JP4303549B2 - Electronic still camera - Google Patents

Description

  The present invention relates to an electronic still camera suitable for a camera having a focal plane shutter such as a single-lens reflex type.

  In recent years, various cameras using a so-called silver salt film and having a focal plane shutter, for example, an electronic still camera (digital single-lens reflex camera) using a single-lens reflex camera body have been developed. The optical elements of a digital single-lens reflex camera based on a single-lens reflex camera body using a silver salt film are shown in FIG. The subject luminous flux that has passed through the photographic lens L is reflected by the quick return mirror 13, passes through a focusing screen 15 that is disposed at a position equivalent to the designed imaging plane position IP, is converged by a condenser lens 17, and is pentagonal prism 19. Then, the user observes the subject image formed on the focusing screen 15 as an erect real image by the subject luminous flux. On the other hand, at the time of exposure, the quick return mirror 13 is raised, the focal plane shutter curtain 23 is opened, and a subject image is formed at the imaging plane position IP. That is, a subject image in the same focus state as the subject image formed on the focusing screen 15 is formed at the imaging plane position IP and exposed.

  In a digital single-lens reflex camera based on a single-lens reflex camera body for this type of silver salt film, the imaging plane position IP of the lens and the sensor plane 103 of the image sensor 101 are optically equivalent. When an automatic focus detection (AF) device is provided, the focus state of the subject image at the imaging plane position IP is usually detected.

  On the other hand, in a general electronic still camera, an imaging element 101 such as a CCD image sensor has optical elements such as a protective glass, an optical low-pass filter, and an IR (infrared) cut filter on the photographing lens L side from the sensor surface 103. Has been placed. Therefore, if the image sensor 101 is arranged behind the focal plane shutter curtain 23 so that the sensor surface 103 coincides with the imaging plane position IP, the optical element comes into contact with the focal plane shutter. For this reason, the sensor surface 103 of the image sensor 101 cannot be made coincident with the imaging surface position IP, and must be disposed at a position farther from the photographing lens L than the imaging surface position IP. Then, it was out of focus and a clear image could not be obtained.

As a means to solve such problems, an optical low-pass filter or the like is separated from the image sensor, an optical low-pass filter or the like is disposed on the photographing lens side with respect to the focus calplane shutter curtain, and the sensor surface is interlocked with the quick return mirror. A lens that is moved back and forth in the optical axis direction of the photographic lens (Patent Document 1) or an image sensor is held movably in the optical axis direction of the photographic lens, and light is moved according to the rotational displacement of the quick return mirror and the opening / closing of the shutter curtain. The one that is moved in the axial direction (Patent Document 2) has been proposed.
JP 2000-324370 A JP 2000-101887

  However, since the structures of the cited references 1 and 2 require a mechanical drive mechanism, there are problems such as an increase in the number of parts and an increase in size because a space for housing is required.

  The present invention has been made in view of the problem of an image sensor for a digital single-lens reflex camera using the above-described conventional single-lens reflex camera for a silver salt film. An object of the present invention is to provide an electronic still camera equipped with an image sensor that can be converted into a digital camera without using a mechanism.

The present invention that achieves this object has a photographic optical system and a focal plane shutter disposed on the photographic optical system side of the imaging position of a subject image formed by this photographic optical system, In an electronic still camera in which an optical element provided in front of the sensor surface interferes with the focal plane shutter when the surface is arranged at a position coincident with the imaging position, the optical element interferes with the focal plane shutter. when placed at a position not, characterized in that the optical element is shaped to the imaging position is shifted backward Ru match with the sensor surface of the object image.
The optical element includes a concave lens shape having negative power. More practically, it includes a concave lens shape whose surface on the photographing optical system side is concave, or a concave lens shape whose surface on the sensor surface side is concave.

Actually, the imaging element includes a protective glass on the photographing optical system side with respect to the sensor surface, and the optical element is mounted on the photographing lens side with respect to the protective glass.
The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter that are bonded together in order from the photographing optical system side, and the IR cut filter has a curved shape with a concave surface on the photographing optical system side. The surface on which the optical adhesive layer is in close contact with the IR cut filter, that is, the surface on the photographing optical system side, has a plano-concave lens shape. In this case, if the refractive index of the adhesive layer is larger than the refractive index of the IR cut filter, the adhesive layer alone acts as a plano-concave lens.
The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter that are in close contact with each other from the photographing optical system side, and the IR cut filter has a concave-convex lens shape with a concave surface on the photographing optical system side.

  The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter that are in close contact with each other from the photographing optical system side, and the optical low-pass filter has a curved shape with a concave surface on the sensor surface side, and the optical adhesive layer Is a plano-concave lens shape having a concave on the sensor surface side. In this case, if the refractive index of the adhesive layer is larger than the refractive index of the optical low-pass filter, the adhesive layer alone acts as a plano-concave lens.

  The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter in order from the photographing optical system side. The IR cut filter has a curved surface shape with a concave surface on the photographing optical system side. The agent layer is a plano-concave lens shape having a concave surface that is in close contact with the IR cut filter, and is fixed to the imaging element in a state of sealing the space between the sensor surface and the sensor lens side of the sensor surface.

  The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter that are in close contact with each other from the photographing optical system side, and the IR cut filter has a plano-concave lens shape with a concave surface on the photographing optical system side, It is fixed to the image sensor in a state where the space between the sensor surface and the sensor surface is sealed to the photographic lens side.

The transparent protective plate itself mounted on the imaging element closer to the photographing optical system than the sensor surface may be used as the optical element.
In this case, the transparent protective plate has a concave curved surface on the photographing lens side, and a transparent liquid having a refractive index larger than that of the transparent protective plate is filled between the transparent protective plate and the sensor surface.
Alternatively, the transparent protective plate is formed into a plano-concave lens shape that is concave on the photographing lens side.

In the present invention, since an optical element provided in a general image sensor that acts as a concave lens is arranged in front of the sensor surface of the image sensor, the imaging plane position of the photographing lens that forms the subject image is shifted backward. Even if there is an imaging plane position immediately after the focal plane shutter, it is possible to shift the imaging plane position to the sensor plane so that the imaging plane position matches the sensor plane. It was.

  The present invention will be described below with reference to the drawings. FIG. 2 is a diagram showing main optical elements when the image pickup device of the present invention is mounted on a single-lens reflex camera, and FIG. 3 is a longitudinal section of the main configuration of the embodiment in which the image pickup device is mounted on a single-lens reflex camera body along the optical axis. It is sectional drawing shown. The same elements as those of the optical element of the single-lens reflex camera shown in FIG.

The camera body 11 of this embodiment shown in FIG. 3 has the same optical and mechanical elements as the conventional single-lens reflex camera body for a silver salt film except for the image sensor and the back cover. The camera body 11 includes a finder optical system including a quick return mirror 13, a focusing screen 15, a condenser lens 17, a pentaprism 19, and an eyepiece lens 21. Further, the subject light flux that has passed through the quick return mirror 13 is reflected by the sub mirror 14 toward the AF sensor unit 27. The AF sensor unit 27 is a well-known pupil division phase difference type sensor that divides a subject image formed at an equivalent position to the imaging plane position IP into a so-called pupil division and irradiates a pair of subject images onto the line sensor. It is converted into a pair of electrical subject image signals (luminance distribution signals). A CPU (MPU) built in the camera body 11 detects the phase difference between the pair of subject images based on the pair of subject image signals output from the line sensor, and calculates the defocus amount at the equivalent position.
In the camera body 11, a photographic lens is detachably attached to a body mount 25, and a designed image plane position IP is set immediately after the focal plane shutter curtain 23.

  The above configuration is the same as the configuration and processing of a conventional single-lens reflex camera using a silver salt film. Next, features of the present embodiment will be described. In the single-lens reflex camera body 11, an image sensor 51 is disposed behind the focal plane shutter curtain 23. The image sensor 51 is attached to the back cover equivalent member or the single-lens reflex camera body 11 main body. That is, in the case of a camera body for a silver salt film, the image sensor 51 is held at a position where the film and the pressure plate are arranged.

  Here, the imaging element 51 is provided with an optical element such as a protective glass, an IR (infrared) cut filter, an optical low-pass filter, or the like that shifts the imaging plane position to the rear of the imaging lens on the imaging lens side or on the imaging element 51 itself. It has been. The optical element of the illustrated embodiment functions as a plano-concave lens as a whole, and due to the concave lens action of the plano-concave optical element 52, the image plane position IP in the design of the single-lens reflex camera body is rearward in the optical axis direction (shooting) In the direction away from the lens), and the shifted image plane position IP ′ after the shift coincides with the sensor surface 53. That is, the image of the subject focused on the basis of the defocus amount obtained by the AF sensor unit 27 is formed on the sensor surface 53 in a focused state.

  Next, an example of the image sensor 51 will be described below with reference to FIGS. These drawings are cross-sectional views showing only the main optical elements by cutting along a plane passing through the designed optical axis O. FIG. FIGS. 4 to 7 show Examples 1, 2, 3, and 4 in which an optical element formed separately from the image sensor is attached to and integrated with the image sensor. FIGS. 8 and 9 show the optical element in the image sensor. FIGS. 9 and 10 show Examples 7 and 8 using optical elements provided in the image sensor itself.

  The imaging elements 51 (51A to 51D) shown in FIGS. 4 to 7 are arranged on the photographing lens side (the side on which the subject light comes) from the sensor surface 53 (531 to 534), and the sensor surface 53 (531 to 534). The protective glass 59 (591-594) which seals is provided. In these embodiments, the optical element 52 (52A to 52D) is attached to and integrated with the surface of the protective glass 59 (591 to 594) (the surface on the photographing lens side).

  In the first and second embodiments shown in FIGS. 4 and 5, the optical elements 52A and 52B arranged on the photographic lens side with respect to the sensor surfaces 531 and 532 of the imaging elements 51A and 51B are the most photographic lens side. The surface (frontmost surface, incident-side first surface) is concave.

In the first embodiment shown in FIG. 4, an IR cut filter 551, an optical adhesive layer 561, and an optical low-pass are arranged in order from the photographing lens side as the optical element 52 </ b> A arranged on the photographing lens side with respect to the sensor surface 531 of the imaging element 51 </ b> A. A filter 571 and a protective glass are provided, and an optical low-pass filter 571 is bonded to the side of the photographing lens of the protective glass 591 via an optical adhesive layer 581.

  In the first embodiment, the IR cut filter 551 has a concave curved surface on the photographic lens side, the low pass filter 571 has a parallel flat plate, and the IR cut filter 551 and the low pass filter 571 are separated from each other by a predetermined distance. And is bonded with an optical adhesive layer 561, and the optical adhesive layer 561 has a feature of being a plano-concave lens having a concave shape on the photographing lens side.

In Example 1, the IR cut filter 551, the optical adhesive layer 561, the optical low-pass filter 571, the optical adhesive layer 581 and the protective glass 591 function as a bonded plano-concave lens with the photographing lens side as a concave surface as a whole. The image plane position IP is shifted backward with respect to the taking lens. The position of the image plane after the shift is indicated by reference numeral IP ′.
In particular, in Example 1, by forming the optical adhesive layer 561 with an adhesive having a refractive index larger than that of the IR cut filter 551, the optical adhesive layer 561 also functions as a plano-concave lens. The amount by which the image plane position IP is shifted backward with respect to the taking lens increases.

  In Example 2 shown in FIG. 5, an IR cut filter 552, an optical adhesive layer 562, and an optical low-pass are arranged in order from the photographing lens side as the optical element 52B disposed on the photographing lens side with respect to the sensor surface 532 of the image sensor 51B. A filter 572, an optical adhesive layer 582, and a protective glass 592 are provided. Thus, the IR cut filter 552 located closest to the photographing lens is characterized by having a plano-concave lens shape with a concave surface on the photographing lens side (incident side).

In Example 2, the IR cut filter 552, the optical adhesive layer 562, the optical low-pass filter 572, the optical adhesive layer 582, and the protective glass 592 function as a bonded plano-concave lens having a photographic lens side surface as a concave surface as a whole. The IR cut filter 552 also acts as a plano-concave lens having the incident side surface as a concave surface, and shifts the imaging plane position IP to the shifted imaging plane position IP ′ that is away from the photographing lens.
In the second embodiment, since the IR cut filter 552 farthest from the sensor surface 532 acts as a plano-concave lens, the distance between the image plane position IP and the shift image plane position IP ′, that is, the shift amount can be increased. .

  In the third embodiment shown in FIG. 6, the surface on the sensor surface 533 side facing the protective glass 593 is made concave among the optical elements 52C mounted on the photographing lens side with respect to the sensor surface 533 of the image sensor 51C.

  In Example 3 shown in FIG. 6, an IR cut filter 553, an optical adhesive layer 563, and an optical low pass are arranged in order from the photographing lens side as the optical element 52 </ b> C disposed on the photographing lens side with respect to the sensor surface 533 of the image sensor 51 </ b> C. A filter 573 and a protective glass 593 are provided.

  The IR cut filter 553 is a parallel flat plate, the optical low-pass filter 573 has a curved shape with the sensor surface 533 concave, and the optical cut is filled with the IR cut filter 553 and the optical low-pass filter 573 separated by a predetermined length. Then, a concave / concave lens-shaped optical adhesive layer 563 is formed on the sensor surface 533 side between the IR cut filter 553 and the optical low-pass filter 573. Further, the optical low-pass filter 573 and the protective glass 593 are bonded at the periphery with an optical adhesive layer 583, and an air layer A1 is hermetically formed between the optical low-pass filter 573 and the protective glass 593.

  As described above, in Example 3, the IR cut filter 553, the optical adhesive layer 563, and the optical low-pass filter 573 constitute a bonded plano-concave lens shape in which the sensor surface 533 side (exit side) is concave as a whole. . Due to the action of the plano-concave lens shape, the imaging plane position IP is shifted backward with respect to the photographing lens to the shifted imaging plane position IP ′.

  Furthermore, in Example 3, the optical adhesive layer 563 is formed of an optical adhesive having a refractive index larger than that of the optical low-pass filter 573, so that the optical adhesive layer 563 alone acts as a plano-concave lens. The image plane position IP is shifted backward with respect to the taking lens. According to the third embodiment, since the transmittance of each part of the IR cut filter 553 is uniform, the spectral sensitivity characteristics are uniform.

  In Example 3, the IR cut filter 553, the optical adhesive layer 563, and the optical low-pass filter 573 are integrated, and this is adhered to the protective glass 593 by the optical adhesive layer 583 provided on the peripheral edge of the protective glass 593. Therefore, the image pickup element 51c can be easily manufactured. That is, if an integral structural member composed of the IR cut filter 553, the optical adhesive layer 563, and the optical low-pass filter 573 is prepared in advance, the integral structural member is completed simply by being attached to the protective glass 593.

  In the third embodiment, the IR cut filter 553 and the optical low-pass filter 573 are bonded with the optical adhesive layer 583. However, the present invention is not limited to this example. For example, the integral structural member is pressed against the protective glass 593 via a spacer. It is also possible to attach the peripheral edge of the IR cut filter 553 and the peripheral edge of the image sensor 51C by sandwiching them with a leaf spring.

  In Example 4 illustrated in FIG. 7, an IR cut filter 554, an optical adhesive layer 564, and an optical element are arranged in order from the photographing lens side as the optical element 52D disposed on the photographing lens side with respect to the sensor surface 534 of the imaging element 51D. A low-pass filter 574 is provided.

  The IR cut filter 554 is a parallel flat plate, the optical low-pass filter 574 is a plano-concave lens shape with the sensor surface 534 side concave, and the optical low-pass filter 574 and the protective glass 594 are bonded to each other with an optical adhesive layer 584. Thus, an air layer A2 is formed between the optical low-pass filter 574 and the protective glass 594. The IR cut filter 554, the optical adhesive layer 564, and the optical low-pass filter 574 constitute a bonded plano-concave lens shape in which the exit side surface (the surface on the protective glass 594 side) of the optical low-pass filter 574 is concave.

  According to the fourth embodiment, the IR-cut filter 554, the optical adhesive layer 564, and the optical low-pass filter 574 as a whole include an optical low-pass filter 574 that forms a concave plano-concave lens on the sensor surface 534 side. The image plane position IP is shifted rearward in the optical axis direction to the shift image plane IP ′.

  Further, the fourth embodiment is easy to manufacture as in the third embodiment, and the transmittance of each part of the IR cut filter 554 is uniform, so that the spectral sensitivity characteristics are uniform.

  In Examples 5 and 6 shown in FIGS. 8 and 9, members corresponding to the protective glasses 591 to 594 of Examples 1 to 4 are excluded from the imaging elements 51E and 51F. Thus, the optical elements 52E and 52F are directly attached to the imaging elements 51E and 51F.

In Example 5 of FIG. 8, as the optical element 52E disposed on the photographing lens side with respect to the sensor surface 535 of the image sensor 51E, the IR cut filter 555, the optical adhesive layer 565, and the optical low-pass from the incident (photographing lens) side. A filter 575 is provided.
In Example 6 of FIG. 9, as an optical element 52F disposed on the photographing lens side with respect to the sensor surface 536 of the image sensor 51F, an IR cut filter 556, an optical adhesive layer 566, and an optical low-pass from the incident (photographing lens) side. A filter 576 is provided.

  Thus, in Example 5, the IR cut filter 555 closest to the photographic lens (incident) side has a concave curved surface on the photographic lens side, the optical low-pass filter 575 is a parallel plane plate, and the IR cut filter 555 and the optical low-pass filter. An optical adhesive layer 565 is formed by filling the optical adhesive with 575 spaced apart by a predetermined distance. That is, a bonded plano-concave lens having a concave surface on the incident side as a whole is formed.

  According to the fifth embodiment, the image formation surface position IP is shifted rearward in the optical axis direction to the shift image formation surface IP ′ by the concave lens action of the optical adhesive layer 565 constituting the concave plano-concave lens on the photographing lens side.

  In the sixth embodiment shown in FIG. 9, the IR cut filter 556 closest to the photographic lens (incident) side has a concave / concave lens shape on the photographic lens side, the optical low-pass filter 576 is a parallel flat plate, the IR cut filter 556 and the optical An optical adhesive layer 566 is formed by filling the optical adhesive with a predetermined interval between the low-pass filters 576. That is, a bonded plano-concave lens having a concave surface on the incident side as a whole is formed.

  According to the sixth embodiment, due to the concave lens action of the IR cut filter 556 that forms a concave plano-concave lens on the photographic lens side, the imaging plane position IP is shifted rearwardly away from the photographic lens to the shift imaging plane IP ′. .

  In Examples 5 and 6, since there is no protective glass, the thickness of the optical element in front of the sensor surfaces 535 and 536 is reduced, and the sensor surfaces 535 and 536 are disposed closer to the focal plane shutter curtain 23. Is possible.

  Examples 7 and 8 shown in FIGS. 10 and 11 are characterized in that the optical low-pass filter and the infrared cut filter are separated from the imaging elements 51G and 51H, and the incident side surfaces of the protective glasses 597 and 598 are concave. .

In Example 7 shown in FIG. 10, the curved glass-shaped protective glass 597 whose concave side is the photographing lens is fixed to the opening of the image sensor 51G, and the space between the protective glass 597 and the sensor surface 537 is filled with the filler 60. It is characterized in that a concave plano-concave lens is formed on the photographic lens side by filling and filling material 60. As the filler 60, a substance having a refractive index larger than that of the protective glass 597 is used.
According to the seventh embodiment, the image plane position IP is shifted rearward in the optical axis direction to the shift image plane IP ′ by the concave lens action of the filler 60 constituting the concave plano-concave lens on the photographing lens side.

In Example 8 shown in FIG. 11, a plano-concave protective lens 598 having a concave surface on the photographing lens side is fixed to the opening of the image sensor 51H, and the space between the sensor surface 538 is sealed. It has the characteristics.
According to the eighth embodiment, the image forming surface position IP is shifted to the shift image forming surface IP ′ in the direction away from the image taking lens by the concave lens action of the protective lens 598 constituting the concave plano-concave lens on the image taking lens side.

  In the seventh and eighth embodiments, the protective glass 597, 598 is formed as a concave lens, and the image plane position IP is shifted to the rear of the photographing lens, and the optical low-pass filter and the infrared cut filter are separated separately. Therefore, the optical low-pass filter and the infrared cut filter can be separately arranged, and the degree of freedom in mounting is high.

  As described above, in the embodiment of the present invention, since the optical element that acts as a concave lens is disposed on the photographing lens side with respect to the sensor surface of the image sensor, the design imaging plane position IP of the single-lens reflex camera body 11 is shifted. It is possible to make an electronic still camera by mounting an image sensor that can form a subject image on the sensor surface without changing the optical element of the camera body 11 for the silver salt film. Became.

As described above, in the illustrated embodiment, the optical element having the concave lens shape is a plano-concave lens, but may be a biconcave lens shape or a meniscus shape. The shape of the concave surface may be spherical or aspherical (rotationally symmetric aspherical).
In the illustrated embodiment, the concave surface acting as a concave lens is a single surface, but a plurality of surfaces and surfaces of a plurality of optical elements may be concave surfaces. Moreover, what kind of lens shape each optical element has may be a concave lens as a whole. In all the embodiments, the space in front of the sensor surface is filled with gas, liquid or the like so as not to oxidize.

It is an optical path figure at the time of applying the conventional image sensor to a single-lens reflex camera. 1 is an optical path diagram of an electronic still camera in which an image pickup device is mounted on a single-lens reflex camera according to an embodiment of the present invention. It is the longitudinal cross-sectional view longitudinally cut by the optical axis which shows the main optical elements at the time of applying the electronic still camera of embodiment of the same invention to the single-lens reflex camera body. It is the longitudinal cross-sectional view longitudinally cut by the optical axis which shows Example 1 of the optical element and imaging device in the electronic still camera of this invention. It is the longitudinal cross-sectional view longitudinally cut by the optical axis which shows Example 2 of the optical element and imaging device in the electronic still camera of this invention. It is the longitudinal cross-sectional view longitudinally cut by the optical axis which shows Example 3 of the optical element and imaging device in the electronic still camera of this invention. It is the longitudinal cross-sectional view longitudinally cut by the optical axis which shows Example 4 of the optical element and imaging device in the electronic still camera of this invention. It is the longitudinal cross-sectional view longitudinally cut by the optical axis which shows Example 5 of the optical element and imaging device in the electronic still camera of this invention. It is the longitudinal cross-sectional view longitudinally cut by the optical axis which shows Example 6 of the optical element and imaging device in the electronic still camera of this invention. It is the longitudinal cross-sectional view longitudinally cut by the optical axis which shows Example 7 of the optical element and imaging device in the electronic still camera of this invention. It is the longitudinal cross-sectional view longitudinally cut by the optical axis which shows Example 8 of the optical element and imaging device in the electronic still camera of this invention.

Explanation of symbols

11 camera body 13 quick return mirror 15 focusing screen 17 condenser lens 19 pentaprism 21 eyepiece lens 23 focal plane shutter curtain 27 AF sensor unit 29 rear body cover 51 image sensor 52 concave lens shape 53 sensor surface 52A optical element 511 image sensor 531 sensor surface 551 IR cut filter 561 Optical adhesive layer 571 Optical low-pass filter 581 Optical adhesive layer 591 Protective glass IP Imaging surface position IP ′ Shift imaging surface position

Claims (20)

An imaging optical system and a focal plane shutter disposed on the imaging optical system side with respect to the imaging position of the subject image formed by the imaging optical system, and the sensor surface of the imaging device coincides with the imaging position. In an electronic still camera in which an optical element provided in front of the sensor surface interferes with the focal plane shutter when disposed at a position,
When the imaging element the optical element is disposed at a position not interfering with the focal plane shutter has a shape wherein the optical element is Ru match with the sensor surface by shifting the imaging position of the object image to the rear This is an electronic still camera. The optical element, an electronic still camera according to claim 1 comprising a concave shape having a negative power. The electronic still camera according to claim 2 , wherein the optical element includes a concave lens shape having a concave surface on the photographing optical system side. The electronic still camera according to claim 2 , wherein the optical element includes a concave lens shape having a concave surface on the sensor surface side. The imaging device than said sensor surface equipped with a protective glass, the imaging optical system side, electrons of any one of claims 1 to 4 wherein the optical element to the photographing lens side of the protective glass is attached Still camera. The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter that are bonded together in order from the photographing optical system side, and the IR cut filter has a curved shape with a concave surface on the photographing optical system side, The electronic still camera according to claim 5, wherein the optical adhesive layer has a plano-concave lens shape having a concave surface on the photographing optical system side. The electronic still camera according to claim 6 , wherein a refractive index of the adhesive layer is larger than a refractive index of the IR cut filter. The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter that are in close contact with each other from the photographing optical system side, and the IR cut filter has a plano-concave lens shape with a concave surface on the photographing optical system side. Item 6. The electronic still camera according to Item 5 . The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter that are in close contact with each other from the photographing optical system side, and the optical low-pass filter has a curved shape with a concave surface on the sensor surface side, and the optical adhesive layer 6. The electronic still camera according to claim 5 , wherein said sensor surface side has a concave-convex lens shape. The electronic still camera according to claim 9 , wherein a refractive index of the adhesive layer is larger than a refractive index of the low-pass filter. The optical element, IR cut filter in close contact in order from the photographing optical system side, optical adhesive layer and comprises an optical low-pass filter, the optical low-pass filter is the sensor surface according to claim 5, wherein a plano-concave lens concave shape Electronic still camera. The electronic still camera according to any one of claims 5 to 8 , wherein the optical low-pass filter and the protective glass are bonded together through an adhesive layer. The electronic still camera according to claim 5, wherein the optical low-pass filter and the protective glass are separated from each other by a predetermined distance, and their peripheral portions are bonded with an optical adhesive. The optical element on the image sensor, an electronic still camera according to any one of claims 1 to 4 are fixed in a state where sealing between the sensor surface to the imaging lens side of the sensor surface. The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter in order from the photographing optical system side. The IR cut filter has a curved surface shape with a concave surface on the photographing optical system side. The electronic still camera according to claim 14, wherein the agent layer has a plano-concave lens shape having a concave surface that is in close contact with the IR cut filter. The electronic still camera according to claim 15 , wherein a refractive index of the optical adhesive layer is larger than a refractive index of the IR cut filter. The optical element includes an IR cut filter, an optical adhesive layer, and an optical low-pass filter that are in close contact with each other in order from the photographing optical system side, and the IR cut filter has a plano-concave lens shape with a concave surface on the photographing optical system side. Item 15. An electronic still camera according to Item 14 . The electronic still camera according to claim 3 , wherein the optical element is a transparent protective plate attached to the imaging element closer to the photographing optical system than the sensor surface. The transparent protective plate as the optical element has a concave curved surface on the photographing lens side, and a transparent liquid having a refractive index larger than that of the transparent protective plate is filled between the transparent protective plate and the sensor surface. The electronic still camera according to claim 18 . The electronic still camera according to claim 18, wherein the transparent protective plate as the optical element has a plano-concave lens shape concave on the photographing lens side.