JPH04117777A - Electronic still camera - Google Patents

Abstract

PURPOSE:To attain focus adjustment even for a dark object by providing a detection means detecting an incident position and an incident area of a range finding light reflected in an object into an image pickup sensor based on an output signal from the image pickup sensor and a lens moving means moving a lens in the optical axis direction through the calculation with a signal from the detection means to the camera. CONSTITUTION:A light from an object 16 is divided into two by a half mirror 15, a half of the light is transmitted therethrough and its image is formed on a CCD 17. A microcomputer 30 driving the CCD 17 and a detection circuit 31 detecting an incident position and an incident area of a spot light from a video signal and outputting respectively a position signal and an area signal are connected to a video signal processing circuit 26. An arithmetic section 38 connecting to the detection circuit 31 calculates a distance of the object from the position signal to give a range finding signal to a control section 39 and a focus signal generated when an area of a fog image is minimized from an area signal to the control section 39 respectively. A lens drive section 40 connecting to the control section 39 moves an image pickup lens 3 via a driver 41. Thus, accurate focusing is implemented even under a lower brightness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electronic still camera having an improved autofocus device.

[Conventional technology]

Electronic still cameras use image sensors rather than lenses.
An optical image is formed on the image sensor, and the photoelectric signal obtained from the image sensor is magnetically recorded on a still video floppy.
In order to form a clear optical image on an image sensor, some devices automate lens focusing using an autofocus device.

These types of autofocus devices include focus detection methods that perform focusing based on the light that passes through the lens, such as contrast and phase difference methods, as well as active distance measurement methods. As shown in Fig. 2, there is a camera that projects a distance measuring light onto the subject, receives the reflected light with a light receiving element, and determines the center position of the lens according to the distance to the subject detected by triangulation. .

[Problem to be solved by the invention]

However, although the focus detection method has the advantage of eliminating parallax because focusing is performed using TTL, the detection accuracy decreases for low-brightness objects, and the focus detection method uses a closed loop to determine the focus position of the lens due to the light passing through the lens. The disadvantage is that it takes a long time to focus.

On the other hand, active distance measuring systems have the advantage of not being affected by the brightness of the subject, but may cause errors in focusing due to parallax, and are used to capture light that is not only used for imaging but also for receiving reflected light from the subject. The disadvantage is that a lens and a light receiving element are required, which increases the number of parts.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an electronic still camera that allows accurate focusing without parallax even under low brightness and does not require a separate light-receiving element for focusing. shall be.

[Means to solve the problem]

In order to achieve the above object, the present invention focuses on the fact that in electronic still cameras, an optical image of a subject is captured by an image sensor, and the sensor receives reflected light from the subject through a lens, which is necessary for active distance measurement. In addition to measuring the distance using the sensor, it is also possible to perform focusing using a focus detection method based on the pattern of reflected light incident on the sensor. Therefore, the electronic still camera of the present invention includes a detection means for detecting the incident position and incident area of the ranging light reflected by the subject on the sensor based on the output signal from the imaging sensor, and a signal from the detection means. A lens moving means for moving the lens in the optical axis direction is provided.

[Effect]

According to the above configuration, when the projected distance measuring light is reflected by the subject and enters the imaging sensor via the lens,
The detection means outputs a signal corresponding to the output signal from the sensor to the lens moving means.

The lens moving means calculates the signal and moves the lens according to the incident position and incident area.

〔Example〕

FIG. 3 shows an electronic still camera of the present invention,
The camera body 2 has a photographic lens 3. 4. Light projection window that emits near-infrared light. Strobe light emitting section 5. A release button 6 and a liquid crystal panel 7 are provided.

A loading port 8 is formed on the front side of the camera body 2, and a memory cartridge 9 for recording video signals is loaded into the loading port 8 from the direction of the arrow in the figure.

FIG. 1 shows the electrical configuration of an electronic still camera, in which a half mirror 15 is provided behind the photographing lens 3 at an angle of 45 degrees. The light from the subject 16 that has passed through the photographic lens 3 is divided into two by a half mirror 15, and half of the light is transmitted and formed into an image on an image sensor such as a CCD 17 located behind the camera. On the front surface of the CCD 17, a filter 18 that is inserted on the optical axis 3a during photography and cuts off near-infrared light passing through the photographic lens 3 is provided so as to be freely removable. type position sensor 18a.

Further, the light reflected by the half mirror 15 is imaged on a focusing glass 21 provided on the lower surface of the pentaprism 20. The optical image formed on the focusing glass 21 is observed through the finder objective lens 22.

A video signal processing circuit 26 is connected to the CCD 17 via an amplifier 25, which converts the signal from the CCD 17 into a video signal and outputs the video signal. This video signal processing circuit 2
6 is connected to a recording section 27, which converts the video signal into a digital image signal and writes this into the memory cartridge 9.

The video signal processing circuit 26 includes a microcomputer 30 that drives the CCD 17 via a driver 29, and a detection circuit that detects the incident position and incident area of the spot light from the video signal and outputs a position signal and an area signal, respectively. The circuit 31 is connected. A signal generator 6a is connected to the microcomputer 30, which outputs a half-press signal and a full-press signal when the release button 6 is pressed. The microcomputer 30
A light emitting diode 33 that emits near-infrared light is connected via a driver 32 to.

This near-infrared light is projected onto the subject 16a as a spot light by a filter 34 and a projection lens 35. In this embodiment, a spot light is used as the distance measuring light, but a slit light may also be used. Since the optical axis 35a of the light projecting lens 35 is frequently photographed with objects around 3 meters away, the optical axis 35a of the projecting lens 35 is set so that it intersects with the optical axis 3a 3 meters in front of the photographing lens 3, as shown in FIG. 2(a). Therefore, the spot light reflected by the object 16a located at a distance of 3 meters is focused on the reference point A at the center of the CCD 17 by the photographing lens 3 at the focusing position. The spot light reflected by an arbitrary object is located at a different position from the reference point A in FIG. As shown, a blurred image is formed.The area of this blurred image converges on point B when the photographing lens 3 is moved to the in-focus position.

In this figure, the closest distance between the optical axis 3a and the light emitting diode 42 is the distance i between the H9 subject 16b and the photographing lens 3! 1
(object distance), the distance between reference point A and point B is α, and the focal length of the photographic lens 3 is f, then there is a distance of L between them.
=H−f/α2 holds true, and the object distance is calculated by triangulation. In this embodiment, the position where the optical axes 35a and 3a intersect is set at 3 meters in front of the photographic lens 3, but this position may be moved back or forth as appropriate.

A calculation unit 38 is connected to the detection circuit 31, and this calculation unit 38 determines whether the point B is above or below the reference point A based on the position signal, and calculates the distance α therebetween. Then, from the formula L=H-f/α, the control section calculates the object path ML to generate a distance measurement signal, and the area signal generates a focusing signal created when the area of the blurred image becomes the minimum. 3
Send to 9.

A lens drive unit 40 is connected to the control unit 39, and a motor 42 for moving the photographing lens 3 on the optical axis 3 is connected to the lens drive unit 40 via a driver 41. . This control unit 40 uses the distance measurement signal to
After the motor 42 is rotated at high speed and the photographing lens 3 is extended to a position corresponding to the distance measurement signal, the motor 42 is rotated at low speed. Then, the low speed rotation of the motor 42 is stopped in response to the focus signal. Further, this control section 40 is connected to the microcomputer 30, and in response to a photographing completion signal from the microcomputer 30, drives a motor 42 via a lens driving section 40 to move the photographing lens 3 to infinity.

The microcomputer 30 is connected to the position sensor 18a, and checks whether the filter 18 is retracted when the power is turned on. If the filter 18 is not retracted, the microcomputer 30 drives the motor 44 via the driver 43, and the filter 18 is retracted.
8 to the retreat position.

In the electronic still camera 2 configured in this way, when the release button 6 is pressed halfway, the microcomputer 30 activates the driver 2.
9. Via 32, CCD 17 and light emitting diode 33
drive each. Near-infrared light emitted from the light emitting diode 33 is projected toward the subject 16 as spot light. The spot light reflected by the subject 16 is directed to the photographic lens 3 at infinity. Pass through half mirror 15, CC
A blurred image is formed on D17. When the subject 16 is, for example, more than 3 meters away, the reflected spot light forms a blurred image surrounding a point C above the reference point A, as shown in FIG. 4(a).

The incident position and incident area of this blurred image are detected by a detection circuit 31. Based on the position signal, the calculation unit 38 determines that point C is above the reference point A, creates a distance measurement signal, and sends this to the control unit 39. The control unit 39 rotates the motor 42 at high speed via the lens drive unit 40.
A photographic lens 3 is advanced at high speed from infinity to a position corresponding to a distance measurement signal. Thereafter, when the focus signal is output from the detection circuit 31, the control unit 39 causes the motor 42 to rotate at a low speed.
The process is stopped when the area of the blurred image becomes the minimum as shown in FIG. 4(b).

When the photographing lens 3 moves to the in-focus position in this manner, the microcomputer 30 drives the motor 44 via the driver 43 to insert the filter 18 on the optical axis. Thereafter, when the release button 6 is fully pressed, the microcomputer 30 stops driving the light emitting diode 33 and performs high-speed sweeping of the CCD 17. After this, it passes through the filter 18 and the C
The optical image of the subject 16 formed on the CD17 is
is read out as a signal. This signal is sent to a video signal processing circuit 26 via an amplifier 25 and converted into a video signal. This video signal is converted into a digital image signal by the recording section 27 and written into the memory cartridge 9. When the photographing is completed, the microcomputer 30 drives the motor 44 to move the filter 18 to the retracted position and outputs a photographing completion signal to the control section 39. Then, the control section 39 drives the motor 51 via the lens drive section 40 to move the photographic lens 3 to infinity, thus preparing for the next focus adjustment.

In this embodiment, the half mirror 15 described above is fixed, but it may be flipped up during photographing using a well-known quick return mechanism, such as in an eye reflex camera. In addition, when a quick return mechanism is used, the half mirror 15 may be replaced with a cyclo-like mirror that reflects visible light and transmits light with longer wavelengths than near-infrared light.

Furthermore, if a mirror holding member 50 shown in FIG. 5 is used in place of the half mirror 15, the filter 18 can be omitted. A pair of apertures 52 and 53 are formed in the mirror holding member 25 fixed to a shaft 51 parallel to the optical axis 3a, a half mirror 54 is provided in the aperture 52, and a near-infrared light cut filter is provided in the aperture 28. 55 is attached to the shaft 51 at an angle of 45 degrees. It should be noted that a groic mirror may be used for the opening 52 instead of the half mirror 54. The mirror holding member 50 configured in this manner rotates as shown in the figure during distance measurement, and is used by inserting the half mirror 54 onto the optical axis 3a. Further, during photographing, the shaft 26 is rotated clockwise and the near-infrared light cuff filter 55 is inserted onto the optical axis 3a.

FIG. 6 shows an embodiment of the present invention that performs multi-point distance measurement. In this embodiment, three spot lights are projected onto the subject in order to prevent hollow spots. As a result, a blurred image is formed on the CCDIT at three points D-F as shown in the figure, but if the subject distances of each point D-F are different, the closest point from the photographing lens 3 For example, focusing is performed using a dot distance measurement signal and a focus signal. Although three spot lights were used in this embodiment, the electronic still camera 2 of the present invention uses an imaging CCD 17 as a light receiving element.
, the number of spot lights can be easily increased or decreased by simply replacing the filter 34.

Furthermore, in the above embodiment, the photographic lens 3 was set to infinity and the photographic lens 3 was extended, but the spot light reflected by the subject at a distance of 3 meters from the set position of the photographic lens 3 forms an image on the reference point A. It may be placed in a position where At this time, when the subject distance is longer than 3 meters, the photographing lens 3 may be moved to the infinity side, and when the subject distance is less than 3 meters, the photographing lens 3 may be extended.

In this way, the moving distance of the photographic lens 3 can be reduced, and the time required for focus adjustment can be shortened.

C. Effects of the Invention] As described above in detail, according to the electronic still camera of the present invention, the incident position and incidence of the ranging light reflected by the subject on the sensor is determined based on the output signal from the imaging sensor. Since a detection means for detecting the area and a lens movement means for calculating based on the signal from the detection means and moving the lens in the optical axis direction are provided, the active distance measuring method and the focus detection method can be used together. This allows you to adjust the focus with high precision even on dark subjects. Furthermore, since an imaging sensor is used as a light-receiving element that receives reflected light, a light-receiving lens and light-receiving element are not required, and an inexpensive electronic still camera can be used. moreover,
Since the photographing lens can be moved at high speed to the position corresponding to the distance measurement signal calculated by triangulation distance measurement, the time required for focus adjustment can be shortened.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the electrical configuration of an electronic still camera according to the present invention. FIGS. 2(a) and 2(b) are explanatory diagrams of focus adjustment performed in the electronic still camera of the present invention. FIG. 3 is a perspective view showing the external appearance of the electronic still camera shown in FIG. 1. FIGS. 4(a) and 4(b) are explanatory views for explaining the contrast method performed in the electronic still camera shown in FIG. FIG. 5 is a perspective view showing the mirror holding member. FIG. 6 is an explanatory diagram of multi-point distance measurement performed by the electronic still camera of the present invention. 2...Electronic still camera 3...Photographing lenses 16.16a, 16b-,. 17...CCD 36...Detection circuit Subject 38...Calculation unit 39...Control unit 40...Lens drive unit 42...Light emitting diode. fig. fig. fig. fig. υ hi

Claims (2)

[Claims] (1) In an electronic still camera in which a distance measuring light is projected toward a subject and the lens is focused by receiving reflected light from the subject, an optical image of the subject is formed through the lens, and the reflected light is A two-dimensional sensor into which light is incident, a detection means for detecting the incident position and incident area of the reflected light on the sensor based on an output signal from this sensor, and a calculation based on the signal from this detection means to detect the reflected light. 1. An electronic still camera comprising: a lens moving means for moving the lens in an optical axis direction according to a light incident position and incident area. (2) A dichroic mirror that is removably installed on the optical axis of the lens and that reflects visible light toward the finder optical system and passes infrared light that is used as the distance measuring light is installed when shooting. The electronic still camera according to claim 1, wherein the electronic still camera is retracted from the axis.