromatic aberration of magnification at 2a chromatic aberration of magnification at the wavelength of F line 3a chromatic aberration of magnification at the wavelength of e line 4a chromatic aberration of magnification at the wavelength of d line 5a chromatic aberration of magnification at the wavelength of C line L1 first lens L2 Second lens I Image element surface S Astigmatism on sagittal surface T Astigmatism on tangential surface Y Image height 10 Eye point position 11 First lens 12 Second lens 13 Lens holder 14 Reflective liquid crystal display device 15 Front Light unit 16 Drive circuit board 17 FPC
18 Cover plate 19 Case

Claims (9)

A viewfinder eyepiece characterized by comprising, in order from the pupil side, a positive first lens and a negative second lens and satisfying the following conditional expression:
(1) 1.0 <TL / f <1.3
(2) 1.9 <f / (D1 + D2 + D3) <2.9
However,
TL: Distance on the optical axis from the first lens surface to the image element surface (parallel plane portion is air length converted)
f: focal length of all lens system D1: thickness on optical axis of first lens D2: distance on optical axis of second and third surfaces D3: thickness on optical axis of second lens The finder eyepiece according to claim 1, wherein the first lens is a double-sided convex lens, and satisfies the following conditional expression.
(3) 1.5 <f / f1 <2.0
(4) -1.5 <R1 / R2 <-1.1
However,
f1: Focal length R1 of the first lens R1: Paraxial radius of curvature of the pupil side surface of the first lens R2: Paraxial radius of curvature of the image element side surface of the first lens 3. The finder eyepiece according to claim 1, wherein the second lens is a concave lens having a concave surface directed toward the pupil, and satisfies the following conditional expression.
(5) -1.25 <f / f2 <-0.75
(6) -2.65 <f / R3 <−1.85
However,
f2: focal length of the second lens R3: paraxial radius of curvature of the pupil side surface of the second lens The finder eyepiece according to claim 1, 2, or 3, wherein the first lens and the second lens further satisfy the following conditional expression.
(7) 0.9 <R2 / R3 <1.2
(8) -17.1 <f2 / D3 <-6.5
(9) 2.6 <(ν1 + ν2) / ν2
However,
R2: paraxial radius of curvature of image element side surface of first lens R3: paraxial radius of curvature of pupil side surface of second lens f2: focal length of second lens D3: thickness on optical axis of second lens ν1: first Abbe number of lens material ν2: Abbe number of second lens material   5. The finder eyepiece according to claim 1, wherein both side surfaces of the first lens and both side surfaces of the second lens are aspherical.   The finder eyepiece according to claim 1, 2, 3, 4, or 5, wherein each lens is made of a resin material.   7. An eyepiece for a finder according to claim 5 or 6, wherein the length of the curvature shape on each surface in the optical axis direction from the top of each surface is defined as a sag amount, the aspherical shape of the side surface of the image element of the second lens. Is a viewfinder eyepiece characterized by having a region where the amount of sag from the center to the peripheral edge increases and decreases at least once.   8. An electronic viewfinder, comprising: a viewfinder eyepiece according to claim 1; and a liquid crystal display element disposed at the image element surface position.   9. The electronic viewfinder according to claim 8, wherein the liquid crystal display element is a reflective liquid crystal display device having a front light unit.

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