JP5646440B2 - Eyepiece - Google Patents

Description

  The present invention relates to an eyepiece suitable for a display image observation device for enlarging an image such as a liquid crystal display of a night vision device, and in particular, image enhancement of weak light condensed by an objective lens in a night vision optical device. The present invention relates to an optical system for magnifying and observing an image formed on a display surface by multiplying by a tube.

  As an eyepiece having a long eye relief with a wide field of view, a five-lens configuration including a glass cemented lens, a long eye relief with a wide field of view with a viewing angle of 51.2 ° and an eye relief of 1.18f (f is a focal length) An invention that makes this possible is known (Patent Document 1).

  In addition, an invention has been proposed in which an aspheric resin lens surface is effectively used in a two-group four-lens configuration as an eyepiece that allows a virtual image to be seen over a wide angle of view even when the pupil deviates from the entrance pupil position. (Patent Document 2). In the present invention, a viewing angle of 40.8 ° and an eye relief of 40 mm are achieved.

  As an eyepiece for observing the display of the night vision optical device, eye relief: 25 mm (18.5 mm when f = 20 mm), entrance pupil diameter: An invention that achieves φ15 mm (when f = 20 mm, entrance pupil diameter: φ11.1 mm) has been proposed (Patent Document 3). Similarly, as an eyepiece lens for observing the display of the night vision optical device, an invention has been proposed in which a DOE (Diffractive Optical Element) surface is utilized to achieve a compact configuration with four lenses. (Patent Document 4).

  Further, as a binocular lens system in which chromatic aberration is corrected to achieve a reduction in size and weight, an invention has been proposed in which a three-group three-lens configuration is used, one of which is a DOE surface (Patent Document 5).

U.S. Pat. No. 4,054,370 Japanese Patent Laid-Open No. 11-133316 JP 2000-105344 A JP 2001-66522 A JP-A-5-210054

  However, in the invention of Patent Document 1, since the F value is f / 5.3, when f = 20 mm, the entrance pupil diameter is φ3.8 mm, which is too small for use in a dark place and a bright image is obtained. I can't observe. Moreover, the weight of the glass becomes about 60 g, and the apparatus becomes heavy. In the invention of Patent Document 2, the eye relief is as long as 40 mm, but f = 70 mm, which increases the size of the apparatus. When f = 20 mm, the eye relief is as short as 11.4 mm and the entrance pupil diameter is as small as φ2 mm (f / 10) at the maximum. In addition, an aspherical surface is effectively used by a resin lens, but the lens thickness is large due to the use of a cemented lens. (Distance to the surface) becomes longer. On the other hand, in the invention of Patent Document 3, the viewing angle is as narrow as 38 °, and the number of lenses is large. Even in the invention of Patent Document 4, the viewing angle is as narrow as 38 °. Furthermore, since the invention of Patent Document 5 is a type that observes with binocular eyes, the lens diameter increases. Further, since the focal length f is increased, the observation magnification is reduced, and the viewing angle is limited. In addition, the total length of the optical system (the distance from the pupil-side surface of the lens arranged closest to the pupil side to the object (image) -side imaging surface) is as large as about 1.85 to 2f.

  In general, it is difficult to achieve both a wide viewing angle and a sufficiently long eye relief for an eyepiece because there is a tendency to trade off between both elements. This is because as the distance from the entrance pupil to the front surface of the eyepiece lens (the apex of the lens surface closest to the pupil), that is, the eye relief, increases, the incident height of the off-axis light beam increases and the diameter of the eyepiece lens needs to be enlarged. Because. The lens diameter increases in proportion to the viewing angle. In addition, if the eye relief is made long, off-axis aberrations increase and image quality around the field of view may deteriorate. In particular, in the case of an eyepiece used in a night vision device or the like, since a human pupil opens as wide as 7 to 8 mm in a dark place, it is necessary to design a large aperture entrance pupil (that is, an optical system having a small F value). Is more difficult to secure. Furthermore, for head mounting, it is necessary to add a margin and set a larger entrance pupil diameter so that even when the eye position is shifted, it is necessary to set a larger entrance pupil diameter. It is difficult.

  On the other hand, in a binocular lens optical system intended for observers to observe with both eyes, it is inevitable due to an increase in the number of lenses to ensure long eye relief and a large aperture entrance pupil diameter. In addition to the complicated lens structure, the total length of the optical system (from the first surface of the first lens to the imaging surface) becomes as large as about 1.85 to 2.0 f. As the focal length increases, the magnification of the eyepiece lens also decreases.

  The present invention has been devised to solve such problems, and two monocular eyepieces or two identical eyepieces required for a small and light eyepiece to be mounted on the head are arranged. An object of the present invention is to provide a small and light eyepiece that is suitable for a binocular eyepiece, has a long eye relief, has a good characteristic over a wide field of view, and has a large entrance pupil diameter.

In order to solve the above problems, according to one aspect of the present invention, an eyepiece having a three-group three-lens configuration in which first, second, and third lenses (11, 12, and 13) are sequentially arranged from the pupil side. a (1), wherein the first lens (11) is a convex lens to the material of glass, and when the focal length of the entire system was f, and the focal length of the first lens and f _1, 0. The first to third lenses have refractive power satisfying 3 <f / f ₁ <1, and satisfy n ₁ > 1.75 when the refractive index of the glass of the first lens is n _1. At least three of the surfaces (21 to 26) are aspherical, and at least one of the surfaces (23 to 26) of the second and third lenses is a diffractive optical surface. . When the entrance pupil diameter is φ and the eye relief is R, 0.5 <φ × R / f ² <0.8 is satisfied.

According to this configuration, the first lens has a great refractive power that satisfies 0.3 <f / f ₁ <1, and the three eyepiece lenses are configured so that the light is emitted from the entrance pupil. A wide field-of-axis off-axis light beam can be effectively deflected and guided to the imaging surface, realizing a long eye relief and a wide field of view, as well as simplifying the configuration and shortening the total lens thickness. realizable. On the other hand, a large aberration is expected to occur due to the large refractive power of the first lens. However, when the refractive index of the glass of the first lens is n ₁ > 1.75, the aberration due to the first lens is reduced. It can be minimized. In addition, in order to ensure performance with a thin and small number of components, it is difficult to correct aberrations with a configuration using only a spherical lens. Therefore, by using an aspherical surface for the first to third lenses effectively (multiple surfaces of three or more surfaces) as described above, aberrations, especially off-axis field curvature, coma aberration, etc. can be corrected well. it can. On the other hand, in order to correct chromatic aberration, it is effective to join lenses made of glass materials having different dispersions. However, if a cemented lens is used, the total thickness and weight of the lens are increased. Therefore, by making at least one surface of the second or third lens a diffractive optical surface as described above, the chromatic aberration can be corrected satisfactorily with only a single lens without using a cemented lens, and the eyepiece The total thickness of the lens can be shortened by reducing the weight and reducing the center thickness of each lens.

The larger the value of φ × R / f ² , the larger the entrance pupil diameter, the longer the eye relief, and the wider the visual field. Therefore, if this value is below the lower limit value, it means that the entrance pupil diameter cannot be secured or the eye relief has an insufficient length of eye relief. On the other hand, when the upper limit is exceeded, the entrance pupil diameter and eye relief length are easy to ensure, but the lens outer diameter becomes large in order to obtain an eyepiece with a wide field of view. As described above, by satisfying 0.5 <φ × R / f ² <0.8, it is possible to provide a small wide-field eyepiece having a large entrance pupil diameter and a long eye relief.

  According to another aspect of the present invention, the second lens (12) may be a meniscus convex lens or a meniscus concave lens having a convex surface (23) directed toward the pupil side.

  According to this configuration, since the surface of the second lens located on the pupil side is a convex surface, it is possible to minimize the occurrence of field curvature and coma for off-axis light beams. In addition, since the principal point of the eyepiece lens moves forward (pupil side), the overall length of the optical system can be shortened.

  Further, according to one aspect of the present invention, when the total thickness of the first to third lenses is Σd and the eye relief is R, the lens satisfies 0.8 <Σd / R <1. Can be miniaturized.

  In order to realize a small eyepiece while ensuring a long eye relief, it is necessary to reduce the number of constituent lenses as much as possible, and to reduce the center thickness of each lens and the distance between the lenses. Below the lower limit, there is an advantage in securing a long eye relief, but the total thickness of the lens is shortened, and the configuration of three lenses becomes substantially difficult. On the other hand, as the total lens thickness increases, the total lens length TL (from the first surface of the first lens to the imaging surface) increases and the size increases, and the working distance decreases and the eye relief space is eroded. As a result, it is difficult to secure a long eye relief.

  By setting so as to satisfy the above conditions, when the distance from the first surface (21) located on the pupil side of the first lens to the object-side image plane (2) is TL, A small configuration satisfying 4 <TL / f <1.8 can be achieved. Thereby, a small eyepiece can be realized while ensuring a long eye relief.

Further, according to one aspect of the present invention, the diffractive optical surface has a plurality of concentric annular zones having a kinoform shape, and 2 × 10 ⁻³ mm when the minimum pitch of the annular zones is p. <P <30 × 10 ⁻³ mm can be satisfied.

  When the diffractive optical surface is composed of a kinoform-like annular zone arranged concentrically, the achromatic effect becomes stronger as the minimum pitch becomes smaller, but the manufacturing difficulty increases. Conversely, the larger the minimum pitch, the easier the manufacturing, but the achromatic effect is weakened. According to this configuration, since the minimum pitch is about 3 μm, manufacturing is easy by precision machining or the like, and achromaticity can be effectively performed. Although it is desirable for the eyepiece lens to be visible achromatic, depending on the light emission characteristics of the phosphor screen of the night vision device such as P20, it may not be necessary to erase the entire visible range. In that case, even if the minimum pitch is relatively large, there is an achromatic effect and the manufacture becomes easier.

  In addition, according to one aspect of the present invention, the second and third lenses can be made of resin.

  According to this configuration, the precision mold is manufactured by machining, and the second and third lenses are molded using these, thereby improving productivity and reducing the weight of the eyepiece. be able to.

  As described above, according to the present invention, it is possible to provide an eyepiece suitable for a small and light night vision device having a long eye relief, good characteristics over a wide field of view, and a large entrance pupil diameter.

Configuration diagram of an eyepiece lens according to Example 1 Configuration diagram of an eyepiece according to Example 2 Configuration diagram of an eyepiece according to Example 3 Configuration diagram of an eyepiece according to Example 4 Configuration diagram of an eyepiece according to Example 5 Various aberration diagrams of the eyepiece according to Example 1. Various aberration diagrams of the eyepiece according to Example 2 Various aberration diagrams of the eyepiece according to Example 3 Various aberration diagrams of the eyepiece according to Example 4 Various aberration diagrams of the eyepiece according to Example 5 Comparison table of eyepieces according to embodiments and conventional examples

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, an eyepiece 1 according to the present invention is attached to a night vision optical device for magnifying and observing an image formed on an image display surface 2 (an image forming surface on the object side). , An eyepiece optical system having a three-group three-element configuration in which a first lens 11, a second lens 12, and a third lens 13 are arranged in order from the pupil (incidence pupil position) side. On the image display surface 2, weak light collected by the objective lens of the night vision optical device is displayed by being multiplied by an image intensifier. Hereinafter, the six surfaces of the first to third lenses 11 to 13 are referred to as a first surface 21 to a sixth surface 26 in order from the pupil side.

The first lens 11 is a convex lens made of glass, and the first surface 21 facing the pupil side is a convex surface. When the focal length of the entire system of the eyepiece lens 1 is f, the focal length of the first lens 11 is f ₁ , and the refractive index of the glass of the first lens 11 is n ₁ , the first lens 11 has 0.3 <f It has a refractive power satisfying / f ₁ <1 and also satisfies n ₁ > 1.75. The second lens 12 is a meniscus lens made of resin, with the third surface 23 facing the pupil forming a convex surface and the fourth surface 24 facing the image display surface 2 forming a concave surface. The third lens 13 is a convex lens made of resin. At least three of the six surfaces (first surface 21 to sixth surface 26) of the first to third lenses 11 to 13 are aspherical.

ただし、
ｃ：球面の頂点の曲率（曲率半径ｒの逆数） ｃ＝１／ｒ
ｙ：光軸からの高さ
ｋ：円錐定数
Ａ、Ｂ、Ｃ、Ｄ：４次、６次、８次、１０次の非球面係数
である。 A formula representing the aspherical shape is represented by the following formula (1).

However,
c: curvature of the vertex of the spherical surface (reciprocal of radius of curvature r) c = 1 / r
y: Height from the optical axis k: Conical constant A, B, C, D: Fourth, sixth, eighth, and tenth aspheric coefficients.

  In addition, a diffractive optical element in which at least one of the four surfaces (third surface 23 to sixth surface 26) of the second and third lenses 12 and 13 has a plurality of annular zones having a kinoform shape arranged concentrically. It is considered as a surface.

The phase function of the diffractive optical surface is expressed by the following equation (2).
φ (y) = P ₂ y ² + P ₄ y ⁴ + P ₆ y ⁶ + (2)
However,
y: height from the optical axis P ₂ , P ₄ , P ₆ ,...: phase coefficients of second order, fourth order, sixth order,.

When the entrance pupil diameter of the eyepiece 1 is φ, the eye relief is R, and the total thickness of the first to third lenses 11 to 13 is Σd, the eyepiece 1 has 0.5 <φ × R / f ² <0. .8 and 0.8 <Σd / R <1. Further, when the total length of the optical system, that is, the distance from the first surface 21 located on the pupil side of the first lens 11 to the image display surface 2 is TL, the eyepiece lens 1 has 1.4 <TL / f <1. .8 is satisfied. Furthermore, the diffractive optical surface satisfies 2 × 10 ⁻³ mm <p <30 × 10 ⁻³ mm , where p is the minimum pitch of the annular zone.

  Hereinafter, the configuration shown in FIG. 1 is referred to as Example 1, and five examples including other Examples 2 to 5 are sequentially described with reference to the configuration diagrams of FIGS. 2 to 5 and the comparison table of FIG. .

The lens data of Example 1 are shown in Tables 1 to 3.

  In the present embodiment, as shown in FIG. 1 and Tables 1 to 3, the first lens 11 is a convex lens, and both surfaces (the first surface 21 and the second surface 22) are aspherical surfaces. The second lens 12 is a meniscus concave lens, and both surfaces thereof (the third surface 23 and the fourth surface 24) are aspherical surfaces. The third lens 13 has both aspheric surfaces (fifth surface 25 and sixth surface 26) and a fifth surface 25 located on the pupil side as a diffractive optical surface.

As shown in FIG. 11, the eyepiece lens 1 according to the present example has a focal length f of the entire system of 19.93 mm, and a focal length f ₁ of the first lens 11 is 25.938 mm. Therefore, f / f ₁ = 0.768, which satisfies 0.3 <f / f ₁ <1. The refractive index n ₁ of the glass of the first lens 11 is 1.85060, and the eyepiece lens 1 satisfies n ₁ > 1.75. Further, the entrance pupil diameter φ of the eyepiece 1 is 10 mm (f / 1.99), and the eye relief R is 25 mm (1.254 f). Therefore, φ × R / f ² = 0.629, and the eyepiece 1 satisfies 0.5 <φ × R / f ² <0.8. The total thickness Σd of the first to third lenses 11 to 13 is 22.167, Σd / R = 0.877, and the eyepiece 1 satisfies 0.8 <Σd / R <1. Further, TL / f = 1.538, and the eyepiece 1 satisfies 1.4 <TL / f <1.8. The minimum pitch p of the annular zone of the diffractive optical surface formed on the third lens 13 (fifth surface 25) is 0.005867 mm. Therefore, the eyepiece 1 satisfies 2 × 10 ⁻³ mm <p <30 × 10 ⁻³ mm . Further, the viewing angle 2ω of the eyepiece 1 is 51 °, and the F value is 1.99. Various aberrations are as shown in FIG.

Tables 4 to 6 show lens data of Example 2.

  In the present embodiment, as shown in FIG. 2 and Tables 4 to 6, the first lens 11 is a meniscus convex lens. The second lens 12 is a meniscus convex lens, and both surfaces (the third surface 23 and the fourth surface 24) are aspherical surfaces. The third lens 13 is a convex lens whose both surfaces (the fifth surface 25 and the sixth surface 26) are aspheric surfaces, and the fifth surface 25 on the pupil side is a diffractive optical surface.

As shown in FIG. 11, the eyepiece 1 according to the present example has a focal length f of the entire system of 19.87 mm, and the focal length f ₁ of the first lens 11 is 39.899 mm. Therefore, f / f ₁ = 0.498, and 0.3 <f / f ₁ <1 is satisfied. The refractive index n ₁ of the glass of the first lens 11 is 2.003300, and the eyepiece lens 1 satisfies n ₁ > 1.75. Further, the entrance pupil diameter φ of the eyepiece 1 is 12 mm (f / 1.66), and the eye relief R is 25 mm (1.258 f). Therefore, φ × R / f ² = 0.760, and the eyepiece 1 satisfies 0.5 <φ × R / f ² <0.8. The total thickness Σd of the first to third lenses 11 to 13 is 23.596, Σd / R = 0.944, and the eyepiece lens 1 satisfies 0.8 <Σd / R <1. Further, TL / f = 1.514, and the eyepiece 1 satisfies 1.4 <TL / f <1.8. The minimum pitch p of the annular zone of the diffractive optical surface formed on the third lens 13 (fifth surface 25) is 0.003599 mm. Therefore, the eyepiece 1 satisfies 2 × 10 ⁻³ mm <p <30 × 10 ⁻³ mm . Further, the viewing angle 2ω of the eyepiece 1 is 52 °, and the F value is 1.66. Various aberrations are as shown in FIG.

Tables 7 to 9 show lens data of Example 3.

  In this embodiment, as shown in FIG. 3 and Tables 7 to 9, the first lens 11 is a meniscus convex lens. The second lens 12 is a meniscus convex lens whose both surfaces (third surface 23 and fourth surface 24) are aspherical surfaces, and the fourth surface 24 on the image display surface 2 side is a diffractive optical surface. The third lens 13 has two aspheric surfaces (fifth surface 25 and sixth surface 26).

As shown in FIG. 11, the eyepiece lens 1 according to the present example has a focal length f of the entire system of 20.8 mm, and a focal length f ₁ of the first lens 11 is 42.85 mm. Therefore, f / f ₁ = 0.485, which satisfies 0.3 <f / f ₁ <1. The refractive index n ₁ of the glass of the first lens 11 is 1.88300, and the eyepiece lens 1 satisfies n ₁ > 1.75. Further, the entrance pupil diameter φ of the eyepiece 1 is 10 mm (f / 2.08), and the eye relief R is 25 mm (1.202 f). Therefore, φ × R / f ² = 0.578, and the eyepiece 1 satisfies 0.5 <φ × R / f ² <0.8. The total thickness Σd of the first to third lenses 11 to 13 is 22.300, Σd / R = 0.892, and the eyepiece 1 satisfies 0.8 <Σd / R <1. Further, TL / f = 1.435, and the eyepiece lens 1 satisfies 1.4 <TL / f <1.8. The minimum pitch p of the annular zone of the diffractive optical surface formed on the second lens 12 (fourth surface 24) is 0.007732 mm. Therefore, the eyepiece 1 satisfies 2 × 10 ⁻³ mm <p <30 × 10 ⁻³ mm . Further, the viewing angle 2ω of the eyepiece 1 is 51 °, and the F value is 2.08. Various aberrations are as shown in FIG.

Tables 10 to 12 show lens data of Example 4.

  In this embodiment, as shown in FIG. 4 and Tables 10 to 12, the first lens 11 is a meniscus convex lens. The second lens 12 is a meniscus convex lens, and both surfaces (the third surface 23 and the fourth surface 24) are aspherical surfaces. The third lens 13 is a convex lens whose both surfaces (the fifth surface 25 and the sixth surface 26) are aspheric surfaces, and the sixth surface 26 on the image display surface 2 side is a diffractive optical surface.

As shown in FIG. 11, the eyepiece lens 1 according to the present example has a focal length f of the entire system of 19.8 mm, and a focal length f ₁ of the first lens 11 is 39.899 mm. Therefore, f / f ₁ = 0.496, which satisfies 0.3 <f / f ₁ <1. The refractive index n ₁ of the glass of the first lens 11 is 2.00330, and the eyepiece lens 1 satisfies n ₁ > 1.75. Further, the entrance pupil diameter φ of the eyepiece 1 is 10 mm (f / 1.98), and the eye relief R is 26.5 mm (1.338 f). Therefore, φ × R / f ² = 0.676, and the eyepiece 1 satisfies 0.5 <φ × R / f ² <0.8. The total thickness Σd of the first to third lenses 11 to 13 is 23.914, Σd / R = 0.902, and the eyepiece 1 satisfies 0.8 <Σd / R <1. Further, TL / f = 1.524, and the eyepiece 1 satisfies 1.4 <TL / f <1.8. The minimum pitch p of the annular zone of the diffractive optical surface formed on the third lens 13 (sixth surface 26) is 0.003634 mm. Therefore, the eyepiece 1 satisfies 2 × 10 ⁻³ mm <p <30 × 10 ⁻³ mm . Further, the viewing angle 2ω of the eyepiece lens 1 is 50 °, and the F value is 1.98. Various aberrations are as shown in FIG.

Tables 13 to 15 show lens data of Example 5.

  In the present embodiment, as shown in FIG. 5 and Tables 13 to 15, the first lens 11 is a convex lens whose both surfaces (first surface 21 and second surface 22) are aspherical surfaces. The second lens 12 is a meniscus concave lens, and both surfaces thereof (the third surface 23 and the fourth surface 24) are aspherical surfaces. The third lens 13 has both aspheric surfaces (fifth surface 25 and sixth surface 26) and a fifth surface 25 on the pupil side as a diffractive optical surface.

As shown in FIG. 11, the ocular lens 1 according to the present embodiment has a focal length f of the entire system of 19.88 mm, and a focal length f ₁ of the first lens 11 is 22.449 mm. Therefore, f / f ₁ = 0.886, and 0.3 <f / f ₁ <1 is satisfied. The refractive index n ₁ of the glass of the first lens 11 is 1.81482, and the eyepiece lens 1 satisfies n ₁ > 1.75. Further, the entrance pupil diameter φ of the eyepiece 1 is 10 mm (f / 1.99), and the eye relief R is 25 mm (1.258 f). Therefore, φ × R / f ² = 0.633, and the eyepiece 1 satisfies 0.5 <φ × R / f ² <0.8. The total thickness Σd of the first to third lenses 11 to 13 is 21.048, Σd / R = 0.842, and the eyepiece 1 satisfies 0.8 <Σd / R <1. Further, TL / f = 1.488, and the eyepiece 1 satisfies 1.4 <TL / f <1.8. The minimum pitch p of the annular zone of the diffractive optical surface formed on the third lens 13 (fifth surface 25) is 0.006422 mm. Accordingly, the ocular lens 1 satisfies ^{2 × 10 -3 mm <p <} 30 × 10 -3 mm. Further, the viewing angle 2ω of the eyepiece 1 is 51 °, and the F value is 1.99. Various aberrations are as shown in FIG.

As described above, in any of the embodiments, the first lens 11 has a great refractive power that satisfies 0.3 <f / f ₁ <1, and the ocular lens 1 has a three-group three-lens configuration. Since the off-axis light beam having a wide field of view emitted from the entrance pupil can be effectively deflected and introduced into the image display surface 2, a long eye relief R and a wide field of view can be realized, and the structure can be simplified. In addition, it is possible to reduce the total lens thickness Σd. On the other hand, when a large refractive power is applied to the first lens 11, a large aberration is expected to occur. However, when the refractive index n ₁ of the glass of the first lens 11 is set to n ₁ > 1.75, the first lens 11 The aberration due to can be minimized. Also, in order to ensure performance with a thin and small number of components, it is difficult to correct aberrations with the configuration of only a spherical lens, but an aspherical surface is effective for the first to third lenses 11 to 13 (three or more surfaces). ), It is possible to satisfactorily correct aberrations, particularly off-axis field curvature and coma. On the other hand, by correcting at least one surface of the second or third lens 12 or 13 as a diffractive optical surface in order to correct chromatic aberration, the chromatic aberration can be corrected satisfactorily by using only a single lens without using a cemented lens. In addition, the weight of the eyepiece lens 1 is reduced, and the total thickness Σd of the lens can be shortened by reducing the center thickness of each lens.

  Further, since the third surface 23 located on the pupil side of the second lens 12 is a convex surface, the occurrence of field curvature and coma aberration with respect to the off-axis light beam is minimized. Further, since the principal point of the eyepiece 1 moves forward (pupil side), the total length (TL) of the optical system can be shortened. In addition, when this inventor confirmed about the case where each lens was arrange | positioned by reversing only the direction of the 2nd lens 12, in the 1st-5th Example, the value of TL is 2.13 mm, 2.85 mm, respectively. 2.81 mm, 2.46 mm and 1.69 mm larger. That is, it was confirmed that the orientation of the second lens 12 contributes to shortening the overall length of the optical system.

Further, by satisfying 0.5 <φ × R / f ² <0.8, the eyepiece 1 having a large entrance pupil diameter φ and a long eye relief R, and having a small size and a wide field of view can be provided. In addition, when the eyepiece 1 satisfies 0.8 <Σd / R <1 or 1.4 <TL / f <1.8, the center thickness of each lens and the distance between the lenses are shortened, and the total number of lenses is reduced. The thickness Σd can be shortened. Further, when the eyepiece 1 satisfies 2 × 10 ⁻³ mm <p <30 × 10 ⁻³ mm , the minimum pitch p of the zonal zone is easy to manufacture by precision machining or the like, and achromaticity is effective. Can be done automatically. In addition, since the second and third lenses 12 and 13 are made of resin, a precision mold can be manufactured by machining, and the second and third lenses 12 and 13 can be molded using these. Therefore, productivity can be improved and the weight of the eyepiece 1 can be reduced.

On the other hand, in the prior art shown as a comparative example in FIG. 11, in the case of the configuration of Patent Document 1 (US Pat. No. 4,054,370), the viewing angle 2ω is a wide angle of 51.2 °, but the F value is 5.3. The entrance pupil diameter φ is 5 mm, and a large aperture entrance pupil diameter cannot be realized. Moreover, φ × R / f ² is extremely small as 0.214, and TL / f is 1.369, which is not less than 1.4. Further, in the configuration of Patent Document 2 (Japanese Patent Laid-Open No. 11-133316), the viewing angle 2ω is as narrow as 40.8 °, and φ × R / f ² is too small as 0.032. Even in the configurations of Patent Document 3 (Japanese Patent Laid-Open No. 2000-105344) and Patent Document 4, the viewing angle 2ω is as small as 41.8 ° and 38.8 °, respectively, and the lens weight is also large. In the configuration of Patent Document 5 (Japanese Patent Laid-Open No. 5-210054), since specific data is not disclosed, simulation cannot be performed and an accurate numerical value cannot be calculated. The viewing angle 2ω is as narrow as 40 °, and TL / f is as large as 1.850. Note that the estimated value of Patent Document 5 is TL / f 1 according to the description in the same specification that “the prior art has about twice the focal length, whereas the total length could be reduced by 15%”. .850, each length (eye relief R, Σd, entrance pupil diameter φ) is estimated from the figure using an average eye width of 60 to 70 mm as an index. The viewing angle 2ω was estimated based on the optical path in the figure.

  The technique of Patent Document 5 discloses a three-group three-lens configuration binocular lens, which at first glance appears to be close to the configuration of the present invention, but the present invention has a large aperture such that the F value <1. In order to achieve the lens, the total length is increased, and the configuration is advantageous for correcting spherical aberration and chromatic aberration, but is disadvantageous for correcting curvature of field and coma, and 50 as in the present invention. It is also impossible to achieve a wide field of view that exceeds °°. In other words, the configuration of Patent Document 5 is advantageous in that the same image can be observed with both eyes as compared with a monocular eyepiece or a binocular eyepiece, but it is disadvantageous for miniaturization and wide field of view.

  The description of the specific embodiment is finished above, but the present invention is not limited to the above embodiment. For example, in the above-described embodiment, the eyepiece 1 according to the present invention is applied to the night vision optical device, but it can also be applied to other devices. Further, the specific shapes and arrangements of the members constituting the eyepiece 1 are not limited to the above-described embodiments, and can be changed as appropriate without departing from the spirit of the present invention.

1 Eyepiece 2 Image display surface (imaging surface on the object side)
11 1st lens 12 2nd lens 13 3rd lens 21 1st surface (surface on the pupil side of 1st lens 11)
23 3rd surface (the pupil side surface of the second lens 12)
24 4th surface (surface of the second lens 12 on the image display surface 12 side)
25 Fifth surface (the pupil-side surface of the third lens 13)
26 Sixth surface (the surface of the third lens 13 on the image display surface 12 side)
R Eye relief f Focal length f ₁ Focal length of the first lens 11 n ₁ Refractive index of the first lens 11 p Minimum pitch of the annular zone Σd Total thickness of the lens

Claims (5)

An eyepiece having a three-group, three-element configuration in which first, second, and third lenses are arranged in order from the pupil side,
The first lens is a convex lens made of glass, and satisfies 0.3 <f / f ₁ <1 where f is the focal length of the entire system and f ₁ is the focal length of the first lens. And satisfying n ₁ > 1.75, where n ₁ is the refractive index of the glass of the first lens,
At least three of the surfaces of the first to third lenses are aspheric surfaces;
Ri least one surface diffractive optical surface der among the surfaces of the second and third lens,
An eyepiece characterized by satisfying 0.5 <φ × R / f ² <0.8, where φ is an entrance pupil diameter and R is an eye relief .   The eyepiece according to claim 1, wherein the second lens is a meniscus convex lens or a meniscus concave lens having a convex surface directed toward the pupil side. The eyepiece according to claim 1 or 2 , wherein when the total thickness of the first to third lenses is Σd and the eye relief is R, 0.8 <Σd / R <1 is satisfied. lens. The diffractive optical surface has a plurality of concentric annular zones having a kinoform shape, and satisfies 2 × 10 ⁻³ mm <p <30 × 10 ⁻³ mm , where p is the minimum pitch of the annular zones. The ocular lens according to any one of claims 1 to 3 , wherein: The eyepiece according to any one of claims 1 to 4 , wherein the second and third lenses are made of resin.

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