Patent ID: 12222524

DESCRIPTION OF THE EMBODIMENT

Hereinafter, an ocular optical system and a head mounted display according to the present embodiment will be described with reference to the drawings. As shown inFIG.1, an ocular optical system EL (1) as an example of an ocular optical system EL according to the present embodiment is configured to comprise a Fresnel lens L1having a plurality of Fresnel zones FR formed on the lens surface on an observation object side. The ocular optical system EL according to the present embodiment may be an ocular optical system EL (2) shown inFIG.7, an ocular optical system EL (3) shown inFIG.13, an ocular optical system EL (4) shown inFIG.19, or an ocular optical system EL (5) shown inFIG.25.

For example, as shown inFIG.31, a first Fresnel zone FR (1) located on the most central axis side of the Fresnel lens L1out of a plurality of Fresnel zones FR is formed in a disk shape which is coaxial with the central axis of the Fresnel lens L1. The first Fresnel zone FR (1) has a Fresnel surface portion FRa (1) having an aspherical shape. A second and subsequent Fresnel zones FR which are counted from the central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR are formed in annular shapes which are coaxial with the central axis of the Fresnel lens L1. The second and subsequent Fresnel zones FR each include a Fresnel surface portion FRa having an aspherical shape, and a stepped and wall-shaped wall surface portion FRb. Note that the first Fresnel zone FR (1) is formed in a shape (disk-like shape) that is not a ring-shaped (annular shape), but it is assumed in the present embodiment that the first Fresnel zone FR (1) is also included in a plurality of Fresnel zones FR. InFIG.31andFIGS.2,8,14,20, and26which will be described later, the signs of the Fresnel surface portions FRa and the wall surface portions FRb of the second and third Fresnel zones counted from the central axis side of the Fresnel lens L1(the second Fresnel zone FR(2) and the third Fresnel zone FR(3)) out of the plurality of Fresnel zones FR are shown in these figures, but the signs of the Fresnel surface portions FRa and the wall surface portions FRb of the fourth and subsequent Fresnel zones are omitted from illustration.

The plurality of Fresnel zones FR are arranged concentrically side by side along an aspherical surface having a shape which is rotationally symmetric with respect to a central axis of the Fresnel lens L1(hereinafter, may be referred to as an arrangement reference aspherical surface for convenience). For example, the vertex portions of the respective Fresnel zones FR are arranged side by side along an aspherical surface that is rotationally symmetric with respect to the central axis of the Fresnel lens L1. Further, for example, valley portions formed at the boundaries of adjacent Fresnel zones FR may be arranged side by side along an aspherical surface which is rotationally symmetric with respect to the central axis of the Fresnel lens L1.

The shape of the Fresnel surface portion FRa of each Fresnel zone FR is the shape of a divided surface obtained by dividing an aspherical surface (hereinafter referred to as a shape reference aspherical surface for convenience) constituting an aspherical lens (see, for example, a two-dotted chain line inFIG.31) achieving desired optical performance in a ring-belt shape. This makes it possible to obtain a Fresnel lens L1that is thinner than a normal aspherical lens. In the present embodiment, the plurality of Fresnel zones FR are not arranged along a plane perpendicular to a central axis as in a conventional Fresnel lens (see, for example, the two-dotted chain line inFIG.31), but are arranged along an aspherical surface (arrangement reference aspherical surface) having an intermediate curvature which is larger than the curvature of the plane and smaller than the curvature of the shape reference aspherical surface (Fresnel surface portion FRa). As a result, the pitch (the distance between the vertex portions) in the radial direction of a plurality of Fresnel zones FR can be set to be larger in a neighborhood portion of the central axis of the Fresnel lens L1while suppressing increase in thickness of the Fresnel lens L1as compared with the conventional Fresnel lens. In other words, the number of discontinuous portions (wall surface portions FRb) of the Fresnel zones FR in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced as compared with the conventional Fresnel lens. Therefore, it is possible to reduce flare occurring in the central part of the visual field (that is, in the neighborhood portion of the central axis of the Fresnel lens L1), which is often visually recognized when the head mounted display is used.

In the ocular optical system EL according to the present embodiment, it is preferable that the following conditional expression (1) is satisfied.
0<PAE1/PAC1≤0.50  (1),
where PAE1 represents an average pitch in a radial direction of Fresnel zones FR formed in a portion having a radius of 15 mm or more from the central axis of the Fresnel lens L1out of the plurality of Fresnel zones FR, and

PAC1 represents an average pitch in the radial direction of Fresnel zones FR formed in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens L1excluding a first Fresnel zone FR (1) located on a most central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR.

The conditional expression (1) is a conditional expression for defining the ratio of the average pitch in the radial direction of Fresnel zones FR formed side by side in the portion having the radius of 15 mm or more from the central axis of the Fresnel lens L1to the average pitch in the radial direction of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1. When the conditional expression (1) is satisfied, the average pitch in the radial direction of the Fresnel zones FR increases and the number of discontinuous portions (wall surface portions FRb) of the Fresnel zones FR decreases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (1) exceeds the upper limit value, the average pitch in the radial direction of the Fresnel zones FR decreases and the number of the discontinuous portions (wall surface portions FRb) of the Fresnel zones FR increases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that it becomes difficult to reduce the flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1. In order to ensure the effect of the present embodiment, the upper limit value of the conditional expression (1) may be preferably set to 0.45. In order to avoid difficulty in manufacturing the Fresnel lens L1, a lower limit value of the conditional expression (1) may be preferably set to 0.30 or more.

In the ocular optical system EL according to the present embodiment, the following conditional expression (2) may be satisfied.
0<PAE2/PAC1≤0.55  (2),
where PAE2 represents an average pitch in the radial direction of Fresnel zones FR formed in a portion having a radius of 15 mm to 22.5 mm from the central axis of the Fresnel lens L1out of the plurality of Fresnel zones FR.

The conditional expression (2) is a conditional expression for defining the ratio of the average pitch in the radial direction of Fresnel zones FR formed side by side in the portion having the radius of 15 mm to 22.5 mm from the central axis of the Fresnel lens L1to the average pitch in the radial direction of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1. When the conditional expression (2) is satisfied, the average pitch in the radial direction of the Fresnel zones FR increases and the number of the discontinuous portions (wall surface portions FRb) of the Fresnel zones FR in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (2) exceeds the upper limit value, the average pitch in the radial direction of the Fresnel zones FR decreases and the number of the discontinuous portions (wall surface portions FRb) of the Fresnel zones FR increases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that it becomes difficult to reduce the flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1. In order to ensure the effect of the present embodiment, the upper limit value of the conditional expression (2) may be preferably set to 0.51. In order to avoid difficulty in manufacturing the Fresnel lens L1, a lower limit value of the conditional expression (2) may be preferably set to 0.30 or more.

In the ocular optical system EL according to the present embodiment, the following conditional expression (3) may be satisfied.
0<PAE3/PAC1≤0.60  (3),
where PAE3 represents an average pitch in the radial direction of Fresnel zones FR formed in a portion having a radius of 15 mm to 20 mm from the central axis of the Fresnel lens L1out of the plurality of Fresnel zones FR.

The conditional expression (3) is a conditional expression for defining the ratio of the average pitch in the radial direction of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm to 20 mm from the central axis of the Fresnel lens L1to the average pitch in the radial direction of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1. When the conditional expression (3) is satisfied, the average pitch in the radial direction of the Fresnel zones FR increases and the number of discontinuous portions (wall surface portions FRb) of the Fresnel zones FR decreases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that the flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (3) exceeds the upper limit value, the average pitch in the radial direction of the Fresnel zones FR decreases and the discontinuous portions (wall surface portions FRb) of the Fresnel zones FR increases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that it becomes difficult to reduce the flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1. In order to ensure the effect of the present embodiment, the upper limit value of the conditional expression (3) may be preferably set to 0.55. In order to avoid difficulty in manufacturing the Fresnel lens L1, a lower limit value of the conditional expression (3) may be preferably set to 0.30 or more.

In the ocular optical system EL according to the present embodiment, the following conditional expression (4) may be satisfied.
PAC1≥1.0 [mm]  (4)

The conditional expression (4) is a conditional expression for defining the average pitch in the radial direction of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1. When the conditional expression (4) is satisfied, the average pitch in the radial direction of the Fresnel zones FR increases and the number of discontinuous portions (wall surface portions FRb) of the Fresnel zones FR decreases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (4) is less than the lower limit value, the average pitch in the radial direction of the Fresnel zones FR decreases and the number of the discontinuous portions (wall surface portions FRb) of the Fresnel zones FR increases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that it becomes difficult to reduce the flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1. In order to ensure the effect of the present embodiment, the lower limit value of the conditional expression (4) may be preferably set to 1.5 [mm]. In order to prevent the Fresnel lens L1from increasing in size, an upper limit value of the conditional expression (4) may be preferably set to 3.5 [mm] or less.

In the ocular optical system EL according to the present embodiment, the following conditional expression (5) may be satisfied.
PMX1/PMN1≥10.0  (5),
where PMX1 represents a maximum pitch in the radial direction of the plurality of Fresnel zones FR, andPMN1 represents a minimum pitch in the radial direction of the plurality of Fresnel zones FR.

The conditional expression (5) is a conditional expression for defining the ratio of the maximum pitch in the radial direction of the plurality of Fresnel zones FR to the minimum pitch in the radial direction of the plurality of Fresnel zone FR. The pitch in the radial direction of the Fresnel zones FR becomes relatively larger as they are closer to the central axis side of the Fresnel lens L1. When the conditional expression (5) is satisfied, the pitch in the radial direction of the Fresnel zones FR increases and the number of discontinuous portions (wall surface portions FRb) of the Fresnel zones FR decreases in the neighborhood portion of the central axis of the Fresnel lens L1, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (5) is less than the lower limit value, the pitch in the radial direction of the Fresnel zones FR decreases and the number of discontinuous portions (wall surface portions FRb) of the Fresnel zones FR increases in the neighborhood portion of the central axis of the Fresnel lens L1, so that it becomes difficult to reduce flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1. In order to ensure the effect of the present embodiment, the lower limit value of the conditional expression (5) may be preferably set to 15.0. In order to avoid difficulty in manufacturing the Fresnel lens L1, an upper limit value of the conditional expression (5) may be preferably set to 35.5 or less.

In the ocular optical system EL according to the present embodiment, the following conditional expression (6) may be satisfied.
1<PMX2/PMN2≤7.5  (6),
where PMX2 represents a maximum pitch in the radial direction of Fresnel zones FR formed in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens L1out of the plurality of Fresnel zones FR, and

PMN2 represents a minimum pitch in the radial direction of the Fresnel zones FR formed in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1out of the plurality of Fresnel zones FR.

The conditional expression (6) is a conditional expression for defining the ratio of the maximum pitch in the radial direction of Fresnel zones FR formed side by side in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens L1to the minimum pitch in the radial direction of Fresnel zones FR formed side by side in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1. When the conditional expression (6) is satisfied, the change of the pitch in the radial direction of the Fresnel zones FR moderates and the number of discontinuous portions (wall surface portions FRb) of the Fresnel zones FR decreases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (6) exceeds the upper limit value, the change in the pitch in the radial direction of the Fresnel zones FR becomes sharp and the number of the discontinuous portions (wall surface portions FRb) increases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that it becomes difficult to reduce the flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1. In order to ensure the effect of the present embodiment, the upper limit value of the conditional expression (6) may be preferably set to 6.5.

In the ocular optical system EL according to the present embodiment, the following conditional expression (7) may be satisfied.
1<PMX3/PMN3≤2.5  (7),
where PMX3 represents a maximum pitch in the radial direction of Fresnel zones FR formed in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens L1excluding a first Fresnel zone FR (1) out of the plurality of Fresnel zones FR, and

PMN3 represents a minimum pitch in the radial direction of the Fresnel zones FR formed in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1excluding the first Fresnel zone FR (1) out of the plurality of Fresnel zones FR.

The conditional expression (7) is a conditional expression for defining the ratio of the maximum pitch in the radial direction of Fresnel zones FR formed side by side in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens L1to the minimum pitch in the radial direction of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1in the case of exclusion of the first Fresnel zone FR (1). When the conditional expression (7) is satisfied, the change of the pitch in the radial direction of the Fresnel zones FR moderates and the number of discontinuous portions (wall surface portions FRb) of the Fresnel zones FR decreases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (7) exceeds the upper limit value, the change in the pitch in the radial direction of the Fresnel zones FR becomes sharp and the number of discontinuous portions (wall surface portions FRb) of the Fresnel zones FR increases in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1, so that it becomes difficult to reduce flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1. In order to ensure the effect of the present embodiment, the upper limit value of the conditional expression (7) may be preferably set to 2.0.

In the ocular optical system EL according to the present embodiment, the following conditional expression (8) may be satisfied.
QE1/QC1≥2.0  (8),
where QE1 represents the number of Fresnel zones FR formed in a portion having a radius of 15 mm to 22.5 mm from the central axis of the Fresnel lens L1out of the plurality of Fresnel zones FR, andQC1 represents the number of Fresnel zones FR formed in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens L1excluding a first Fresnel zone FR (1) out of the plurality of Fresnel zones FR.

The conditional expression (8) is a conditional expression for defining the number of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm to 22.5 mm from the central axis of the Fresnel lens L1to the number of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1. When the conditional expression (8) is satisfied, the number of the Fresnel zones FR in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1decreases, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (8) falls below the lower limit value, the number of the Fresnel zones FR in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1increases, so that it becomes difficult to reduce the flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1. In order to ensure the effect of the present embodiment, the lower limit value of the conditional expression (8) may be preferably set to 2.5. In order to avoid difficulty in manufacturing the Fresnel lens L1, an upper limit value of the conditional expression (8) may be preferably set to 5.0 or less.

In the ocular optical system EL according to the present embodiment, the following conditional expression (9) may be satisfied.
QE2/QC1≥1.0  (9),
where QE2 represents the number of Fresnel zones FR formed in a portion having a radius of 15 mm to 20 mm from the central axis of the Fresnel lens L1out of the plurality of Fresnel zones FR, andQC1 represents the number of Fresnel zones FR formed in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens L1excluding a first Fresnel zone FR (1) out of the plurality of Fresnel zones FR.

The conditional expression (9) is a conditional expression for defining the number of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm to 20 mm from the central axis of the Fresnel lens L1to the number of the Fresnel zones FR formed side by side in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1. When the conditional expression (9) is satisfied, the number of the Fresnel zones FR in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1decreases, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (9) is less than the lower limit value, the number of the Fresnel zones FR in the portion having the radius of 15 mm or less from the central axis of the Fresnel lens L1increases, so that it becomes difficult to reduce the flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1. In order to ensure the effect of the present embodiment, the lower limit value of the conditional expression (9) may be preferably set to 1.5. In order to avoid difficulty in manufacturing the Fresnel lens L1, an upper limit value of the conditional expression (9) may be preferably set to 3.0 or less.

In the ocular optical system EL according to the present embodiment, the wall surface portions FRb in the plurality of Fresnel zones FR extend in parallel to the central axis of the Fresnel lens L1, but they are not limited to this configuration. For example, as shown inFIG.32B, the wall surface portions FRb of the Fresnel zones FR may be inclined in a direction opposite to a direction in which the Fresnel surface portions FRa are inclined (with respect to the central axis of the Fresnel lens L1). As a result, light incident on the Fresnel surface portions FRa in the Fresnel zones FR are less likely to reach the wall surface portions FRb, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

In the ocular optical system EL according to the present embodiment, the wall surface portions FRb of the plurality of Fresnel zones FR may be provided with light-shielding members (not shown). As a result, even if light incident on the Fresnel surface portions FRa in the Fresnel zones FR reach the wall surface portions FRb, the light is shielded by the light-shielding members, so that flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced. Examples of the light-shielding member provided on the wall surface portion FRb of the Fresnel zone FR include a paint using a black synthetic resin such as a curable acrylic urethane paint and a phthalic acid resin enamel paint, which can be coated on the wall surface portion FRb.

In the ocular optical system EL according to the present embodiment, an aspherical surface (arrangement reference aspherical surface) on which the vertex portions of the respective Fresnel zones FR are arranged is expressed by using the following expression (A).

[Expression⁢⁢1]Zd=y2/Rd1+1-(1+kd)⁢y2/Rd2+∑i=210⁢A2⁢i×y2⁢i,(A)
where Zdrepresents a sag amount (in the central axis direction of the Fresnel lens L1) of the arrangement reference aspherical surface at a distance y from the central axis of the Fresnel lens L1,Rdrepresents a radius of curvature of a reference spherical surface in the arrangement reference aspherical surface (paraxial radius of curvature),kdrepresents a conic constant of the arrangement reference aspherical surface, andA2irepresents a (2×i)-order aspherical coefficient.

Further, the shape reference aspherical surface that is the base of the Fresnel surface portion FRa in the Fresnel zone FR is expressed by using the following expression (B).

[Expression⁢⁢2]Zr=y2/Rr1+1-(1+kr)⁢y2/Rr2+∑i=210⁢B2⁢i×y2⁢i,(B)
where Zrrepresents a sag amount (in the central axis direction of the Fresnel lens L1) of the shape reference aspherical surface at the distance y from the central axis of the Fresnel lens L1,Rrrepresents the radius of curvature of a reference spherical surface in the shape reference aspherical surface (paraxial radius of curvature),krrepresents a conic constant of the shape reference aspherical surface, andB2irepresents a (2×i)-order aspherical coefficient.

Here, the relationship between the sag amount Zdof the arrangement reference aspherical surface and the sag amount Zrof the shape reference aspherical surface can be defined by using the following expression (C).
[Expression 3]
(Zr−zd)/Sg=q+m(C)
where Sg represents the length in the central axis direction of the wall surface portion FRb in the Fresnel zone FR,q represents the quotient of division on the left side of the expression (C), andm represents the residual of division on the left side of the expression (C).

The Fresnel surface portion FRa in the Fresnel zone FR is expressed by using the following expression (D) based on the expressions (A) to (C). Note that inFIG.31andFIGS.2,8,14,20, and26described later, the sag amount Zfof the Fresnel surface portion FRa (the sag amount Zdof the arrangement reference aspherical surface and the sag amount Zrof the shape reference aspherical surface) is indicated by assigning a sign of minus (−) to a value advancing from a tangent plane (reference plane) passing through the vertex of the aspherical surface to an eyepoint side.
[Expression 4]
Zf=Zr−(q×Sg)  (D),
where Zfrepresents a sag amount (in the central axis direction of the Fresnel lens L1) of the Fresnel surface portion FRa at the distance y from the central axis of the Fresnel lens L1.

In the ocular optical system EL according to the present embodiment, the following conditional expression (10) may be satisfied.
kd≤−5.0  (10)

The conditional expression (10) is a conditional expression for defining the conic constant in the expression (A) of the aspherical surface (arrangement reference aspherical surface) on which a plurality of Fresnel zones FR are arranged. When the conditional expression (10) is satisfied, flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

When the corresponding value of the conditional expression (10) exceeds the upper limit value, this is not preferable because the number of discontinuous portions (wall surface portions FRb) of Fresnel zones FR in a region near to the central axis of the Fresnel lens L1increases. In order to ensure the effect of the present embodiment, the upper limit value of the conditional expression (10) may be preferably set to −10.0. In order to avoid difficulty in reducing flare, a lower limit value of the conditional expression (10) may be preferably set to −30.0 or more.

In the ocular optical system EL according to the present embodiment, the following conditional expression (11) may be satisfied.
kd<kr(11)

The conditional expression (11) is a conditional expression for defining the relationship between the conic constant in the arrangement reference aspherical surface and the conic constant in the shape reference aspherical surface. When the conditional expression (11) is satisfied, flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1can be reduced.

Note that not only a case where the vertex portions of the respective Fresnel zones FR are arranged side by side along the arrangement reference aspherical surface, but also even a case where the valley portions of the respective Fresnel zones FR are arranged side by side along the arrangement reference aspherical surface, it is possible to represent the arrangement reference aspherical surface based on the expression (A). Not only a case where the wall surface portions FRb of the Fresnel zones FR extends in parallel to the central axis of the Fresnel lens L1, but also even a case where the wall surface portions FRb of the Fresnel zones FR are inclined with respect to the central axis of the Fresnel lens L1, it is also possible to represent the arrangement reference aspherical surface based on the expression (A). The lengths Sg in the central axial direction of the wall surface portions FRb in the Fresnel zones FR are set to a constant value, but may be set to different values among the Fresnel zones FR. Further, it is desirable that the outer diameter of the Fresnel lens L1is 30 mm to 75 mm in diameter.

A head mounted display according to the present embodiment is configured to comprise the ocular optical system having the above-described configuration. As a specific example, a head mounted display comprising the above-described ocular optical system EL will be described with reference toFIG.33. The head mounted display1shown inFIG.33is used while fixed to the head of a user. The head mounted display1is configured to comprise an image display part11, an ocular optical system EL (not shown inFIG.33), and a housing12for accommodating these components. Further, speakers14for providing voice information to the user are arranged on the right and left sides of the housing12. Further, a band16for fixing the housing12to the user's head is attached to a rear portion of the housing12.

The image display part11and the ocular optical system EL are configured to be arranged so as to face the user's eyes with the housing12being fixed to the user's head. Although detailed illustration is omitted, the image display part11is configured by using, for example, a liquid crystal display device or the like. Further, two sets of ocular optical systems EL are provided so as to correspond to both the user's eyes. In such a head mounted display1, when the image display part11displays a predetermined image, light from the image display part11passes through the ocular optical systems EL and reaches the user's eyes. As a result, the user can see the image displayed on the image display part11via the ocular optical systems EL. According to the above configuration, by mounting the ocular optical systems EL, it is possible to obtain a head mounted display that has a wide viewing angle in spite of a thin type design and is successfully corrected for various aberrations such as astigmatism.

Note that the image to be displayed by the image display part11may be a still image or a video image. Further, the image display part11may be configured to display a parallax image for the right eye and a parallax image for the left eye respectively so that the parallax images are recognized as a stereoscopic image by the user who views the parallax images via the ocular optical systems EL. Further, the image display part11is not limited to the configuration provided integrally with the housing12. For example, it may be configured so that a mobile terminal or the like which is provided separately from the housing and capable of displaying an image may be attached to the housing and used as an image display part.

EXAMPLES

Hereinafter, the ocular optical system EL according to examples of the present embodiment will be described with reference to the drawings.FIG.1,FIG.7,FIG.13,FIG.19, andFIG.25are diagrams showing lens configurations of ocular optical systems EL {EL (1) to EL (5)} according to first to fifth examples.FIG.2,FIG.8,FIG.14,FIG.20, andFIG.26are enlarged views showing the shapes of the Fresnel lenses L1of the ocular optical systems EL {EL (1) to EL (5)} according to the first to fifth examples.

InFIG.1,FIG.2,FIG.7,FIG.8,FIG.13,FIG.14,FIG.19,FIG.20,FIG.25andFIG.26, each lens is represented by a combination of a character L and a numeral (or alphabet). In this case, in order to prevent the types and numbers of characters and numerals from being multiplied and thus complicated, lens groups and the like are represented by independently using combinations of characters and numerals on an example basis. Therefore, even if a combination of the same character and the same numeral is used among the examples, it does not mean that the combination represents the same configuration.

Tables 1 to 5 will be presented below. Table 1 to Table 5 are tables indicating specification values of first to fifth examples, respectively. In each example, d-line (wavelength λ=587.6 nm), e-line (wavelength λ=546.1 nm), g-line (wavelength λ=435.8 nm), C-line (wavelength λ=656.3 nm), and F-line (wavelength λ=486.1 nm) are selected as targets for calculation of aberration characteristics.

In [Specification Data] of each table, f represents the focal length of the ocular optical system, w represents a viewing angle (unit is “°”), ER represents an eye relief, TL represents the entire length of the ocular optical system (the distance from an eyepoint to an image display part (observation object)), and DA represents the outer diameter of the Fresnel lens. PAC1, PAE1, PAE2, and PAE3 indicated in [Specification Data] are the same as those described in the above-described embodiment. PMX1, PMN1, PMX2, PMN2, PMX3, and PMN3 indicated in [Specification Data] are the same as those described in the above-described embodiment. QC1, QE1, and QE2 indicated in [Specification Data] are the same as those described in the above-described embodiment.

In [Lens Data], the surface number represents the number of each lens surface counted from the eyepoint side, R represents the radius of curvature of each lens surface, D represents the interval between respective lens surfaces, nd represents a refractive index with reference to d-line (wavelength λ=587.6 nm), and νd represents an Abbe number with reference to d-line (wavelength λ=587.6 nm). Note that *a attached on the right side of a first column (surface number) indicates that the lens surface is aspherical, and *b attached on the right side of the first column (surface number) indicates that the lens surface is a Fresnel surface (Fresnel surface portion of Fresnel zone FR) having an aspherical shape. The radius of curvature “∞” indicates a flat surface or an aperture, and the description of the refractive index nd=1.0000 of air is omitted.

In [Aspherical Surface Data], when the corresponding lens surface is a Fresnel surface having an aspherical shape, the aspherical coefficient of the above-mentioned expression (A) for the arrangement reference aspherical surface and the aspherical coefficient of the above-mentioned expression (B) for the shape reference aspherical surface are indicated. When the corresponding lens surface is a general aspherical surface, an aspherical coefficient expressed by the following expression (E) is indicated.

[Expression⁢⁢5]Z=y2/R1+1-(1+k)⁢y2/R2+∑i=210⁢C2⁢i×y2⁢i,(E)
where Z represents the sag amount (in the central axis direction of the lens) of an aspherical surface at the distance y from the central axis of the lens,R represents the radius of curvature of a reference spherical surface on an aspherical surface (paraxial radius of curvature),k represents the conic constant of the aspherical surface, andC2irepresents the (2×i)-order aspherical coefficient.

In [Aspherical Surface Data], “E-n” represents “×10−n”. For example, “1.234E-05” represents “1.234×10−5”. In [Fresnel Data], “zone” indicates the order of a Fresnel zone counted from the central axis of the Fresnel lens. “Valley coordinate y” indicates the distance from the central axis of the Fresnel lens at the valley portion formed at the boundary between the (N)-th Fresnel zone and the (N+1)-th Fresnel zone which correspond to the order (N)−(N+1) indicated in “zone”. “Valley coordinate z” indicates the sag amount (in the central axis direction of the Fresnel lens) of the valley portion formed at the boundary between the (N)-th Fresnel zone and the (N+1)-th Fresnel zone. “Mountain coordinate y” indicates the distance from the central axis of the Fresnel lens at the vertex portion of the (N+1)-th Fresnel zone and “Mountain coordinate z” indicates the sag amount (in the central axis direction of the Fresnel lens) at the vertex portion of the (N+1)-th Fresnel zone. “Pitch” indicates the pitch in the radial direction (y-direction) between the (N)-th Fresnel zone and the (N+1)-th Fresnel zone. [Conditional Expression Corresponding Value] indicates the corresponding value of each conditional expression.

Note that “mm” is generally used as the units of the focal length f, the radius of curvature R, and other lengths listed in all the following specification values, but it is not specifically limited because the optical system may have same level optical performance even when it is proportionally expanded or proportionally contracted. The foregoing description on the tables are common to all the examples, and the duplicate description thereon is omitted.

First Example

The first example will be described with reference toFIGS.1to6and Table 1. The ocular optical system of each example is used as an ocular optical system for observing an image displayed on the image display part11.FIG.1is a diagram showing a lens configuration of the ocular optical system according to the first example of the present embodiment. The ocular optical system EL (1) according to the first example comprises a biconvex Fresnel lens L1having a positive refractive power.

An aspherical surface is formed on the lens surface on an eyepoint EP side of the Fresnel lens L1. A plurality of Fresnel zones FR are formed on the lens surface on an image display part11side (observation object side) of the Fresnel lens L1. As shown inFIG.2, the first Fresnel zone FR (1) located on the most central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR is formed in a disk-like shape coaxial with the central axis of the Fresnel lens L1. The first Fresnel zone FR (1) has an aspherical Fresnel surface portion FRa (1). The second and subsequent Fresnel zones FR counted from the central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR are formed in an annular shape coaxial with the central axis of the Fresnel lens L1. The second and subsequent Fresnel zones FR each have an aspherical Fresnel surface portion FRa and a stepped and wall-shaped wall surface portion FRb. The vertex portions of the respective Fresnel zones FR are arranged side by side along the above-mentioned arrangement reference aspherical surface.

The following Table 1 lists specification values of the ocular optical system according to the first example.

TABLE 1[Specification Data]f = 41.65ω = ±55°ER = 14.30TL = 68.91DA = 66.00PAC1 = 2.02PAE1 = 0.69PAE2 = 0.96PAE3 = 1.11PMX1 = 9.60PMN1 = 0.45PMX2 = 9.60PMN2 = 1.70PMX3 = 2.34PMN3 = 1.70QC1 = 2QE1 = 9QE2 = 5[Lens Data]Surface NumberRDνdnd1*a86.864980415.4057.071.49292*b−25.3095268339.21[Aspherical Surface Data]1st Surfacek = −2.29C4 = 0.00E+00, C6 = −2.62E−09, C8 = 4.41E−12,C10 = −2.34E−15, C12 = 2.14E−19C14 = 0.00E+00, C16 = 0.00E+00, C18 = 0.00E+00,C20 = 0.00E+002nd Surface (arrangement reference aspherical surface)kd = −12.45A4 = 0.00E+00, A6 = 0.00E+00, A8 = 0.00E+00,A10 = 0.00E+00, A12 = 0.00E+00A14 = 0.00E+00, A16 = 0.00E+00, A18 = 0.00E+00,A20 = 0.00E+002nd Surface (shape reference aspherical surface)kr = −1.48B4 = 0.00E+00, B6 = −8.98E−09, B8 = 1.22E−11,B10 = −4.89E−15, B12 = 0.00E+00B14 = 0.00E+00, B16 = 0.00E+00, B18 = 0.00E+00,B20 = 0.00E+00[Fresnel Data]ValleyValleyMountainMountainCoordinateCoordinateCoordinateCoordinateZoneyzyzPitch1-29.6008−1.79689.6508−1.41539.602-311.9393−2.365911.9987−1.99322.343-413.6438−2.801913.7094−2.43631.704-515.0395−3.168515.1095−2.80901.405-616.2448−3.490616.3183−3.13641.216-717.3188−3.781017.3950−3.43171.077-818.2956−4.047718.3740−3.70280.988-919.1974−4.295619.2776−3.95470.909-1020.0394−4.528420.1210−4.19120.8410-1120.8326−4.748920.9153−4.41500.7911-1221.5853−4.958921.6690−4.62800.7512-1322.3040−5.160222.3884−4.83200.7213-1422.9938−5.354123.0788−5.02830.6914-1523.6589−5.541423.7443−5.21790.6715-1624.3027−5.723224.3883−5.40160.6416-1724.9279−5.900225.0137−5.58030.6317-1825.5369−6.072925.6227−5.75450.6118-1926.1316−6.241926.2174−5.92480.5919-2026.7136−6.407626.7993−6.09150.5820-2127.2842−6.570227.3696−6.25510.5721-2227.8444−6.730127.9294−6.41580.5622-2328.3948−6.887428.4793−6.57370.5523-2428.9358−7.042229.0198−6.72910.5424-2529.4676−7.194629.5510−6.88190.5325-2629.9900−7.344430.0726−7.03210.5226-2730.5026−7.491630.5844−7.17960.5127-2831.0048−7.635931.0856−7.32430.5028-2931.4957−7.777131.5754−7.46590.4929-3031.9743−7.914832.0528−7.60410.4830-3132.4394−8.048832.5166−7.73870.4731-3232.8900−8.178732.9658−7.86920.45[Conditional Expression Corresponding Value]Conditional Expression (1) PAE1/PAC1 = 0.34Conditional Expression (2) PAE2/PAC1 = 0.48Conditional Expression (3) PAE3/PAC1 = 0.45Conditional Expression (4) PAC1 = 2.02Conditional Expression (5) PMX1/PMN1 = 21.31Conditional Expression (6) PMX2/PMN2 = 5.63Conditional Expression (7) PMX3/PMN3 = 1.37Conditional Expression (8) QE1/QC1 = 4.5Conditional Expression (9) QE2/QC1 = 2.5Conditional Expression (10) kd= −12.45Conditional Expression (11) kr= −1.48(>kd)

FIG.3shows various aberration graphs of the ocular optical system according to the first example.FIG.4shows a lateral aberration graph of the ocular optical system according to the first example.FIG.5is a spot diagram of the ocular optical system according to the first example. In each aberration graph, d represents d-line (wavelength λ=587.6 nm), e represents e-line (wavelength λ=546.1 nm), g represents g-line (wavelength λ=435.8 nm), C represents C-line (wavelength λ=656.3 nm), and F represents F-line (wavelength λ=486.1 nm). In the astigmatism diagram, a solid line represents a sagittal image surface, and a broken line represents a meridional image surface. In the lateral aberration graph, RFH represents an image height ratio (Relative Field Height). In the spot diagram, the vertical axis shows a field position, and the horizontal axis shows a defocus amount.

FIG.6is a flare comparative diagram of the ocular optical system according to the first example. Here, a method of measuring flare shown inFIG.6will be described. A measuring device shown inFIG.32Ais assumed as a device for measuring the flare shown inFIG.6, and the flare was calculated by a light beam tracing simulation. The measuring device shown inFIG.32Acomprises, in order from a light source, a point light source Pm, ocular optical systems EL {EL(1) to EL(5)} as lenses under test, an aperture stop Sm, a measuring optical system Lm, and a light receiver Dm. The aperture stop Sm is arranged at the position of the eyepoint EP in the ocular optical system EL. The aperture stop Sm corresponds to an iris diaphragm of a human eye. A character θ inFIG.32Arepresents the angle of a light beam incident on the human eye.

Light from the point light source Pm passes through the ocular optical system EL as the lens under test, is restricted by the aperture stop Sm, passes through the measuring optical system Lm, and then reaches the light receiver Dm. Signal values of the light from the point light source Pm and the flare can be calculated based on a detection signal of the light detected by the light receiver Dm. When the signal values are calculated, the point light source Pm is made large enough to clarify a range indicating the signal value of the light from the point light source Pm. The vertex portions of the second and subsequent Fresnel zones FR counted from the central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR do not have perfect edge shapes, but actually have rounded shapes as shown inFIG.32B. Therefore, when the signal value is calculated, the approximation is performed so that the radiuses of curvature Rm of the vertex portions of the second and subsequent Fresnel zones FR are set to 50 μm. The signal values (signal intensities) of the light from the point light source Pm and the flare which are calculated according to light beam tracing by using such a measuring device are shown in the flare comparative diagram ofFIG.6.

In the flare comparative diagram ofFIG.6, the light intensity (signal intensity) on the vertical axis is standardized so that the signal intensity corresponding to the light intensity of emission light emitted from the point light source Pm is 1, and is logarithmically displayed. The position x on the horizontal axis is a relative position on a light receiving surface in the light receiver Dm. A relatively high signal intensity in a region where the position x is about 55 to 65 [pixels] indicates the signal intensity of the light from the point light source Pm, and a relatively low signal intensity in a region out of the former region indicates the signal intensity of the flare.

Note that the signal values (signal intensities) of light from the point light source Pm and the flare which were calculated by the light beam tracing simulation using a comparative Fresnel lens as a lens under test as indicated by a two-dotted chain line inFIG.31are shown as comparative data. The comparative Fresnel lens is a Fresnel lens in which a plurality of Fresnel zones are arranged concentrically along a spherical surface. As is apparent fromFIG.31, the number of discontinuous portions (wall surface portions) of the Fresnel zones in the comparative Fresnel lens is smaller than that of the conventional Fresnel lens, and larger than that of the Fresnel lens L1according to each example. Therefore, if the flare calculated when the ocular optical system EL {EL(1) to EL(5)} according to each example is used as the lens under test is smaller than the flare calculated when the comparative Fresnel lens is used as the lens under test, from the correlation of the number of discontinuous portions (wall surface portions) of the Fresnel zones, it is possible to evaluate that the flare is reduced as compared with the conventional Fresnel lens.

Note that in the aberration graph and flare comparative diagram of each example shown below, the same numerals and characters as those of the present example are used, and duplicate description thereof is omitted. It is apparent from each aberration graph and the flare comparative diagram that in the first example, various aberrations are successfully corrected, flare is reduced as compared with the conventional Fresnel lens, and excellent image formation performance is obtained.

Second Example

A second example will be described with reference toFIGS.7to12and Table 2.FIG.7is a diagram showing a lens configuration of an ocular optical system according to the second example of the present embodiment. The ocular optical system EL (2) according to the second example comprises a biconvex Fresnel lens L1having a positive refractive power.

An aspherical surface is formed on the lens surface on an eyepoint EP side of the Fresnel lens L1. A plurality of Fresnel zones FR are formed on the lens surface on an image display part11side (observation object side) of the Fresnel lens L1. As shown inFIG.8, the first Fresnel zone FR (1) located on the most central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR is formed in a disk shape coaxial with the central axis of the Fresnel lens L1. The first Fresnel zone FR (1) has a Fresnel surface portion FRa (1) having an aspherical shape. The second and subsequent Fresnel zones FR counted from the central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR are formed in an annular shape coaxial with the central axis of the Fresnel lens L1. The second and subsequent Fresnel zones FR each have an aspherical Fresnel surface portion FRa and a stepped and wall-shaped wall surface portion FRb. The vertex portions of the respective Fresnel zones FR are arranged side by side along the above-mentioned arrangement reference aspherical surface.

The following Table 2 lists specification values of the ocular optical system according to the second example.

TABLE 2[Specification Data]f = 41.96ω = ±55°ER = 14.30TL = 69.29DA = 64.00PAC1 = 2.03PAE1 = 0.65PAE2 = 1.00PAE3 = 1.12PMX1 = 10.20PMN1 = 0.29PMX2 = 10.20PMN2 = 1.71PMX3 = 2.34PMN3 = 1.71QC1 = 2QE1 = 8QE2 = 5[Lens Data]Surface NumberRDνdnd1*a94.111444815.4056.461.52732*b−27.2888436339.59[Aspherical Surface Data]1st Surfacek = −2.02C4 = 0.00E+00, C6 = −4.33E−09, C8 = 8.40E−12,C10 = −6.13E−15, C12 = 5.79E−19C14 = 0.00E+00, C16 = 0.00E+00, C18 = 0.00E+00,C20 = 0.00E+002nd Surface (arrangement reference aspherical surface)kd = −14.00A4 = 0.00E+00, A6 = 0.00E+00, A8 = 0.00E+00,A10 = 0.00E+00, A12 = 0.00E+00A14 = 0.00E+00, A16 = 0.00E+00, A18 = 0.00E+00,A20 = 0.00E+002nd Surface (shape reference aspherical surface)kr = −1.67B4 = 0.00E+00, B6 = −1.37E−08, B8 = 2.32E−11,B10 = −1.29E−14, B12 = 0.00E+00B14 = 0.00E+00, B16 = 0.00E+00, B18 = 0.00E+00,B20 = 0.00E+00[Fresnel Data]ValleyValleyMountainMountainCoordinateCoordinateCoordinateCoordinateZoneyzyzPitch1-210.1972−1.875710.2499−1.494910.202-312.5364−2.425112.5984−2.05292.343-414.2489−2.844414.3169−2.47911.714-515.6527−3.196015.7251−2.83671.405-616.8664−3.504316.9421−3.15031.216-717.9492−3.782318.0275−3.43301.087-818.9358−4.037619.0162−3.69260.998-919.8485−4.275319.9306−3.93410.919-1020.7025−4.498820.7859−4.16100.8510-1121.5085−4.710621.5930−4.37600.8111-1222.2744−4.912622.3597−4.58090.7712-1323.0058−5.106223.0916−4.77700.7313-1423.7067−5.292123.7930−4.96540.7014-1524.3800−5.471224.4665−5.14680.6715-1625.0275−5.643825.1140−5.32150.6516-1725.6501−5.810025.7365−5.48990.6217-1826.2482−5.970026.3343−5.65200.6018-1926.8216−6.123626.9072−5.80780.5719-2027.3699−6.270727.4548−5.95720.5520-2127.8926−6.411127.9767−6.10000.5221-2228.3893−6.544728.4725−6.23620.5022-2328.8598−6.671328.9419−6.36560.4723-2429.3042−6.791129.3852−6.48830.4424-2529.7232−6.904029.8028−6.60430.4225-2630.1173−7.010430.1956−6.71390.3926-2730.4878−7.110430.5647−6.81730.3727-2830.8360−7.204530.9114−6.91480.3528-2931.1631−7.292931.2370−7.00680.3329-3031.4707−7.376131.5431−7.09350.3130-3131.7601−7.454431.8311−7.17540.29[Conditional Expression Corresponding Value]Conditional Expression (1) PAE1/PAC1 = 0.32Conditional Expression (2) PAE2/PAC1 = 0.50Conditional Expression (3) PAE3/PAC1 = 0.55Conditional Expression (4) PAC1 = 2.03Conditional Expression (5) PMX1/PMN1 = 35.23Conditional Expression (6) PMX2/PMN2 = 5.95Conditional Expression (7) PMX3/PMN3 = 1.37Conditional Expression (8) QE1/QC1 = 4.0Conditional Expression (9) QE2/QC1 = 2.5Conditional Expression (10) kd= −14.00Conditional Expression (11) kr= −1.67(>kd)

FIG.9shows various aberration graphs of the ocular optical system according to the second example.FIG.10shows a lateral aberration graph of the ocular optical system according to the second example.FIG.11is a spot diagram of the ocular optical system according to the second example.FIG.12is a flare comparative diagram of the ocular optical system according to the second example. From each aberration graph and the flare comparative diagram, it is apparent that in the second example, various aberrations are successfully corrected, flare is also reduced as compared with the conventional Fresnel lens, and excellent image formation performance is obtained.

Third Example

A third example will be described with reference toFIGS.13to18and Table 3.FIG.13is a diagram showing a lens configuration of an ocular optical system according to the third example of the present embodiment. The ocular optical system EL (3) according to the third example comprises a biconvex Fresnel lens L1having a positive refractive power.

An aspherical surface is formed on the lens surface on the eyepoint EP side of the Fresnel lens L1. A plurality of Fresnel zones FR are formed on the lens surface on the image display part11side (observation object side) of the Fresnel lens L1. As shown inFIG.14, the first Fresnel zone FR (1) located on the most central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR is formed in a disk shape coaxial with the central axis of the Fresnel lens L1. The first Fresnel zone FR (1) has a Fresnel surface portion FRa (1) having an aspherical shape. The second and subsequent Fresnel zones FR counted from the central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR are formed in an annular shape coaxial with the central axis of the Fresnel lens L1. The second and subsequent Fresnel zones FR each have an aspherical Fresnel surface portion FRa and a stepped and wall-shaped wall surface portion FRb. The vertex portions of the respective Fresnel zones FR are arranged side by side along the above-mentioned arrangement reference aspherical surface.

The following Table 3 lists specification values of the ocular optical system according to the third example.

TABLE 3[Specification Data]f = 41.82ω = ±55°ER = 14.30TL = 66.83DA = 64.00PAC1 = 2.37PAE1 = 0.70PAE2 = 1.16PAE3 = 1.26PMX1 = 8.90PMN1 = 0.28PMX2 = 8.90PMN2 = 1.97PMX3 = 2.76PMN3 = 1.97QC1 = 2QE1 = 7QE2 = 5[Lens Data]Surface NumberRDνdnd1*a142.197793912.1023.891.64172*b−31.9800115540.43[Aspherical Surface Data]1st Surfacek = 18.64C4 = 0.00E+00, C6 = −4.59E−09, C8 = 2.76E−12,C10 = 3.29E−15, C12 = −5.20E−18C14 = 0.00E+00, C16 = 0.00E+00, C18 = 0.00E+00,C20 = 0.00E+002nd Surface (arrangement reference aspherical surface)kd = −20.34A4 = 0.00E+00, A6 = 0.00E+00, A8 = 0.00E+00,A10 = 0.00E+00, A12 = 0.00E+00A14 = 0.00E+00, A16 = 0.00E+00, A18 = 0.00E+00,A20 = 0.00E+002nd Surface (shape reference aspherical surface)kr = −1.72B4 = 0.00E+00, B6 = −9.08E−09, B8 = 1.46E−11,B10 = −8.80E−15, B12 = 0.00E+00B14 = 0.00E+00, B16 = 0.00E+00, B18 = 0.00E+00,B20 = 0.00E+00[Fresnel Data]ValleyValleyMountainMountainCoordinateCoordinateCoordinateCoordinateZoneyzyzPitch1-28.8989−1.22528.9463−0.83828.902-311.6559−1.693611.7150−1.31482.763-413.6301−2.057813.6968−1.68571.974-515.2287−2.365215.3008−1.99901.605-616.5985−2.635516.6748−2.27461.376-717.8116−2.879417.8911−2.52321.217-818.9094−3.103018.9914−2.75121.108-919.9182−3.310720.0021−2.96281.019-1020.8555−3.505420.9410−3.16100.9410-1121.7336−3.688921.8202−3.34790.8811-1222.5611−3.863022.6485−3.52500.8312-1323.3442−4.028523.4321−3.69340.7813-1424.0873−4.186324.1755−3.85390.7414-1524.7934−4.336824.8817−4.00710.7115-1625.4647−4.480325.5528−4.15320.6716-1726.1025−4.617026.1902−4.29260.6417-1826.7078−4.747226.7950−4.42540.6118-1927.2813−4.870727.3678−4.55160.5719-2027.8238−4.987927.9094−4.67160.5420-2128.3360−5.098728.4206−4.78530.5121-2228.8189−5.203328.9023−4.89290.4822-2329.2736−5.301929.3557−4.99470.4523-2429.7013−5.394929.7821−5.09090.4324-2530.1036−5.482430.1830−5.18160.4025-2630.4818−5.564830.5598−5.26740.3826-2730.8377−5.642330.9142−5.34830.3627-2831.1728−5.715431.2478−5.42480.3428-2931.4885−5.784431.5621−5.49710.3229-3031.7864−5.849531.8586−5.56560.30[Conditional Expression Corresponding Value]Conditional Expression (1) PAE1/PAC1 = 0.30Conditional Expression (2) PAE2/PAC1 = 0.49Conditional Expression (3) PAE3/PAC1 = 0.53Conditional Expression (4) PAC1 = 2.37Conditional Expression (5) PMX1/PMN1 = 31.61Conditional Expression (6) PMX2/PMN2 = 4.51Conditional Expression (7) PMX3/PMN3 = 1.40Conditional Expression (8) QE1/QC1 = 3.5Conditional Expression (9) QE2/QC1 = 2.5Conditional Expression (10) kd= −20.34Conditional Expression (11) kr= −1.72(>kd)

FIG.15shows various aberration graphs of the ocular optical system according to the third example.FIG.16shows a lateral aberration graph of the ocular optical system according to the third example.FIG.17is a spot diagram of the ocular optical system according to the third example.FIG.18is a flare comparative diagram of the ocular optical system according to the third example. From each aberration graph and the flare comparative diagram, it is apparent in the third example that various aberrations are successfully corrected, flare is reduced as compared with the conventional Fresnel lens, and excellent image formation performance is obtained.

Fourth Example

A fourth example will be described with reference toFIGS.19to24and Table 4.FIG.19is a diagram showing a lens configuration of an ocular optical system according to a fourth example of the present embodiment. The ocular optical system EL (4) according to the fourth example comprises, in order from an eyepoint EP, a biconvex Fresnel lens L1having a positive refractive power, and an aspherical lens L2having aspherical lens surfaces on both sides thereof.

An aspherical surface is formed on the lens surface on an eyepoint EP side of the Fresnel lens L1. A plurality of Fresnel zones FR are formed on the lens surface on an image display part11side (observation object side) of the Fresnel lens L1. As shown inFIG.20, the first Fresnel zone FR (1) located on the most central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR is formed in a disk shape coaxial with the central axis of the Fresnel lens L1. The first Fresnel zone FR (1) has a Fresnel surface portion FRa (1) having an aspherical shape. The second and subsequent Fresnel zones FR counted from the central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR are formed in an annular shape coaxial with the central axis of the Fresnel lens L1. The second and subsequent Fresnel zones FR each have an aspherical Fresnel surface portion FRa and a stepped and wall-shaped wall surface portion FRb. The vertex portions of the respective Fresnel zones FR are arranged side by side along the above-mentioned arrangement reference aspherical surface.

The following Table 4 lists specification values of the ocular optical system according to the fourth example.

TABLE 4[Specification Data]f = 35.80ω = ±55°ER = 14.30TL = 63.80DA = 62.00PAC1 = 1.62PAE1 = 0.59PAE2 = 0.75PAE3 = 0.83PMX1 = 8.13PMN1 = 0.49PMX2 = 8.13PMN2 = 1.15PMX3 = 2.31PMN3 = 1.15QC1 = 4QE1 = 10QE2 = 6[Lens Data]Surface NumberRDνdnd1*a72.1167712614.0057.071.49292*b−22.238980.143*a344.52941516.5157.071.49294*a407.042174128.85[Aspherical Surface Data]1st Surfacek = −3.92C4 = 0.00E+00, C6 = −9.21E−09, C8 = 1.20E−11,C10 = −2.09E−15, C12 = −2.57E−18C14 = 0.00E+00, C16 = 0.00E+00, C18 = 0.00E+00,C20 = 0.00E+002nd Surface (arrangement reference aspherical surface)kd = −12.45A4 = 0.00E+00, A6 = 0.00E+00, A8 = 0.00E+00,A10 = 0.00E+00, A12 = 0.00E+00A14 = 0.00E+00, A16 = 0.00E+00, A18 = 0.00E+00,A20 = 0.00E+002nd Surface (shape reference aspherical surface)kr = −1.58B4 = 0.00E+00, B6 = −1.77E−08, B8 = 2.29E−11,B10 = −8.01E−15, B12 = 0.00E+00B14 = 0.00E+00, B16 = 0.00E+00, B18 = 0.00E+00,B20 = 0.00E+003rd Surfacek = 100.00C4 = 0.00E+00, C6 = −1.11E−09, C8 = 3.55E−13,C10 = 5.83E−17, C12 = 0.00E+00C14 = 0.00E+00, C16 = 0.00E+00, C18 = 0.00E+00,C20 = 0.00E+004th Surfacek = −100.00C4 = 0.00E+00, C6 = −2.18E−09, C8 = −3.24E−12,C10 = 2.36E−15, C12 = 0.00E+00C14 = 0.00E+00, C16 = 0.00E+00, C18 = 0.00E+00,C20 = 0.00E+00[Fresnel Data]ValleyValleyMountainMountainCoordinateCoordinateCoordinateCoordinateZoneyzyzPitch1-28.1313−1.46348.1704−1.07738.132-310.4394−1.996210.4883−1.61842.313-412.0991−2.406112.1547−2.03531.664-513.4457−2.750513.5064−2.38601.355-614.5998−3.052214.6646−2.69341.156-715.6207−3.323315.6889−2.96971.027-816.5430−3.570916.6139−3.22230.928-917.3889−3.800117.4621−3.45610.859-1018.1737−4.014318.2488−3.67460.7810-1118.9085−4.216018.9853−3.88040.7311-1219.6019−4.407319.6801−4.07540.6912-1320.2604−4.589820.3398−4.26140.6613-1420.8892−4.764720.9697−4.43950.6314-1521.4928−4.933121.5742−4.61100.6015-1622.0747−5.095922.1568−4.77660.5816-1722.6379−5.254022.7207−4.93710.5617-1823.1851−5.407923.2685−5.09330.5518-1923.7186−5.558323.8025−5.24570.5319-2024.2405−5.705724.3249−5.39500.5220-2124.7525−5.850524.8373−5.54140.5121-2225.2565−5.993425.3416−5.68560.5022-2325.7539−6.134625.8393−5.82790.5023-2426.2462−6.274526.3318−5.96880.4924-2526.7348−6.413626.8207−6.10860.4925-2627.2211−6.552227.3071−6.24760.4926-2727.7063−6.690727.7925−6.38630.4927-2828.1917−6.829428.2780−6.52500.4928-2928.6786−6.968628.7650−6.66410.4929-3029.1682−7.108829.2545−6.80380.4930-3129.6616−7.250229.7478−6.94460.4931-3230.1598−7.393230.2459−7.08660.5032-3330.6637−7.537930.7497−7.23030.50[Conditional Expression Corresponding Value]Conditional Expression (1) PAE1/PAC1 = 0.37Conditional Expression (2) PAE2/PAC1 = 0.46Conditional Expression (3) PAE3/PAC1 = 0.52Conditional Expression (4) PAC1 = 1.62Conditional Expression (5) PMX1/PMN1 = 16.76Conditional Expression (6) PMX2/PMN2 = 7.05Conditional Expression (7) PMX3/PMN3 = 2.00Conditional Expression (8) QE1/QC1 = 2.5Conditional Expression (9) QE2/QC1 = 1.5Conditional Expression (10) kd= −12.45Conditional Expression (11) kr= −1.58(>kd)

FIG.21shows various aberration graphs of the ocular optical system according to the fourth example.FIG.22shows a lateral aberration graph of the ocular optical system according to the fourth example.FIG.23is a spot diagram of the ocular optical system according to the fourth example.FIG.24is a flare comparative diagram of the ocular optical system according to the fourth example. From each aberration graph and the flare comparison diagram, it is apparent in the fourth embodiment that various aberrations are successfully corrected, flare is reduced as compared with the conventional Fresnel lens, and excellent image formation performance is obtained.

Fifth Example

A fifth example will be described with reference toFIGS.25to30and Table 5.FIG.25is a diagram showing a lens configuration of an ocular optical system according to a fifth example of the present embodiment. The ocular optical system EL (5) according to the fifth example comprises, in order from an eyepoint EP side, a first biconvex Fresnel lens L1having a positive refractive power, and a second biconvex lens L2having a positive refractive power.

An aspherical surface is formed on the lens surface on an eyepoint EP side of the first Fresnel lens L1. A plurality of Fresnel zones FR are formed on the lens surface on an image display part11side (observation object side) of the first Fresnel lens L1. As shown inFIG.26, the first Fresnel zone FR (1) located on the most central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR is formed in a disk shape coaxial with the central axis of the Fresnel lens L1. The first Fresnel zone FR (1) has a Fresnel surface portion FRa (1) having an aspherical shape. The second and subsequent Fresnel zones FR counted from the central axis side of the Fresnel lens L1out of the plurality of Fresnel zones FR are formed in an annular shape coaxial with the central axis of the Fresnel lens L1. The second and subsequent Fresnel zones FR each have an aspherical Fresnel surface portion FRa and a stepped and wall-shaped wall surface portion FRb. The vertex portions of the respective Fresnel zones FR are arranged side by side along the above-mentioned arrangement reference aspherical surface.

An aspherical surface is formed on the lens surface on an eyepoint EP side of the second Fresnel lens L2. A plurality of Fresnel zones FS are formed on the lens surface on an image display part11side (observation object side) of the second Fresnel lens L2. Each Fresnel zone FS of the second Fresnel lens L2has a shape similar to that of each Fresnel zone FR of the first Fresnel lens L1, but does not satisfy the conditions of the conditional expression (1) and the like.

The following Table 5 lists specification values of the ocular optical system according to the fifth example.

TABLE 5[Specification Data]f = 33.15ω = ±55°ER = 14.30TL = 62.26DA = 58.00PAC1 = 1.76PAE1 = 0.76PAE2 = 0.89PAE3 = 0.96PMX1 = 8.59PMN1 = 0.52PMX2 = 8.59PMN2 = 1.36PMX3 = 2.28PMN3 = 1.36QC1 = 3QE1 = 9QE2 = 6[Lens Data]Surface NumberRDνdnd1*a133.761556712.1257.071.49292*b−23.566163070.103*a118.03054229.7057.071.49294*b−180.000000026.05[Aspherical Surface Data]1st Surfacek = −5.69C4 = 0.00E+00, C6 = −4.13E−09, C8 = 9.50E−12,C10 = −6.03E−15, C12 = −3.33E−19C14 = 0.00E+00, C16 = 0.00E+00, C18 = 0.00E+00,C20 = 0.00E+002nd Surface (arrangement reference aspherical surface)kd = −13.00A4 = 0.00E+00, A6 = 0.00E+00, A8 = 0.00E+00,A10 = 0.00E+00, A12 = 0.00E+00A14 = 0.00E+00, A16 = 0.00E+00, A18 = 0.00E+00,A20 = 0.00E+002nd Surface (shape reference aspherical surface)kr = −1.25B4 = 0.00E+00, B6 = −7.41E−09, B8 = 2.01E−11,B10 = −1.30E−14, B12 = 0.00E+00B14 = 0.00E+00, B16 = 0.00E+00, B18 = 0.00E+00,B20 = 0.00E+003rd Surfacek = 0.72C4 = 0.00E+00, C6 = −5.61E−09, C8 = 9.74E−12,C10 = −3.75E−15, C12 = −1.97E−18C14 = 0.00E+00, C16 = 0.00E+00, C18 = 0.00E+00,C20 = 0.00E+004th Surface (arrangement reference aspherical surface)kd = −10.00A4 = 0.00E+00, A6 = 0.00E+00, A8 = 0.00E+00,A10 = 0.00E+00, A12 = 0.00E+00A14 = 0.00E+00, A16 = 0.00E+00, A18 = 0.00E+00,A20 = 0.00E+004th Surface (shape reference aspherical surface)kr = −3.05B4 = 0.00E+00, B6 = −1.55E−08, B8 = 1.88E−11,B10 = −8.57E−15, B12 = 0.00E+00B14 = 0.00E+00, B16 = 0.00E+00, B18 = 0.00E+00,B20 = 0.00E+00[Fresnel Data]ValleyValleyMountainMountainCoordinateCoordinateCoordinateCoordinateZoneyzyzPitch1-18.5915−1.55578.6404−1.17348.592-310.8706−2.083310.9301−1.71042.283-412.5259−2.489812.5926−2.12461.664-513.8843−2.833813.9566−2.47551.365-615.0634−3.138415.1401−2.78611.186-716.1209−3.415416.2014−3.06871.067-817.0906−3.672117.1743−3.33040.978-917.9938−3.913218.0803−3.57610.909-1018.8454−4.142118.9345−3.80920.8510-1119.6561−4.361319.7475−4.03220.8111-1220.4340−4.572520.5274−4.24700.7812-1321.1852−4.777421.2805−4.45510.7513-1421.9145−4.977122.0116−4.65770.7314-1522.6255−5.172322.7241−4.85570.7115-1623.3208−5.363823.4209−5.04970.7016-1724.0021−5.551924.1036−5.24020.6817-1824.6703−5.736824.7729−5.42740.6718-1925.3250−5.918425.4286−5.61130.6519-2025.9650−6.096326.0694−5.79160.6420-2126.5882−6.269726.6932−5.96760.6221-2227.1916−6.438027.2968−6.13870.6022-2327.7718−6.600027.8771−6.30390.5823-2428.3256−6.754828.4305−6.46230.55[Conditional Expression Corresponding Value]Conditional Expression (1) PAE1/PAC1 = 0.43Conditional Expression (2) PAE2/PAC1 = 0.51Conditional Expression (3) PAE3/PAC1 = 0.55Conditional Expression (4) PAC1 = 1.76Conditional Expression (5) PMX1/PMN1 = 16.38Conditional Expression (6) PMX2/PMN2 = 6.32Conditional Expression (7) PMX3/PMN3 = 1.68Conditional Expression (8) QE1/QC1 = 3.0Conditional Expression (9) QE2/QC1 = 2.0Conditional Expression (10) kd= −13.00Conditional Expression (11) kr= −1.25(>kd)

FIG.27shows various aberration graphs of the ocular optical system according to the fifth example.FIG.28shows a lateral aberration graph of the ocular optical system according to the fifth example.FIG.29is a spot diagram of the ocular optical system according to the fifth example.FIG.30is a flare comparative diagram of the ocular optical system according to the fifth example. From each aberration graph and the flare comparison diagram, it is apparent in the fifth example that various aberrations are successfully corrected, flare is reduced as compared with the conventional Fresnel lens, and excellent image formation performance is obtained.

As described above, according to each example, it is possible to realize an ocular optical system in which flare occurring in the neighborhood portion of the central axis of the Fresnel lens L1is reduced.

In each example, the wall surface portions FRb of a plurality of Fresnel zones FR may be coated with light-shielding members (not shown) made of paint using black synthetic resin. Examples of the paint using the black synthetic resin include curable acrylic urethane paint, phthalic acid resin enamel paint and the like.

Note that the following contents can be appropriately adopted as long as the optical performance of the optical system of the present embodiment is not impaired.

As numerical examples of the ocular optical system of the present embodiment a one-sheet configuration and a two-sheet configuration are shown. However, the present application is not limited to these configurations, and an ocular optical system having other configurations (for example, three-sheet configuration and the like) may be configured. Specifically, a lens or a lens group may be added on the most object side or the most image surface side of the ocular optical system of the present embodiment.

The lens surface may be formed of a spherical surface or a flat surface, or may be formed of an aspherical surface. When the lens surface is a spherical surface or a flat surface, lens processing and assembly adjustment are facilitated, and deterioration of optical performance caused by errors in processing and assembly adjustment can be prevented.

When the lens surface is an aspherical surface, the aspherical surface may be any one of an aspherical surface formed by grinding, a glass mold aspherical surface formed by forming glass into an aspherical shape with a mold, and a composite type aspherical surface formed by forming resin on the surface of glass in an aspherical shape. Further, the lens surface may be a diffractive optical surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

EXPLANATION OF NUMERALS AND CHARACTERS

1Head mounted display11image display part (observation object)EL ocular optical systemL1Fresnel lensFR Fresnel zoneEP eyepoint