JPH10170822A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce the lowering of optical performance caused by a diffracted light beams of unnecessary order with respect to wavelength other than optimized wavelength obtained in the case a diffraction type optical element is used so as to highly accurately perform image picking-up, by limiting the wavelength band area of a light passing through the diffraction type optical element so that the influence of the diffracted light beams of the order, which is unnecessary for image formation among the diffracted light beams by the diffraction type optical element is reduced. SOLUTION: The image of an object is formed on the photoelectric conversion surface of a solid image pickup element 12 through an image formation optical system 11, the output signal of the element 12 is processed at a signal processing circuit 13, so that a video signal is obtained. The system 11 has a lens group 14, the diffraction type optical element 15, and an optical member 16. A low-pass filter is provided on the member 16, and also a wavelength band area limiting filter constituting a wavelength band area limiting means having a spectral transmission factor is provided. Thus, the intensity of the diffracted light beams having the order unnecessary for image formation can be reduced to an ignorable extent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus which forms an image of an object on an electronic image pickup device such as a solid-state image pickup device or an image pickup tube by an image formation optical system, and more particularly to an image formation optical system. The present invention relates to an imaging device including a diffractive optical element.

[0002]

2. Description of the Related Art It is known that a diffractive optical element has a function of branching optical paths of a plurality of diffraction orders and a function of condensing diffracted light by a ring-shaped diffraction grating. For example, a diffractive optical element configured to have a light condensing function can easily generate an aspherical wave, so that it has a large effect on aberration correction, and since it has substantially no thickness,
It has a high degree of freedom in configuration and is effective in realizing a compact optical system.In addition, the dispersion characteristic has a negative value corresponding to the Abbe number of a refraction lens. It is known that there is a great effect in correcting chromatic aberration.

[0003] With respect to improving the performance of an optical system by utilizing such features, for example, Binary Optics
Technology: The Theory and Design of Multi-Level D
iffractive Optical Element, Gary J. Swanson, Techno
logy Report 854, MIT Lincoln Laboratory, August 19
See Section 89. In addition, for example, Japanese Patent Application Laid-Open
JP-A-331941 and JP-A-6-324262 describe an apparatus including such a diffractive optical element as an imaging lens. Further, as a device utilizing a branching action of an optical path by a plurality of diffraction orders of a diffraction optical element, for example, Japanese Patent Application Laid-Open No. Hei 4-9803 discloses a device used as a low-pass filter for removing moire of an electronic image pickup device. But also patent 2524569.
In each of the publications, the one used as a color separation optical system is described.

On the other hand, light incident on a diffractive optical element is generally decomposed into a plurality of orders of diffracted light. For example, when the diffractive optical element is configured as a lens element,
The presence of a plurality of orders of diffracted light is equivalent to the presence of a plurality of focal points, and therefore is not preferable as an imaging optical system except in special cases.

[0005] Therefore, when constructing an optical system using diffracted light of a specific order, when diffracted light of other orders has an adverse effect, it is necessary to remove the diffracted light of other orders. Occurs. For such issues,
Conventionally, as shown in FIG. 16, the cross-sectional shape of a relief pattern 2 for diffraction formed on a transparent substrate 1 at a wavelength to be used is made saw-toothed (blazed), and energy is given to diffracted light of a specific order. It is known to concentrate and avoid diffracted light of other orders.

[0006]

However, FIG.
As shown in the figure, even if the cross-sectional shape of the relief pattern 2 is processed into a sawtooth shape, the wavelength at which energy can be concentrated to the maximum (hereinafter referred to as an optimized wavelength) differs depending on the depth of the sawtooth-shaped groove. It is impossible to concentrate the energy of the band light having
Such a phenomenon is not a problem when, for example, using a monochromatic light source, such as laser light, but, for example, in an imaging device using white light such as a camera, at a wavelength other than the optimized wavelength, There is a problem that diffraction efficiency is reduced and energy is dispersed in diffracted lights of other orders.

FIG. 17 shows the relationship between the first-order diffraction efficiency and the wavelength used for the diffractive optical element having the sectional shape shown in FIG. Here, the relief pattern has a first-order diffraction efficiency of 100 at a wavelength λ = 500 nm.
% Is determined on the base material of BK7 with the groove depth determined. Although the wavelength band shown in FIG. 17 is from λ = 400 nm to λ = 700 nm, which can be generally regarded as a visible wavelength region, it can be seen that the diffraction efficiency decreases as the distance from the optimization wavelength λ = 500 nm increases.

FIG. 18 shows that the wavelength λ = 5 as described above.
FIG. 9 shows the respective relationships between the 0th-order diffraction efficiency and the 2nd-order diffraction efficiency and the wavelength of the diffractive optical element optimized so that the first-order diffraction efficiency becomes 100% at 00 nm.
As is clear from FIG. 18, in the short wavelength region and the long wavelength region where the first-order diffracted light decreases, the 0th-order diffracted light and the second-order diffracted light respectively increase.

For this reason, such a diffractive optical element is
For example, when used as a lens element of a camera using white light, diffracted light of an order other than the specific diffracted light to be used appears as a colored flare or ghost, which causes deterioration in imaging performance. For this reason, when a diffractive optical element is used in an imaging device that uses image formation by an imaging lens, orders other than the specific diffraction order light used for wavelengths other than the optimized wavelength are removed or affected. However, this point has not been proposed in the past.

SUMMARY OF THE INVENTION The present invention has been made in view of the above point, and it is possible to effectively reduce the decrease in optical performance due to unnecessary orders of diffracted light with respect to wavelengths other than the optimized wavelength when a diffractive optical element is used. It is an object of the present invention to provide an imaging device appropriately configured to enable accurate imaging.

[0011]

In order to achieve the above object, the present invention relates to an image pickup apparatus wherein an image of an object is formed on an electronic image pickup device by an image forming optical system. Is a diffractive optical element having an image forming action, or an action of improving the image forming performance in combination with another lens element, and limiting the wavelength band of light passing through the diffractive optical element, Wavelength band limiting means for reducing the influence of diffracted light of an order unnecessary for image formation among the diffracted light by the optical element.

Further, according to the present invention, in an image pickup apparatus in which an image of an object is formed on an electronic image pickup device by an image forming optical system, the image forming optical system has a diffraction type having an annular diffraction grating. An optical element and a wavelength band limiter for limiting the wavelength band of light passing through the diffractive optical element to reduce the influence of diffracted light of an order unnecessary for image formation among the diffracted light by the diffractive optical element. Means.

Further, according to the present invention, in an image pickup apparatus in which an image of an object is formed on an electronic image pickup device by an image forming optical system, the image forming optical system comprises: a diffractive optical element;
Wavelength band limiting means for limiting the wavelength band of the light passing through the diffractive optical element and reducing the influence of the diffracted light of the order unnecessary for image formation among the diffracted light by the diffractive optical element. The electronic image pickup device is characterized in that signal processing means for processing the output signal and correcting the color information of the object is connected to the electronic image pickup device.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image of an object is formed, for example, on a single solid-state imaging device or a plurality of solid-state imaging devices through an imaging lens, and an output signal of an electronic imaging device is processed to produce a color image. In an imaging device for obtaining an image signal, usually, the three primary colors red (R), green (G),
A wavelength band limiting unit such as an absorption filter or an interference filter that transmits light in the blue (B) or their complementary colors, cyan (C), magenta (M), and yellow (Y), is arranged, and RGB is Video signals of three primary colors or complementary colors of CMY are obtained. In such an imaging device,
For example, when a color image signal is obtained by forming an image in the wavelength bands of the three primary colors RGB, the spectral characteristics of the light intensity received by the image sensor include the spectral distribution of a light source, the spectral transmittance of a typical lens,
In consideration of the spectral sensitivity of the image sensor, the image is generally as shown in FIG.

Here, in the imaging apparatus having the spectral characteristics shown in FIG. 19, if the imaging optical system uses, for example, a diffractive optical element having the first-order light diffraction efficiency shown in FIG. The characteristics are as shown in FIG. In this case, the spectral characteristics of the zero-order and second-order diffracted light unnecessary for image formation are as shown in FIG.

As is apparent from FIG. 21, in the G wavelength band of the three primary colors RGB, the 0th order and 2nd order unnecessary for image formation are obtained.
The next amount of diffracted light is about 1% of the total amount of light in the G wavelength band, which is negligible. However, in the R wavelength band, the zero-order and second-order diffracted light amounts unnecessary for image formation are R
In the wavelength band of B, the spectral characteristic actually contributes to image formation even at a wavelength shorter than 400 nm, and is therefore unnecessary for image formation. The 0th-order and 2nd-order diffracted light amounts exceed 10% of the total light amount in the B wavelength band. For this reason, in such an imaging apparatus, deterioration of image quality cannot be ignored.

As described above, in the diffractive optical element, as the distance from the optimized wavelength increases, the amount of diffraction light of an unnecessary order increases accordingly. Therefore, in one embodiment of the present invention,
In a shorter wavelength region and a longer wavelength region than the optimized wavelength of the diffracted light of the order to be used, a wavelength band contributing to image formation is limited. By doing so, the ratio of the amount of diffracted light of orders unnecessary for image formation can be made lower than the total amount of light in the target wavelength band, so that the effect on image formation can be reduced. Becomes For example, as mentioned above,
When a color image signal is obtained using the RGB three primary color filters, the short wavelength region of the wavelength band for obtaining the B image and the long wavelength region of the wavelength band for obtaining the R image are determined by using the wavelength band limiting means. By cutting, it is possible to reduce the influence of the diffracted light of the order unnecessary for image formation.

In this case, the amount of light of each of RGB required to obtain an original color image is reduced, and the wavelength band is narrowed.
Correction is performed so that the color information of the object is not impaired by a method such as normalizing the signal strength of each of the GBs or shifting the color to be expressed.

The wavelength band limiting means for limiting the wavelength band specifically includes, in a target wavelength band where the amount of diffracted light of an order unnecessary for image formation becomes a nonnegligible level, the total light amount (A) in the target wavelength band. _It is preferable that the light quantity (A ₀ ) of the diffracted light of the order unnecessary for image formation with respect to _a ) satisfies A ₀ / A _a <0.1 (1). If this conditional expression (1) is satisfied, it is possible to effectively ignore the deterioration of the image quality due to the diffracted light of the order unnecessary for image formation.

[0020] More specifically, in the short wavelength region than optimizing the wavelength lambda _o, to limit the wavelength band, the wavelength lambda _s to cut amount 50%, the following conditional expression (2)
It is desirable to satisfy _{0.7 <λ s / λ o <} 0.95 (2)

Further, in the wavelength region longer than the optimized wavelength lambda _o, to limit the wavelength band, the wavelength lambda _L to cut amount 50%, it is desirable to satisfy the following conditional expression (3) . 1.2 <λ _L / λ _o <1.5 (3)

Here, λ _s / λ _o is a small value exceeding the lower limit of conditional expression (2), and λ _L / λ _o is a large value exceeding the upper limit of conditional expression (3). In this case, the influence of unnecessary orders of diffracted light cannot be sufficiently reduced, and it becomes difficult to prevent the image performance from deteriorating. Also, λ _s / λ _o
Is larger than the upper limit of conditional expression (2), or is smaller than λ _L / λ _o below the lower limit of conditional expression (3). too close to lambda _o, the wavelength bandwidth of forming a color image becomes narrow, it can not be kept sufficient color reproducibility, which is not preferable.

As described above, the diffraction efficiency of the diffractive optical element with respect to the wavelength decreases with respect to the wavelength to be optimized on both the short wavelength side and the long wavelength side. Therefore, maintaining good color reproducibility, and to sufficiently reduce the effects of unwanted orders of diffracted light for image formation is optimized wavelength lambda _o is the wavelength band λ ₁ <λ <λ ₂ used | C ₁ −C ₂ | <20% (4) However,
C ₁ and C ₂ indicate the diffraction efficiencies (%) of the used diffraction orders at the wavelengths λ ₁ and λ ₂ when the diffraction orders used at the wavelength λ _o are optimized.

Here, assuming that the diffraction order to be used is the first order, the m-th order diffraction efficiency C _m at an arbitrary wavelength λ with respect to the optimized wavelength λ _o can be calculated by the following equation (5). .

(Equation 1)

Therefore, for example, when a diffractive optical element formed on quartz glass is used in a wavelength band of 400 nm <λ <700 nm using first-order diffracted light, the optimized wavelength λ _o satisfying (4) is Approximately, 475 nm <λ _o <540 nm (6).

Here, if | C ₁ -C ₂ | is set to a large value exceeding the upper limit of conditional expression (4), unnecessary diffraction order light in a short wavelength region or a long wavelength region increases. Therefore, since the quality of the image is significantly reduced, it is difficult to maintain the color balance if the wavelength band is limited as described above.

In the present invention, in order to further improve the image quality, the following conditional expression (7) is used instead of conditional expression (1), and the following conditional expression is used instead of conditional expression (2). (8) is replaced by conditional expression (9) below instead of conditional expression (3), and conditional expression (1) below instead of conditional expression (4)
It is desirable to satisfy 0). _{A o / A a <0.05 (} 7) 0.8 <λ s / λ o <0.95 (8) 1.2 <λ L / λ o <1.4 (9) | C 1 -C 2 | <10% (10)

More preferably, the following conditional expression (11) should be satisfied instead of conditional expression (10). | C ₁ -C ₂ | <5% (11)

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows the configuration of the imaging apparatus according to the first embodiment of the present invention.
This imaging apparatus forms an image of an object on a photoelectric conversion surface of a solid-state imaging device 12 via an imaging optical system 11, processes an output signal of the solid-state imaging device 12 by a signal processing circuit 13, and generates a video signal. Is obtained. Imaging optical system 11
Has a lens group 14, a diffractive optical element 15, and an optical member 16. In FIG. 1, these lens groups 14,
The diffraction optical element 15 and the optical member 16 are schematically arranged.

In this embodiment, as shown in plan and sectional views in FIGS. 2A and 2B, the diffractive optical element 15 has a relief pattern concentrically formed on a parallel plate-shaped optical material substrate 21. 22 are formed. here,
The relief pattern 22 is formed so as to utilize the first-order diffracted light, and to optimize the imaging performance in accordance with the correlation with other lens elements. In addition, the optical member 16 is provided with a low-pass filter and a wavelength band limiting filter constituting a wavelength band limiting unit having the spectral transmittance shown in FIG. Further, the image sensor 12 has RGB3 having the spectral characteristics shown in FIG.
A mosaic color filter of primary colors is provided.

As described above, in the solid-state image pickup device 12, the image of the object formed through the image forming optical system 11 is converted into an electric signal in accordance with the light intensity and supplied to the signal processing circuit 13, Here, the color information of the object is corrected so that the color information of the object is not impaired by a method such as normalization of the signal strength of each of RGB and shifting of the color to be expressed as necessary, and converted into a color video signal. Write or output to external devices such as personal computers, display devices, and printers. Note that such processing is controlled by an external control device or a CPU incorporated in the imaging device.

FIG. 5 shows the structure of the diffractive optical element 15 incident on the solid-state imaging device 12 when the optical member 16 is not provided with the wavelength band limiting filter in the configuration shown in FIG.
It shows the spectral characteristics of the first-order diffracted light and zero-order diffracted light. FIG. 6 shows the spectral characteristics of the second-order diffracted light and the zero-order diffracted light when the optical member 16 is provided with the wavelength band limiting filter having the spectral characteristics shown in FIG. is there. As is clear from FIGS. 5 and 6, according to this embodiment, the intensity of the diffracted light of the order unnecessary for image formation can be reduced to a negligible level.

In this embodiment, the wavelength band limiting filter is provided on the optical member 16. However, the wavelength band limiting filter may be provided before the lens group 14,
The same effect can be obtained by arranging at an arbitrary position on the imaging optical path to the photoelectric conversion surface. In particular, the image sensor 1
If the cover glass for protecting the photoelectric conversion surface of No. 2 is constituted by a wavelength band limiting filter, it is effective in reducing the number of parts and miniaturizing the optical system.

In the second embodiment of the present invention, in the configuration shown in FIG. 1, an infrared cut filter having a spectral transmittance shown in FIG. 7 is provided in the optical member 16 instead of the wavelength band limiting filter. The surface of the diffractive optical element 15 opposite to the surface on which the relief pattern is formed is coated with a multilayer film, and wavelength band limiting means having spectral transmittance characteristics as shown in FIG. 8 is provided. Here, the multilayer films are formed of SiO ₂ :
66.46 nm, TiO ₂ : 28.62 nm, Si
O ₂ : 53.06 nm, TiO ₂ : 42.47 nm, S
iO ₂ : 68.16 nm, TiO ₂ : 35.44 nm,
SiO ₂ : 55.57 nm, TiO ₂ : 38.89 n
m, so as to overlap each other. In this way, the harmful infrared light and the diffracted light of the order unnecessary for imaging are simultaneously limited.

FIG. 9 shows the spectral characteristics of the second-order diffracted light and the zero-order diffracted light in the diffractive optical element 15 incident on the solid-state imaging device 12 in this embodiment. Also in this embodiment, as is clear from the comparison with FIG. 5, similarly to the first embodiment, the intensity of the diffracted light of the order unnecessary for image formation can be reduced to a negligible extent.

In this embodiment, the diffractive optical element 14 is provided with the multilayer film constituting the wavelength band limiting means.
Even if a similar multilayer film is coated on the refracting surface of the lens element constituting the lens group 14, the optical member 16, or the cover glass for protecting the photoelectric conversion surface of the imaging device 12,
The same effect can be obtained.

In the third embodiment of the present invention, in the configuration shown in FIG. 1, instead of providing a wavelength band limiting filter on the optical member 16, a mosaic color of three primary colors of RGB provided on the photoelectric conversion surface of the image pickup device 12. By configuring the filter to have the spectral characteristics shown in FIG. 10, the color filter also functions as wavelength band limiting means.

FIG. 11 shows the spectral characteristics of the second-order diffracted light and the zero-order diffracted light in the diffractive optical element 15 incident on the solid-state imaging device 12 in this embodiment.
Also in this embodiment, as is clear from the comparison with FIG. 5, the intensity of the diffracted light of the order unnecessary for image formation can be reduced to a negligible level.

In this embodiment, the RGB color filters have the spectral sensitivity of each of the RGB filters shown in FIG.
In addition to the filter having the general spectral sensitivity shown in FIG. 4 and the spectral filter shown in FIG. It can also be configured with a two-layer structure with a filter. In addition, in order to reduce the influence of unnecessary order light in the short wavelength region, in particular, S for controlling the transmittance in the short wavelength region provided on the surface layer of the photoelectric conversion surface of the imaging element 12 is used.
It is also possible to control the spectral characteristics in the short wavelength region by adjusting the thickness of the multilayer film of iO ₂ and polycrystalline Si, or by increasing the thickness of the P-type impurity implantation layer for removing dark current. The effect can be achieved.

In the above-described first to third embodiments, the imaging optical system 11 includes, for example, a first lens 25, a diaphragm 26, a second lens 27, a third lens 28, as shown in FIG.
Fourth lens 29, fifth lens 30, and sixth lens 31
Can be configured. Table 1 shows the focal length of 7.
9 shows data of an example of each lens when the F number is set to 00 mm and the F number is set to 2.9. In FIG. 12,
The third lens 28 is a diffractive optical element. Table 1
Where ♯ is the lens number, r is the radius of curvature of the refraction surface, d
Denotes the thickness or lens interval at the center of the lens, nd denotes the refractive index of the d-line, vd denotes the Abbe number of the d-line, and the surface marked with * denotes an aspheric surface.

[0041]

[Table 1]

The above-mentioned aspherical surface is formed so as to have, for example, an aspherical surface coefficient shown in Table 2.

[0043]

[Table 2] As is clear from Tables 1 and 2, the diffractive optical element constituting the third lens 28 is treated as a so-called high refractive index approximation having a refractive index of 1001 and an Abbe ratio of about -3.45.

The diffractive optical element is not limited to the one in which the relief pattern 22 is formed on the flat substrate 21 as shown in FIG. 2, but the relief pattern 22 is formed on a spherical substrate or an aspherical substrate. The relief pattern 22 is not limited to the concentric shape, and the imaging optical system 1
According to the first function, for example, when rotationally asymmetric imaging performance is required, an elliptical pattern or a parallel pattern having the same function as a cylindrical lens can be used. In the embodiment, the first order light is used as the design order of the diffractive optical element, but a higher order may be used.

In each of the above embodiments, the image sensor 1
Although a so-called primary-color single-chip image pickup device in which mosaic RGB filters are arranged before 2 is configured, a so-called complementary-color single-plate image pickup device in which CMYG filters are arranged in a mosaic shape can of course be configured. It is also possible to configure a multi-chip imaging device represented by a so-called three-chip imaging device in which a photographing light beam is split into light beams having different wavelength bands by a color separation prism or the like, and a color image is obtained by, for example, three image sensors of RGB. .

FIG. 13 shows a configuration of a main part of a fourth embodiment of the present invention. This embodiment shows a three-plate type imaging device, in which an image of an object is decomposed into RGB by an imaging optical system 41, and corresponding solid-state imaging devices 42R, 42R.
G, 42B. The imaging optical system 41 includes a lens system 43 including a diffractive optical element as shown in FIG.
A color separation prism 44 for separating the color into GB. Here, the color separation is generally performed using a dichroic film also from the viewpoint of the high light utilization rate.

In this embodiment, the dichroic film of the color separation prism 44 is provided with a spectral transmittance characteristic as shown in FIG. It also functions as a wavelength band limiting means for reducing the unnecessary order diffracted light from the light. In this embodiment, the diffractive optical element is
It is optimized at a wavelength of 530 nm.

FIG. 15 shows the spectral characteristics of the second-order diffracted light and the zero-order diffracted light in the diffractive optical elements incident on the image pickup devices 42R, 42G, and 42B in this embodiment. As is clear from FIG. 15, in this embodiment, similarly to the above-described embodiment, the intensity of the diffracted light of the order unnecessary for image formation can be reduced to a negligible level.

In this embodiment, the spectral transmittance characteristic of R of the color separation prism 44 is extended to a long wavelength range, and an infrared cut filter is arranged in the imaging optical path.
The spectral transmittance characteristics shown in FIG. 14 can be obtained by the action of both the color separation prism 44 and the infrared cut filter.

In each of the embodiments described above, the solid-state image pickup device is used as the electronic image pickup device.
The present invention can be effectively applied, and the same effect can be obtained.

Additional Items 1. In an image pickup apparatus configured to form an image of an object on an electronic image pickup device by an image forming optical system, the image forming optical system has a ring-shaped diffraction grating, and forms an image forming function or another lens. A diffractive optical element having an effect of improving the imaging performance by a combination of elements, and restricting the wavelength band of light passing through the diffractive optical element, of diffracted light by the diffractive optical element, for forming an image. An imaging apparatus comprising: a wavelength band limiting unit for reducing an influence of an unnecessary order of diffracted light. 2. In an image pickup apparatus configured to form an image of an object on an electronic image pickup device by an image forming optical system, the image forming optical system has an image forming function or an image forming performance by a combination with another lens element. A diffractive optical element having an effect of improving, and by limiting the wavelength band of light passing through the diffractive optical element, of the diffracted light by the diffractive optical element, the influence of the diffracted light of an order unnecessary for image formation is reduced. An image pickup apparatus, comprising: a wavelength band limiting unit for reducing, and a signal processing unit for processing an output signal of the electronic image pickup device and correcting color information of the object. . 3. In an image pickup apparatus in which an image of an object is formed on an electronic image pickup device by an image forming optical system, the image forming optical system includes a diffractive optical element having a ring-shaped diffraction grating, and the diffractive optical element. Wavelength band limiting means for limiting the wavelength band of light that has passed through, and of reducing the influence of diffracted light of an order unnecessary for image formation, out of the diffracted light by the diffractive optical element, The element processes the output signal,
An imaging apparatus, wherein signal processing means for correcting color information of the object is combined. 4. The imaging device according to claim 1, wherein the imaging device satisfies at least one of the conditional expressions (1) to (4). 5. The imaging device according to claim 1, wherein the imaging device satisfies at least one of the conditional expressions (7) to (10). 6. In the imaging device according to additional item 4 or 5, the conditional expression (11) may be used as the conditional expression (4) or (10).
An imaging device characterized by using: 7. The imaging apparatus according to claim 1, wherein the imaging optical system includes a filter that limits a wavelength band. 8. 4. The imaging apparatus according to claim 1, wherein the wavelength band limiting unit is provided on a cover glass that protects a photoelectric conversion surface of the electronic imaging device. 9. 4. The image pickup apparatus according to claim 1, wherein said wavelength band limiting means comprises a multilayer film provided on a surface of an optical member constituting said imaging optical system. 10. The imaging device according to claim 1, 2, or 3,
The imaging apparatus according to claim 1, wherein the wavelength band limiting unit includes a wavelength band limiting filter having a function of limiting a wavelength band reaching a photoelectric conversion surface of the electronic image sensor in order to obtain a color image. 11. 11. The imaging device according to claim 7 or 10, wherein the filter or the wavelength band limiting filter comprises a filter containing a dye. 12. 11. The imaging device according to claim 7 or 10, wherein the filter or the wavelength band limiting filter comprises an interference filter. 13. 11. The imaging device according to claim 10, wherein the electronic imaging device is configured to be one and a color image is obtained. 14． 11. The imaging device according to claim 10, wherein a plurality of electronic imaging elements are used to obtain a color image. 15. In the imaging device according to additional item 13 or 14,
An imaging apparatus, wherein a filter used to obtain the color image also constitutes the wavelength band limiting unit. 16. In the imaging device according to additional item 13 or 14,
A filter used to obtain the color image, in order to obtain a color image, a filter member having a function of limiting a wavelength band reaching the photoelectric conversion surface of the electronic imaging device,
An image pickup apparatus, comprising: a filter member for reducing the influence of diffracted light of an order unnecessary for image formation. 17． The imaging device according to claim 1, 2, or 3,
An image pickup apparatus, wherein the wavelength band limiting means includes a short wavelength absorption layer provided on a photoelectric conversion surface of the electronic image pickup device. 18. 18. The imaging device according to any one of additional items 7 to 17, wherein at least one of the conditional expressions (1) to (4) is satisfied. 19. 18. The imaging device according to any one of additional items 7 to 17, wherein at least one of the conditional expressions (7) to (10) is satisfied. 20. In the imaging device according to additional item 18 or 19,
An imaging apparatus characterized by using the conditional expression (11) as the conditional expression (4) or (10).

[0052]

According to the present invention, it is possible to effectively reduce a decrease in optical performance due to unnecessary orders of diffracted light with respect to wavelengths other than the optimized wavelength when a diffractive optical element is used.
A highly accurate imaging device can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of the diffractive optical element shown in FIG.

FIG. 3 is a diagram illustrating spectral characteristics of a wavelength band limiting filter used in the first embodiment.

FIG. 4 is a diagram illustrating spectral characteristics of RGB color filters used in the first embodiment.

FIG. 5 is a diagram illustrating spectral characteristics of diffracted light unnecessary for image formation when wavelength band limitation is not applied in the first embodiment.

FIG. 6 is a diagram illustrating spectral characteristics of diffracted light unnecessary for image formation when wavelength bands are restricted in the first embodiment.

FIG. 7 is a diagram showing a spectral transmittance characteristic of an infrared cut filter used in a second embodiment of the present invention.

FIG. 8 is a diagram illustrating spectral transmittance characteristics of a multilayer film used in a second embodiment.

FIG. 9 is a diagram illustrating spectral characteristics of diffracted light unnecessary for image formation when wavelength bands are restricted in the second embodiment.

FIG. 10 is a diagram illustrating spectral characteristics of an RGB color filter used in a third embodiment of the present invention.

FIG. 11 is a diagram illustrating spectral characteristics of diffracted light unnecessary for image formation when wavelength bands are restricted in the third embodiment.

FIG. 12 is a diagram illustrating a configuration of an example of an imaging optical system including a diffractive optical element.

FIG. 13 is a schematic configuration diagram showing a fourth embodiment of the present invention.

FIG. 14 is a diagram showing spectral transmittance characteristics of a dichroic film used in a fourth embodiment.

FIG. 15 is a diagram illustrating spectral characteristics of diffracted light unnecessary for image formation when wavelength bands are restricted in the fourth embodiment.

FIG. 16 is a diagram showing a blazed relief pattern.

FIG. 17 is a diagram showing the relationship between the wavelength of the diffractive optical element optimized for the first-order diffracted light and the diffraction efficiency of the first-order diffracted light.

FIG. 18 is a diagram illustrating a relationship between the wavelength of the diffractive optical element optimized for the first-order diffracted light and the diffraction efficiencies of the zero-order diffracted light and the second-order diffracted light.

FIG. 19 is a diagram illustrating spectral characteristics of an imaging device that forms a color image.

FIG. 20 is a diagram illustrating the spectral characteristics of diffracted light that contributes to image formation when a diffractive optical element is used.

FIG. 21 is a diagram showing spectral characteristics of diffracted light unnecessary for image formation when a diffractive optical element is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Imaging optical system 12 Solid-state image sensor 13 Signal processing circuit 14 Lens group 15 Diffractive optical element 16 Optical member 21 Substrate 22 Relief pattern

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuya Ishii 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd.

Claims (3)

[Claims] 1. An image pickup apparatus in which an image of an object is formed on an electronic image pickup device by an image forming optical system, wherein the image forming optical system has an image forming function or a combination with another lens element. A diffractive optical element having an effect of improving the imaging performance by limiting the wavelength band of light passing through the diffractive optical element, of the diffracted light by the diffractive optical element, of an order unnecessary for image formation. An imaging apparatus comprising: a wavelength band limiting unit for reducing an influence of diffracted light. 2. An image pickup apparatus in which an image of an object is formed on an electronic image pickup device by an image forming optical system, wherein the image forming optical system includes a diffractive optical element having an annular diffraction grating; Wavelength band limiting means for limiting the wavelength band of the light passing through the diffractive optical element and reducing the influence of diffracted light of an order unnecessary for image formation among the diffracted light by the diffractive optical element. An imaging device characterized by the above-mentioned. 3. An image pickup apparatus in which an image of an object is formed on an electronic image pickup device by an image forming optical system, wherein the image forming optical system passes through a diffractive optical element and the diffractive optical element. A wavelength band limiting unit for limiting the wavelength band of light, of the diffracted light by the diffractive optical element, for reducing the influence of the diffracted light of the order unnecessary for image formation; and An image pickup apparatus, further comprising a signal processing unit for processing the output signal and correcting the color information of the object.