JP6800611B2 - Observation optical system and observation equipment having it - Google Patents

Description

The present invention relates to an observation optical system suitable for a head-mounted display or the like for observing an original image displayed on an image display element such as a liquid crystal.

In an observation device such as a head-mounted display, the observation optical system used in the observation device is required to have a wide viewing angle and high optical performance. Further, it is required to reduce the weight of the entire device. Patent Document 1 discloses an observation optical system in which a Fresnel lens having a serrated concave surface facing the observation side is arranged at a position closest to the eye.

Japanese Unexamined Patent Publication No. 7-244246

Since the observation optical system of Patent Document 1 uses only one Fresnel lens, it is difficult to obtain high optical performance. In order to obtain an observation optical system that has a wide field of view, high optical performance, and is lightweight as a whole, it is necessary to appropriately set the number, arrangement, and shape of Fresnel lenses.

An object of the present invention is to provide an observation optical system having a wide field of view, high optical performance, a small observation optical system, and an observation device having the same.

The observation optical system as one aspect of the present invention is an observation optical system for observing an image displayed on an image display surface, and is a positive lens arranged in order from the observation surface side to the image display surface side. 1 Fresnel lens, a second Fresnel lens, the first Fresnel lens and the second Fresnel lens, each image display surface side is Fureneruren's of positive refractive power is a Fresnel surface, the focal point of the first Fresnel lens When the distance is f1 and the focal distance of the observation optical system is f, the condition equation of 1.5 <f1 / f <5.0 is satisfied.
Further, the observation optical system as another aspect of the present invention is an observation optical system for observing an image displayed on the image display surface, and is arranged in order from the observation surface side to the image display surface side. It has a lens, a first Fresnel lens, and a second Fresnel lens. The first Fresnel lens is a Fresnel lens having a negative refractive force whose observation surface side is a Fresnel surface, and the second Fresnel lens has a Fresnel surface on the image display surface side. This is a Fresnel lens having a positive refractive power, and when the focal distance of the first Fresnel lens is f1 and the focal distance of the observation optical system is f, 1.5 << f1 | / f <5.0. It is characterized by satisfying a conditional expression.
Further, the observation optical system as another aspect of the present invention is an observation optical system for observing an image displayed on the image display surface, and is arranged in order from the observation surface side to the image display surface side. It has a lens, a first Fresnel lens, a second Fresnel lens, and a third Fresnel lens, and each of the first Fresnel lens and the third Fresnel lens is a Fresnel lens having a positive refractive force whose image display surface side is a Fresnel surface. The second Fresnel lens is a Fresnel lens having a negative refractive force whose observation surface side is a Fresnel surface, and when the focal distance of the first Fresnel lens is f1 and the focal distance of the observation optical system is f, 1. It is characterized in that it satisfies the conditional expression of 5 <f1 / f <5.0.
Further, the observation optical system as another aspect of the present invention is an observation optical system for observing an image displayed on the image display surface, and is arranged in order from the observation surface side to the image display surface side. It has a lens, a first Fresnel lens, and a second Fresnel lens. The first Fresnel lens is a Fresnel lens having a positive refractive force whose image display surface side is a Fresnel surface, and the second Fresnel lens has a Fresnel surface on the observation surface side. This is a Fresnel lens having a negative refractive power, and when the focal distance of the second Fresnel lens is f2 and the focal distance of the observation optical system is f, 1.5 << f2 | / f <5.0. It is characterized by satisfying a conditional expression.

According to the present invention, it is possible to obtain a small observation optical system and an observation device having the same, which have high optical performance while having a wide field of view.

Cross-sectional view of the lens of Example 1 of the present invention (A), (B) Longitudinal aberration diagram at eye relief 10 mm and eye relief 20 mm according to Example 1 of the present invention. Cross-sectional view of the lens of Example 2 of the present invention (A), (B) Longitudinal aberration diagram at eye relief 10 mm and eye relief 20 mm according to Example 2 of the present invention. Cross-sectional view of the lens of Example 3 of the present invention (A), (B) Longitudinal aberration diagram at eye relief 10 mm and eye relief 20 mm according to Example 3 of the present invention. Cross-sectional view of the lens of Example 4 of the present invention (A), (B) Longitudinal aberration diagram at eye relief 10 mm and eye relief 20 mm according to Example 4 of the present invention. Cross-sectional view of the lens of Example 5 of the present invention (A), (B) Longitudinal aberration diagram at eye relief 10 mm and eye relief 20 mm according to Example 5 of the present invention. (A), (B) Optical path diagram when the observation side surface is given a finite curvature and the optical path diagram when the image display side surface is given a finite curvature in two lenses with positive refractive power. (A), (B) An optical path diagram and a negative refractive power when a finite curvature is applied to the image display side surface of the negative refractive power lens in each of the positive and negative refractive power lenses. Optical path diagram when the observation side surface of the lens is given a finite curvature (A), (B), (C) Explanatory drawing of Fresnel lens according to the present invention

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The observation optical system of the present invention is an observation optical system for observing an image displayed on an image display surface, and the observation optical system is a first Fresnel lens and a second Fresnel lens in order from the observation surface side to the image display surface side. It has a Fresnel lens. When the Fresnel lens included in the observation optical system has a positive refractive power, the image display surface side of the Fresnel lens has a Fresnel shape. When the Fresnel lens included in the observation optical system has a negative refractive power, the observation surface side of the Fresnel lens has a Fresnel shape.

FIG. 1 is a cross-sectional view of a lens of an observation device having an observation optical system according to a first embodiment of the present invention. 2 (A) and 2 (B) are longitudinal aberration diagrams of the observation optical system of Example 1 of the present invention at an eye relief of 10 mm and an eye relief of 20 mm. FIG. 3 is a cross-sectional view of a lens of an observation device having an observation optical system according to a second embodiment of the present invention. 4 (A) and 4 (B) are longitudinal aberration diagrams of the observation optical system of the second embodiment of the present invention at an eye relief of 10 mm and an eye relief of 20 mm.

FIG. 5 is a cross-sectional view of a lens of an observation device having an observation optical system according to a third embodiment of the present invention. 6 (A) and 6 (B) are longitudinal aberration diagrams of the observation optical system of the third embodiment of the present invention at an eye relief of 10 mm and an eye relief of 20 mm. FIG. 7 is a cross-sectional view of a lens of an observation device having an observation optical system according to a fourth embodiment of the present invention. 8 (A) and 8 (B) are longitudinal aberration diagrams of the observation optical system of the fourth embodiment of the present invention at an eye relief of 10 mm and an eye relief of 20 mm.

FIG. 9 is a cross-sectional view of a lens of an observation device having an observation optical system according to a fifth embodiment of the present invention. 10 (A) and 10 (B) are longitudinal aberration diagrams of the observation optical system of Example 5 of the present invention at an eye relief of 10 mm and an eye relief of 20 mm. 11 (A) and 11 (B) show an optical path diagram and an image display when the Fresnel lens assembly according to the present invention is provided with a finite curvature on the surface on the observation surface side in two lenses having a positive refractive power. It is an optical path diagram when a finite curvature is given to the surface on the surface side.

FIG. 12A shows a Fresnel lens assembly according to the present invention having a finite curvature on the surface of the negative refractive power on the image display surface side in each of the positive refractive power lens and the negative refractive power lens. It is an optical path diagram when it is attached. FIG. 12B is an optical path diagram when a finite curvature is applied to the surface of the lens having a negative refractive power on the observation surface side. 13 (A), (B), and (C) are explanatory views of a Fresnel lens according to the present invention.

In the lens cross-sectional view, L0 is an observation optical system, and has a lens (positive lens) LP having a positive refractive power and a Fresnel lens aggregate FL. Here, the lens LP is a curved surface having a curved lens surface, and is a lens that refracts on the curved surface, and does not include a Fresnel lens. The ID is an image display surface, and for example, a liquid crystal display element ID1 is arranged. The SP is an observation surface, and the observer's pupil is located. A diaphragm SP1 may be arranged on the observation surface SP.

In the lens cross-sectional view of each embodiment, the eye relief represents the distance between the eye point and the lens surface on the most observed side on the optical axis. Regarding the evaluation of aberrations, the aberrations on the observation surface side where the light rays are blown from the image display surface and the aberrations on the image display surface when the light rays are blown from the observation surface side have a one-to-one correspondence. Aberrations on the display surface are evaluated. Further, the aperture diaphragm diameter of each embodiment is set to 3.5 mm as an example of the human pupil diameter.

By having a plurality of Fresnel lenses, the Fresnel lens assembly FL according to the present invention has obtained high optical performance while maintaining the weight reduction of the entire system.

In the present invention, the Fresnel lens assembly FL constituting the observation optical system L0 has a first Fresnel lens L1 and a second Fresnel lens L2 in order from the observation surface SP side to the image display surface ID side. When the Fresnel lens has a positive refractive power, the image display surface ID side of the Fresnel lens has a Fresnel shape. When the Fresnel lens has a negative refractive power, the observation surface SP side of the Fresnel lens has a Fresnel shape.

In each embodiment, the Fresnel lens divides the lens surface having a radius of curvature r into a plurality of concentric regions as shown in FIG. 13 (A). At this time, the cross-sectional shape is a shape in which only the saw-toothed Fresnel lattice (prism) FP is concentrically arranged on a plane according to the value of the radius of curvature r. Multiple concentric Fresnel grids have different or identical angles. Also, the lattice pitch of the Fresnel lattice differs or is the same from the center (optical axis) to the periphery.

In the numerical data described later, the radius of curvature r of the Fresnel lens surface Fre corresponds to the radius of curvature r of the lens surface shown in FIG. 13 (A). One of the parameters when determining the focal length of the Fresnel lens surface is the radius of curvature r, which is the same as when determining the focal length of a normal lens. The focal length f, plate thickness (center thickness), effective dimensions (effective diameter) W, V, etc. of the Fresnel lens are as shown in FIGS. 13 (B) and 13 (C). For the radius of curvature of the Fresnel lens surface in the conditional expression described later, the radius of curvature r of the lens surface before the Fresnel shape is used.

Next, as an example, the optical characteristics when the Fresnel aggregate FL is composed of two Fresnel lenses, the first Fresnel lens L1 has a positive refractive power, and the second Fresnel lens L2 has a positive refractive power will be described. To do. Here, both the first Fresnel lens L1 having a positive refractive power and the second Fresnel lens L2 having a positive refractive power have a Fresnel shape on the image display surface ID side. The technical contents will be described with reference to FIG.

The optical system of FIG. 11 shows a case where two ordinary lenses having a flat side are arranged for convenience of explanation. FIG. 11 (A) shows a case where a finite curvature is applied to the observation surface SP side, and the shape is such that the convex surface is directed to the observation surface SP side. It becomes too incident and many high-order aberrations occur. Mainly astigmatism and curvature of field increase.

FIG. 11B shows a case where a finite curvature is applied to the image display surface ID side, the convex surface is directed to the image display surface ID side, and the light beam is gently incident on the curvature. Therefore, astigmatism and curvature of field can be reduced. That is, higher optical performance can be obtained by arranging a surface having a strong curvature on the image display surface ID side. For convenience, one side is flattened, but the surface having a large curvature is on the image display surface ID side. Therefore, by making the surface on the image display surface ID side a Fresnel shape, the weight becomes lighter.

Next, as an example, the optical characteristics when the Fresnel lens assembly FL is composed of two Fresnel lenses, the first Fresnel lens L1 has a positive refractive power, and the second Fresnel lens L2 has a negative refractive power. Will be described. Here, the negative refractive power second Fresnel lens L2 has a Fresnel shape on the observation surface SP side, and the positive refractive power first Fresnel lens L1 has a Fresnel shape on the image display surface ID side. .. The reason why the image display surface ID side of the first Fresnel lens L1 having a positive refractive power has a Fresnel shape is the same as described above.

The technical contents of the Fresnel shape of the second Fresnel lens L2 having a negative refractive power as the surface on the observation surface SP side will be described with reference to FIGS. 12 (A) and 12 (B). In the optical systems of FIGS. 12A and 12B, two ordinary lenses having a flat side are arranged for convenience of explanation.

FIG. 12A shows a case where the surface of the second Fresnel lens L2 having a negative refractive power on the image display surface ID side is provided with a finite curvature, and the concave surface is directed toward the image display surface ID side. In the case of a wide field of view, the light beam is obliquely incident with respect to the curvature, and many high-order aberrations occur. Mainly astigmatism and curvature of field increase.

FIG. 12B shows a case where the surface of the second Fresnel lens L2 having a negative refractive power on the observation surface ID side has a finite curvature, and the concave surface faces the observation surface SP side. On the other hand, the light beam is gently incident. Therefore, astigmatism and curvature of field can be mainly reduced. That is, higher optical performance can be obtained by arranging a surface having a strong curvature on the observation surface SP.

For convenience, one side is flattened, but the surface with a large curvature of the second Fresnel lens L2 with negative refractive power is on the observation surface SP side, so by making the surface on the observation surface SP side a Fresnel shape, it becomes lighter. Become.

With the above configuration, a wide field of view, high optical performance, and a lightweight observation optical system have been achieved.

The optical characteristics when the Fresnel lens assembly FL is composed of two Fresnel lenses, the first Fresnel lens L1 has a negative refractive power, and the second Fresnel lens L2 has a positive refractive power are also described above. The same is true. Further, the Fresnel lens assembly FL is composed of three Fresnel lenses, the first Fresnel lens L1 has a positive refractive power, the second Fresnel lens L2 has a negative refractive power, and the third Fresnel lens L3 The optical characteristics when having a positive refractive power are the same as those described above.

Next, an observation device having an observation optical system L0 and an observation optical system L0 of each embodiment will be described. The observation optical system L0 of the first embodiment has a positive refractive power lens (positive lens LP), a first Fresnel lens L1, and a second Fresnel lens L2 in this order from the observation surface SP side. The observation optical system L0 of the second embodiment has a first Fresnel lens L1 and a second Fresnel lens L2 in this order from the observation surface SP side. At this time, it is preferable to satisfy one or more of the following conditional expressions.

The first Fresnel lens L1 has a positive refractive power, and the second Fresnel lens L2 has a positive refractive power. Let f1 be the focal length of the first Fresnel lens L1 and f be the focal length of the observation optical system L0. Let the focal length of the second Fresnel lens L2 be f2. Let R11 be the radius of curvature of the surface of the first Fresnel lens L1 on the observation surface SP side. Let R12 be the radius of curvature of the surface of the first Fresnel lens L1 on the IP side of the image display surface. Let R21 be the radius of curvature of the surface of the second Fresnel lens L2 on the observation surface side. Let R22 be the radius of curvature of the surface of the second Fresnel lens L2 on the image display surface side.

The observation device having the observation optical system L0 of Examples 1 and 2 has an image display element. The image of the image display element magnified by the observation optical system L0 is observed from the observation surface SP side via the observation optical system L0. At this time, let d be the distance from the surface apex of the first Fresnel lens L1 on the image display surface ID side to the principal point of the second Fresnel lens L2 on the observation surface SP side. Let L be the distance from the surface apex on the observation surface SP side of the lens (the positive lens LP in Example 1 and the first Fresnel lens L1 in Example 2) arranged closest to the observation surface SP side to the image display surface ID.

The center thickness of the first Fresnel lens L1 is d1, and the center thickness of the second Fresnel lens L2 is d2. Let y be the real image height of the image display surface ID at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm, and y0 be an ideal image height of the image display surface ID at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm. At this time, it is preferable to satisfy one or more of the following conditional expressions.

1.5 <f1 / f <5.0 ... (1X)
1.0 <f2 / f <6.0 ... (2X)
-1.4 <(R12 + R11) / (R12-R11) <-0.6 ... (3X)
-1.5 <(R22 + R21) / (R22-R21) <-0.5 ... (4X)
0.005 <d / L <0.200 ... (5X)
0.01 <(d1 + d2) / L <0.10 ... (6X)
-0.3 <(y-y0) / y0 <-0.1 ... (7X)

More preferably, the numerical range of the conditional expressions (1X) to (7X) is set as follows.
1.8 <f1 / f <4.7 ... (1Xa)
1.5 <f2 / f <5.8 ... (2Xa)
-1.3 <(R12 + R11) / (R12-R11) <-0.7 ... (3Xa)
-1.4 <(R22 + R21) / (R22-R21) <-0.7 ... (4Xa)
0.02 <d / L <0.15 ... (5Xa)
0.02 <(d1 + d2) / L <0.08 ... (6Xa)
-0.26 <(y-y0) / y0 <-0.12 ... (7Xa)

More preferably, the numerical range of the conditional expressions (1Xa) to (7Xa) is set as follows.
2.0 <f1 / f <4.4 ... (1Xb)
1.7 <f2 / f <5.6 ... (2Xb)
-1.2 <(R12 + R11) / (R12-R11) <-0.8 ... (3Xb)
-1.3 <(R22 + R21) / (R22-R21) <-0.8 ... (4Xb)
0.04 <d / L <0.08 ... (5Xb)
0.03 <(d1 + d2) / L <0.07 ... (6Xb)
-0.25 <(y-y0) / y0 <-0.15 ... (7Xb)

Next, the technical meaning of each of the above conditional expressions will be described.
The conditional expression (1X) defines the ratio of the focal length of the first Fresnel lens L1 to the focal length of the entire system. When the lower limit of the conditional expression (1X) is exceeded, the refractive power of the first Fresnel lens L1 becomes too strong, and curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, when the number of lenses of the other constituent lenses is small, the refractive power of each lens becomes too strong and various aberrations increase. On the contrary, when the number of lenses of the other lenses configured is large, the weight increases.

The conditional expression (2X) defines the ratio of the focal length of the second Fresnel lens L2 to the focal length of the entire system. When the lower limit of the conditional expression (2X) is exceeded, the refractive power of the second Fresnel lens L2 becomes too strong, and curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, when the number of lenses of the other constituent lenses is small, the refractive power of each lens becomes too strong and various aberrations increase. On the contrary, when the number of lenses of the other lenses configured is large, the weight of the entire system increases.

The conditional expression (3X) defines the shape factor of the first Fresnel lens L1. When the lower limit of the conditional expression (3X) is exceeded, the curvature of the surface of the first Fresnel lens L1 on the image display surface ID side becomes too strong, and the curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, the curvature of the surface of the first Fresnel lens L1 on the observation surface SP side becomes too strong, and the curvature of field and astigmatism mainly increase.

The conditional expression (4X) defines the shape factor of the second Fresnel lens L2. When the lower limit of the conditional expression (4X) is exceeded, the curvature of the surface of the second Fresnel lens L2 on the image display surface ID side becomes too strong, and the curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, the curvature of the surface of the second Fresnel lens L2 on the observation surface SP side becomes too strong, and the curvature of field and astigmatism mainly increase.

The conditional expression (5X) relates to the position of the second Fresnel lens L2 on the optical axis. By moving the front principal point position of the second Fresnel lens L2 closer to the first Fresnel lens L1 adjacent to the observation surface SP side within an appropriate range so as to satisfy the conditional expression (5X), the incident height of the axial light beam is increased. The second Fresnel lens L2 is arranged at a high position. As a result, the contribution to the focal length of the entire system is increased, the refractive power of the second Fresnel lens L2 can be substantially relaxed, and astigmatism and curvature of field are mainly reduced.

If the lower limit of the conditional expression (5X) is exceeded, the total length of the lens becomes too long and the image display surface ID becomes large, so that the weight of the entire system increases. On the contrary, if the upper limit is exceeded, the refractive power of the second Fresnel lens L2 is too strong, and the occurrence of curvature of field and astigmatism mainly increases.

The conditional expression (6X) relates to the sum of the center thickness of the first Fresnel lens L1 and the center thickness of the second Fresnel lens L2. When the lower limit of the conditional expression (6X) is exceeded, the thickness of one or both of the center thickness of the first Fresnel lens L1 and the center thickness of the second Fresnel lens L2 becomes too thin, and the shape of the Fresnel lens is easily deformed. The optical performance will decrease. On the contrary, when the upper limit is exceeded, the thickness of one or both of the center thickness of the first Fresnel lens L1 and the center thickness of the second Fresnel lens L2 becomes too thick, and the weight of the Fresnel lens assembly FL increases.

The conditional expression (7X) defines the amount of distortion of the observation optical system L0 at an eye relief of 10 mm and a half viewing angle of 45 degrees. If the lower limit of the conditional expression (7X) is exceeded, the positive refractive power is too strong, so that the peripheral light rays are strongly bent in the optical axis direction, and curvature of field and astigmatism mainly increase. On the other hand, if the upper limit is exceeded, the positive refractive power is too small, so that the incident height of the peripheral light rays at each lens position increases and the effective diameter increases, so that the weight of the Fresnel lens assembly FL increases.

With the above configuration, an observation optical system having a wide field of view, high optical performance, and light weight can be obtained.

[Example 1]
Hereinafter, the observation optical system L0 of the embodiment of the present invention will be described with reference to FIG. The observation optical system L0 of the first embodiment is composed of a positive lens LP, a first Fresnel lens L1 having a positive refractive power, and a second Fresnel lens L2 having a positive refractive power in order from the observation surface SP side.

The positive lens LP is a refracting lens having an aspherical lens surface, and mainly corrects spherical aberration. By arranging the positive lens LP at a position where the incident height of the peripheral light rays is low, an increase in weight is prevented. The Fresnel surface Fre1 of the first Fresnel lens L1 having a positive refractive power and the Fresnel surface Fre2 of the second Fresnel lens L2 having a positive refractive power are set as the image display surface ID side. By converting the Fresnel surface Fre1 and Fresnel surface Fre2 into a spherical surface (the same applies hereinafter), the shape is such that the convexity is directed toward the image display surface ID side, thereby suppressing the angle of incidence of light rays on the Fresnel surface, mainly. It suppresses curvature of field and astigmatism.

The front principal point position of the second Fresnel lens L2 is brought closer to the first Fresnel lens L1 adjacent to the observation surface SP side in an appropriate range within an appropriate range satisfying the conditional expression (5X). As a result, the second Fresnel lens L2 is arranged at a high position of the axial light beam, and as a result, the refractive power of the second Fresnel lens L2 is substantially relaxed, and the occurrence of curvature of field and astigmatism is mainly suppressed. ing.

Further, the focal length of the first Fresnel lens L1 is relaxed within an appropriate range satisfying the conditional expression (1X), and curvature of field and astigmatism are mainly suppressed. Further, the focal length of the second Fresnel lens L2 is relaxed within an appropriate range satisfying the conditional expression (2X), and curvature of field and astigmatism are mainly suppressed. Further, the first Fresnel lens L1 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (3X), and is strengthened within an appropriate range to mainly suppress the occurrence of curvature of field and astigmatism. There is.

Further, the second Fresnel lens L2 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (4X), and is strengthened in an appropriate range to mainly suppress curvature of field and astigmatism. Further, the thickness of the first Fresnel lens L1 and the second Fresnel lens L2 is reduced in an appropriate range satisfying the conditional expression (6X) to reduce the weight. Furthermore, by appropriately setting the amount of distortion at an eye relief of 10 mm and a half-viewing angle of 45 degrees so as to satisfy the conditional expression (7X), strong bounce of peripheral rays is suppressed, and mainly curvature of field and astigmatism are suppressed. The occurrence of aberration is suppressed.

[Example 2]
Hereinafter, the observation optical system L0 according to the second embodiment of the present invention will be described with reference to FIG. The observation optical system L0 of the second embodiment is composed of a first Fresnel lens L1 having a positive refractive power and a second Fresnel lens L2 having a positive refractive power in order from the observation surface SP side.

The Fresnel surface Fre1 of the first Fresnel lens L1 having a positive refractive power and the Fresnel surface Fre2 of the second Fresnel lens L2 having a positive refractive power are set as the image display surface ID side. By making the Fresnel surface Fre1 and the Fresnel surface Fre2 convex toward the image display surface ID side, the angle of incidence of the light rays on the Fresnel surface is suppressed, and curvature of field and astigmatism are mainly suppressed. The technical meaning of each conditional expression is the same as that of the first embodiment.

The front principal point position of the second Fresnel lens L2 is brought closer to the first Fresnel lens L1 adjacent to the observation surface SP side in an appropriate range within an appropriate range satisfying the conditional expression (5X). As a result, the second Fresnel lens L2 is arranged at a high position of the axial light beam, and as a result, the refractive power of the second Fresnel lens L2 is substantially relaxed, and curvature of field and astigmatism are mainly suppressed. ..

Further, the focal length of the first Fresnel lens L1 is relaxed within an appropriate range satisfying the conditional expression (1X), and curvature of field and astigmatism are mainly suppressed. Further, the focal length of the second Fresnel lens L2 is relaxed within an appropriate range satisfying the conditional expression (2X), and curvature of field and astigmatism are mainly suppressed. Further, the first Fresnel lens L1 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (3X), and is strengthened in an appropriate range to mainly suppress curvature of field and astigmatism.

Further, the second Fresnel lens L2 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (4X), and is strengthened in an appropriate range to mainly suppress curvature of field and astigmatism. Further, the thickness of the first Fresnel lens L1 and the second Fresnel lens L2 is reduced in an appropriate range satisfying the conditional expression (6X) to reduce the weight. Furthermore, by appropriately setting the amount of distortion at an eye relief of 10 mm and a half-viewing angle of 45 degrees so as to satisfy the conditional expression (7X), strong bounce of peripheral rays is suppressed, and mainly curvature of field and astigmatism are suppressed. The occurrence of aberration is suppressed.

Next, the observation optical system L0 of Example 3 has a positive lens LP, a first Fresnel lens L1, a second Fresnel lens L2, and a third Fresnel lens L3 in order from the observation surface SP side. At this time, it is preferable to satisfy one or more of the following conditional expressions.

The first Fresnel lens L1 has a positive refractive power, the second Fresnel lens L2 has a negative refractive power, and the third Fresnel lens L3 has a positive refractive power. Let f1 be the focal length of the first Fresnel lens L1 and f be the focal length of the observation optical system L0. Let the focal length of the third Fresnel lens L3 be f3. The radius of curvature of the surface of the first Fresnel lens L1 on the observation surface SP side is R11, and the radius of curvature of the surface of the first Fresnel lens L1 on the image display surface ID side is R12. The radius of curvature of the surface of the third Fresnel lens L3 on the observation surface SP side is R31, and the radius of curvature of the surface of the third Fresnel lens L3 on the image display surface ID side is R32.

The observation device having the observation optical system L0 of the third embodiment has an image display element for displaying image information. The image information of the image display element enlarged by the observation optical system L0 is observed from the observation surface SP side via the observation optical system L0. Let d be the distance from the surface apex on the image display surface ID side of the first Fresnel lens L1 to the principal point on the observation surface SP side of the third Fresnel lens L3. Let L be the distance from the surface apex on the observation surface SP side of the lens (positive lens LP) arranged on the observation surface SP side to the image display surface ID. The center thickness of the first Fresnel lens L1 is d1, and the center thickness of the third Fresnel lens L3 is d3.

Let y be the real image height of the image display surface ID at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm, and y0 be an ideal image height of the image display surface ID at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm. At this time, it is preferable to satisfy one or more of the following conditional expressions.

1.5 <f1 / f <5.0 ... (1W)
1.0 <f3 / f <6.0 ... (2W)
-1.4 <(R12 + R11) / (R12-R11) <-0.6 ... (3W)
-1.5 <(R32 + R31) / (R32-R31) <-0.5 ... (4W)
0.005 <d / L <0.200 ... (5W)
0.01 <(d1 + d3) / L <0.10 ... (6W)
-0.3 <(y-y0) / y0 <-0.1 ... (7W)

More preferably, the numerical range of the conditional expressions (1W) to (7W) is set as follows.
1.8 <f1 / f <4.7 ... (1Wa)
1.5 <f3 / f <5.8 ... (2Wa)
-1.3 <(R12 + R11) / (R12-R11) <-0.7 ... (3Wa)
-1.4 <(R32 + R31) / (R32-R31) <-0.7 ... (4Wa)
0.02 <d / L <0.15 ... (5Wa)
0.02 <(d1 + d3) / L <0.08 ... (6Wa)
-0.26 <(y-y0) / y0 <-0.12 ... (7Wa)

More preferably, the numerical range of the conditional expressions (1 Wa) to (7 Wa) is set as follows.
2.0 <f1 / f <4.4 ... (1Wb)
1.7 <f3 / f <5.6 ... (2Wb)
-1.2 <(R12 + R11) / (R12-R11) <-0.8 ... (3Wb)
-1.3 <(R32 + R31) / (R32-R31) <-0.8 ... (4Wb)
0.04 <d / L <0.08 ... (5Wb)
0.03 <(d1 + d3) / L <0.07 ... (6Wb)
-0.25 <(y-y0) / y0 <-0.15 ... (7Wb)

Next, the technical meaning of each of the above conditional expressions will be described. The conditional expression (1W) defines the ratio of the focal length of the first Fresnel lens L1 to the focal length of the entire system. When the lower limit of the conditional expression (1W) is exceeded, the refractive power of the first Fresnel lens L1 becomes too strong, and curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, when the number of lenses of the other constituent lenses is small, the refractive power of each lens becomes too strong and various aberrations increase. On the contrary, when the number of lenses of the other lenses configured is large, the weight increases.

The conditional expression (2W) defines the ratio of the focal length of the third Fresnel lens L3 to the focal length of the entire system. When the lower limit of the conditional expression (2W) is exceeded, the refractive power of the third Fresnel lens L3 becomes too strong, and curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, when the number of lenses of the other constituent lenses is small, the refractive power of each lens becomes too strong and various aberrations increase. On the contrary, when the number of lenses of the other lenses configured is large, the weight of the entire system increases.

The conditional expression (3W) defines the shape factor of the first Fresnel lens L1. When the lower limit of the conditional expression (3W) is exceeded, the curvature of the surface of the first Fresnel lens L1 on the image display surface ID side becomes too strong, and the curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, the curvature of the surface of the first Fresnel lens L1 on the observation surface SP side becomes too strong, and the curvature of field and astigmatism mainly increase.

The conditional expression (4W) defines the shape factor of the third Fresnel lens L3. When the lower limit of the conditional expression (4W) is exceeded, the curvature of the surface of the third Fresnel lens L3 on the image display surface ID side becomes too strong, and the curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, the curvature of the surface of the third Fresnel lens L3 on the observation surface SP side becomes too strong, and the curvature of field and astigmatism mainly increase.

The conditional expression (5W) relates to the position of the third Fresnel lens L3 on the optical axis. By moving the front principal point position of the third Fresnel lens L3 closer to the first Fresnel lens L1 adjacent to the observation surface SP side within an appropriate range so as to satisfy the conditional expression (5W), the incident height of the axial light beam is increased. The third Fresnel lens L3 is arranged at a high position. As a result, the contribution to the focal length of the entire system is increased, the refractive power of the third Fresnel lens L3 can be substantially relaxed, and the occurrence of astigmatism and curvature of field is mainly reduced.

If the lower limit of the conditional expression (5W) is exceeded, the total length of the lens becomes too long and the image display surface ID becomes large, so that the weight of the entire system increases. On the contrary, if the upper limit is exceeded, the refractive power of the third Fresnel lens L3 is too strong, and curvature of field and astigmatism mainly increase.

The conditional expression (6W) relates to the sum of the center thickness of the first Fresnel lens L1 and the center thickness of the third Fresnel lens L3. When the lower limit of the conditional expression (6W) is exceeded, the thickness of one or both of the center thickness of the first Fresnel lens L1 and the center thickness of the third Fresnel lens L3 becomes too thin, and the shape of the Fresnel lens is easily deformed. The optical performance will decrease. On the contrary, when the upper limit is exceeded, the thickness of one or both of the center thickness of the first Fresnel lens L1 and the center thickness of the third Fresnel lens L3 becomes too thick, and the weight of the Fresnel lens assembly FL increases.

The conditional expression (7W) defines the amount of distortion of the observation optical system L0 at an eye relief of 10 mm and a half viewing angle of 45 degrees. If the lower limit of the conditional expression (7W) is exceeded, the positive refractive power is too strong, so that the peripheral light rays are strongly bent in the optical axis direction, and curvature of field and astigmatism mainly increase. On the other hand, if the upper limit is exceeded, the positive refractive power is too small, so that the incident height of the peripheral light rays at each lens position increases and the effective diameter increases, so that the weight of the Fresnel lens assembly FL increases.
With the above configuration, an observation optical system having a wide field of view, high optical performance, and light weight can be obtained.

[Example 3]
Hereinafter, the observation optical system L0 of the third embodiment of the present invention will be described with reference to FIG. The observation optical system L0 of the third embodiment is, in order from the observation surface SP side, a positive lens LP, a first Fresnel lens L1 having a positive refractive power, a second Fresnel lens L2 having a negative refractive power, and a third Fresnel lens having a positive refractive power. It is composed of a Fresnel lens L3.

The positive lens LP is a refracting lens having an aspherical lens surface, and mainly corrects spherical aberration. By arranging the positive lens LP at a position where the incident height of the peripheral light rays is low, an increase in weight is prevented. The Fresnel surface Fre1 of the first Fresnel lens L1 having a positive refractive power and the Fresnel surface Fre3 of the third Fresnel lens L3 are designated as image display surface IDs. By making the Fresnel surface Fre1 and Fresnel surface Fre3 convex toward the image display surface ID side, the angle of light incident on the Fresnel surface is suppressed, and the curvature of field and the occurrence of astigmatism are mainly suppressed. .. By arranging the second Fresnel lens L2 having a negative refractive power, the chromatic aberration of magnification is mainly corrected satisfactorily.

By bringing the front principal point position of the third Fresnel lens L3 closer to the first Fresnel lens L1 adjacent to the observation surface side ID in an appropriate range within an appropriate range satisfying the conditional expression (5W), the axial light beam is high. The third Fresnel lens L3 is arranged at the position. As a result, the refractive power of the third Fresnel lens L3 is substantially relaxed, and curvature of field and astigmatism are mainly suppressed.

Further, the focal length of the first Fresnel lens L1 is relaxed within an appropriate range satisfying the conditional expression (1W), and curvature of field and astigmatism are mainly suppressed. Further, the focal length of the third Fresnel lens L3 is relaxed within an appropriate range satisfying the conditional expression (2W), and curvature of field and astigmatism are mainly suppressed. Further, the first Fresnel lens L1 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (3W), and is strengthened in an appropriate range to mainly suppress curvature of field and astigmatism.

Further, the third Fresnel lens L3 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (4W), and is strengthened in an appropriate range to mainly suppress curvature of field and astigmatism. Further, the thickness of the first Fresnel lens L1 and the third Fresnel lens L3 is reduced in an appropriate range satisfying the conditional expression (6W) to reduce the weight. Furthermore, by appropriately setting the amount of distortion at an eye relief of 10 mm and a half-viewing angle of 45 degrees so as to satisfy the conditional expression (7W), strong bounce of peripheral rays is suppressed, and mainly curvature of field and astigmatism are suppressed. Aberration is suppressed.

The observation optical system L0 of the fourth embodiment has a positive lens LP, a first Fresnel lens L1, and a second Fresnel lens L2 in order from the observation surface SP side. At this time, it is preferable to satisfy one or more of the following conditional expressions.

The first Fresnel lens L1 has a negative refractive power, and the second Fresnel lens L2 has a positive refractive power. Let f1 be the focal length of the first Fresnel lens L1 and f be the focal length of the observation optical system L0. Let the focal length of the second Fresnel lens L2 be f2. The radius of curvature of the surface of the first Fresnel lens L1 on the observation surface SP side is R11, and the radius of curvature of the surface of the first Fresnel lens L1 on the image display surface ID side is R12. The radius of curvature of the surface of the second Fresnel lens L2 on the observation surface SP side is R21, and the radius of curvature of the surface of the second Fresnel lens L2 on the image display surface ID side is R22.

The observation device having the observation optical system L0 of the fourth embodiment has an image display element. The image of the image display element magnified by the observation optical system L0 is observed from the observation surface SP side via the observation optical system L0. At this time, let d be the distance from the surface apex of the first Fresnel lens L1 on the image display surface ID side to the principal point of the second Fresnel lens L2 on the observation surface SP side. Let L be the distance from the surface apex on the observation surface SP side of the lens (positive lens LP) arranged on the observation surface SP side to the image display surface ID.

The center thickness of the first Fresnel lens L1 is d1, and the center thickness of the second Fresnel lens L2 is d2. Let y be the real image height of the image display surface ID at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm, and y0 be an ideal image height of the image display surface ID at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm. At this time, it is preferable to satisfy one or more of the following conditional expressions.

1.5 << f1 | / f <5.0 ... (1Y)
3.0 <f2 / f <6.5 ... (2Y)
0.6 <(R12 + R11) / (R12-R11) <1.5 ... (3Y)
-1.5 <(R22 + R21) / (R22-R21) <-0.6 ... (4Y)
0.005 <d / L <0.200 ... (5Y)
0.01 <(d1 + d2) / L <0.15 ... (6Y)
-0.3 <(y-y0) / y0 <-0.1 ... (7Y)

More preferably, the numerical range of the conditional expressions (1Y) to (7Y) is set as follows.
2.0 << | f1 | / f <4.9 ... (1Ya)
3.4 <f2 / f <5.6 ... (2Ya)
0.7 <(R12 + R11) / (R12-R11) <1.4 ... (3Ya)
-1.4 <(R22 + R21) / (R22-R21) <-0.7 ... (4Ya)
0.01 <d / L <0.10 ... (5Ya)
0.02 <(d1 + d2) / L <0.10 ... (6Ya)
-0.26 <(y-y0) / y0 <-0.12 ... (7Ya)

More preferably, the numerical range of the conditional expression (1Ya) to (7Ya) is set as follows.
2.2 << f1 | / f <4.8 ... (1Yb)
3.6 <f2 / f <5.4 ... (2Yb)
0.75 <(R12 + R11) / (R12-R11) <1.30 ... (3Yb)
-1.3 <(R22 + R21) / (R22-R21) <-0.8 ... (4Yb)
0.015 <d / L <0.060 ... (5Yb)
0.025 <(d1 + d2) / L <0.060 ... (6Yb)
-0.25 <(y-y0) / y0 <-0.19 ... (7Yb)

Next, the technical meaning of each of the above conditional expressions will be described.
The conditional expression (1Y) defines the ratio of the focal length of the first Fresnel lens L1 to the focal length of the entire system. When the lower limit of the conditional expression (1Y) is exceeded, the refractive power of the first Fresnel lens L1 becomes too strong, and curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, when the number of lenses of the other constituent lenses is small, the refractive power of each lens becomes too strong and various aberrations increase. On the contrary, when the number of lenses of the other lenses configured is large, the weight increases.

The conditional expression (2Y) defines the ratio of the focal length of the second Fresnel lens L2 to the focal length of the entire system. When the lower limit of the conditional expression (2Y) is exceeded, the refractive power of the second Fresnel lens L2 becomes too strong, and curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, when the number of lenses of the other constituent lenses is small, the refractive power of each lens becomes too strong and various aberrations increase. On the contrary, when the number of lenses of the other lenses configured is large, the weight of the entire system increases.

The conditional expression (3Y) defines the shape factor of the first Fresnel lens L1. When the lower limit of the conditional expression (3Y) is exceeded, the curvature of the surface of the first Fresnel lens L1 on the image display surface ID side becomes too strong, and the curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, the curvature of the surface of the first Fresnel lens L1 on the observation surface SP side becomes too strong, and the curvature of field and astigmatism mainly increase.

The conditional expression (4Y) defines the shape factor of the second Fresnel lens L2. When the lower limit of the conditional expression (4Y) is exceeded, the curvature of the surface of the second Fresnel lens L2 on the image display surface ID side becomes too strong, and the curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, the curvature of the surface of the second Fresnel lens L2 on the observation surface SP side becomes too strong, and the curvature of field and astigmatism mainly increase.

The conditional expression (5Y) relates to the position of the second Fresnel lens L2 on the optical axis. By moving the front principal point position of the second Fresnel lens L2 closer to the first Fresnel lens L1 adjacent to the observation surface SP side within an appropriate range so as to satisfy the conditional expression (5Y), the incident height of the axial light beam is increased. The second Fresnel lens L2 is arranged at a high position. As a result, the contribution to the focal length of the entire system is increased, the refractive power of the second Fresnel lens L2 can be substantially relaxed, and the occurrence of astigmatism and curvature of field is mainly reduced.

If the lower limit of the conditional expression (5Y) is exceeded, the total length of the lens becomes too long and the image display surface ID becomes large, so that the weight of the entire system increases. On the contrary, if the upper limit is exceeded, the refractive power of the second Fresnel lens L2 is too strong, and the occurrence of curvature of field and astigmatism mainly increases.

The conditional expression (6Y) relates to the sum of the center thickness of the first Fresnel lens L1 and the center thickness of the second Fresnel lens L2. When the lower limit of the conditional expression (6Y) is exceeded, the thickness of one or both of the center thickness of the first Fresnel lens L1 and the center thickness of the second Fresnel lens L2 becomes too thin, and the shape of the Fresnel lens is easily deformed. The optical performance will decrease. On the contrary, when the upper limit is exceeded, the thickness of one or both of the center thickness of the first Fresnel lens L1 and the center thickness of the second Fresnel lens L2 becomes too thick, and the weight of the Fresnel lens assembly FL increases.

The conditional expression (7Y) defines the amount of distortion of the observation optical system L0 at an eye relief of 10 mm and a half viewing angle of 45 degrees. If the lower limit of the conditional expression (7Y) is exceeded, the positive refractive power is too strong, so that the peripheral light rays are strongly bent in the optical axis direction, and curvature of field and astigmatism mainly increase. On the other hand, if the upper limit is exceeded, the positive refractive power is too small, so that the incident height of the peripheral light rays at each lens position increases and the effective diameter increases, so that the weight of the Fresnel lens assembly FL increases.
With the above configuration, an observation optical system having a wide field of view, high optical performance, and light weight can be obtained.

[Example 4]
Hereinafter, the observation optical system L0 of the fourth embodiment of the present invention will be described with reference to FIG. 7. The observation optical system L0 of the fourth embodiment is composed of a positive lens LP, a first Fresnel lens L1 having a negative refractive power, and a second Fresnel lens L2 having a positive refractive power in this order from the observation surface SP1 side.

The positive lens L1 is a refracting lens having an aspherical surface, and mainly corrects spherical aberration. By arranging the positive lens LP at a position where the incident height of the peripheral light rays is low, an increase in weight is prevented. The Fresnel surface Fre1 of the first Fresnel lens L1 having a negative power is the observation surface SP side, and the Fresnel surface Fre2 of the second Fresnel lens L2 having a positive power is the image display surface ID side. By making the Fresnel surface Fre1 and the Fresnel surface Fre2 convex toward the image display surface ID side, the angle of incidence of the light rays on the Fresnel surface is suppressed, and curvature of field and astigmatism are mainly suppressed.

By bringing the front principal point position of the second Fresnel lens L2 closer to the first Fresnel lens L1 adjacent to the observation surface side ID in an appropriate range within an appropriate range satisfying the conditional expression (5Y), the axial light beam is high. The second Fresnel lens L2 is arranged at the position. As a result, the refractive power of the second Fresnel lens L2 is substantially relaxed, and curvature of field and astigmatism are mainly suppressed.

Further, the focal length of the first Fresnel lens L1 is relaxed within an appropriate range satisfying the conditional expression (1Y), and curvature of field and astigmatism are mainly suppressed. Further, the focal length of the second Fresnel lens L2 is relaxed within an appropriate range satisfying the conditional expression (2Y), and curvature of field and astigmatism are mainly suppressed. Further, the first Fresnel lens L1 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (3Y), and is strengthened in an appropriate range to mainly suppress curvature of field and astigmatism.

Further, the second Fresnel lens L2 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (4Y), and is strengthened in an appropriate range to mainly suppress curvature of field and astigmatism. Further, the thickness of the first Fresnel lens L1 and the second Fresnel lens L2 is reduced in an appropriate range satisfying the conditional expression (6Y) to reduce the weight. Furthermore, by appropriately setting the amount of distortion at an eye relief of 10 mm and a half-viewing angle of 45 degrees so as to satisfy the conditional expression (7Y), strong bounce of peripheral rays is suppressed, and mainly curvature of field and astigmatism are suppressed. Aberration is suppressed.

The observation optical system L0 of the fifth embodiment has a positive lens SP, a first Fresnel lens L1, and a second Fresnel lens L2 in this order from the observation surface SP side. At this time, it is preferable to satisfy one or more of the following conditional expressions.

The first Fresnel lens L1 has a positive refractive power, and the second Fresnel lens L2 has a negative refractive power. Let f2 be the focal length of the second Fresnel lens L2 and f be the focal length of the observation optical system L0. Let the focal length of the first Fresnel lens L1 be f1. The radius of curvature of the surface of the first Fresnel lens L1 on the observation surface SP side is R11, and the radius of curvature of the surface of the first Fresnel lens L1 on the image display surface ID side is R12. The radius of curvature of the surface of the second Fresnel lens L2 on the observation surface SP side is R21, and the radius of curvature of the surface of the second Fresnel lens L2 on the image display surface ID side is R22.

The observation device having the observation optical system L0 of the fifth embodiment has an image display element. The image of the image display element magnified by the observation optical system L0 is observed from the observation surface SP side via the observation optical system L0. At this time, let d be the distance from the surface apex of the second Fresnel lens L2 on the observation surface SP side to the principal point of the first Fresnel lens L1 on the image display surface side. Let L be the distance from the surface apex on the observation surface SP side of the lens (positive lens LP) arranged on the observation surface SP side to the image display surface ID.

The center thickness of the first Fresnel lens L1 is d1, and the center thickness of the second Fresnel lens L2 is d2. Let y be the real image height of the image display surface ID at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm, and y0 be an ideal image height of the image display surface ID at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm. At this time, it is preferable to satisfy one or more of the following conditional expressions.

3.0 <f1 / f <6.5 ... (1Z)
1.5 << f2 | / f <5.0 ... (2Z)
-1.5 <(R12 + R11) / (R12-R11) <-0.6 ... (3Z)
0.6 <(R22 + R21) / (R22-R21) <1.5 ... (4Z)
0.005 <d / L <0.200 ... (5Z)
0.01 <(d1 + d2) / L <0.15 ... (6Z)
-0.3 <(y-y0) / y0 <-0.1 ... (7Z)

More preferably, the numerical range of the conditional expressions (1Z) to (7Z) is set as follows.
3.4 <f1 / f <5.6 ... (1Za)
2.0 << | f2 | / f <4.9 ... (2Za)
-1.4 <(R12 + R11) / (R12-R11) <-0.7 ... (3Za)
0.7 <(R22 + R21) / (R22-R21) <1.4 ... (4Za)
0.01 <d / L <0.10 ... (5Za)
0.02 <(d1 + d2) / L <0.10 ... (6Za)
-0.26 <(y-y0) / y0 <-0.12 ... (7Za)

More preferably, it is preferable to set the numerical range of the conditional expression (1Za) to (7Za) as follows.
3.6 <f1 / f <5.4 ... (1Zb)
2.2 << f2 | / f <4.8 ... (2Zb)
-1.3 <(R12 + R11) / (R12-R11) <-0.8 ... (3Zb)
0.75 <(R22 + R21) / (R22-R21) <1.30 ... (4Zb)
0.015 <d / L <0.060 ... (5Zb)
0.025 <(d1 + d2) / L <0.060 ... (6Zb)
-0.25 <(y-y0) / y0 <-0.19 ... (7Zb)

Next, the technical meaning of each of the above conditional expressions will be described. The conditional expression (2Z) defines the ratio of the focal length of the second Fresnel lens L2 to the focal length of the entire system. The conditional expression (1Z) defines the ratio of the focal length of the first Fresnel lens L1 to the focal length of the entire system. When the lower limit of the conditional expression (1Z) is exceeded, the refractive power of the first Fresnel lens L1 becomes too strong, and curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, when the number of lenses of the other constituent lenses is small, the refractive power of each lens becomes too strong and various aberrations increase. On the contrary, when the number of lenses of the other lenses configured is large, the weight increases.

When the lower limit of the conditional expression (2Z) is exceeded, the refractive power of the second Fresnel lens L2 becomes too strong, and curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, when the number of lenses of the other constituent lenses is small, the refractive power of each lens becomes too strong and various aberrations increase. On the contrary, when the number of lenses of the other lenses configured is large, the weight of the entire system increases.

The conditional expression (3Z) defines the shape factor of the first Fresnel lens L1. When the lower limit of the conditional expression (3Z) is exceeded, the curvature of the surface of the first Fresnel lens L1 on the image display surface ID side becomes too strong, and the curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, the curvature of the surface of the first Fresnel lens L1 on the observation surface SP side becomes too strong, and the curvature of field and astigmatism mainly increase.

The conditional expression (4Z) defines the shape factor of the second Fresnel lens L2. When the lower limit of the conditional expression (4Z) is exceeded, the curvature of the surface of the second Fresnel lens L2 on the image display surface ID side becomes too strong, and the curvature of field and astigmatism mainly increase. On the contrary, when the upper limit is exceeded, the curvature of the surface of the second Fresnel lens L2 on the observation surface SP side becomes too strong, and the curvature of field and astigmatism mainly increase.

The conditional expression (5Z) relates to the position of the first Fresnel lens L1 on the optical axis. By moving the front principal point position of the first Fresnel lens L1 closer to the second Fresnel lens L2 adjacent to the image display surface ID side within an appropriate range so as to satisfy the conditional expression (5Z), the incident height of the axial light beam The first Fresnel lens L1 is arranged at a high position. As a result, the contribution to the focal length of the entire system is increased, the refractive power of the first Fresnel lens L1 can be substantially relaxed, and the occurrence of astigmatism and curvature of field is mainly reduced.

If the lower limit of the conditional expression (5Z) is exceeded, the total length of the lens becomes too long and the image display surface ID becomes large, so that the weight of the entire system increases. On the contrary, if the upper limit is exceeded, the refractive power of the first Fresnel lens L1 is too strong, and the occurrence of curvature of field and astigmatism mainly increases.

The conditional expression (6Z) relates to the sum of the center thickness of the first Fresnel lens L1 and the center thickness of the second Fresnel lens L2. When the lower limit of the conditional expression (6Z) is exceeded, the thickness of one or both of the center thickness of the first Fresnel lens L1 and the center thickness of the second Fresnel lens L2 becomes too thin, and the shape of the Fresnel lens is easily deformed. The optical performance will decrease. On the contrary, when the upper limit is exceeded, the thickness of one or both of the center thickness of the first Fresnel lens L1 and the center thickness of the second Fresnel lens L2 becomes too thick, and the weight of the Fresnel lens assembly FL increases.

The conditional expression (7Z) defines the amount of distortion of the observation optical system L0 at an eye relief of 10 mm and a half viewing angle of 45 degrees. If the lower limit of the conditional expression (7Z) is exceeded, the positive refractive power is too strong, so that the peripheral light rays are strongly bent in the optical axis direction, and curvature of field and astigmatism mainly increase. On the other hand, if the upper limit is exceeded, the positive refractive power is too small, so that the incident height of the peripheral light rays at each lens position increases and the effective diameter increases, so that the weight of the Fresnel lens assembly FL increases.
With the above configuration, an observation optical system having a wide field of view, high optical performance, and light weight can be obtained.

[Example 5]
Hereinafter, the observation optical system L0 of the sixth embodiment of the present invention will be described with reference to FIG. The observation optical system L0 of the sixth embodiment is composed of a positive lens LP, a first Fresnel lens L1 having a positive refractive power, and a second Fresnel lens L2 having a negative refractive power in this order from the observation surface SP side.

The positive lens LP is a refracting lens having an aspherical surface, and mainly corrects spherical aberration. By arranging the positive lens LP at a position where the height of the peripheral light rays is low, an increase in weight is prevented. The Fresnel surface Fre2 of the second Fresnel lens L2 having a negative power is the observation surface SP side, and the Fresnel surface Fre1 of the first Fresnel lens L1 having a positive power is the image display surface ID side. By forming the Fresnel surface Fre2 and the Fresnel surface Fre1 with a convex shape toward the image display surface ID side, the angle of incidence of the light beam on the Fresnel surface is suppressed, and curvature of field and astigmatism are mainly suppressed.

Further, by arranging the second Fresnel lens L2 having a negative refractive power, the chromatic aberration of magnification is satisfactorily corrected.
The front principal point position of the first Fresnel lens L1 is brought closer to the second Fresnel lens L2 adjacent to the observation surface SP side in an appropriate range within an appropriate range satisfying the conditional expression (5Z). As a result, the first Fresnel lens L1 is arranged at a high position of the axial light beam, and as a result, the refractive power of the first Fresnel lens L1 is substantially relaxed, and curvature of field and astigmatism are mainly suppressed. ..

Further, the focal length of the second Fresnel lens L2 is relaxed within an appropriate range satisfying the conditional expression (2Z), and curvature of field and astigmatism are mainly suppressed. Further, the focal length of the first Fresnel lens L1 is relaxed within an appropriate range satisfying the conditional expression (1Z), and curvature of field and astigmatism are mainly suppressed. Further, the second Fresnel lens L2 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (4Z), and is strengthened in an appropriate range to mainly suppress curvature of field and astigmatism.

Further, the first Fresnel lens L1 has a convex shape toward the image display surface ID side so as to satisfy the conditional expression (3Z), and is strengthened in an appropriate range to mainly suppress curvature of field and astigmatism. Further, the thickness of the first Fresnel lens L1 and the second Fresnel lens L2 is reduced in an appropriate range satisfying the conditional expression (6Z) to reduce the weight. Furthermore, by appropriately setting the amount of distortion at an eye relief of 10 mm and a half-viewing angle of 45 degrees so as to satisfy the conditional expression (7Z), strong bounce of peripheral rays is suppressed, and mainly curvature of field and astigmatism are suppressed. Aberration is suppressed.

Although the preferred embodiments of the present invention have been described above, the observation optical system of the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist thereof. For example, when combined with an image display surface such as a CRT or LCD, electrical processing may be applied to the image display surface side depending on the amount of distortion and the amount of chromatic aberration of magnification.

Next, the numerical data in each example is shown below. In the numerical data, i indicates the order of the planes from the observation plane, ri is the radius of curvature of the i-th optical plane, di is the lens wall thickness and air spacing between the i-th plane and the i + 1 plane, ni, νi. Represents the refractive index and Abbe number of the i-th optical member with respect to the d-line, respectively.

Further, K, A4, A6, A8, A10 and the like described on the aspherical surface are aspherical coefficient. The aspherical shape is defined by the following equation when the displacement in the optical axis direction at the height h from the optical axis is x with respect to the surface apex.
x = (h ² / R) / [1 + {1- (1 + k) (h / R) ² } ^1/2 ] + A4h ⁴ + A6h ⁶ + A8h ⁸ + A10h ¹⁰

However, here R is the radius of curvature. The Fresnel surface represents an ideal thin-walled state having an aspherical effect, and the actual shape is a Fresnel shape within the indicated center thickness d. The Fresnel surface is marked with * Fre on the right side of the surface number.

In the surface number of each numerical data, 1 corresponds to the observation surface (aperture) and the image surface corresponds to the image display surface. In the numerical data 1, 4 and 5, the surface numbers 2 and 3 correspond to the lens LP, the surface numbers 4 and 5 correspond to the first Fresnel lens, and the surface numbers 6 and 7 correspond to the second Fresnel lens. Further, in the numerical data 2, the surface numbers 2 and 3 correspond to the first Fresnel lens, and the surface numbers 4 and 5 correspond to the second Fresnel lens.

In the numerical data 3, surface numbers 2 and 3 correspond to a positive lens, surface numbers 4 and 5 correspond to a first Fresnel lens, surface numbers 6 and 7 correspond to a second Fresnel lens, and surface numbers 8 and 9 correspond to a third Fresnel lens. .. The total length of the lens is the distance from the first lens surface on the observation surface SP side to the image display surface ID. BF is the distance from the final lens surface to the image display surface. Table 1 shows the relationship between the parameters based on the above-mentioned numerical data and each conditional expression.

(Numerical data 1)
Unit mm

Surface data Surface number rd nd νd Diameter
1 (Aperture) ∞ (Variable) 3.50
2 * 410.761 8.00 1.54000 56.0 49.00
3 * -80.000 2.00 49.00
4 ∞ 1.20 1.53200 56.0 63.00
5 * Fre -90.000 2.49 63.00
6 ∞ 1.20 1.49000 58.0 69.00
7 * Fre -90.000 d7 69.00
Image plane ∞

Aspherical data second surface
K = 0.00000e + 000 A 4 = -3.66700e-006 A 6 = 9.11471e-009 A 8 = -7.83777e-012 A10 = 1.57785e-015

Third side
K = 0.00000e + 000 A 4 = -9.84117e-007 A 6 = -9.13282e-010 A 8 = 5.73799e-013

Side 5
K = 0.00000e + 000 A 4 = -3.30573e-007 A 6 = -3.98357e-010 A 8 = -9.37008e-013

7th page
K = 0.00000e + 000 A 4 = 1.22105e-006 A 6 = 1.98445e-009 A 8 = -8.98292e-014

Various data Zoom ratio 1.00

Focal length 53.20 53.20
F number 15.20 15.20
Angle of view 55.00 45.00
Image height 48.51 40.84
Total lens length (L) 64.13 64.13
BF 49.24 49.24
d 2.783

d 1 10.00 20.00
d 7 49.24 49.24

Entrance pupil position 0.00 0.00
Exit pupil position -30.05 -60.90
Front principal point position 17.50 27.50
Rear principal point position -3.96 -3.96

Zoom lens group Data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 ∞ 0.00 0.00 -0.00
2 2 53.20 14.89 7.50 -3.96

Single lens Data lens Start surface Focal length
1 1 124.71
2 4 169.17
3 6 183.67

(Numerical data 2)
Unit mm

Surface data Surface number rd nd νd Diameter
1 (Aperture) ∞ (Variable) 3.50
2 -800.000 1.50 1.53156 55.8 50.00
3 * Fre -65.000 2.71 50.00
4 800.000 2.00 1.53156 55.8 65.00
5 * Fre -65.000 d5 65.00
Image plane ∞

Aspherical data third surface
K = 0.00000e + 000 A 4 = -1.47795e-005 A 6 = -4.92691e-009 A 8 = 6.99900e-012 A10 = 1.23590e-014

Side 5
K = 0.00000e + 000 A 4 = 1.53013e-005 A 6 = 1.00039e-009 A 8 = -9.98155e-012

Various data Zoom ratio 1.00

Focal length 62.11 62.11
F number 17.75 17.75
Angle of view 55.00 45.00
Image height 65.32 52.22
Total lens length (L) 66.43 66.43
BF 60.23 60.23
d 39.17
d 1 10.00 20.00
d 5 60.23 60.23

Entrance pupil position 0.00 0.00
Exit pupil position -18.60 -38.83
Front principal point position 13.17 23.17
Rear principal point position -1.89 -1.89

Zoom lens group Data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 ∞ 0.00 0.00 -0.00
2 2 62.11 6.21 3.17 -1.89

Single lens Data lens Start surface Focal length
1 1 133.00
2 4 113.18

(Numerical data 3)
Unit mm

Surface data Surface number rd nd νd Diameter
1 (Aperture) ∞ (Variable) 3.50
2 * 273.504 8.00 1.77250 49.6 48.00
3 * -79.442 1.26 48.00
4 1000.000 1.50 1.49000 58.0 62.00
5 * Fre -79.821 1.21 62.00
6 * Fre -1500.000 1.00 1.64000 23.5 66.00
7 ∞ 3.00 66.00
8-1100.000 1.20 1.49000 58.0 70.00
9 * Fre -112.282 d9 70.00
Image plane ∞

Aspherical data second surface
K = 0.00000e + 000 A 4 = -3.06549e-006 A 6 = 8.19002e-009 A 8 = -7.48943e-012 A10 = 1.57785e-015

Third side
K = 0.00000e + 000 A 4 = -7.50418e-007 A 6 = -5.41742e-010 A 8 = 8.09511e-013

Side 5
K = 0.00000e + 000 A 4 = -2.772628e-008 A 6 = -2.86482e-010 A 8 = -9.40282e-013

Side 6
K = 0.00000e + 000 A 4 = 0.00000e + 000 A 6 = 0.00000e + 000 A 8 = 0.00000e + 000

Side 9
K = 0.00000e + 000 A 4 = 1.22105e-006 A 6 = 1.98445e-009 A 8 = -8.98292e-014

Various data Zoom ratio 1.00

Focal length 46.02 46.02
F number 13.15 13.15
Angle of view 60.00 46.50
Image height 44.89 36.34
Total lens length (L) 56.52 56.52
BF 39.34 39.34
d 3.897
d 1 10.00 20.00
d 9 39.34 39.34

Entrance pupil position 0.00 0.00
Exit pupil position -31.28 -66.61
Front principal point position 16.03 26.03
Rear principal point position -6.68 -6.68

Zoom lens group Data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 ∞ 0.00 0.00 -0.00
2 2 46.02 17.17 6.03 -6.68

Single lens Data lens Start surface Focal length
1 1 80.49
2 4 150.93
3 6 -2343.74
4 8 255.09

(Numerical data 4)
Unit mm

Surface data Surface number rd nd νd Diameter
1 (Aperture) ∞ (Variable) 3.50
2 * 174.994 12.50 1.69680 55.5 50.00
3 * -43.000 0.15 50.00
4 * Fre -108.134 1.00 1.63400 23.9 65.00
5 ∞ 2.12 65.00
6 ∞ 1.00 1.53156 55.8 70.00
7 * Fre -110.000 d7 70.00
Image plane ∞

Aspherical data second surface
K = 0.00000e + 000 A 4 = -1.88861e-006 A 6 = 5.15277e-009 A 8 = -7.63508e-012 A10 = 1.57785e-015

Third side
K = 0.00000e + 000 A 4 = 2.84163e-006 A 6 = -6.10903e-009 A 8 = 1.58033e-011 A10 = -1.42660e-014

4th side
K = 0.00000e + 000 A 4 = -1.80555e-005 A 6 = 3.04687e-008 A 8 = -1.57283e-011 A10 = 2.52068e-017

7th page
K = 0.00000e + 000 A 4 = -1.97280e-005 A 6 = 2.69617e-008 A 8 = -1.15047e-011

Various data Zoom ratio 1.00

Focal length 54.10 54.10
F number 15.46 15.46
Angle of view 55.00 45.00
Image height 49.94 41.58
Total lens length (L) 66.55 66.55
BF 49.79 49.79
d 2.771
d 1 10.00 20.00
d 7 49.79 49.79

Entrance pupil position 0.00 0.00
Exit pupil position -28.80 -57.65
Front principal point position 16.86 26.86
Rear principal point position -4.31 -4.31

Zoom lens group Data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 ∞ 0.00 0.00 -0.00
2 2 54.10 16.77 6.86 -4.31

Single lens Data lens Start surface Focal length
1 1 50.73
2 4 -170.56
3 6 206.94

(Numerical data 5)
Unit mm

Surface data Surface number rd nd νd Diameter
1 (Aperture) ∞ (Variable) 3.50
2 * 174.000 12.50 1.53156 55.8 50.00
3 * -43.044 0.15 50.00
4 973.437 1.50 1.53156 55.8 62.00
5 * Fre -65.861 2.78 62.00
6 * Fre -149.437 1.50 1.63400 23.9 70.00
7 -1503.437 d7 70.00
Image plane ∞

Aspherical data second surface
K = 0.00000e + 000 A 4 = -5.92944e-006 A 6 = 1.70481e-008 A 8 = -1.31727e-011 A10 = 1.57785e-015

Third side
K = 0.00000e + 000 A 4 = 2.84163e-006 A 6 = -6.10903e-009 A 8 = 1.58033e-011 A10 = -1.42660e-014

Side 5
K = 0.00000e + 000 A 4 = -1.88496e-005 A 6 = 3.35376e-008 A 8 = -1.28073e-011

Side 6
K = 0.00000e + 000 A 4 = -1.4464e-005 A 6 = 2.85863e-008 A 8 = -1.46135e-011 A10 = 5.11813e-016

Various data Zoom ratio 1.00

Focal length 50.16 50.16
F number 14.33 14.33
Angle of view 60.00 46.50
Image height 45.69 38.71
Total lens length (L) 62.30 62.30
BF 43.87 43.87
d 1.068
d 1 10.00 20.00
d 7 43.87 43.87

Entrance pupil position 0.00 0.00
Exit pupil position -31.59 -63.92
Front principal point position 16.82 26.82
Rear principal point position -6.28 -6.28

Zoom lens group Data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 ∞ 0.00 0.00 -0.00
2 2 50.16 18.43 6.82 -6.28

Single lens Data lens Start surface Focal length
1 1 66.24
2 4 116.11
3 6 -261.83

L0 Observation optical system FL Fresnel lens assembly LP Positive lens SP Observation surface ID Image display surface L1 1st Fresnel lens L2 2nd Fresnel lens L3 3rd Fresnel lens Fre1 1st Fresnel surface Fre2 2nd Fresnel surface Fre3 3rd Fresnel surface

Claims (32)

An observation optical system for observing an image displayed on an image display surface.
It has a positive lens, a first Fresnel lens, and a second Fresnel lens arranged in order from the observation surface side to the image display surface side.
Wherein the first Fresnel lens second fresnel lens each image display surface side is Fureneruren's of positive refractive power is a Fresnel surface,
When the focal length of the first Fresnel lens is f1 and the focal length of the observation optical system is f,
1.5 <f1 / f <5.0
An observation optical system characterized by satisfying the conditional expression. When the focal length of the second Fresnel lens is f2 and the focal length of the observation optical system is f,
1.0 <f2 / f <6.0
The observation optical system according to claim 1 , wherein the observation optical system satisfies the conditional expression. When the radius of curvature of the surface of the first Fresnel lens on the observation surface side is R11 and the radius of curvature of the surface of the first Fresnel lens on the image display surface side is R12,
-1.4 <(R12 + R11) / (R12-R11) <-0.6
The observation optical system according to claim 1 or 2 , wherein the conditional expression is satisfied. When the radius of curvature of the surface of the second Fresnel lens on the observation surface side is R21 and the radius of curvature of the surface of the second Fresnel lens on the image display surface side is R22,
-1.5 <(R22 + R21) / (R22-R21) <-0.5
The observation optical system according to any one of claims 1 to 3 , wherein the conditional expression is satisfied. An observation device comprising the observation optical system according to any one of claims 1 to 4 and an image display element for displaying an image. The distance from the surface apex on the image display surface side of the first Fresnel lens to the principal point on the observation surface side of the second Fresnel lens is d, from the surface apex on the observation surface side of the lens arranged closest to the observation surface side. When the distance to the image display surface is L,
0.005 <d / L <0.200
The observation device according to claim 5 , wherein the observation device satisfies the conditional expression. When the center thickness of the first Fresnel lens is d1, the center thickness of the second Fresnel lens is d2, and the distance from the surface apex on the observation side of the lens arranged on the observation surface side to the image display surface is L. ,
0.01 <(d1 + d2) / L <0.10
The observation device according to claim 5 or 6 , wherein the conditional expression is satisfied. When the real image height of the image display surface at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm is y, and the ideal image height of the image display surface at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm is y0.
-0.3 <(y-y0) / y0 <-0.1
The observation device according to any one of claims 5 to 7 , wherein the observation device satisfies the conditional expression. An observation optical system for observing an image displayed on an image display surface.
It has a positive lens, a first Fresnel lens, and a second Fresnel lens arranged in order from the observation surface side to the image display surface side.
The first Fresnel lens is a Fresnel lens having a negative refractive power whose observation surface side is a Fresnel surface, and the second Fresnel lens is a Fresnel lens having a positive refractive power whose image display surface side is a Fresnel surface.
When the focal length of the first Fresnel lens is f1 and the focal length of the observation optical system is f,
1.5 << f1 | / f <5.0
Observation optics you and satisfies the following condition expression. When the focal length of the second Fresnel lens is f2 and the focal length of the observation optical system is f,
3.0 <f2 / f <6.5
The observation optical system according to claim 9 , wherein the observation optical system satisfies the conditional expression. When the radius of curvature of the surface of the first Fresnel lens on the observation surface side is R11 and the radius of curvature of the surface of the first Fresnel lens on the image display surface side is R12,
0.6 <(R12 + R11) / (R12-R11) <1.5
An observation optical system according to claim 9 or 1 0, characterized by satisfying the conditional expression. When the radius of curvature of the surface of the second Fresnel lens on the observation surface side is R21 and the radius of curvature of the surface of the second Fresnel lens on the image display surface side is R22,
-1.5 <(R22 + R21) / (R22-R21) <-0.6
The observation optical system according to any one of claims 9 to 11, wherein the observation optical system satisfies the conditional expression. An observation optical system according to any one of claims 9 to 1 2, observation apparatus characterized by having an image display device for displaying an image. The distance from the surface apex on the image display surface side of the first Fresnel lens to the principal point on the observation surface side of the second Fresnel lens is d, from the surface apex on the observation surface side of the lens arranged closest to the observation surface side. When the distance to the image display surface is L,
0.005 <d / L <0.200
Observation apparatus according to claim 1 3, characterized by satisfying the conditional expression. When the center thickness of the first Fresnel lens is d1, the center thickness of the second Fresnel lens is d2, and the distance from the surface apex on the observation side of the lens arranged on the observation surface side to the image display surface is L. ,
0.01 <(d1 + d2) / L <0.15
Observation apparatus according to claim 1 3 or 1 4, characterized by satisfying the conditional expression. When the real image height of the image display surface at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm is y, and the ideal image height of the image display surface at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm is y0.
-0.3 <(y-y0) / y0 <-0.1
Observation device according to any one of claims 1 3 to 1 5, characterized by satisfying the conditional expression. An observation optical system for observing an image displayed on an image display surface.
It has a positive lens, a first Fresnel lens, a second Fresnel lens, and a third Fresnel lens arranged in order from the observation surface side to the image display surface side.
The first Fresnel lens and the third Fresnel lens are Fresnel lenses having a positive refractive force whose image display surface side is a Fresnel surface, and the second Fresnel lens has a negative refractive force Fresnel whose observation surface side is a Fresnel surface. It's a lens
When the focal length of the first Fresnel lens is f1 and the focal length of the observation optical system is f,
1.5 <f1 / f <5.0
Observation optics you and satisfies the following condition expression. When the focal length of the third Fresnel lens is f3 and the focal length of the observation optical system is f,
1.0 <f3 / f <6.0
The observation optical system according to claim 17 , wherein the conditional expression is satisfied. When the radius of curvature of the surface of the first Fresnel lens on the observation surface side is R11 and the radius of curvature of the surface of the first Fresnel lens on the image display surface side is R12,
-1.4 <(R12 + R11) / (R12-R11) <-0.6
The observation optical system according to claim 17 or 18 , wherein the conditional expression is satisfied. When the radius of curvature of the surface of the third Fresnel lens on the observation surface side is R31 and the radius of curvature of the surface of the third Fresnel lens on the image display surface side is R32.
-1.5 <(R32 + R31) / (R32-R31) <-0.5
The observation optical system according to any one of claims 17 to 19 , wherein the conditional expression is satisfied. An observation optical system according to any one of claims 17 to 2 0, observation apparatus characterized by having an image display device for displaying an image. The distance from the surface apex on the image display surface side of the second Fresnel lens to the principal point on the observation surface side of the third Fresnel lens is d, from the surface apex on the observation surface side of the lens arranged closest to the observation surface side. When the distance to the image display surface is L,
0.005 <d / L <0.200
Observation apparatus according to claim 2 1, characterized by satisfying the conditional expression. When the center thickness of the first Fresnel lens is d1, the center thickness of the third Fresnel lens is d3, and the distance from the surface apex on the observation side of the lens arranged on the observation surface side to the image display surface is L. ,
0.01 <(d1 + d3) / L <0.10
Observation apparatus according to claim 2 1, 2 2, characterized by satisfying the conditional expression. When the real image height of the image display surface at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm is y, and the ideal image height of the image display surface at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm is y0.
-0.3 <(y-y0) / y0 <-0.1
Observation device according to any one of claims 2 1 to 2 3, characterized by satisfying the conditional expression. An observation optical system for observing an image displayed on an image display surface.
It has a positive lens, a first Fresnel lens, and a second Fresnel lens arranged in order from the observation surface side to the image display surface side.
The first Fresnel lens is a Fresnel lens having a positive refractive power whose image display surface side is a Fresnel surface, and the second Fresnel lens is a Fresnel lens having a negative refractive power whose observation surface side is a Fresnel surface.
When the focal length of the second Fresnel lens is f2 and the focal length of the observation optical system is f,
1.5 << f2 | / f <5.0
An observation optical system characterized by satisfying the conditional expression. When the focal length of the first Fresnel lens is f1 and the focal length of the observation optical system is f,
3.0 <f1 / f <6.5
25. The observation optical system according to claim 25 , which satisfies the conditional expression. When the radius of curvature of the surface of the second Fresnel lens on the observation surface side is R21 and the radius of curvature of the surface of the second Fresnel lens on the image display surface side is R22,
0.6 <(R22 + R21) / (R22-R21) <1.5
The observation optical system according to claim 25 or 26 , wherein the observation optical system satisfies the conditional expression. When the radius of curvature of the surface of the first Fresnel lens on the observation surface side is R11 and the radius of curvature of the surface of the first Fresnel lens on the image display surface side is R12,
-1.5 <(R12 + R11) / (R12-R11) <-0.6
An observation optical system according to any one of claims 25 to 2 7, characterized by satisfying the conditional expression. An observation device comprising the observation optical system according to any one of claims 25 to 28 and an image display element for displaying an image. The distance from the surface apex on the observation surface side of the second Fresnel lens to the principal point on the image display surface side of the first Fresnel lens is d, from the surface apex on the observation surface side of the lens arranged closest to the observation surface side. When the distance to the image display surface is L,
0.005 <d / L <0.200
29. The observation device according to claim 29 , wherein the conditional expression is satisfied. When the center thickness of the first Fresnel lens is d1, the center thickness of the second Fresnel lens is d2, and the distance from the surface apex on the observation side of the lens arranged on the observation surface side to the image display surface is L. ,
0.01 <(d1 + d2) / L <0.15
Observation apparatus according to claim 29 or 3 0, characterized in that to satisfy the condition. When the real image height of the image display surface at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm is y, and the ideal image height of the image display surface at an observation half-viewing angle of 45 degrees at an eye relief of 10 mm is y0.
-0.3 <(y-y0) / y0 <-0.1
The observation device according to any one of claims 29 to 31, characterized in that the conditional expression is satisfied.