WO2018117025A1

WO2018117025A1 - Observation optical system and observation device having same

Info

Publication number: WO2018117025A1
Application number: PCT/JP2017/045313
Authority: WO
Inventors: 裕基江部
Original assignee: キヤノン株式会社
Priority date: 2016-12-21
Filing date: 2017-12-18
Publication date: 2018-06-28

Abstract

An observation optical system according to the present invention comprises a Fresnel lens, and a lens LP having positive refractive power and provided on the light incidence side or light emission side of the Fresnel lens, wherein the length in an optical axis direction from a surface vertex of a central zone of the Fresnel lens to an end of the central zone thereof is denoted by h0, the length in the optical axis direction of a grating wall surface of a first zone adjacent to the central zone is denoted by h1, and both the lengths are appropriately set.

Description

Observation optical system and observation apparatus having the same

The present invention relates to an observation optical system suitable for, for example, a head mounted display for displaying an enlarged original image displayed on an image display element such as liquid crystal and observing the same.

Conventionally, an original image displayed using an image display element such as a CRT or an LCD is enlarged and displayed through the observation optical system, and a large screen image is given to the user, so that realistic observation can be performed. An observation device such as a head mounted display has been proposed. In recent years, with regard to observation devices, it has been desired that a higher sense of reality can be obtained, and for that reason, observation optical systems used in observation devices are required to be compatible with wide viewing angles and have high optical performance. ing. Furthermore, when used in a head-mounted or hand-held type observation apparatus, it is required that the observation optical system be compact and lightweight.

Conventionally, an eyepiece image display apparatus in which a Fresnel lens is disposed in an optical path is known as an observation optical system which achieves a wide viewing angle and weight reduction (Patent Document 1). In addition, a resin lens is used to reduce the weight of the observation optical system, and at this time, a diffractive lens structure is provided in the peripheral portion of the lens to suppress shift in focus due to temperature fluctuations of the resin lens. An objective lens for a head is known (Patent Document 2).

Japanese Patent Application Publication No. 07-244246 JP 2002-122780 A

In order to obtain an observation optical system having high optical performance and a light weight as a whole while having a wide viewing angle, it is necessary to appropriately set the lens configuration, in particular, the shape and lens configuration of the Fresnel lens when using a Fresnel lens. There is.

In the eyepiece optical system of Patent Document 1, a Fresnel lens having a sawtooth shape and having a concave surface directed to the observation side is disposed at a position closest to the eye (observation surface). And it is aiming at wide viewing angle and weight reduction of the whole system. The Fresnel grating of the Fresnel lens according to Patent Document 1 has a tendency that the incident light becomes unnecessary light (ghost) when the light is incident on the molding defect (surface sag) or the like of the wall surface or the projection, and the image quality is deteriorated. The Further, since the Fresnel lens of Patent Document 1 forms a Fresnel surface from the central area of the Fresnel lens, the image quality of the observation image tends to be deteriorated in the central area of the observation screen where the observer can easily watch.

The objective lens of Patent Document 2 uses the central area of the lens as a lens surface of a continuous shape as a refractive action, and the peripheral part as a sawtooth-shaped diffractive lens configuration, utilizing a first-order diffraction action. In this way, it is intended to suppress the focus position shift due to the temperature change. Since the objective lens of Patent Document 2 is configured of a single lens, it tends to be difficult to obtain high optical performance.

The present invention is an observation optical system capable of observing image information displayed on an image display surface with high optical performance while having a wide viewing angle while achieving downsizing and weight reduction of the entire system, and observation having the same The purpose is to provide a device.

The optical system according to the present invention has a Fresnel lens and a lens LP of positive refractive power provided on the light incident side or the light output side of the Fresnel lens, and the center annular zone from the vertex of the central annular zone of the Fresnel lens Let h0 be the length in the optical axis direction to the end of the frame, and h1 be the length in the optical axis direction of the grating wall surface of the first annular zone adjacent to the central annular zone,
0.01 <h1 / h0 <0.80
It is characterized by satisfying the following conditional expression.

According to the present invention, an observation optical system capable of observing image information displayed on an image display surface with high optical performance while having a wide viewing angle while achieving downsizing and weight reduction of the entire system, and the same An observation device is obtained.

FIG. 1 is a lens cross-sectional view of an observation apparatus having an observation optical system of Example 1 of the present invention. Longitudinal aberration figure in eye relief 10 mm of the observation optical system of Example 1 of this invention. Longitudinal aberration figure in eye relief 20 mm of the observation optical system of Example 1 of this invention. The lens sectional view of the observation apparatus which has an observation optical system of Example 2 of this invention. The longitudinal aberration figure in 10 mm of eye reliefs of the observation optical system of Example 2 of this invention. FIG. 7 is a longitudinal aberration diagram of the observation optical system of the second embodiment of the present invention at an eye relief of 20 mm. The lens sectional view of the observation apparatus which has an observation optical system of Example 3 of this invention. FIG. 7 is a longitudinal aberration diagram of the observation optical system of the Example 3 of the present invention at an eye relief of 10 mm. FIG. 7 is a longitudinal aberration diagram of the observation optical system of Example 3 of the present invention at an eye relief of 20 mm. The lens sectional view of the observation apparatus which has an observation optical system of Example 4 of this invention. FIG. 7 is a longitudinal aberration diagram of the observation optical system of the fourth embodiment of the present invention at an eye relief of 10 mm. FIG. 7 is a longitudinal aberration diagram of the observation optical system of the fourth embodiment of the present invention at an eye relief of 20 mm. The lens sectional view of the observation apparatus which has an observation optical system of Example 5 of this invention. FIG. 7 is a longitudinal aberration diagram at an eye relief of 10 mm of an observation optical system of Example 5 of the present invention. FIG. 7 shows longitudinal aberration at eye relief of 20 mm of the observation optical system of Example 5 of the present invention. The length from the surface vertex of the central ring of the Fresnel lens of the observation optical system of the present invention to the end, the length of the wall surface of the Fresnel grating and the surface vertex of the central ring of the Fresnel lens Definition explanatory drawing of the diameter up to, the effective diameter of a Fresnel lens, etc. FIG. The length from the surface vertex of the central ring of the Fresnel lens of the observation optical system of the present invention to the end, the length of the wall surface of the Fresnel grating and the surface vertex of the central ring of the Fresnel lens Definition explanatory drawing of the diameter up to, the effective diameter of a Fresnel lens, etc. FIG. Explanatory drawing of a Fresnel lens. Explanatory drawing of a Fresnel lens. Explanatory drawing of a Fresnel lens. Explanatory drawing of the image height in 45 degrees of half viewing angles.

Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. The optical system of each embodiment is an observation optical system for observing an image displayed on the image display surface, and has a Fresnel lens LF and a lens (positive lens) LP of positive refractive power.
In the present specification, the Fresnel lens refers to an optical element having a Fresnel grating. The surface shapes of the optical surface on the light incident side of the Fresnel lens and the optical surface on the light output side (when the optical surface has a Fresnel grating, it is a curved surface even if it is a flat surface) Also good. When the Fresnel lens has a curved optical surface, the curved optical surface is not limited to a spherical shape, and may be a free curved surface.

FIG. 1 is a lens cross-sectional view of an observation apparatus having an observation optical system of Example 1 of the present invention. FIG. 2A and FIG. 2B are respectively longitudinal aberration diagrams at eye relief 10 mm and eye relief 20 mm of the observation optical system of Example 1 of the present invention. FIG. 3 is a lens cross-sectional view of an observation apparatus having an observation optical system of Example 2 of the present invention. FIG. 4A and FIG. 4B are respectively longitudinal aberration diagrams in eye relief 10 mm and eye relief 20 mm of the observation optical system of Example 2 of this invention.

FIG. 5 is a lens sectional view of an observation apparatus having an observation optical system according to a third embodiment of the present invention. FIGS. 6A and 6B are respectively longitudinal aberration diagrams at an eye relief of 10 mm and an eye relief of 20 mm of the observation optical system of Example 3 of the present invention. FIG. 7 is a lens cross-sectional view of an observation apparatus having an observation optical system of Example 4 of the present invention. FIGS. 8A and 8B are respectively longitudinal aberration diagrams at an eye relief of 10 mm and an eye relief of 20 mm of the observation optical system of Example 4 of the present invention.

FIG. 9 is a lens cross-sectional view of an observation apparatus having an observation optical system of Example 5 of the present invention. FIG. 10A and FIG. 10B are respectively longitudinal aberration diagrams in eye relief 10 mm and eye relief 20 mm of the observation optical system of Example 5 of this invention. 11A and 11B illustrate the definition of the length in the optical axis direction from the surface vertex of the central ring zone of the Fresnel lens to the end of the central ring zone in the present specification and the length in the optical axis direction of the grating wall surface FIG. 12A, 12B and 12C are explanatory views of a Fresnel lens.

In the lens sectional view, L0 is an observation optical system, and has a lens (positive lens) LP of positive refractive power and a Fresnel lens LF. Fre is a Fresnel surface of the Fresnel lens LF. The positive lens LP is a positive lens having the largest refractive power when the observation optical system L0 has a plurality of positive lenses. Here, the positive lens LP is a curved surface having a curvature on the lens surface, and the curved surface is a refractive lens, and does not include a Fresnel lens. ID is an image display surface, and, for example, a liquid crystal display element ID1 is disposed. SP is a viewing plane, where the observer's pupil is located. A stop (SP1) may be disposed on the observation surface SP.

In the lens cross-sectional view of each embodiment, the eye relief represents the distance between the eye point on the optical axis and the lens surface closest to the viewing surface SP. Each aberration diagram shows, in order from the left, spherical aberration, astigmatism, distortion, and lateral chromatic aberration. The spherical aberration diagrams show spherical aberration for d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagrams, S and M respectively indicate astigmatism on the sagittal image plane and the meridional image plane. The distortion is shown for d-line. The chromatic aberration diagram shows the chromatic aberration at the g-line.

In the evaluation of the aberration, the aberration on the viewing surface SP side where the light beam is blown from the image display surface ID and the aberration on the image display surface ID where the light beam is blown from the observation surface SP side correspond one to one. The aberration at the image display surface ID is evaluated for convenience. Further, the aperture stop diameter of the stop SP1 of each embodiment is set to 3.5 mm as an example of the human pupil diameter. In addition, since the eye relief differs depending on the observer or corresponds to a state where glasses are worn, the variation of the aberration due to the eye relief is suppressed. Therefore, the aberration diagrams typically show aberrations when the eye relief is 10 mm and the eye relief 20 mm.

11A and 11B are explanatory diagrams for defining each element of the Fresnel lens LF according to the present invention. Fre is a Fresnel surface, and a plurality of concentric Fresnel gratings FP are arranged at a predetermined grating pitch. F0 is a central annular zone, is a continuous surface, and is formed of a spherical surface, an aspheric surface, and the like. La is an optical axis. Φ 1 is the effective diameter of the Fresnel lens LF. Φ 0 is the effective diameter of the central annular zone F 0 of the Fresnel lens F 0. That is, it is the diameter from one end FL2 of the central annular zone F0 to the other end FL2. Fr is a Fresnel ring zone in which a Fresnel grating is formed.

In FIG. 11A and FIG. 11B, the nth Fresnel grating (a ring from the optical axis La in the direction of the optical axis La from the surface vertex FL1 to the end FL2 of the central annular zone F0 of the Fresnel lens LF) The length of the wall of the band is hn.

Next, the configuration of the observation optical system L0 of the present invention will be described. The observation optical system L0 of the present invention has a positive lens LP and a Fresnel lens LF. The observation optical system L0 is composed of a plurality of lenses. Thereby, when the Fresnel lens LF has positive refractive power, the curvature of each surface can be relaxed, the amount of aberration generation on each surface is reduced, and the amount of aberration as a whole is also reduced. In addition, when the Fresnel lens LF has negative refractive power, the Petzval sum as a whole can be reduced, and field curvature can be reduced. In addition, chromatic aberration of magnification is also reduced.

The length in the optical axis direction from the surface vertex FL1 of the central annular zone F0 of the Fresnel lens LF to the end portion FL2 of the central annular zone F0 is h0. Length in the optical axis direction of the grating wall surface of the first annular zone counted from the optical axis center of the Fresnel annular zone Fr of the Fresnel lens LF (optical axis of the grating wall surface of the first annular zone adjacent to the central annular zone F0 Let h1 be the length of the direction). At this time,
0.01 <h1 / h0 <0.80 (1)
Satisfy the following conditional expression.

The conditional expression (1) is the length h1 in the optical axis direction of the grating wall surface of the first annular zone of the Fresnel annular zone Fr of the Fresnel lens LF and the light from the surface vertex FL1 to the end FL2 of the central annular zone F0 of the Fresnel lens LF The ratio of the axial length h0 is defined. The length in the optical axis direction from the surface vertex FL1 to the end FL2 of the central annular zone F0 of the Fresnel lens LF is made larger than the length in the optical axis direction of the grating wall surface of the first annular zone of the Fresnel lens LF .

As a result, the ratio of the continuously shaped area (central annular zone) F0 in the radial direction of the Fresnel lens LF is increased, and the image quality deterioration factor due to the sawtooth shape of the Fresnel lens LF is reduced in the screen central area where the observer easily gazes To improve the optical performance.

If the lower limit of the conditional expression (1) is exceeded, the length in the optical axis direction from the surface vertex FL1 to the end FL2 of the central annular zone F0 becomes too long, and the weight increases. Alternatively, the length in the optical axis direction of the grating wall surface of the first annular zone of the Fresnel lens LF becomes too short, flare due to diffraction increases, and optical performance deteriorates.

Conversely, if the upper limit of the conditional expression (1) is exceeded, if the refractive power of the Fresnel lens LF is strong, the length in the optical axis direction from the surface vertex FL1 to the end FL2 of the central annular zone F0 becomes too short. As a result, the sawtooth shape of the Fresnel lens LF is formed in the screen central area where the observer can easily gaze, and the optical performance is degraded. If the refractive power of the Fresnel lens LF is weak, the refractive powers of the other lenses that constitute it become too strong, and various off-axis aberrations increase. On the contrary, the length in the optical axis direction of the grating wall surface of the first annular zone of the Fresnel lens LF becomes too long, the unnecessary light (ghost) reflected by the wall surface increases, and the optical performance is degraded.

More preferably, the numerical range of the conditional expression (1) is set as follows.
0.02 <h1 / h0 <0.65 (1a)
More preferably, the numerical range of the conditional expression (1a) may be set as follows.
0.03 <h1 / h0 <0.50 (1b)
With the above configuration, an observation optical system having a wide field of view and high optical performance, and having a lightweight overall system is obtained.

The observation optical system L0 may satisfy the following conditional expression (2) instead of the above-mentioned conditional expression (1). By satisfying the formula (2), it is possible to obtain an observation optical system having a wide optical field while having a wide field of view, and having a lightweight system as a whole.
0.3 <Φ0 / Φ1 <0.7 (2)
In conditional expression (2), Φ0 is the diameter of the central annular zone F0 of the Fresnel lens LF, and Φ1 is the effective diameter of the Fresnel lens LF.
Conditional expression (2) defines the ratio of the effective diameter (diameter) 0 0 of the central annular zone F 0 of the Fresnel lens LF to the effective diameter Φ 1 of the Fresnel lens LF. If the lower limit of the conditional expression (2) is exceeded, the sawtooth shape of the Fresnel lens LF is formed in the screen central area where the observer can easily gaze, and the optical performance is lowered. Conversely, if the upper limit of the conditional expression (2) is exceeded, the region (lens surface) forming the continuous shape becomes too large, and the weight of the entire system increases.
More preferably, the numerical range of the conditional expression (2) is set as follows.
0.32 <Φ0 / Φ1 <0.65 (2a)
More preferably, the numerical range of the conditional expression (2a) may be set as follows.
0.34 <Φ0 / Φ1 <0.62 (2b)
The observation optical system L0 may satisfy both the conditional expression (1) and the conditional expression (2).

Furthermore, it is preferable to satisfy one or more of the following conditional expressions. Here, the focal length of the Fresnel lens LF is fh, and the focal length of the observation optical system L0 is F. When the observation optical system L0 has one or more lenses with positive refractive power, the lens with the largest refractive power is a positive lens LP, and the focal length of the positive lens LP is fp. Of the positive lens LP and the Fresnel lens LF, the distance on the optical axis from the lens surface on the observation surface side of the lens closest to the observation side to the lens surface on the image display surface side of the lens closest to the image display surface Let d be.

Further, the distance on the optical axis from the lens surface on the observation surface side of the lens positioned closest to the observation surface side of the observation optical system L0 to the image display surface is L. When the Fresnel lens LF has positive refractive power, the curvature radius of the surface on the observation surface side of the Fresnel lens LF is Rp11, and the curvature radius of the surface on the image display surface side of the Fresnel lens LF is Rp12. When the Fresnel lens LF has negative refractive power, the curvature radius of the surface on the observation surface side of the Fresnel lens LF is Rn11, and the curvature radius of the surface on the image display surface side of the Fresnel lens LF is Rn12. The curvature radius of the lens surface of the positive lens LP on the observation surface side is R21, and the curvature radius of the lens surface of the positive lens LP on the image display surface side is R22.

Further, the average value of the length in the optical axis direction of the grating wall surface in the effective surface of the Fresnel lens LF is set to have (mm), and the length of the wavelength of the d-line is set to λ (mm). The grating pitch of the first annular zone of the Fresnel lens LF is w1, and the grating pitch of the outermost annular zone in the effective surface of the Fresnel lens LF is we.

The ideal image height of the image display surface at a half viewing angle of 45 degrees is 10 mm with an eye relief of 10 mm, and the actual image height of the image display surface at a half viewing angle of 45 degrees is y with an eye relief of 10 mm. The ideal image height y0 at an eye relief of 10 mm and a half viewing angle of 45 degrees is a value given by y0 = F × tan 45 °. The "actual image height y" is the height in the direction perpendicular to the optical axis at the paraxial imaging position of the chief ray incident on the observation optical system L0 at an eye relief of 10 mm and a half viewing angle of 45 degrees. . FIG. 13 is a diagram for explaining y in the observation optical system L0. In FIG. 13, the chief ray of the viewing angle θ (= 45 °) incident on the observation optical system L0 from the stop SP has reached the position of height y on the paraxial imaging position of the observation optical system L0. Is represented.

1.5 <| fh | / F <5.0 (3)
1.2 <fp / F <2.0 (4)
0.1 <d / L <0.4 (5)
-1.6 <(Rp12 + Rp11) / (Rp12-Rp11) <-0.5 (6)
0.8 <(Rn12 + Rn11) / (Rn12-Rn11) <1.7 (7)
-1.6 <(R22 + R21) / (R22-R21) <-0.4 (8)
50.0 <have / λ <500.0 (9)
1.2 <w1 / we <10.0 (10)
−0.35 <(y−y0) / y0 <−0.10 (11)
0.5 <y / F <1.1 (12)

Next, technical meanings of the above-mentioned conditional expressions will be described. Conditional expression (3) defines the ratio of the focal length of the Fresnel lens LF to the focal length of the observation optical system L0. If the refractive power of the Fresnel lens LF is too strong (the absolute value of the refractive power is large) beyond the lower limit of the conditional expression (3), the grating pitch of each Fresnel grating forming the sawtooth shape becomes too fine. As a result, the angle at which diffracted light diffracts becomes too large, and flare increases. Conversely, if the upper limit of conditional expression (3) is exceeded, the refractive power of each lens becomes too strong when the number of other lenses being configured is small, and various off-axis aberrations increase. If the number of other lenses being configured is large, the weight of the entire system increases.

Condition (4) defines the ratio of the focal length of the positive lens LP to the focal length of the observation optical system L0. If the lower limit of the conditional expression (4) is exceeded, the refractive power of the positive lens LP becomes too strong, and mainly curvature of field and astigmatism increase. Conversely, if the upper limit of conditional expression (4) is exceeded, the refractive power of each lens becomes too strong when the number of other lenses being configured is small, and various off-axis aberrations increase. If the number of other lenses being configured is large, the weight of the entire system increases.

The conditional expression (5) is that of the positive lens LP and the Fresnel lens LF, from the lens surface on the observation surface side of the lens closest to the observation surface SP side to the image display surface side of the lens closest to the image display surface ID Assuming that the distance on the optical axis to the lens surface is d, the ratio of the distance from the lens surface on the viewing surface side of the lens closest to the viewing surface SP to the image display surface ID to the distance d is defined.

If the lower limit of the conditional expression (5) is exceeded, the distance between the lenses becomes too short, and it becomes difficult to mechanically hold each lens. Alternatively, the thickness of the lens is too thin, the lens surface is easily deformed, and the optical performance is easily reduced. Conversely, when the upper limit of conditional expression (5) is exceeded, the distance between lenses becomes too long, and the effective diameter of the lens positioned on the image display surface side becomes large, and the weight increases. Alternatively, the thickness of the lens becomes too thick and the weight increases.

Conditional expression (6) defines the form factor of the Fresnel lens LF when the Fresnel lens LF has positive refractive power. If the lower limit of the conditional expression (6) is exceeded, the curvature of the surface on the image display surface side of the Fresnel lens LF becomes too strong, and mainly the curvature of field and astigmatism increase. Conversely, when the upper limit of conditional expression (6) is exceeded, the curvature of the surface on the observation surface side of the Fresnel lens LF becomes too strong, and distortion mainly increases.

The conditional expression (7) defines the form factor of the Fresnel lens LF when the Fresnel lens LF has negative refractive power. If the lower limit of the conditional expression (7) is exceeded, the curvature of the surface on the image display surface side of the Fresnel lens LF becomes too strong, and field curvature and astigmatism mainly increase. On the contrary, when the upper limit of the conditional expression (7) is exceeded, the curvature of the surface on the observation surface side of the Fresnel lens LF becomes too strong, and mainly the field curvature and astigmatism increase.

Condition (8) defines the form factor of the positive lens LP. If the lower limit of the conditional expression (8) is exceeded, the curvature of the surface on the image display surface side of the positive lens LP becomes too strong, and field curvature and astigmatism mainly increase. Conversely, if the upper limit of conditional expression (8) is exceeded, the curvature of the surface on the observation surface side of the positive lens LP becomes too strong, and distortion mainly increases.

The conditional expression (9) defines the ratio of the average of the wall heights of the Fresnel grating in the effective system of the Fresnel lens LF to the length of the wavelength of the d-line. If the lower limit of the conditional expression (9) is exceeded, the wall height of the Fresnel grating in the effective system of the Fresnel lens LF becomes too small, the intensity of the diffracted light increases, and the optical performance decreases. Conversely, when the upper limit of conditional expression (9) is exceeded, the wall length of the Fresnel grating of the Fresnel lens LF becomes too long, unnecessary light (ghost) reflected by the wall increases, and the optical performance decreases. .

Conditional expression (10) defines the ratio of the grating pitch of the Fresnel grating in the first annular zone of the Fresnel lens LF to the grating pitch of the Fresnel grating in the outermost annular zone in the light beam effective diameter Φ1 of the Fresnel lens LF ing. If the lower limit of conditional expression (10) is exceeded, the grating pitch of the Fresnel grating in the first orbicular zone becomes too small, the diffraction angle of light to be diffracted becomes too large, flare effects occur at the screen center, and optical performance It is falling.

Conversely, when the upper limit of conditional expression (10) is exceeded, the grating pitch of the Fresnel grating in the outermost annular zone in the effective beam diameter Φ1 becomes too small, and the diffraction angle of light to be diffracted becomes too large. The effect of flare is the cause of deterioration in optical performance.

Conditional expression (11) defines the distortion amount on the image display surface ID at an eye relief of 10 mm and a half viewing angle of 45 degrees. If the lower limit of the conditional expression (11) is exceeded, the positive refractive power is too strong, so light rays around the screen are strongly bent in the optical axis direction, and various off-axis aberrations increase. Conversely, if the upper limit of conditional expression (11) is exceeded, the positive refractive power is too small, so the incident height of the marginal rays at each lens position becomes too high, and the effective diameter increases, so the weight of the entire system increases. Do.

The conditional expression (12) is the actual image height of the chief ray at a half viewing angle of 45 degrees in the observation optical system L0 at an eye relief of 10 mm (the height in the direction perpendicular to the optical axis at the paraxial imaging position The ratio of y) to the focal length F of the observation optical system L0 is defined. This represents the refractive power of the peripheral portion corresponding to the viewing angle of 45 degrees of the observation optical system L0. Since y becomes smaller as the refractive power of the peripheral portion becomes stronger, satisfying the conditional expression (12) makes it possible to widen the viewing angle while configuring the image display element in a small size.
If the focal length F of the observation optical system L0 is too long beyond the lower limit of the conditional expression (12), the total length of the observation optical system L0 is elongated and enlarged. Alternatively, the refractive power at the periphery of the observation optical system becomes too strong, and in particular astigmatism and field curvature increase.
On the other hand, if y exceeds the upper limit of the conditional expression (12) and y is too large, the image display surface becomes too large, and the image display element becomes large.
According to the above-described configuration, it is possible to obtain an observation optical system which has high optical performance and a light whole system while having a wide field of view.

More preferably, the numerical ranges of the conditional expressions (3) to (12) may be set as follows.
1.6 <| fh | / F <4.8 ... (3a)
1.23 <fp / F <1.95 (4a)
0.12 <d / L <0.35 (5a)
-1.5 <(Rp12 + Rp11) / (Rp12-Rp11) <-0.6
... (6a)
0.9 <(Rn12 + Rn11) / (Rn12-Rn11) <1.6
... (7a)
-1.5 <(R22 + R21) / (R22-R21) <-0.5
... (8a)
75.0 <have / λ <400.0 (9a)
1.4 <w1 / we <8.0 (10a)
-0.34 <(y-y0) / y0 <-0.15 (11a)
0.6 <y / F <1.0 (12a)

More preferably, the numerical ranges of the conditional expressions (3a) to (12a) may be set as follows.
1.7 <| fh | / F <4.6 (3b)
1.25 <fp / F <1.90 ・・・ (4b)
0.14 <d / L <0.33 (5b)
-1.4 <(Rp12 + Rp11) / (Rp12-Rp11) <-0.7
... (6b)
0.95 <(Rn12 + Rn11) / (Rn12-Rn11) <1.55
... (7b)
-1.4 <(R22 + R21) / (R22-R21) <-0.6
... (8b)
100.0 <have / λ <300.0 (9b)
1.6 <w1 / we <7.0 (10b)
−0.33 <(y−y0) / y0 <−0.19 (11 b)
0.7 <y / F <0.9 (12 b)

Next, the observation optical system L0 of each embodiment will be described.

Example 1
Example 1 of the observation optical system L0 of the present invention will be described below with reference to FIG. The observation optical system L0 of Example 1 includes, in order from the observation surface side to the image display surface side, a Fresnel lens LF of positive refractive power and a lens (positive lens) LP of positive refractive power. By sharing the positive refractive power between the two lenses, the curvature on each surface is loosened, thereby reducing the occurrence of various aberrations. The Fresnel lens LF of positive refractive power has the image display surface ID side as the Fresnel surface.

The length h0 in the optical axis direction from the surface vertex FL1 to the end portion FL2 of the central annular zone of the Fresnel lens LF is increased in an appropriate range that satisfies the conditional expression (1). As a result, the ratio of the continuously shaped area in the radial direction of the Fresnel lens LF is increased, and the optical performance in the screen range in which the observer can easily gaze is improved.

Furthermore, the region of continuous shape is set within an appropriate range satisfying the conditional expression (2), and the optical performance is improved and the weight is reduced. Furthermore, the focal length of the Fresnel lens LF is loosened in an appropriate range satisfying the conditional expression (3) to prevent the grating pitch of the Fresnel grating from becoming too small, and flare due to diffraction is reduced. Furthermore, the focal length of the positive lens LP is reduced within an appropriate range that satisfies the conditional expression (4) to mainly reduce the occurrence of field curvature and astigmatism. Furthermore, the weight reduction of the entire system is achieved by reducing the thickness of each of the Fresnel lens LF and the positive lens LP within an appropriate range that satisfies the conditional expression (5).

Furthermore, to satisfy the conditional expression (6), the curvature of the surface on the image display surface side is intensified relative to the curvature of the surface on the observation surface SP side of the Fresnel lens LF, and the convex shape is directed to the image display surface side. Of the observation surface SP. Thereby, the incident angle of the off-axis light beam is relaxed, and the occurrence of various off-axis aberrations is reduced.

Furthermore, the curvature of the surface on the image display surface ID side is intensified with respect to the curvature of the surface on the observation surface SP side of the positive lens LP so as to satisfy the conditional expression (8), and the convex shape is directed to the image display surface ID. Thus, it has a concentric shape with respect to the viewing surface SP. Thereby, the incident angle of the off-axis light beam is relaxed, and the occurrence of various off-axis aberrations is reduced.

Furthermore, by increasing the average value of the wall heights of the Fresnel gratings in the effective system of the Fresnel lens LF within an appropriate range that satisfies the conditional expression (9), the generation of diffracted light, which is unnecessary light, is prevented. I am trying to improve the performance. Further, the grating pitch of the Fresnel grating in the first annular zone of the Fresnel lens LF and the grating pitch of the Fresnel grating in the outermost annular zone in the light beam effective diameter 11 are set so as to satisfy the conditional expression (10) This prevents the generation of diffracted light on the entire screen and improves optical performance.

Further, by appropriately setting the distortion amount so as to satisfy the conditional expression (11), it is possible to prevent the light ray in the periphery of the screen from being strongly bent in the optical axis direction, and to improve the optical performance.
Further, by appropriately setting the refractive power so as to satisfy the conditional expression (12), downsizing of the image display element and widening of viewing angle of the observation optical system L0 are achieved.

Example 2
Example 2 of the observation optical system L0 of the present invention will be described below with reference to FIG. The observation optical system L0 of Example 2 includes, in order from the observation surface side to the image display surface side, a lens of positive refractive power (positive lens) LP, a lens of negative refractive power (negative lens) L3, and positive refractive power. It comprises a Fresnel lens LF. By sharing the positive refractive power between the two lenses, the curvature on each surface is relaxed, thereby reducing the occurrence of various aberrations.

Further, by disposing the negative lens L3, lateral chromatic aberration and field curvature are reduced. In addition, by arranging the Fresnel lens LF of positive refractive power at the position closest to the image display surface, that is, the position where the effective diameter becomes large among the three lenses described above, weight reduction of the entire system is achieved. . The other configuration is the same as that of the first embodiment.

[Example 3]
Example 3 of the observation optical system L0 of the present invention will be described below with reference to FIG. The observation optical system L0 of Example 3 includes, in order from the observation surface side to the image display surface side, a parallel flat plate (optical member) Lt, a lens of positive refractive power (positive lens) LP, and a Fresnel lens LF of positive refractive power. It is configured. If the positive lens LP is in the exposed (exposed to the outside) state, the lens may be deformed or cracked if oil or the like is touched. The flat lens Lt plays a role of protecting the positive lens LP.

In addition, by arranging the Fresnel lens LF of positive refractive power at the position closest to the image display surface, that is, the position where the effective diameter becomes large among the three lenses described above, weight reduction of the entire system is achieved. . The other configuration is the same as that of the first embodiment.

Example 4
Example 4 of the observation optical system L0 of the present invention will be described below with reference to FIG. The observation optical system L0 of Example 4 includes, in order from the observation surface side to the image display surface side, a Fresnel lens LF of negative refractive power, a lens (positive lens) LP of positive refractive power, and a lens L3 of positive refractive power. It is configured. By sharing the positive refractive power between the two lenses, the curvature on each surface is relaxed, thereby reducing the occurrence of various aberrations. In addition, the chromatic aberration of magnification and the curvature of field are reduced by disposing the Fresnel lens LF of negative refractive power.

In order to satisfy the conditional expression (7), the curvature of the surface on the observation surface side is intensified with respect to the curvature of the surface on the image display surface side of the Fresnel lens LF, and the concave shape is directed to the observation surface SP. As a result, the incident angle of the off-axis light beam is relaxed in a concentric form with respect to the observation surface SP, and the occurrence of various off-axis aberrations is reduced. The other configuration is the same as that of the first embodiment.

[Example 5]
Example 5 of the observation optical system L0 of the present invention will be described below with reference to FIG. The observation optical system L0 of Example 5 includes, in order from the observation surface side to the image display surface side, a lens of positive refractive power (positive lens) LP, a Fresnel lens of negative refractive power LF, a lens of positive refractive power (positive The lens L3 is composed of a lens (positive lens) L4 of positive refractive power. By sharing the positive refractive power with the three lenses, the curvature on each surface is further relaxed, thereby reducing the occurrence of various aberrations. Further, by arranging a funnel lens LF of negative refractive power, lateral chromatic aberration and field curvature are reduced.

In order to satisfy the conditional expression (7), the curvature of the surface on the observation surface side is increased relative to the curvature of the surface on the image display surface side of the Fresnel lens LF, and the concave shape is directed to the observation surface SP. It is in the form of a concentric form for the SP. As a result, the incident angle of the off-axis ray is relaxed and the occurrence of off-axis aberrations is reduced. The other configuration is the same as that of the first embodiment.

As mentioned above, although the preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary. For example, when combined with an image display element such as a CRT or LCD, electrical processing may be added to the image display element depending on the amount of distortion and the amount of lateral chromatic aberration.

Next, a Fresnel lens will be described with reference to FIGS. 12A to 12C. Generally, as shown in FIG. 12A, a Fresnel lens has a shape in which a lens surface having a radius of curvature r is divided into a plurality of concentric regions. At this time, according to the value of the radius of curvature r, the cross-sectional shape is a shape in which a Fresnel grating (prism) FP having a sawtooth shape is arranged concentrically on a plane. The plurality of concentric Fresnel gratings have different or identical angles. Also, the grating pitch of the Fresnel grating is different or identical from the center (optical axis) to the periphery.

The radius of curvature r at the Fresnel lens surface Fre corresponds to the radius of curvature r of the lens surface shown in FIG. 12A. One of the parameters for determining the focal length of the Fresnel lens surface uses the radius of curvature r as in the case of determining the focal length of a normal lens. The focal length f of the Fresnel lens, the plate thickness (center thickness), the effective diameter 11, etc. are as shown in FIGS. 12B and 12C. The radius of curvature of the Fresnel lens surface in the conditional expression to be described later uses the radius of curvature of the lens surface before forming the Fresnel shape (that is, the radius of curvature of the central annular zone).

Next, numerical data in each example are shown below. In the numerical data, i indicates the order of the surface from the observation surface, ri indicates the radius of curvature of the i-th optical surface, di indicates the lens thickness and air gap between the i-th surface and the (i + 1) -th surface, ni, ii Represents the refractive index and Abbe number of the optical member between the i-th surface and the (i + 1) -th surface with respect to the d-line, respectively. Also, K, A4, A6, A8, A10, etc. described on the aspheric surface are aspheric coefficients. The aspheric surface shape is defined by the following equation when the displacement in the optical axis direction at the position of height h from the optical axis is x with respect to the surface vertex.
x = (h ² / R) / [1 + {1-(1 + K) (h / R) ² } ^1/2 ] + A4h ⁴ + A6h ⁶ + A8h ⁸ + A10h ¹⁰
However, R is a curvature radius here. The Fresnel surface represents an ideal thin-walled state having an aspheric effect, and the actual shape is a Fresnel shape within the written center thickness d. The Fresnel surface is described as * Fre next to the surface number. In the surface numbers 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, the surface numbers 2 and 3 correspond to the Fresnel lens LF, and the surface numbers 4 and 5 correspond to the positive lens LP. In the numerical data 2, the surface numbers 2 and 3 correspond to the positive lens LP, and the surface numbers 6 and 7 correspond to the Fresnel lens LF. In the numerical data 3, the surface numbers 4 and 5 correspond to the positive lens LP, and the surface numbers 6 and 7 correspond to the Fresnel lens LF. In the numerical data 4, the surface numbers 2 and 3 correspond to the Fresnel lens LF, and the surface numbers 4 and 5 correspond to the positive lens LP. In the numerical data 5, the surface numbers 2 and 3 correspond to the positive lens LP, and the surface numbers 4 and 5 correspond to the Fresnel lens LF.

The total lens length is the distance from the first lens surface on the viewing surface side to the image display surface ID. BF is a distance from the surface of the image display surface ID to the image display surface. Tables 1 and 2 show the relationship between parameters based on the above-mentioned numerical data and each conditional expression.

(Numerical data 1)
Unit mm

Surface data surface number r d nd d d effective diameter
1 (aperture) ∞ (variable) 3.50
2 10000.000 3.50 1.53110 56.0 48.76
3 * Fre -80.546 0.70 52.00
4 * 237.548 15.00 1.53110 56.0 53.30
5 *-36.019 40.89 55.34
Image plane ∞

Aspheric surface data surface 3
K = 0.00000e + 000 A 4 = -1. 35561 e-005 A 6 = 2. 66207 e-008
A 8 = -1.06533 e-011

Fourth side
K = 0.00000e + 000A 4 =-2.18599e-005 A 6 = 4.07744e-008
A 8 = -2.04247e-011 A10 = 1.57785e-015

Fifth side
K = 0.00000e + 000 A 4 = 2.20301e-006 A 6 =-7.68945e-009
A 8 = 1.19113e-011

Various data zoom ratio 1.00

Focal length 44.99 44.99
F number 12.85 12.85
Half angle of view (degrees) 55.00 45.00
Image height 43.00 36.35
Lens total length 70.09 70.09
BF 40.89 40.89

d 1 10.00 20.00

Entrance pupil position 0.00 0.00
Exit pupil position -37.93 -88.19
Front principal point position 19.31 29.31
Rear principal point position -4.10 -4.10

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear side principal point position 1 1 ∞ 0.00 0.00 -0.00
2 2 44.99 19.20 9.31-4.10

Single lens data lens Start surface Focal length 1 1 151.54
2 4 60.03

(Numerical data 2)
Unit mm

Surface data surface number r d nd d d effective diameter
1 (aperture) ∞ (variable) 3.50
2 * 11. 11.72 1.48749 70.4 47.52
3 *-39.013 0.50 49.92
4 -104.408 3.20 1.63400 23.9 55.12
5-550.468 0.50 61.09
6-550.000 5.00 1.53110 56.0 62.00
7 * Fre-55.766 60.66 68.33
Image plane ∞

Aspheric data second surface
K = 0.00000e + 000 A 4 = 1.89729e-006 A 6 = -8.84019e-010
A8 = -1.250103e-012 A10 = 1.57785e-015

Third side
K = 0.00000e + 000 A 4 = 8.01465e-006 A 6 = -1. 13123e-008
A 8 = 6.33741e-012

Seventh side
K = 0.00000e + 000 A 4 = -1.82721e-006 A 6 = 2.98900e-009
A 8 = -7.03142e-013

Various data zoom ratio 1.00

Focal length 63.48 63.48
F number 18.14 18.14
Half angle of view (degrees) 60.00 47.00
Image height 66.68 53.16
Lens total length 91.58 91.58
BF 60.66 60.66

d 1 10.00 20.00

Entrance pupil position 0.00 0.00
Exit pupil position -35.24 -65.18
Front principal point position 21.46 31.46
Rear principal point position -2.82 -2.82

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear side principal point position
1 1 ∞ 0.00 0.00-0.00
2 2 63.48 20.92 11.46-2.82

Single lens data lens Start surface Focal length
1 1 80.00
2 4 -203.79
3 6 116.44

(Numerical data 3)
Unit mm

Surface data surface number r d nd d d effective diameter
1 (aperture) ∞ (variable) 3.50
2 0.8 0.80 1.49000 55.0 47.43
3 1.00 48.00
4 * -265.909 13.39 1.53110 56.0 49.38
5 * -36.393 0.20 54.33
6 1964.346 3.00 1.53110 56.0 67.88
7 * Fre-105.000 54.56 69.90
Image plane ∞

Aspheric surface data surface 4
K = 0.00000e + 000 A 4 = -6.79879e-007 A 6 = 4.81597e-009
A 8 = -1.81252e-012

Fifth side
K = 0.00000e + 000 A 4 = 2.76286e-006 A 6 = -4.27243e-009
A 8 = 8.19904e-012

Various data zoom ratio 1.00

Focal length 55.16 55.16
F number 15.76 15.76
Half angle of view (degrees) 57.50 47.50
Image height 55.41 47.21
Lens total length 82.96 82.96
BF 54.56 54.56

d 1 10.00 20.00

Entrance pupil position 0.00 0.00
Exit pupil position -36.31 -75.00
Front principal point position 21.68 31.68
Rear principal point position -0.60 -0.60

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear side principal point position
1 1 ∞ 0.00 0.00-0.00
2 2 55.16 18.39 11.68-0.60

Single lens data lens Start surface Focal length
1 1 0.00
2 4 77.81
3 6 187.76

(Numerical data 4)
Unit mm

Surface data surface number r d nd d d effective diameter
1 (aperture) ∞ (variable) 3.50
2 * Fre-129.970 1.20 1.63400 23.9 49.15
3 0.4 0.46 50.00
4 * 976.710 20.02 1.53110 56.0 51.22
5-37.804 1.00 58.00
6 1140.401 17.35 1.53110 56.0 73.16
7 * -58.000 47.34 75.91
Image plane ∞

Aspheric surface data surface 4
K = 0.00000e + 000 A 4 = 3.00662e-006 A 6 =-1. 60330e-008
A 8 = 1.45886e-011

Seventh side
K = 0.00000e + 000 A 4 = 2.75248e-006 A 6 = -1. 49902e-009
A 8 = 1.96913e-013

Various data zoom ratio 1.00

Focal length 51.11 51.11
F number 14.60 14.60
Half angle of view (degree) 50.00 40.00
Image height 45.06 37.39
Lens total length 97.38 97.38
BF 47.34 47.34

d 1 10.00 20.00

Entrance pupil position 0.00 0.00 0.00
Exit pupil position -88.54 -235.84 3414.02
Front principal point position 31.88 41.88 51.88
Back side principal point position -3.77 -3.77 -3.77

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear side principal point position
1 1 ∞ 0.00 0.00-0.00
2 2 51.11 40.04 21.88-3.77

Single lens data lens Start surface Focal length 1 1 -204.97
2 4 69.00
3 6 104.45

(Numerical data 5)
Unit mm

Surface data Surface number r d nd d d Effective diameter 1 (aperture) ∞ (variable) 3.50
2 * 4627.206 11.83 1.53110 56.0 48.02
3-45.008 1.00 49.95
4 * Fre-102.526 2.50 1.64000 23.5 57.04
5-500.000 1.20 58.01
6 * 122.504 9.67 1.53110 56.0 61.38
7-129.021 1.00 64. 47
8 239.832 17.55 1.53110 56.0 71.66
9 * -72.370 31.51 73.45
Image plane ∞

Aspheric surface data second surface K = 0.00000e + 000 A 4 = -4.61041e-006 A 6 = 1.21044e-008
A 8 = -3.52960e-012

Fourth surface K = 0.00000e + 000 A 4 = 2.17893e-006 A 6 =-2.20791e-010

Sixth surface K = 0.00000e + 000 A 4 = -1.56415e-006 A 6 = 1.72159e-009
A 8 = -2.99784e-012

The ninth face K = 0.00000e + 000 A 4 = 6.74838e-007 A 6 =-9.11601e-010
A 8 = 6.34371e-014

Various data zoom ratio 1.00

Focal length 45.59 45.59
F number 13.03 13.03
Half angle of view (degrees) 50.00 41.00
Image height 38.30 30.80
Lens total length 86.26 86.26
BF 31.51 31.51

d 1 10.00 20.00

Entrance pupil position 0.00 0.00
Exit pupil position -89.84 -260.05
Front principal point position 28.46 38.46
Rear principal point position -14.08 -14.08

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear side principal point position 1 1 ∞ 0.00 0.00 -0.00
2 2 45.59 44.75 18.46-14.08

Single lens data lens Start surface Focal length 1 1 84.00
2 4-202.01
3 6 119.92
4 8 106.76

This application claims the priority of Japanese Patent Application No. 2016-247731 filed on Dec. 21, 2016 and Japanese Patent Application No. 2017-234844 filed on Dec. 7, 2017, The contents thereof are cited as part of this application.

L0 Observation optical system LP Positive lens LF Fresnel lens SP Observation surface ID Image display surface Fre Fresnel surface

Claims

A Fresnel lens, and a positive lens LP provided on the light incident side or the light output side of the Fresnel lens,
The length in the optical axis direction from the surface vertex of the central annular zone of the Fresnel lens to the end of the central annular zone is h0, the length in the optical axis direction of the grating wall surface of the first annular zone adjacent to the central annular zone And let h1 be
0.01 <h1 / h0 <0.80
An optical system characterized by satisfying the following conditional expression.
When the diameter of the central annular zone is Φ0 and the effective diameter of the Fresnel lens is 11,
0.3 <Φ0 / Φ1 <0.7
An optical system according to claim 1, wherein the following conditional expression is satisfied.
A Fresnel lens, and a positive lens LP provided on the light incident side or the light output side of the Fresnel lens,
When the diameter of the central annular zone of the Fresnel lens is Φ0 and the effective diameter of the Fresnel lens is 11,
0.3 <Φ0 / Φ1 <0.7
An optical system characterized by satisfying the following conditional expression.
When the focal length of the Fresnel lens is fh and the focal length of the optical system is F,
1.5 <| fh | / F <5.0
The optical system according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
The positive lens LP is a positive lens having the largest refractive power among positive lenses of the optical system, and when the focal length of the positive lens LP is fp and the focal length of the optical system is F,
1.2 <fp / F <2.0
The optical system according to any one of claims 1 to 4, wherein the following conditional expression is satisfied.
Assuming that the average length of the grating wall in the optical axis direction in the effective surface of the Fresnel lens is have (mm), and the wavelength length of the d-line is λ (mm),
50.0 <have / λ <500.0
The optical system according to any one of claims 1 to 5, wherein the following conditional expression is satisfied.
Assuming that the grating pitch of the first orbicular zone of the Fresnel lens is w1, and the grating pitch of the outermost orbicular zone in the effective surface of the Fresnel lens is we:
1.2 <w1 / we <10.0
The optical system according to any one of claims 1 to 6, wherein the following conditional expression is satisfied.
The optical system according to any one of claims 1 to 7, wherein the central annular zone is formed of a continuous surface.
An observation apparatus comprising: an image display element for displaying image information; and the optical system according to any one of claims 1 to 8 for observing the image information displayed on the image display element. .
Assuming that the ideal image height of the image display surface at an eye relief of 10 mm and a half viewing angle of 45 degrees is y0, the eye relief of 10 mm, and the actual image height of an image display surface at a half viewing angle of 45 degrees is y.
-0.35 <(y-y0) / y0 <-0.10
The observation apparatus according to claim 9, wherein the following conditional expression is satisfied.
Of the positive lens LP and the Fresnel lens, the optical axis from the lens surface on the observation surface side of the lens closest to the observation surface to the lens surface on the image display surface side of the lens closest to the image display surface When the distance on the optical axis from the lens surface on the viewing surface side of the lens closest to the viewing surface to the image display surface is L,
0.1 <d / L <0.4
The observation apparatus according to claim 9 or 10, wherein the following conditional expression is satisfied.
The Fresnel lens has a positive refractive power, and the curvature radius of the surface on the observation surface side of the Fresnel lens is Rp11, and the curvature radius of the surface on the image display surface side of the Fresnel lens is Rp12,
-1.6 <(Rp12 + Rp11) / (Rp12-Rp11) <-0.5
The observation apparatus according to any one of claims 9 to 11, wherein the following conditional expression is satisfied.
The Fresnel lens has negative refractive power, and the curvature radius of the surface on the observation surface side of the Fresnel lens is Rn11, and the curvature radius of the surface on the image display surface side of the Fresnel lens is Rn12,
0.8 <(Rn12 + Rn11) / (Rn12-Rn11) <1.7
The observation apparatus according to any one of claims 9 to 12, wherein the following conditional expression is satisfied.
Assuming that the curvature radius of the lens surface on the observation surface side of the positive lens LP is R21, and the curvature radius of the lens surface on the image display surface side of the positive lens LP is R22,
-1.6 <(R22 + R21) / (R22-R21) <-0.4
The observation apparatus according to any one of claims 9 to 13, wherein the following conditional expression is satisfied.
Assuming that the focal length of the optical system is F, the actual image height of the image display surface at an eye relief of 10 mm and a half viewing angle of 45 degrees is y,
0.5 <y / F <1.1
The observation apparatus according to any one of claims 9 to 14, wherein the following conditional expression is satisfied.
A Fresnel lens having a Fresnel surface,
The length in the optical axis direction from the surface vertex of the central annular zone of the Fresnel lens to the end of the central annular zone is h0, the length in the optical axis direction of the grating wall surface of the first annular zone adjacent to the central annular zone And let h1 be
0.01 <h1 / h0 <0.80
A Fresnel lens characterized by satisfying the following conditional expression.
When the diameter of the central annular zone is Φ0 and the effective diameter of the Fresnel lens is 11,
0.3 <Φ0 / Φ1 <0.7
The Fresnel lens according to claim 16, wherein the following conditional expression is satisfied.
A Fresnel lens having a Fresnel surface,
When the diameter of the central annular zone of the Fresnel lens is Φ0 and the effective diameter of the Fresnel lens is 11,
0.3 <Φ0 / Φ1 <0.7
A Fresnel lens characterized by satisfying the following conditional expression.