JP2522283B2 - Automatic focusing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a single-lens reflex camera including a focus detection element for autofocus and a focus detection optical system.

(Prior Art) Conventionally, a single-lens reflex camera having an autofocus function using a silver salt film of 35 mm size has a structure as shown in FIG. 2 (a), for example.

In FIG. 2 (a), 101 is a taking lens, and the light flux transmitted through the taking lens 101 is reflected upward by a quick return mirror 102 arranged at an angle of 45 ° with respect to the optical axis,
An image is formed on the focusing screen 105.

The image formed on the focusing screen 105 is observed by the photographer through the penta prism 106 and the eyepiece lens 107.

On the other hand, a part of the light flux transmitted through the taking lens 101 is transmitted through a half mirror section 102a provided in a part of the quick return mirror 102, is reflected by an auxiliary mirror 103, and is guided to a focus detection element 104. Then, based on the output value of the focus detection element 104 in response to a half-press operation of the shutter release button, etc., the photographing lens 101 is moved by a lens driving mechanism (not shown) in the direction of arrow A so as to be in focus. Move the lens 101.

Shutter 108 behind the quick return mirror 102
When the shutter release signal is generated when the film 109 and the film 109 are arranged, as shown in FIG. 2B, the quick return mirror is placed between the taking lens 101 and the shutter 108.
102 and the auxiliary mirror 103 are retracted, the shutter 108 is opened, and the film 109 is exposed.

(Problems to be Solved by the Invention) However, the structure of a single-lens reflex camera using a silver salt film as shown in FIG. 2 is an electronic still using a CCD or other solid-state imaging device instead of the silver salt film. There were the following problems when trying to apply to a camera.

First, in an image sensor generally used in an electronic still camera, for example, in a 2 / 3-inch size image sensor, the diagonal length of the shooting screen is about 11 mm, which is considerably smaller than the diagonal length of 43.3 mm of a 35 mm silver salt film. Has become.

Therefore, the size of the quick return mirror is also relatively small in the electronic still camera, so that a half mirror part that transmits light is formed in a part of the quick return mirror, or the light that has passed through the half mirror part is not reflected. It is difficult to have a structure including an auxiliary mirror that reflects the focus detection element in terms of size and accuracy.

In addition, in electronic still cameras, the spectral sensitivity of optical visual elements such as optical low-pass filters that prevent moire patterns when using an image sensor and elements that were not used in conventional silver halide film cameras and the spectral sensitivity of the image sensor are Since an optical filter equipped with an infrared absorption filter for approaching sensitivity is installed near the shutter,
In order to effectively use the space inside the camera, there is no space behind the quick retort mirror,
There is a demand for an arrangement position of a focus detection element and a focus detection optical system different from those used in a conventional silver halide camera.

(Means for Solving the Problems) The present invention has been made in view of the above-described conventional problems, and includes a quick return mirror, an optical filter, a shutter, and a shutter which are sequentially arranged along the optical axis of a photographing lens. Provided is a focus focusing device which can achieve both compactness of a camera and high focus detection accuracy by providing a focus detection element and its detection optical system at an optimum position which becomes an empty space in the camera without affecting the image pickup element. The purpose is to do.

To achieve this object, according to the present invention, in a single-lens reflex camera in which an optical filter is arranged between a solid-state image sensor and a quick return mirror, a magnifying lens is provided in an optical path between a photographing lens of the camera and a viewfinder image forming surface. The beam splitter is placed on the exit side of the magnifying lens, the light beam of the image magnified by the magnifying lens is split by the beam splitter, and the space where the split light flux forms an image and above the optical filter The focus detection element is arranged in the.

(Operation) According to such a configuration of the present invention, the focus detection element is
Since the image is formed by the light flux divided by the optical path splitting means disposed in the space above the optical filter disposed on the front surface of the image sensor and provided in the middle of the primary imaging path to the finder optical system, Compared to the case where the focus detection element is placed at a position other than, for example, compared to the conventional silver halide camera, it is not necessary to form a half mirror section or auxiliary mirror in the quick return mirror, so the focus detection optical system is simpler. In addition, the focus detection element and its detection optical system are installed in the optimum position, and the size of the entire camera can be greatly reduced.

Further, by incorporating a magnifying lens in the focus detecting optical system, a magnified image can be formed on the focus detecting element, and the accuracy of focus detection can be greatly improved.

Furthermore, the magnifying lens built into the focus detection system also magnifies and forms an image on the finder optical system at the same time, which prevents the finder image from becoming small corresponding to the image sensor, and provides a clear viewfinder. You can also get a statue.

(Embodiment) FIG. 1 is an explanatory view showing an embodiment of the present invention.

First, the configuration will be described. Reference numeral 1 denotes a taking lens, which can be moved in the optical axis direction by a lens driving mechanism (not shown), and automatic focus control for obtaining a focused state is performed by the movement in the optical axis direction. The light passing through the taking lens 1 is reflected by a quick return mirror 2 which is arranged at an angle of 45 ° with respect to the optical axis thereof, and passes through a concave lens 3 as an image expanding means, a beam splitter 4 as an optical path splitting means, and a condenser lens 6. Then, an image is formed on the focusing screen 7 of the finder optical system. The image formed on the focusing screen 7 passes through the focusing screen dustproof cover 8 and is reflected at a right angle by the finder mirror 9, and the relay lens group 11
The image is formed on the secondary image plane 12 as an aerial image. A display member 14 is provided on the same plane as the secondary image forming surface 12, and a light emitting diode 19 is incorporated in the display member 14 so that display information by the display member 14 can be observed even in a dark place. ing. Therefore, the photographer can observe the aerial image of the secondary image plane and the image of the display member 14 through the eyepiece lens group 13.

On the other hand, the concave lens 3 and the beam splitter 4 provided in the middle of the primary image forming path from the quick return mirror 2 to the focusing plate 7 of the focusing optical system constitute a focus detection optical system, and the beam passes through the concave lens 3 to form a beam. A part of the light flux incident on the splitter 4 is split in the right direction orthogonal to the primary imaging path,
An image is formed on the light receiving surface of the focus detection element 5 through the convex lens 6a.

Further, the finder mirror 9 provided in the finder optical system has a half mirror portion 9a formed in a part thereof, and the light flux transmitted through this half mirror portion 9a is applied to the light receiving member 10 for measuring the brightness of the photographing screen. It is incident.

On the other hand, an optical filter 15, a shutter 16 and a photographing element 17 are sequentially arranged behind the quick return mirror 2, and when photographing by a shutter release, the quick return mirror 2 jumps upward, and at the same time, a front curtain of the shutter 16. By opening 16a, the light flux passing through the taking lens 1 passes through the optical filter 15 and forms an image on the light receiving surface of the image sensor 17. The image pickup device 17 reads the signal charges obtained by the image formed on the light receiving surface by a recording device (not shown) and records them as image information on a floppy disk or the like.

The optical filter 15 provided in front of the shutter 16 in front of the image pickup device 17 is an optical low-pass filter for preventing the occurrence of a so-called moire pattern that occurs when a two-dimensional image is taken by using the image pickup device 17. Alternatively, it is composed of an infrared absorption filter for making the spectral sensitivity of the screen imaged by the image sensor 17 closer to the human visual spectral sensitivity.

The optical filter 15 can be provided at an appropriate position as long as it is in front of the image pickup device 17, but in order to prevent the shutter efficiency of the shutter 16 that transmits the light beam incident on the image pickup device 17 for a necessary exposure time from being lowered, the image pickup is performed. It is desirable to provide the shutter 16 on the front surface of the element 17 as shown, and as a result, the optical filter 15 is arranged on the front surface of the shutter 16 so that the shutter 16 is as close to the image pickup element 17 as possible.

By adopting such an arrangement, as shown in FIG. 1, the concave lens 3, the beam splitter 4, the convex lens 6a and the focus detecting element are provided on the finder optical path side in a conjugate relationship with the optical path length from the 45 ° mirror 2 to the image pickup element 17. Arranging 5 is easy. As a result, the focus detecting element 5 is arranged on the primary image forming plane similarly to the focusing screen 7, so that the focusing optical system dedicated to the focus detecting element 5 except for the convex lens 6a corresponding to the condenser lens 6 is formed. It is possible to place the focus detection element 5 above the optical filter 15 at a position sandwiched between the viewfinder optical systems 3, 4, 6 and the shutter 16 without the need for the.

Next, the details of the embodiment shown in FIG. 1 will be described together with its operation.

The light flux passing through the taking lens 1 is reflected by the quick return mirror 2 and then guided to the concave lens 3. Here, the concave lens 3 has the following two functions.

(A) The image formed on the focus detection element 5 is magnified by the concave lens 3 to improve the accuracy of focus detection.

(B) Since the image formed on the focusing screen 7 is enlarged by the concave lens 3, the focusing screen 7 having a large area can be used.

By the action of the concave lens 3 as described above, not only the detection accuracy by the focus detection element 5 is improved, but also the so-called finder is provided without enlarging the enlargement magnification of the relay lens group 11 and the eyepiece lens group 13 provided in the finder optical system. The magnification can be set to a practically sufficient size, and the unevenness on the surface, which is a general feature of the focusing screen 7, can be prevented from being noticeable.

The light flux passing through the concave lens 3 is then split by a beam splitter 4 as an optical path splitting means, and a part of the split light flux is guided to a focus detection element 5 through a convex lens 6a. As described above, the focus detection element 5 is arranged in the space surrounded by the optical filter 15, the shutter 16 and the condenser lens 6, and by disposing the focus detection element 5 at this position, a finder optical system is configured. An empty space other than the dedicated space for the optical member, the shutter 16 and the optical filter 15 can be used without waste, and by arranging the focus detecting element 5 and its focus detecting optical system, the outer shape of the camera can be made compact. Can be put together.

On the other hand, the light flux that has passed through the beam splitter 4 passes through the condenser lens 6 and forms an image on the focusing screen 7. A transparent focusing screen dustproof cover 8 is provided above the focusing screen 7.
The focusing screen 7 and the focusing screen dustproof cover 8 are attached to both ends of the holding frame 18 and have a sealed structure inside to prevent dust and the like from entering the surface of the focusing screen 7 from the outside.

Here, the light flux emitted from the image formed on the focusing screen 7 enters the light receiving member 10 through the half mirror portion 9a provided in a part of the finder mirror 9, and the light receiving member 10 measures the brightness of the subject. .

On the other hand, the light flux reflected by the finder mirror 9 is formed as an aerial image on the secondary image forming surface 12 by the relay lens group 11. A display member 14 is provided on the same plane as the secondary image plane 12.
Are arranged, and the display member 14 is inserted through the eyepiece lens group 13.
The aerial image of the secondary image plane 12 can be observed by the photographer.

The reason why the display member 14 is provided not on the focus plate 7 which is the primary image forming surface but on the secondary image forming surface is as follows.

Generally, the display member 14 and the light emitting diode 19 as an illumination source thereof are often used for displaying the photographing information,
In an electronic still camera having a screen size smaller than that of a silver halide camera of a size, when a light emitting element is provided in the vicinity of the focusing screen 7, the light receiving member 10 for measuring the luminous flux from the focusing screen 7 emits the luminous flux emitted from the display member. There is a possibility that part of the light will be incident and accurate photometry will not be possible. Therefore, in the present invention, the photometry of the photographing screen is performed by the light receiving member 10 based on the light flux from the focusing screen 7 serving as the primary image forming surface, while the display of the photographing information is provided on the secondary image forming surface 12. By using the display member 14, the light flux emitted from the display member 14 is prevented from entering the light receiving member 10, and more accurate photometry of the photographic screen is enabled.

Further, a display member provided on substantially the same plane as the secondary image plane 12
Since 14 is placed within the depth of field of the photographer's eyes, the display on the display member 14 can be clearly observed.

The present invention can also be applied to a camera without a mechanical shutter.

(Effects of the Invention) As described above, according to the present invention, a part of the light flux incident on the focusing screen is divided and imaged on the focus detection element arranged in the space above the optical filter. Therefore, it is possible to obtain the arrangement of parts that makes effective use of the space inside the camera, and because the conventional mechanism for focus detection with a structure in which a sub mirror is attached to the quick return mirror consisting of a half mirror is not required, The structure can be simple and small. Further, since the images whose magnification is formed on the focusing screen are magnified at the same time on the focus detection element, the focus detection accuracy can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention, and FIG. 2 is an explanatory view showing a conventional silver halide still camera. 1: Shooting lens 2: Quick return mirror 3: Concave lens (magnifying lens) 4: Beam splitter (optical path splitting means) 5: Focus detection element 6: Condenser lens 6a: Convex lens 7: Focus plate 8: Dust cover 9: Viewfinder mirror 9a : Half mirror section 10: Light receiving member (for photometry) 11: Relay lens group 12: Secondary image forming surface 13: Eyepiece lens group 14: Display member 15: Optical filter 16: Shutter 16a: Front curtain 16b: Rear curtain 17: Image sensor 18: Holding frame 19: Light emitting diode

Claims (1)

(57) [Claims] 1. A single-lens reflex camera in which an optical filter is arranged between a solid-state image sensor and a quick return mirror,
A magnifying lens is arranged in the optical path between the taking lens of the camera and the viewfinder image forming surface, a beam splitter is arranged on the exit side of the magnifying lens, and the light flux of the image magnified by the magnifying lens is converted by the beam splitter. An automatic focusing device characterized in that a focus detection element is arranged in a space above the optical filter at a position where the divided light beam is imaged.