JP2012108296A - Eyepiece optical system and optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eyepiece optical system that is easy to manufacture, able to restrain occurrence of flare, is inexpensive, is satisfactorily corrected in various aberrations such as chromatic aberration of magnification, and has a long eye relief, and to provide an optical device having this eyepiece optical system.SOLUTION: An eyepiece optical system 3 used for the optical device such as a telescopic optical system TS comprises, in order from an observation eye side, a first lens group G1 having a lens with positive refractive power; a second lens group G2 that has a diffractive optical element GD formed from two diffraction element components L22 and L23 and two optical members L21 and L24 joined to one sides of these two diffraction element components, and having a diffractive optical surface D in which diffraction grating grooves are formed in the other sides of the two diffraction element components L22 and L23 and they are arranged opposite to each other; and a third lens group having a cemented lens composed of a positive lens 31 and negative lens L32 cemented together and having positive refractive power as a whole. At least the optical members L21 or L24 of the diffractive optical element GD is a parallel flat plate.

Description

  The present invention relates to an eyepiece optical system and an optical apparatus.

  In an eyepiece optical system, having a large angle of view is one important performance, but if you try to increase the angle of view, various aberrations such as chromatic aberration of magnification are easily affected, and these aberrations are improved. Is an important issue. On the other hand, in recent years, diffractive optical elements having a configuration significantly different from that of conventional optical systems have been proposed as various optical systems, in particular, optical systems using diffractive optical elements in order to suppress the occurrence of chromatic aberration (for example, Patent Document 1). reference).

US Pat. No. 6,130,785

  However, it is difficult to stably manufacture the diffractive optical element, and the eyepiece optical system using the diffractive optical element has a problem that the price is high.

  The present invention has been made in view of such problems, and is easy to manufacture and capable of suppressing the occurrence of flare. It is inexpensive by using a common diffractive optical element in ocular optical systems having different focal lengths, and lateral chromatic aberration. It is an object of the present invention to provide an eyepiece optical system having a long eye relief in which various aberrations are well corrected, and an optical apparatus having the eyepiece optical system.

  In order to solve the above problems, an eyepiece optical system according to the present invention includes, in order from the observation eye side, a first lens group having a lens having a positive refractive power, two diffractive element elements, and two of these A diffractive optical element having two diffractive optical surfaces, each of which is composed of two optical members bonded to one surface of each of the diffractive element elements, and is disposed opposite to each other by forming a diffraction grating groove on the other surface of the two diffractive element elements And a third lens group having a cemented lens having a positive refractive power as a whole, and at least one of the optical members of the diffractive optical element is It is a parallel plate.

In such an eyepiece optical system, when the Abbe number of the medium of the positive lens constituting the cemented lens is νp, the curvature radius of the cemented surface of the cemented lens is r, and the focal length of the diffractive optical surface is fdoe, νp <70
| Fdoe / r | <50
It is preferable to satisfy the following conditions.

In such an eyepiece optical system, the focal length of the entire system is f, the focal length of the diffractive optical surface is fdoe, and the focal length when two optical members constituting the diffractive optical element are joined is fbase. Then, the following expression | (1 / fbase + 1 / fdoe) / (1 / f) | <1.0
It is preferable to satisfy the following conditions.

In addition, such an eyepiece optical system has an eye relief as ER, and a distance on the optical axis from the lens surface closest to the observation eye to the focal plane on the observation eye side of the first lens group is BF. Formula | BF / ER | <10
It is preferable to satisfy the following conditions.

  In such an eyepiece optical system, it is preferable that the two diffractive element elements of the diffractive optical element are joined with the diffraction grating grooves in close contact.

  An optical apparatus according to the present invention includes any one of the above-described eyepiece optical systems.

  By constructing the present invention as described above, it is easy to manufacture and can suppress the occurrence of flare, and it is inexpensive by sharing a diffractive optical element in an eyepiece optical system having a different focal length, and various aberrations such as lateral chromatic aberration are good. It is possible to provide an eyepiece optical system having a long eye relief corrected to 1 and an optical apparatus having the eyepiece optical system.

It is explanatory drawing which shows the structure of the telescope optical system which is an example of an optical instrument. It is a lens block diagram which shows the structure of the eyepiece optical system which concerns on 1st Example. FIG. 6 is a diagram illustrating all aberrations of the eyepiece optical system according to the first example. It is a graph which shows the relationship between the distance from the optical axis in the diffractive optical surface of the eyepiece optical system which concerns on the said 1st Example, and the average value of the incident angle of a light ray. It is a lens block diagram which shows the structure of the eyepiece optical system which concerns on 2nd Example. FIG. 6 is various aberration diagrams of the eyepiece optical system according to the second example. It is a graph which shows the relationship between the distance from the optical axis in the diffractive optical surface of the eyepiece optical system which concerns on the said 2nd Example, and the average value of the incident angle of a light ray. It is a lens block diagram which shows the structure of the eyepiece optical system which concerns on 3rd Example. FIG. 12 is a diagram illustrating all aberrations of the eyepiece optical system according to the third example. It is a graph which shows the relationship between the distance from the optical axis in the diffractive optical surface of the eyepiece optical system which concerns on the said 3rd Example, and the average value of the incident angle of a light ray. It is a lens block diagram which shows the structure of the eyepiece optical system which concerns on 4th Example. FIG. 10 is a diagram illustrating all aberrations of the eyepiece optical system according to the fourth example. It is a graph which shows the relationship between the distance from the optical axis in the diffractive optical surface of the eyepiece optical system which concerns on the said 4th Example, and the average value of the incident angle of a light ray. It is a lens block diagram which shows the structure of the eyepiece optical system which concerns on 5th Example. FIG. 10 is a diagram illustrating all aberrations of the eyepiece optical system according to the fifth example. It is a graph which shows the relationship between the distance from the optical axis in the diffraction optical surface of the eyepiece optical system which concerns on the said 5th Example, and the average value of the incident angle of a light ray.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, the configuration of the telescope optical system TS shown in FIG. 1 will be described as an optical apparatus having the eyepiece optical system according to the present embodiment. The telescope optical system TS includes an objective lens 1, an erecting prism 2, and an eyepiece optical system 3 in order from the observed object side. The erecting prism 2 is disposed between the objective lens 1 and the eyepiece optical system 3 and inverts an inverted image of the observed object formed by the objective lens 1 vertically and horizontally. As the erecting prism 2, for example, a so-called Porro prism composed of two isosceles triangular prisms can be used. The image I of the object to be observed formed by the objective lens 1 can be magnified and observed by the observation eye located at the eye point EP using the eyepiece optical system 3. Note that the telescope optical system TS shown in FIG. 1 is merely an example, and is not limited to the configuration shown in FIG. For example, in an astronomical telescope or the like, the erecting prism 2 is not necessary. In this case, the erecting prism 2 may be omitted. In addition, it can also be used for field scopes and binoculars.

  The eyepiece optical system 3 according to the present embodiment has a first lens group G1, a second lens group G2, and a third lens group G3 in order from the observation eye side. Here, the first lens group G1 includes at least one lens having a positive refractive power (for example, a positive meniscus lens L11 in FIG. 1). The second lens group G2 includes two diffractive element elements L22 and L23, and two optical members L21 and L24 bonded to one surface of each of the two diffractive element elements L22 and L23. It has a diffractive optical element GD having a diffractive optical surface D disposed opposite to each other by forming a diffraction grating groove on the other surface of the two diffractive element elements L22 and L23. The third lens group G3 includes a cemented lens CL having a positive refractive power as a whole, in which a positive lens L31 and a negative lens L32 are cemented.

  Here, the diffractive optical element GD (diffractive optical surface D) provided in the second lens group G2 has a negative dispersion value (Abbe number = −3.453), a large dispersion, and an anomalous dispersion. Because it is strong, it has a strong ability to correct chromatic aberration. The Abbe number of the optical glass is usually about 30 to 80, but the Abbe number of the diffractive optical element has a negative value as described above. In other words, the diffractive optical surface D of the diffractive optical element GD has a dispersion characteristic that is opposite to that of normal glass (refractive optical element), and the refractive power decreases as the wavelength of light decreases, and the longer the wavelength of light, the greater the curvature. have. Therefore, a large achromatic effect can be obtained by combining with an ordinary refractive optical element. Therefore, by using the diffractive optical element GD, it becomes possible to correct chromatic aberration that cannot be achieved with ordinary optical glass.

  In addition, the eyepiece optical system 3 according to the present embodiment is configured by optical glass having at least one of parallel optical plates among the optical members L21 and L24 constituting the diffractive optical element GD (for example, in the case of FIG. The optical element L21 is composed of a parallel plate). By forming at least one of the optical members L21 and L24 constituting the diffractive optical element GD as a parallel plate, the diffractive optical element GD can be easily manufactured. The eyepiece optical system 3 and the eyepiece optical system 3 The manufacturing cost of the optical device having the above can be reduced. Further, if both of the two optical members L21 and L24 sandwiching the diffraction element elements L22 and L23 are parallel plates, the eye relief ER can be lengthened. The eye relief ER is a distance on the optical axis from the lens surface closest to the observation eye of the eyepiece optical system 3 to the eye point EP.

  In the eyepiece optical system 3 according to this embodiment, the Abbe number of the medium of the positive lens L31 constituting the cemented lens CL of the third lens group G3 disposed on the object side with respect to the diffractive optical element GD is νp, When the radius of curvature of the cemented surface CP of the cemented lens CL is r and the focal length of the diffractive optical surface D of the diffractive optical element GD is fdoe, it is desirable that the following conditional expressions (1) and (2) are satisfied.

νp <70 (1)
| Fdoe / r | <50 (2)

  Conditional expression (1) defines the Abbe number of the medium of the positive lens L31 among the lenses constituting the cemented lens CL included in the third lens group G3. A lens made of a medium exceeding the upper limit value of the conditional expression (1) becomes special glass (ED glass) having an anomalous partial dispersion characteristic, and the cost of the eyepiece optical system 3 is increased. Therefore, the eyepiece optical system 3 according to the present embodiment corrects chromatic aberration (particularly magnification chromatic aberration) without using such ED glass for the positive lens L31 of the cemented lens CL by satisfying conditional expression (2). can do. Usually, chromatic aberration (magnification chromatic aberration) is corrected by changing the radius of curvature r of the cemented surface CP of the cemented lens CL. On the other hand, as described above, the diffractive optical element GD has the characteristics that the dispersion is very high (the Abbe number is low), the chromatic aberration is sensitive to the focal length fdoe of the diffractive optical surface D, and the chromatic aberration is easily changed. Therefore, by satisfying conditional expression (2), it is possible to satisfactorily correct lateral chromatic aberration by balancing the radius of curvature r of the cemented surface CP of the cemented lens CL and the focal length fdoe of the diffractive optical surface D. it can.

  Further, the eyepiece optical system 3 according to the present embodiment configures the diffractive optical element GD by setting the focal length of the entire system of the eyepiece optical system 3 as f and the focal length of the diffractive optical surface D of the diffractive optical element GD as fdoe. It is desirable to satisfy the following conditional expression (3), where fbase is the focal length when the two optical members L21 and L24 are joined.

| (1 / fbase + 1 / fdoe) / (1 / f) | <1.0 (3)

  Conditional expression (3) defines the ratio between the paraxial combined power of the diffractive optical element GD and the power of the entire system. When the eyepiece optical system 3 according to the present embodiment satisfies the conditional expression (3), the diffractive optical element GD may be shared between the eyepiece optical systems 3 having different focal lengths while maintaining good optical performance. And an inexpensive eyepiece optical system 3 can be provided.

  In the eyepiece optical system 3 according to the present embodiment, the eye relief is ER, and the distance on the optical axis from the lens surface closest to the observation eye to the focal plane on the observation eye side of the first lens group G1 is BF. Then, it is desirable to satisfy the following conditional expression (4).

| BF / ER | <10 (4)

  Conditional expression (4) is the distance on the optical axis from the lens surface closest to the observation eye of the eyepiece optical system 3 to the focal plane on the observation eye side of the first lens group G1 and the distance on the optical axis to the eye point. The ratio is defined. In the diffractive optical element GD, flare is likely to occur when the incident angle of the light beam on the diffractive optical surface D is large, but when this conditional expression (4) is satisfied, the eye point EP and the observation eye side of the first lens group G1 Since the distance from the focal point of the diffractive optical surface D becomes close and the light beam incident on the diffractive optical surface D can be made parallel to the optical axis (incident angle is 15 ° or less), flare of the diffractive optical surface D Occurrence can be suppressed.

  In the eyepiece optical system 3 according to the present embodiment, the diffractive optical element GD includes two diffractive element elements L22 and L23 constituting the diffractive optical element GD, and the diffraction grating grooves formed in the diffractive optical element GD are spaced apart from each other. Alternatively, it may be configured as a separated multi-layer type diffractive optical element arranged close to each other, or may be configured as a close-contact multi-layer type diffractive optical element in which these diffraction grating grooves are closely bonded. Here, when the contact multilayer diffractive optical element is used, the manufacturing process can be simplified as compared with the separated multilayer diffractive optical element, so that mass production efficiency is good and the diffraction efficiency with respect to the incident angle of light is good. It has the advantage of. Therefore, the eyepiece optical system 3 using the contact multilayer diffractive optical element is easy to manufacture, and the diffraction efficiency is improved.

  Then, five examples of such an eyepiece optical system 3 are shown below. In each example, the phase difference Φ of the diffractive optical surface D formed on the diffractive optical element GD is expressed as a phase function Φ (h) represented by the following conditional expression (a). In this equation (a), h represents the height from the optical axis, λ represents the wavelength, and C2 to C10 represent phase coefficients. The focal length fdoe of the diffractive optical surface D shown in the above conditional expressions (2) and (3) is defined as the following expression (b) using the secondary phase coefficient C2 among the above phase coefficients. Is done.

Φ (h) = 2π / λ (C2h ² + C4h ⁴ + C6h ⁶ + C8h ⁸ + C10h ¹⁰ ) (a)
fdoe = -0.5 / C2 (b)

[First embodiment]
FIG. 2 shows an eyepiece optical system 3 according to the first example. The eyepiece optical system 3 includes, in order from the observation eye side, a first lens group G1, a second lens group G2, and a third lens group G3. The first lens group G1 includes a positive meniscus lens L11 having a convex surface directed toward the object side. The second lens group G2 has, in order from the observation eye side, a parallel flat optical glass (optical member) L21, two diffraction element elements L22 and L23 formed from different resins, and a convex surface on the object side. The diffractive optical element (adherent multilayer diffractive optical element) in which the directed plano-convex lens (optical member) L24 is joined in this order and a diffraction grating groove (diffractive optical surface D) is formed on the joint surface of the diffractive element elements L22 and L23. Element) GD. The third lens group G3 includes a cemented lens CL in which a biconvex lens (positive lens) L31 and a biconcave lens (negative lens) L32 are cemented in order from the observation eye side.

Table 1 shows the specifications of the eyepiece optical system 3 according to the first example. In Table 1, f shown in the overall specifications is the focal length of the entire eyepiece optical system 3, and ER is on the optical axis from the eye point EP to the lens surface closest to the eye of the eyepiece optical system 3. Indicates distance (eye relief). The first column m of the lens data is the number (surface number) of each optical surface from the observation eye side, the second column r is the radius of curvature of each optical surface, and the third column d is from the optical surface to the next. The fourth column nd and the fifth column νd indicate the refractive index and Abbe number for the d-line (λ = 587.562 nm), respectively, on the optical axis distance (surface interval) to the optical surface. Here, a radius of curvature of 0.000 indicates a plane, and an air refractive index of 1.00000 is omitted. Further, the surface numbers 1 to 10 in Table 1 correspond to the numbers 1 to 10 shown in FIG. The distance between the most object side surface (tenth surface) of the eyepiece optical system 3 is the distance on the optical axis from the most object side surface to the image I of the observed object formed by the objective lens. Show. Further, * is shown on the right side of the surface number of the diffractive optical surface, and the value of the phase coefficient of the phase function Φ (h) on the surface is shown as phase data. In this phase data, ^En represents “× 10 ⁻ⁿ ”. Further, in Table 1, the values of the above conditional expressions (1) to (4) of the eyepiece optical system 3 according to the first example are shown as values corresponding to the conditional expressions. Here, fdoe is the focal length of the diffractive optical surface D, r is the radius of curvature of the cemented surface CP of the cemented lens CL, and fbase is the focal point when the two optical members L21 and L24 constituting the diffractive optical element GD are joined. The distance BF indicates the distance on the optical axis from the lens surface (first surface) closest to the observation eye to the focal plane on the observation eye side of the first lens group G1. The description of these specification tables is the same in the following examples.

  Here, the curvature radius r, the surface interval d, the focal length f and other length units described in all the following specifications are generally “mm” unless otherwise specified, but the optical system is proportionally enlarged. Alternatively, since equivalent optical performance can be obtained even when proportionally reduced, the unit is not limited to “mm”, and other appropriate units can be used.

(Table 1)
Overall specifications f = 16.48
ER = 15.6

Lens data m r d nd νd
1 -50.000 3.90 1.620410 60.25
2 -17.926 0.20
3 0.000 1.00 1.516800 63.88
4 0.000 0.10 1.557100 50.17
5 * 0.000 0.10 1.527800 34.71
6 0.000 5.00 1.620410 60.25
7 -29.941 0.20
8 30.451 9.20 1.729160 54.61
9 -18.552 1.50 1.805180 25.45
10 144.686 8.55

Phase data 5th surface C2 = -6.5000E-04 C4 = 2.2000E-06 C6 = 0 C8 = 0 C10 = 0

Conditional expression corresponding value fdoe = 769.23
r = -18.552
fbase = 48.26
BF = 46.63
(1) νp = 54.61
(2) | fdoe / r | = 41.46
(3) | (1 / fbase + 1 / fdoe) / (1 / f) | = 0.36
(4) | BF / ER | = 2.99

  In Table 1, νp in conditional expression (1) represents the Abbe number of the medium (eighth surface) of the biconvex lens L31, and the radius of curvature r in conditional expression (2) represents the value of the ninth surface. . Thus, it can be seen that the eyepiece optical system 3 according to the first example satisfies all the conditional expressions (1) to (4).

  FIG. 3 shows spherical aberration, astigmatism, and distortion with respect to rays of C-line (λ = 656.273 nm), d-line, F-line (λ = 486.133 nm), and g-line (λ = 435.835 nm) in the first embodiment. The aberration diagrams of various aberrations and lateral chromatic aberration are shown. Here, the spherical aberration diagram shows the aberration amount with respect to the normalized diameter of the entrance pupil when the maximum value of the diameter of the entrance pupil is normalized to 1, and the astigmatism diagram and the distortion aberration diagram show the half angle of view ω. The aberration amount with respect to [°] is shown. In the graph showing astigmatism, a solid line indicates a sagittal image plane for each wavelength, and a broken line indicates a meridional image plane for each wavelength. The explanation of these various aberration diagrams is the same in the following examples. Thus, it can be seen that the eyepiece optical system 3 according to the first example is well corrected for various aberrations such as lateral chromatic aberration.

  FIG. 4 is a graph showing an average [°] incident angle with respect to a distance y from the optical axis of a light beam incident on the diffractive optical surface D of the eyepiece optical system 3 according to the first embodiment. In the eyepiece optical system 3 according to the first example, it can be seen that the incident angle with respect to the diffractive optical surface D is smaller than 10 °. Thereby, generation | occurrence | production of the flare in the diffractive optical surface D can be suppressed.

[Second Embodiment]
FIG. 5 shows an eyepiece optical system 3 according to the second example. The eyepiece optical system 3 includes, in order from the observation eye side, a first lens group G1, a second lens group G2, and a third lens group G3. The first lens group G1 includes a positive meniscus lens L11 having a convex surface directed toward the object side. The second lens group G2 has, in order from the observation eye side, a parallel flat optical glass (optical member) L21, two diffraction element elements L22 and L23 formed from different resins, and a convex surface on the object side. The diffractive optical element (adherent multilayer diffractive optical element) in which the directed plano-convex lens (optical member) L24 is joined in this order and a diffraction grating groove (diffractive optical surface D) is formed on the joint surface of the diffractive element elements L22 and L23. Element) GD. The third lens group G3 includes a cemented lens CL in which a biconvex lens (positive lens) L31 and a negative meniscus lens (negative lens) L32 having a convex surface directed toward the object side are cemented in order from the observation eye side.

  Table 2 shows the specifications of the eyepiece optical system 3 according to the second example. The surface numbers 1 to 10 in Table 2 correspond to the numbers 1 to 10 shown in FIG.

(Table 2)
Overall specifications f = 20.35
ER = 18.1

Lens data m r d nd νd
1 -50.000 3.00 1.620410 60.25
2 -30.325 0.20
3 0.000 1.00 1.516800 63.88
4 0.000 0.10 1.557100 50.17
5 * 0.000 0.10 1.527800 34.71
6 0.000 5.00 1.620410 60.25
7 -29.941 0.20
8 60.320 6.90 1.696800 55.52
9 -19.774 1.50 1.805180 25.45
10 -52.063 15.84

Phase data 5th surface C2 = -6.5000E-04 C4 = 2.2000E-06 C6 = 0 C8 = 0 C10 = 0

Conditional expression corresponding value fdoe = 769.23
r = -19.774
fbase = 48.26
BF = 121.81
(1) νp = 55.52
(2) | fdoe / r | = 38.90
(3) | (1 / fbase + 1 / fdoe) / (1 / f) | = 0.45
(4) | BF / ER | = 6.73

  In Table 2, νp in conditional expression (1) indicates the Abbe number of the medium (eighth surface) of the biconvex lens L31, and the curvature radius r in conditional expression (2) indicates the value of the ninth surface. . Thus, it can be seen that the eyepiece optical system 3 according to the second example satisfies all the conditional expressions (1) to (4).

  FIG. 6 is a diagram showing various aberrations of spherical aberration, astigmatism, distortion, and lateral chromatic aberration with respect to C-line, d-line, F-line, and g-line rays in the second embodiment. Thus, it can be seen that the eyepiece optical system 3 according to the second example is well corrected for various aberrations such as lateral chromatic aberration. FIG. 7 shows a graph of the average (°) incident angle with respect to the distance y from the optical axis of the light beam incident on the diffractive optical surface D of the eyepiece optical system 3 according to the second embodiment. In the eyepiece optical system 3 according to the second example, it can be seen that the incident angle with respect to the diffractive optical surface D is smaller than 12 °. Thereby, generation | occurrence | production of the flare in the diffractive optical surface D can be suppressed.

[Third embodiment]
FIG. 8 shows an eyepiece optical system 3 according to the third example. The eyepiece optical system 3 includes, in order from the observation eye side, a first lens group G1, a second lens group G2, and a third lens group G3. The first lens group G1 includes, in order from the observation eye side, a positive meniscus lens L11 having a convex surface facing the object side, and a positive meniscus lens L12 having a convex surface facing the object side. The second lens group G2 includes, in order from the observation eye side, a parallel plate optical glass (optical member) L21, two diffraction element elements L22 and L23 formed from different resins, and a parallel plate optical glass. (Optical member) L24 is joined in this order, and a diffractive optical element (contact multi-layer diffractive optical element) GD in which a diffraction grating groove (diffractive optical surface D) is formed on the joint surface of the diffractive element elements L22 and L23. Composed. The third lens group G3 includes a cemented lens CL in which a biconvex lens (positive lens) L31 and a biconcave lens (negative lens) L32 are cemented in order from the observation eye side.

  Table 3 shows the specifications of the eyepiece optical system 3 according to the third example. The surface numbers 1 to 12 in Table 3 correspond to the numbers 1 to 12 shown in FIG.

(Table 3)
Overall specifications f = 16.24
ER = 16.1

Lens data m r d nd νd
1 -60.000 3.70 1.620410 60.25
2 -21.149 0.20
3 -81.915 4.00 1.620410 60.25
4 -21.368 0.20
5 0.000 2.00 1.516800 63.88
6 0.000 0.05 1.557100 50.17
7 * 0.000 0.05 1.527800 34.71
8 0.000 2.00 1.516800 63.88
9 0.000 0.20
10 23.631 10.00 1.713000 53.96
11 -16.349 1.50 1.805180 25.45
12 89.893 6.69

Phase 7 surface C2 = -6.2326E-04 C4 = 2.0614E-06 C6 = 0 C8 = 0 C10 = 0

Conditional expression corresponding value fdoe = 802.23
r = -16.349
fbase = 0
BF = 29.18
(1) νp = 53.96
(2) | fdoe / r | = 49.07
(3) | (1 / fbase + 1 / fdoe) / (1 / f) | = 0.02
(4) | BF / ER | = 1.81

  In Table 3, νp in conditional expression (1) indicates the Abbe number of the medium (tenth surface) of the biconvex lens L31, and the radius of curvature r in conditional expression (2) indicates the value on the eleventh surface. . Thus, it can be seen that the eyepiece optical system 3 according to the third example satisfies all the conditional expressions (1) to (4).

  FIG. 9 is a diagram showing various aberrations of spherical aberration, astigmatism, distortion, and lateral chromatic aberration with respect to C-line, d-line, F-line, and g-line rays in the third embodiment. Thus, it can be seen that the eyepiece optical system 3 according to the third example is well corrected for various aberrations such as lateral chromatic aberration. FIG. 10 is a graph showing the average (°) incident angle with respect to the distance y from the optical axis of the light beam incident on the diffractive optical surface D of the eyepiece optical system 3 according to the third embodiment. In the eyepiece optical system 3 according to the third example, it can be seen that the incident angle with respect to the diffractive optical surface D is smaller than 2 °. Thereby, generation | occurrence | production of the flare in the diffractive optical surface D can be suppressed.

[Fourth embodiment]
FIG. 11 shows an eyepiece optical system 3 according to the fourth example. The eyepiece optical system 3 includes, in order from the observation eye side, a first lens group G1, a second lens group G2, and a third lens group G3. The first lens group G1 includes a biconvex lens L11. The second lens group G2 includes, in order from the observation eye side, a parallel plate optical glass (optical member) L21, two diffraction element elements L22 and L23 formed from different resins, and a parallel plate optical glass. (Optical member) L24 is joined in this order, and a diffractive optical element (contact multi-layer diffractive optical element) GD in which a diffraction grating groove (diffractive optical surface D) is formed on the joint surface of the diffractive element elements L22 and L23. Composed. The third lens group G3 includes a cemented lens CL in which a biconvex lens (positive lens) L31 and a biconcave lens (negative lens) L32 are cemented in order from the observation eye side.

  Table 4 shows the specifications of the eyepiece optical system 3 according to the fourth example. The surface numbers 1 to 10 in Table 4 correspond to the numbers 1 to 10 shown in FIG.

(Table 4)
Overall specifications f = 20.07
ER = 21.0

Lens data m r d nd νd
1 191.237 5.40 1.620410 60.25
2 -21.898 0.20
3 0.000 2.00 1.516800 63.88
4 0.000 0.05 1.557100 50.17
5 * 0.000 0.05 1.527800 34.71
6 0.000 2.00 1.516800 63.88
7 0.000 0.20
8 19.164 10.00 1.620410 60.25
9 -26.070 1.50 1.805180 25.45
10 47.866 9.30

Phase data 5th surface C2 = -6.2326E-04 C4 = 2.0614E-06 C6 = 0 C8 = 0 C10 = 0

Conditional expression corresponding value fdoe = 802.23
r = -26.070
fbase = 0
BF = 35.0
(1) νp = 60.25
(2) | fdoe / r | = 30.77
(3) | (1 / fbase + 1 / fdoe) / (1 / f) | = 0.03
(4) | BF / ER | = 1.67

  In Table 4, νp in the conditional expression (1) indicates the Abbe number of the medium (eighth surface) of the biconvex lens L31, and the curvature radius r in the conditional expression (2) indicates the value of the ninth surface. . Thus, it can be seen that the eyepiece optical system 3 according to the fourth example satisfies all the conditional expressions (1) to (4).

  FIG. 12 shows various aberration diagrams of spherical aberration, astigmatism, distortion, and lateral chromatic aberration with respect to the C-line, d-line, F-line, and g-line rays in the fourth embodiment. Thus, it can be seen that the eyepiece optical system 3 according to the fourth example is well corrected for various aberrations such as lateral chromatic aberration. FIG. 13 is a graph showing the average (°) incident angle with respect to the distance y from the optical axis of the light beam incident on the diffractive optical surface D of the eyepiece optical system 3 according to the fourth embodiment. In the eyepiece optical system 3 according to the fourth example, it can be seen that the incident angle with respect to the diffractive optical surface D is smaller than 2.5 °. Thereby, generation | occurrence | production of the flare in the diffractive optical surface D can be suppressed.

[Fifth embodiment]
FIG. 14 shows an eyepiece optical system 3 according to the fifth example. The eyepiece optical system 3 includes, in order from the observation eye side, a first lens group G1, a second lens group G2, and a third lens group G3. The first lens group G1 includes, in order from the observation eye side, a positive meniscus lens L11 having a convex surface facing the object side, and a cemented lens in which a biconvex lens L12 and a plano-concave lens L13 having a concave surface facing the observation eye side are cemented. Is done. The second lens group G2 includes, in order from the observation eye side, a parallel plate optical glass (optical member) L21, two diffraction element elements L22 and L23 formed from different resins, and a parallel plate optical glass. (Optical member) L24 is joined in this order, and a diffractive optical element (contact multi-layer diffractive optical element) GD in which a diffraction grating groove (diffractive optical surface D) is formed on the joint surface of the diffractive element elements L22 and L23. Composed. The third lens group G3 includes a cemented lens CL in which a biconvex lens (positive lens) L31 and a biconcave lens (negative lens) L32 are cemented in order from the observation eye side.

  Table 5 shows the specifications of the eyepiece optical system 3 according to the fifth example. The surface numbers 1 to 13 in Table 5 correspond to the numbers 1 to 13 shown in FIG.

(Table 5)
Overall specifications f = 16.24
ER = 15.0

Lens data m r d nd νd
1 -50.000 5.00 1.620410 60.25
2 -15.274 0.20
3 50.375 5.00 1.713000 53.96
4 -56.852 1.50 1.805180 25.45
5 0.000 0.20
6 0.000 2.00 1.516800 63.88
7 0.000 0.05 1.557100 50.17
8 * 0.000 0.05 1.527800 34.71
9 0.000 2.00 1.516800 63.88
10 0.000 0.20
11 22.849 9.00 1.713000 53.96
12 -18.329 1.50 1.805180 25.45
13 80.000 5.28

Phase data 8th surface C2 = -6.2326E-04 C4 = 2.0614E-06 C6 = 0 C8 = 0 C10 = 0

Conditional expression corresponding value fdoe = 802.23
r = -18.329
fbase = 0
BF = 27.08
(1) νp = 53.96
(2) | fdoe / r | = 43.77
(3) | (1 / fbase + 1 / fdoe) / (1 / f) | = 0.02
(4) | BF / ER | = 1.81

  In Table 5, νp in conditional expression (1) indicates the Abbe number of the medium (11th surface) of the biconvex lens L31, and the radius of curvature r in conditional expression (2) indicates the value of the 12th surface. . Thus, it can be seen that the eyepiece optical system 3 according to the fifth example satisfies all the conditional expressions (1) to (4).

  FIG. 15 is a diagram showing various aberrations of spherical aberration, astigmatism, distortion, and lateral chromatic aberration with respect to C-line, d-line, F-line, and g-line rays in the fifth embodiment. Thus, it can be seen that in the eyepiece optical system 3 according to the fifth example, various aberrations such as lateral chromatic aberration are well corrected. FIG. 16 is a graph showing the average (°) incident angle with respect to the distance y from the optical axis of the light beam incident on the diffractive optical surface D of the eyepiece optical system 3 according to the fifth example. In the eyepiece optical system 3 according to the fifth example, it can be seen that the incident angle with respect to the diffractive optical surface D is smaller than 3 °. Thereby, generation | occurrence | production of the flare in the diffractive optical surface D can be suppressed.

TS telescope optical system (optical device) 3 eyepiece optical system G1 first lens group G2 second lens group GD diffractive optical element L21, L24 optical glass (optical member) L22, L23 diffractive element element D diffractive optical surface G3 third lens group CL Joint lens L31 Positive lens L32 Negative lens CP Joint surface EP Eye point (observation eye)

Claims (6)

From the observation eye side,
A first lens group having a lens having a positive refractive power;
It consists of two diffractive element elements and two optical members bonded to one surface of each of the two diffractive element elements, and forms a diffraction grating groove on the other surface of the two diffractive element elements to face each other. A second lens group having a diffractive optical element having a diffractive optical surface arranged in a row;
A positive lens and a negative lens are cemented, and a third lens group having a cemented lens having a positive refractive power as a whole,
An eyepiece optical system, wherein at least one of the optical members of the diffractive optical element is a parallel plate. When the Abbe number of the medium of the positive lens constituting the cemented lens is νp, the radius of curvature of the cemented surface of the cemented lens is r, and the focal length of the diffractive optical surface is fdoe, the following formula νp <70
| Fdoe / r | <50
The eyepiece optical system according to claim 1, wherein the following condition is satisfied. When the focal length of the entire system is f, the focal length of the diffractive optical surface is fdoe, and the focal length when the two optical members constituting the diffractive optical element are joined is fbase, the following expression | (1 /Fbase+1/fdoe)/(1/f)|<1.0
The eyepiece optical system according to claim 1, wherein the following condition is satisfied. When the eye relief is ER and the distance on the optical axis from the lens surface closest to the observation eye to the focal plane on the observation eye side of the first lens group is BF, the following expression | BF / ER | <10
The eyepiece optical system according to any one of claims 1 to 3, wherein the following condition is satisfied.   The eyepiece optical system according to any one of claims 1 to 4, wherein the two diffractive element elements of the diffractive optical element are joined with the diffraction grating grooves being in close contact with each other.   An optical apparatus comprising the eyepiece optical system according to claim 1.

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