JP2003215661A - Digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital camera capable of reflecting an image substantially equivalent to an image picked up by an imaging device on a finder screen surface. <P>SOLUTION: The digital camera equipped with the imaging device 30 requires an optical device 40 such as an optical low-pass filter 29 and an infrared ray cut filter 28 in order to remove an unnecessary component in luminous flux between a movable mirror 21 for switching an optical path and the imaging device 30 in principle. Then, a correcting optical device 24 for correcting the optical path length of the finder optical system is inserted between the mirror 21 and the finder screen surface 22 so that the image substantially equivalent to the image formed on the imaging device 30 through the optical device 40 may be formed on the surface 22. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera including an image pickup device, a finder optical system, and an optical path switching mechanism, and an optical element such as an optical low-pass filter provided between the optical path switching mechanism and the image pickup device.

[0002]

2. Description of the Related Art Conventionally, a single-lens reflex camera having an image pickup device is constructed so that a subject image incident through a taking lens is switched to a light path by a movable mirror and guided to a finder optical system or an image pickup device. When observing a subject, the incident subject image is reflected by a movable mirror and guided to a finder optical system to form an image on the screen surface of a finder screen (hereinafter simply referred to as a screen) for observation, and at the time of imaging, the movable mirror is retracted from the imaging optical path. A subject image is formed on the imaging surface of the image sensor. As a mechanism for switching the optical path,
Besides the movable mirror, a fixed half mirror can also be used.

Between the movable mirror and the image sensor, an optical low-pass filter (OLPF) and an infrared cut filter (hereinafter referred to as IR) for removing unnecessary components contained in the imaging light flux.
An optical element such as a cut filter) or a protective glass for protecting the image pickup element is attached, and a screen is attached as an optical element to the finder optical system.

The optical low-pass filter (OLPF) is for cutting high-frequency components of the image pickup light flux to prevent the generation of moire fringes and the generation of false colors due to the pixel pitch of the image pickup element. The IR cut filter cuts the infrared component of the imaging light flux and prevents the imaging element from being exposed to infrared light. The protective glass is for protecting the image pickup surface of the image pickup element from scratches and dust.

[0005]

By the way, the single-lens reflex camera itself can record the image observed by the finder optical system as it is, but in the single-lens reflex digital camera using the image pickup device, the movable mirror is used. Since there is an optical element such as an optical low pass filter between the image pickup elements,
When viewed at the center position of the image (center position of the optical axis), the optical path length on the finder side and the optical path length on the image sensor side are different. Therefore, in the conventional single-lens reflex digital camera, the viewfinder screen surface and the image pickup element surface are installed at mechanically different positions so that the two optical optical path lengths match. However, with the conventional configuration, even if the optical optical paths are aligned at the optical axis center position, the optical optical path lengths at positions away from the optical axis differ, and the image on the image sensor side and the image on the finder side greatly differ. Was there. There is a single-lens reflex digital camera in which the thickness of the optical elements such as the optical low-pass filter is made as thin as possible to avoid the above-mentioned problems. It was unavoidable and the fabrication of the optical low-pass filter was difficult and expensive because of the plucking. Further, although the configuration of the optical low-pass filter is almost determined by the pixel pitch of the image sensor, in an extreme case, the optical low-pass filter may be too thin to configure the optical low-pass filter. In addition, there is a configuration without the protective glass of the image sensor,
It was necessary to pay attention to dust and dirt on the surface of the image pickup device when assembling the camera, which made the assembling process complicated and required strict control of the assembling environment.

In view of the above circumstances, it is an object of the present invention to provide a digital camera capable of displaying an image substantially equivalent to an image picked up by an image pickup device on a screen surface.

[0007]

A digital camera according to the present invention comprises a lens for forming an optical image of a subject, an image pickup device for picking up the optical image, and a viewfinder optical system for observing the optical image. An optical path switching mechanism that selectively guides a light beam from the lens to the finder optical system or the image pickup device, a screen surface provided in the finder optical system to form an image of the light beam from the lens, and the optical path. An optical element provided between the switching mechanism and the image pickup element, and an image substantially equivalent to an image formed on the image pickup element through the optical element are formed on the screen surface. A correction optical element provided between the optical path switching mechanism and the screen surface is provided.

In the present invention, an image having substantially the same image quality as the image picked up by the image pickup device can be observed on the screen surface of the finder optical system. An image of the same image quality is reproduced on the screen surface not only in the center of the optical axis but also in the peripheral portion away from the center of the optical axis, which improves usability for the photographer.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram schematically showing a digital camera according to a first embodiment of the present invention.

In FIG. 1, a digital camera 10 is a single-lens reflex camera, and has a lens barrel 1 including an imaging lens 11 for forming an optical image of a subject, and a lens mount 1 having the lens mount portion. The camera main body 2 is detachably attached.

The camera body 2 includes an image pickup device 30 for picking up an optical image of a subject, finder optical systems 22 to 26 for observing the subject image, a movable mirror 21 as an optical path switching mechanism, and the finder. A screen surface 22 which is an image forming surface of an optical system, an optical element 40 provided between the movable mirror 21 and the image pickup surface 301a of the CCD 301 of the image pickup element 30, the movable mirror 21 and the screen surface 22. Correction optical element 24 provided between
And a shutter 27 provided between the movable mirror 21 and the optical element 40.

The finder optical systems 22 to 26 include a screen surface 22 on which a subject image that has passed through the imaging lens 11 is reflected by the movable mirror 21 to form an image when the subject is observed, and a subject image on the screen surface 22 is a vertical, horizontal, and normal image. The roof prism 25 reflects an image formed on the screen surface 22 a plurality of times so that the image can be seen, and an eyepiece 26 that guides the subject image passing through the roof prism 25 to the photographer's eyes. The screen surface 22 is made of, for example, frosted glass provided on one surface of a flat glass plate.

The movable mirror 21 as an optical path switching mechanism is
The subject light flux from the imaging lens 11 is selectively guided to the finder optical systems 22 to 26 or the image pickup device 30. When the subject is observed, the mirror image is lowered (shown by a solid line in the drawing) to form the subject image. 26 to 26, the subject image is guided to the image pickup device 30 by raising the mirror (indicated by a chain double-dashed line in the figure) during photographing.

The shutter 27 has shutter blades 271.
When the image is taken, the shutter blade 271 is opened with the movable mirror 21 up during exposure, so that the subject image is exposed on the image pickup surface 301a (image forming surface) of the image pickup device 30.

The optical element 40 includes an IR cut filter 28 for cutting the infrared ray component of the image pickup light beam in order to prevent the image pickup element 30 from being exposed to infrared rays, and the occurrence of moire fringes and pseudo colors due to the pixel pitch of the image pickup element 30. The optical low-pass filter (OLPF) 29 that cuts off the high-frequency component of the image pickup light flux to prevent the occurrence of the above, and the cover glass 31 as a protection member that protects the image pickup surface of the image pickup element 30 are configured. Note that the cover glass 31 is usually fixed integrally to the front side of the CCD package 301 in advance.

The image pickup device 30 is composed of a CCD 301 and a CCD package 303 having its leads 302. In addition to the CCD, the image sensor 30 is a CM.
It may be configured by the OS.

The correction optical element 24 and the movable mirror 21 and the screen are arranged so that an image substantially equivalent to the image formed on the image pickup element 30 through the optical element 40 is formed on the screen surface 22. It is provided between the surface 22 and the surface 22.

The correction optical element 24 has a screen 23 as a first optical element having the screen surface 22 formed on one surface thereof, the screen 23 and the movable mirror 21.
Flat glass 2 which is a second optical element provided between
And 41.

The thickness of the correction optical element 24 of the finder optical system thus constructed (optically equivalent thickness in the case of being composed of one optical element) is t ', and the refractive index is n ′, the thickness of the optical element 40 formed on the front side of the image pickup element 30 (optically equivalent thickness in the case of being composed of one optical element) is t, and the refractive index is n. In such a case, the thickness t and the refractive index n of the optical element arranged on the front side of the image sensor 30 are often uniquely determined by the pixel pitch and optical characteristics of the image sensor 30 (the refractive index is usually 1.5).
Therefore, if the thickness t ′ and the refractive index n ′ of the correction optical element 24 are determined so that t / n = t ′ / n ′, the image formed on the image pickup element 30 over the entire screen. An image substantially equivalent to can be formed on the screen surface 22. Of course, if an optical material having the same refractive index, dispersion, and spectral transmittance as the optical element 40 has the same thickness and the same position with respect to the imaging lens, the same image or imaging surface 301 is obtained.
Although an image is formed on the screen surface 22 of a and an optical material having almost the same refractive index, the positions with respect to the image forming lens may be different as long as they are formed to the above equivalent thickness.

Therefore, the first and second optical elements 23, 24
Compensation optical element 24 of finder optical system composed of 1
And the optical element 40 of the image pickup optical system including the optical low-pass filter 29, the IR cut filter 28, and the cover glass 31, the thickness of the first optical element 23 of the finder optical system is t1 ′ and the refractive index is n1. 'And then the second
, The optical element 241 has a thickness of t2 'and a refractive index of n2'.
The thickness of the optical low-pass filter 29 is t1, and the refractive index is n1.
The thickness of the IR cut filter 28 is t2, the refractive index is n2, the thickness of the cover glass 31 is t3, and the refractive index is n.
When set to 3, t1 / n1 + t2 / n2 + t3 / n3 = t1 '/ n1' + t2 '
/ N2 ', the thickness t1' of the first optical element 23, the refractive index n1 ', the thickness t2' of the second optical element 241, the refractive index n.
If 2'is determined, an image substantially equivalent to the image formed on the image sensor 30 over the entire screen is displayed on the screen surface 22.
It can be imaged on.

As the optical low-pass filter 29, LiNbO3 (lithium niobate) having a refractive index of about 2.3 may be used. If the optical low-pass filter 29 having a high refractive index is used as described above, the optical element 40 is used. The first and second optical elements 2 of the finder optical system that can be made thin
The correction optical element 24 can be made thin if the same refractive index as 3 and 241 is used (especially in the second optical element 241).

The correction optical element 24 may be composed only of the screen 23 which is a plate-shaped optical element capable of transmitting a light beam. In this case, by providing the screen surface 22 on a surface of the screen 23 on a side different from the side where the movable mirror 21 is installed (that is, the upper surface side of the screen 23 in the drawing), the lower part of the screen surface 22 in the drawing is corrected. It can be used as an optical element.

As shown in FIG. 1, when the screen surface 22 is on the roof prism side, the correction optical element includes both the portion of the screen 23 below the screen surface 22 and the portion of the flat glass 241 provided therebelow. When the screen surface 22 is provided on the movable mirror side (see FIG. 4, which will be described later), the correction optical element only refers to the flat glass 241 provided below the screen 23. .

In the structure of the single-lens reflex digital camera 10 shown in FIG. 1, from the correction optical element 24 provided in the finder optical system, the optical low-pass filter 29, the IR cut filter 28, and the cover glass 31 provided in the imaging optical system. If the optical element 40 is not present, the distance from the reflective surface of the movable mirror 21 to the screen surface (image forming surface) 22 and the distance from the reflective surface of the movable mirror 21 to the image capturing surface (image forming surface) of the image sensor 30. The distance needs to be equal.

Further, in the structure of the single-lens reflex digital camera 10 shown in FIG. 1, there is no correction optical element 24 provided in the finder optical system, and an optical low-pass filter 29, an IR cut filter 28 and a cover provided in the image pickup optical system. Considering the image forming position on the optical axis assuming that the optical element 40 made of the glass 31 exists, the movable mirror 21 is more than the distance from the reflecting surface of the movable mirror 21 to the image formed on the screen side. 21 to the image sensor 30
The distance to the image formed on the side becomes longer. this is,
This is because the optical element 40 is present between the reflecting surface of the movable mirror 21 and the image pickup surface (image forming surface) of the image pickup element 30, so that the optical path length to the image pickup surface of the image pickup element 30 becomes long.

However, in this way, the movable mirror 2
The optical element 4 is provided between the reflection surface of No. 1 and the imaging surface of the image sensor 30.
0 exists, the reflecting surface of the movable mirror 21 and the screen surface 2
If there is no optical element between the two image planes, the distance from the reflecting surface of the movable mirror 21 to each image plane is different on the optical axis, and each image plane outside the optical axis is different. The difference between the positions where the light rays obliquely incident on the image are respectively different from the difference between the image forming positions on the light beam. By this,
Even if the screen surface and the imaging surface are placed at the respective imaging positions on the optical axis, the optical optical path lengths at the positions apart from the optical axis center will be different on the screen surface side and the imaging surface side, An image different from the image formed on the imaging surface will be formed on the screen surface.

This will be described with reference to FIG. Figure 2
Is a drawing in which the optical path in the finder optical system and the optical path in the imaging optical system are superimposed. Here, the movable mirror 21 for switching the optical paths is omitted in order to compare and show the respective optical path lengths. FIG. 3 shows an enlarged main part of FIG. Reference numeral 301a denotes an image pickup surface of the image pickup device 30, which corresponds to the image pickup surface of the CCD 301 in FIG. 22
Is a viewfinder image forming surface (when there is no correction optical element), and corresponds to the screen surface 22 in FIG. Reference numeral 40 denotes an optical element including an optical low-pass filter arranged on the front side of the imaging element on the imaging optical system side, and corresponds to the optical element including the optical low-pass filter 29, the IR cut filter 28 and the cover glass 31 in FIG. .

An optical path (that is, an optical path of the image pickup optical system) on which the image pickup light beam forms an image on the image pickup surface 301a of the image pickup device 30 through the optical element 40 is shown by a dotted line, and the image pickup light beam does not pass through the optical element and the viewfinder image forming surface 22 is formed. The optical path for forming an image on (i.e., the optical path of the finder optical system) is shown by a solid line. On the viewfinder image plane 22, a light beam is imaged at the center of the optical axis, but the central ray incident on the image plane at the periphery away from the center of the optical axis (particularly the point farthest from the center of the optical axis) is Since the light enters obliquely and forms an image, a deviation ΔZ of the image forming position from the central ray on the optical axis occurs.

If the optical path length of the central ray at the center of the optical axis of the optical element 40 is t, and the optical path length of the obliquely incident light with respect to its periphery is s, then s> t, and the finder optical system is used. This is because, if there is no element, even if the central optical path is aligned with the image forming plane, the light ray at the position where the image height is high deviates from the image forming plane and forms an image.

Therefore, in order to eliminate such a problem,
In the present invention, an optical member for correcting the optical path length (that is, the correction optical element 24) is inserted in the finder optical system so that the image formation on the image pickup surface of the image pickup element 30 is faithfully reflected in the observation image in the finder optical system. The configuration is made to be.

FIG. 4 is a schematic diagram showing a digital camera according to the second embodiment of the present invention. 4 is different from FIG. 1 in that the screen surface 22 formed of frosted glass on the screen 23 is provided on the surface of the screen 23 on which the optical path switching movable mirror 21 is installed, and the correction optical element. 24A is the screen surface 22
Is installed at an angle with respect to the screen surface 22
The seal member 33 has a closed structure between the correction optical element 24A and the correction optical element 24A. Other configurations are
It is similar to FIG.

According to such a configuration, by installing the correction optical element 24A made of a flat glass so as to be inclined with respect to the screen surface 22, it is possible to prevent a ghost generated in the finder section.

As shown in FIG. 1, when the correction optical element 24 made of flat glass is installed parallel to the screen surface 22, the light flux incident from the movable mirror 21 is reflected on the screen surface 22. As shown in FIG. 4, the correction optical element 24A is arranged so as to be tilted with respect to the screen surface 22 because a ghost is generated in the finder portion when the light image is reflected on the correction flat glass 24 a plurality of times. This is because the light that appears as a ghost in the viewfinder is reflected obliquely and is not observed and does not become a ghost. That is, the ghost is eliminated by tilting the correction optical element 24A at a position where the ghost cannot be seen.

Further, the screen surface 22 and the correction optical element 2
Since a sealant 33 is provided between 4A and 4A, it is possible to prevent dust from adhering to the screen surface 22 which is an image forming surface. For example, even if dust adheres to the outer surface of the screen 23 opposite to the screen surface 22 (the roof prism side) or the outer surface of the correction optical element 24A distant from the screen surface 22, it does not adhere to the image forming surface. Therefore, it becomes difficult to see dust when observed through the eyepiece 26.

FIG. 5 is a block diagram schematically showing a digital camera according to the third embodiment of the present invention. 5 is different from FIG. 1 in that the Fresnel lens 34 is formed on the surface of the screen 23 different from the screen surface 22 (the side where the movable mirror 21 is installed).
The Fresnel lens 34 and the screen 23 on which the Fresnel lens 34 is formed constitute a correction optical element 24B. As shown in FIG. 1, it is characterized in that it is not provided with a correction optical element 241 separately from the screen 23 and that a Fresnel lens 34 is formed on the screen 23. The other configuration is the same as that of FIG.

According to this structure, the screen 23
Has a screen surface 22 formed on a surface (side of the roof prism) different from the side where the movable mirror 21 is installed,
Since the Fresnel lens 34 is cut on the surface of the screen 23 on which the movable mirror 21 is installed, the finder optical system can be formed compactly and efficiently.
In other words, it is the optimum shape for the finder optical system.

The screen 23 as the correction optical element 24B needs to have a large thickness in order to have a thickness equivalent to that of the optical element 40 including the optical low-pass filter 29, the IR cut filter 28 and the cover glass 31. Since the Fresnel lens 34 is formed integrally with the screen 23, the space can be reduced and the cost can be reduced. In order to make the correction optical element 24B thin, the optical low-pass filter 29 or the like has a high refractive index (the refractive index of a commonly used optical member is around 1.5, but for example, a high refractive index of 2). You can make it thin by using things.

FIG. 6 is a block diagram schematically showing a digital camera according to the fourth embodiment of the present invention. 6 is different from FIG. 1 in that a convex lens 35 is used instead of the flat glass 241 which is the second optical element in FIG. Alternatively, instead of the Fresnel lens 34 in FIG. 5, the convex lens 3 is provided separately from the screen 23.
5 is provided. As a result, a more accurate finder optical system is formed.

According to this structure, the lenses can be formed independently instead of the Fresnel lens, so that the structure is simple and the finder optical system with high accuracy can be formed.

In the embodiments described above, the case where the movable mirror is used as the optical path switching mechanism has been described, but the present invention is not limited to this, and a half mirror is used instead of the movable mirror. It can also be applied in cases.

[0041]

As described above, according to the present invention, an image which is substantially equivalent to the image picked up by the image pickup device can be displayed on the finder screen surface, and a digital camera which is very convenient for the photographer. Can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing a digital camera according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a state in which an image is formed on an image pickup surface of an image pickup element and a state in which an image formation position is displaced on a finder image formation surface.

FIG. 3 is an enlarged view showing a main part of FIG.

FIG. 4 is a configuration diagram schematically showing a digital camera according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram schematically showing a digital camera according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram schematically showing a digital camera according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 ... Lens barrel 2 ... Camera body 10 ... Digital camera 11 ... Imaging lens 21 ... Movable mirror (optical path switching mechanism) 22 ... Screen surface 23 ... Screen 24, 24A, 24B, 24C ... Correction optical element 25 ... roof prism 26 ... Eyepiece 28 ... Infrared cut filter 29 ... Optical low-pass filter 30 ... Image sensor 31 ... Cover glass 301 ... CCD 303 ... CCD package

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Ogata             2-43 Hatagaya, Shibuya-ku, Tokyo Ori             Inside Npus Optical Industry Co., Ltd. F-term (reference) 2H018 AA26 BD07                 5C022 AA00 AC02 AC09 AC12 AC51                       CA00

Claims (8)

[Claims] 1. A lens for forming an optical image of an object, an image pickup device for picking up the optical image, a finder optical system for observing the optical image, and the finder optical system or the image pickup device. An optical path switching mechanism that selectively guides the luminous flux from the lens, a screen surface that is provided in the finder optical system to form an image of the luminous flux from the lens, and is provided between the optical path switching mechanism and the image sensor. Between the optical path switching mechanism and the screen surface so that an image substantially equivalent to the image formed on the image pickup element through the optical element is formed on the screen surface. A camera comprising: a correction optical element provided. 2. The correction optical element is a screen which is a plate-shaped optical element capable of transmitting a light beam, and the screen surface is provided on a surface of the screen on a side different from the side on which the optical path switching mechanism is installed. The digital camera according to claim 1, wherein the digital camera is a digital camera. 3. The digital camera according to claim 2, wherein a Fresnel lens is formed on a surface of the screen different from the screen surface. 4. The correction optical element is configured to include a screen having the screen surface formed thereon and a second optical element provided between the screen and the optical path switching mechanism. The digital camera according to claim 1. 5. The digital camera according to claim 4, wherein the second optical element is a flat glass. 6. The digital camera according to claim 5, wherein the flat glass is installed so as to be inclined with respect to the screen surface. 7. The digital camera according to claim 4, wherein the second optical element forms a lens. 8. The digital camera according to claim 4, wherein a hermetically sealed structure is provided between the screen and the second optical element.