JPH1138315A - Image pickup lens, phase diffraction grating having optical low pass effect, and image pickup optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and compact photographing optical system suitable for a camera for conference using a personal computer by forming a phase diffraction grating having a low pass effect at least on one lens surface in a single focused photographing lens. SOLUTION: The phase diffraction grating having a low pass effect is integrally formed on the refractive surface of a single photographing lens. A phase diffraction grating in the shape of a one-dimensional sine-wave grating having a low pass effect is formed on a second surface. The shape of grating is a rotationally symmetric aspheric surface superposed on a onedimensional sine- wave grating and oriented so as to generate the low pass effect in the longitudinal direction of a rectangular photographic screen. A lens forming a phase diffraction grating is manufactured by mold forming. When injection molding using thermoplastic resin is performed, it is particularly manufactured to be inexpensive and when a glass material is used, a lens having excellent environmental characteristic is obtained. In the phase diffraction grating, the pitch of grating is changed so as to become larger in the peripheral part than the pitch near the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a camera using a solid-state imaging device such as a CD, and more particularly to an imaging lens, an imaging optical system, and the like suitable for a personal computer conference camera.

[0002]

2. Description of the Related Art The imaging optical system of a personal computer conference camera is
Generally, it is desired that the device be compact and inexpensive.

In these imaging optical systems, since a solid-state imaging device such as a CCD is used as an imaging device, an optical low-pass filter for limiting high-frequency components to prevent false colors and moire, and a balance between the spectral sensitivity and the CCD. For this purpose, an infrared cut filter that cuts light of a long wavelength is used.

As an optical low-pass filter, a phase-type low-pass filter having an uneven shape and diffracting the light is known as being inexpensive. Japanese Patent Application Laid-Open No. 64-916 discloses that a lattice pattern having an optical low-pass filter function is applied to the lens surface of a taking lens.

It is also known to integrate an infrared cut filter with an optical low-pass filter.
Japanese Patent Application Laid-Open No. 2-101056 discloses a phase-type low-pass filter in which a phase portion is formed of an interference multilayer film that reflects infrared light. Japanese Patent Application Laid-Open No. Hei 4-9803 discloses a phase-type low-pass filter in which a concave-convex structure is provided on the surface of a resin having a near-infrared absorbing property.

[0006]

SUMMARY OF THE INVENTION The present invention provides an inexpensive or inexpensive and compact optical low-pass effect suitable for a camera using a solid-state image sensor such as a CCD as an image sensor, particularly a camera for a personal computer conference. It is intended to provide an imaging optical system. It is still another object of the present invention to provide an inexpensive optical low-pass filter and an imaging lens suitable for use in these imaging optical systems.

[0007]

The object of the present invention is achieved by adopting the following constitution.

That is, a single focus imaging lens, wherein a phase type diffraction grating having a low-pass effect is formed on at least one lens surface.

A phase type diffraction grating having an optical low-pass effect, which is injection-molded with a synthetic resin material having a near-infrared absorption effect.

[0010] A phase type diffraction grating having an optical low-pass effect, which is injection-molded with a synthetic resin material, is characterized in that the pitch of the grating changes so as to be larger in the periphery than in the vicinity of the optical axis. A phase type diffraction grating having an optical low-pass effect.

Further, there is provided a single-aperture imaging lens having a front diaphragm used together with a phase-type diffraction grating having an optical low-pass effect, wherein the imaging lens satisfies the following conditional expression.

−5.0 ≦ (r2 + r1) / (r2−r1) ≦ 0.0 where ri is the paraxial radius of curvature of the i-th lens surface from the object side.

An imaging optical system comprising a single-focus imaging lens and a phase-type diffraction grating having an optical low-pass effect and injection-molded with a synthetic resin material having a near-infrared absorption effect.

Here, the operation of the imaging lens, the phase type diffraction grating having the optical low-pass effect, and the imaging optical system of the present invention will be described.

Claim 1: On at least one lens surface,
By integrally forming a phase-type diffraction grating having a low-pass effect, an inexpensive single focus imaging lens having a low-pass effect can be obtained. Further, since a separate low-pass filter is not required, the imaging optical system becomes compact.

Claim 2: An inexpensive and compact single-lens imaging lens having a low-pass effect can be obtained.

Claim 3: Mass production can be achieved at low cost by molding. When injection molding is performed using a thermoplastic resin, the cost can be particularly low, and when a glass material is used, an imaging lens excellent in environmental characteristics of temperature change and humidity change can be obtained.

Claim 4: By forming the diffraction grating shape on a rotationally symmetric aspherical surface, the degree of freedom of design for obtaining good imaging performance is increased.

Claim 5: By using a one-dimensional sinusoidal grating as the diffraction grating, the MTF is less deteriorated in a low frequency range, and the off-axis characteristics are relatively good. Also, since the lattice shape is smooth, it is easy to process a mold for molding.

Claim 6: In an imaging lens having a simple structure,
Due to the balance between lens size and aberration correction, it is difficult to configure telecentric. However, if the telecentricity of the imaging lens is poor, the cutoff frequency of the diffraction grating shifts to a lower frequency off-axis. When the center light beam and the off-axis light beam pass through the diffraction grating at different positions, the pitch of the diffraction grating is changed so as to be larger in the periphery than in the vicinity of the optical axis, so that the center light beam and the off-axis light beam are changed. Can be corrected so that the cutoff frequencies are equal.

Claim 7: A lens forming a diffraction grating,
By molding with a synthetic resin material having a near-infrared absorption effect, it is not necessary to use an infrared cut filter separately, and it is possible to reduce the size and cost.

Claim 8: In the front stop single-lens image pickup lens, by satisfying this conditional expression, good imaging performance can be obtained. However, if the lower limit is not reached, the absolute value of the radius of curvature of the image-side lens surface becomes smaller due to the menis shape convex on the image side, and a large underflare occurs at the periphery of the image-side lens surface. Outside the upper limit, the radius of curvature of the object-side refracting surface becomes small due to the biconvex shape, and when the astigmatism generated on the object-side refracting surface is corrected by the aspherical surface, a large extravertive coma is generated.

Preferably, -1.50≤ (r2 + r1) / (r2-r1) ≤-0.
50 is preferably satisfied.

Here, ri is the paraxial radius of curvature of the i-th lens surface from the object side, and on the surface where the lattice shape is superimposed,
The paraxial radius of curvature of the refraction surface serving as a base.

In a ninth aspect, an infrared cut filter and an optical low-pass filter are integrated by injecting a phase-type diffraction grating having a low-pass effect from a synthetic resin material having a near-infrared absorbing effect, so that the device is inexpensive and compact. You can get a filter.

In the tenth aspect, since the lattice shape is a one-dimensional lattice formed on a flat plate-like surface, it is easy to process a mold for injection molding with a synthetic resin material.

Claim 11: By the same action as in claim 6,
It is possible to obtain an inexpensive optical low-pass filter in which the cutoff frequencies of the central light beam and the off-axis light beam are uniform.

The twelfth aspect is the same as the eighth aspect.

It is preferable that the following condition is satisfied: -1.50≤ (r2 + r1) / (r2-r1) ≤-0.50.

Here, ri is the paraxial radius of curvature of the i-th lens surface from the object side.

According to a thirteenth aspect of the present invention, the imaging optical system includes a single-focus imaging lens and a phase-type diffraction grating having an optical low-pass effect and injection-molded with a synthetic resin material having a near-infrared absorption effect. Thus, an inexpensive and compact imaging optical system can be obtained.

[0032]

Examples of the present invention will be described below.

Embodiment 1 In Embodiment 1, a phase type diffraction grating having a low-pass effect is integrally formed on a refracting surface of a single lens imaging lens, and FIG. 1 is a sectional view thereof.
On the second surface, a one-dimensional sinusoidal lattice-like phase-type diffraction grating having a low-pass effect is formed. However, in the cross-sectional views of each embodiment including FIG. 1, the amplitude of the diffraction grating is exaggerated.

The lattice shape is such that a one-dimensional sinusoidal lattice is superimposed on a rotationally symmetric aspherical surface, and is oriented so as to produce a low-pass effect in the longitudinal direction of the rectangular imaging screen.

The following table shows the lens data of the base refraction surface and the data of the diffraction grating to be added, and is designed at a cutoff frequency of 80 lines / mm.

FIG. 2 shows the M at a wavelength of 550 nm in this embodiment.
FIG. 4 is a TF curve diagram showing a low-pass effect in a longitudinal direction of the imaging screen. Hereinafter, the direction of the optical axis is defined as the z-axis, the longitudinal direction of the screen is defined as the x-axis, and the direction perpendicular thereto is defined as the y-axis.

Focal length: 3.71 F number: F2.8 Angle of view: 2ω = 56.4 ° [Lens data of base refraction surface] In each lens data in the table, r is a paraxial radius of curvature, d Is the distance between the shaft upper surfaces,
n _d is the refractive index of the d-line, and ν _d is the Abbe number. The same applies hereinafter.

[0038]

[Table 1]

[0039]

[Table 2]

The aspheric shape is expressed by the following equation.

Where k is a conical constant, Ai is an aspheric coefficient,
Pi is an aspheric power, (i: 1, 2, 3, 4).

[0042]

(Equation 1)

Data pitch of added diffraction grating 0.33 mm Amplitude 0.00021 mm Value of conditional expression (r ₂ + r ₁ ) / (r ₂ -r ₁ ) = − 1.01 <Embodiment 2> , The pitch of the diffraction grating is changed so as to be larger in the peripheral portion than in the vicinity of the optical axis. The lens data of the base refraction surface is the same as that of the first embodiment, and the added diffraction grating is represented by the following equation when the z axis is in the optical axis direction and the x axis is in the direction having the low-pass effect. .

Z = −a · cos (2πx / d) d = d0 (1 + cx ² ) d0: center pitch 0.33 mm a: amplitude 0.00021 mm c: 0.10 FIG. 3 is a cross-sectional view of FIG. However, the amplitude of the diffraction grating is exaggerated.

FIG. 4 is a graph showing the relationship between M and 550 nm in this embodiment.
FIG. 3 is a TF curve diagram in which frequency characteristics of a center light beam and an off-axis light beam are uniform as compared with FIG.

Embodiment 3 In Embodiment 3, a phase-type diffraction grating having a low-pass effect, which is injection-molded with a synthetic resin material having a near-infrared absorption effect, is arranged on the object side of the imaging lens.

The following table shows the configuration data, and the second surface of the phase type diffraction grating is a one-dimensional sine wave grating. As in the first embodiment, the rectangular imaging screen is oriented so as to produce a low-pass effect in the longitudinal direction.

The lens data of the imaging lens is the same as the lens data of the refraction surface serving as the base of the first embodiment, and the focal length, the F number and the angle of view are also the same.

FIG. 5 is a cross-sectional view, and FIG. 6 is an MTF curve at a wavelength of 550 nm in this embodiment.
The same low-pass effect is obtained. FIG. 7 is an aberration curve diagram of the imaging lens, with the diffraction grating removed.

[Lens data of base refraction surface]

[0051]

[Table 3]

[0052]

[Table 4]

Data pitch of diffraction grating 0.33 mm Amplitude 0.00021 mm Value of conditional expression (r ₂ + r ₁ ) / (r ₂ -r ₁ ) = − 1.01 <Embodiment 4> Embodiment 4 is Embodiment 3 In the second embodiment, as in the second embodiment, the pitch of the diffraction grating is changed so as to be larger in the periphery than in the vicinity of the optical axis. It is represented by the same formula as in Example 2, where d0: center pitch 0.33 mm a: amplitude 0.00021 mm c: 0.12. FIG. 8 is a sectional view, and FIG. 9 is an MTF curve at a wavelength of 550 nm in this embodiment. Compared to FIG. 6, the frequency characteristics of the center light beam and the off-axis light beam are uniform.

[0054]

According to the present invention, an inexpensive or inexpensive and compact imaging optical system having an optical low-pass effect and suitable for a camera using a solid-state imaging device such as a CCD as an imaging device, particularly a camera for personal computer conferences. Will be provided. Furthermore, an inexpensive optical low-pass filter and imaging lens suitable for use in these imaging optical systems have been provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an imaging optical system according to a first embodiment.

FIG. 2 is an MTF curve diagram of Example 1.

FIG. 3 is a cross-sectional view of an imaging optical system according to a second embodiment.

FIG. 4 is an MTF curve diagram of Example 2.

FIG. 5 is a cross-sectional view of an imaging optical system according to a third embodiment.

FIG. 6 is an MTF curve diagram of Example 3.

FIG. 7 is an aberration curve diagram of the image pickup optical system according to the third embodiment.

FIG. 8 is a sectional view of an imaging optical system according to a fourth embodiment.

FIG. 9 is an MTF curve diagram of Example 4.

Claims (13)

[Claims] 1. An imaging lens having a single focus, wherein a phase type diffraction grating having a low-pass effect is formed on at least one lens surface. 2. The imaging lens according to claim 1, wherein the imaging lens is a single lens. 3. The imaging lens according to claim 1, wherein the lens forming the phase type diffraction grating is a lens manufactured by molding. 4. The imaging lens according to claim 1, wherein the phase type diffraction grating has a shape in which a grating shape is superimposed on a rotationally symmetric aspherical surface. 5. The imaging lens according to claim 1, wherein the phase type diffraction grating is a one-dimensional sine wave grating. 6. The phase type diffraction grating according to claim 1, wherein the phase type diffraction grating is a one-dimensional grating, and the pitch of the grating changes so as to be larger in a peripheral portion than in a portion near an optical axis. Item 2. The imaging lens according to Item 1. 7. The imaging lens according to claim 1, wherein the lens on which the phase type diffraction grating is formed is formed of a synthetic resin material having a near-infrared absorption effect. . 8. The imaging lens according to claim 2, wherein the imaging lens is a front stop imaging lens and satisfies the following conditional expression. −5.0 ≦ (r2 + r1) / (r2−r1) ≦ 0.0 where ri is a paraxial radius of curvature of the i-th lens surface from the object side, and is a base refraction on a surface where the lattice shape is superimposed. The paraxial radius of curvature of the surface. 9. A phase type diffraction grating having an optical low-pass effect, which is injection-molded with a synthetic resin material having a near-infrared absorption effect. 10. The phase type diffraction device having an optical low-pass effect according to claim 9, wherein the phase type diffraction grating has a one-dimensional grating formed on at least one of the front and rear surfaces of a flat plate. lattice. 11. A phase-type diffraction grating having an optical low-pass effect, which is injection-molded with a synthetic resin material, wherein the pitch of the grating changes so as to be larger in the periphery than in the vicinity of the optical axis. A phase type diffraction grating having an optical low-pass effect. 12. A pre-aperture single-lens imaging lens used with a phase-type diffraction grating having an optical low-pass effect, wherein the imaging lens satisfies the following conditional expression. −5.0 ≦ (r2 + r1) / (r2−r1) ≦ 0.0 where ri is the paraxial radius of curvature of the i-th lens surface from the object side. 13. An imaging optical system comprising: a single-focus imaging lens; and a phase-type diffraction grating having an optical low-pass effect and injection-molded with a synthetic resin material having a near-infrared absorption effect.