JP2009109792A - Autofocusing device and camera using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce wobbling operation to detect a peak of contrast. <P>SOLUTION: A spectroscopic element 24 is arranged to be freely moved in/out between a photographic lens 12 and a photographic sensor 13. In the spectroscopic element 24, a total reflection mirror 11 is arranged on the front face of a parallel plate 21 while a half mirror 23 is arranged on the back face, and a slit 22 is formed in a part of the total reflection mirror 11. A subject light beam transmitted through the photographic lens 12 is incident from the slit 22 to be spectrally split into five subject light beams 25-29 having an optical path length difference by using the internal reflection of the parallel plate 21. The respective subject light beams 25-29 are individually incident on ranging areas 30-34 shifted vertically from one another on an imaging face 13a. From high frequency components of an image signal within a range corresponding to the ranging areas 30-34, five contrast values are detected at the same time. A peak of contrast is found from the five contrast values, and a focusing position of the photographic lens 12 is specified. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a contrast type autofocus device using a difference in optical path length and a camera using the same.

  Conventionally, a contrast AF method in autofocus control of an electronic camera or the like extracts a high frequency component signal from an image signal obtained from an image sensor such as a CCD or CMOS, and evaluates the contrast level based on the extracted signal. An AF evaluation value is obtained.

  The contrast AF method is a full scan method in which the lens is continuously moved from infinity to the closest end to detect an AF evaluation value, and the lens is driven to a position (focus position) corresponding to the maximum value of the AF evaluation value. Alternatively, a hill-climbing method is known in which the lens is driven by a predetermined amount in the direction in which the AF evaluation value increases to detect the maximum AF evaluation value (the top of the mountain).

  However, in the above-described method, since the wobbling operation for detecting the contrast peak is performed while moving the lens minutely in the forward or backward direction of the optical axis, the lens cannot be moved directly to the in-focus position. It takes time, and there is a drawback that the focus variation is recognized on the screen.

Therefore, there is known an optical path length difference method in which focus drive is smoothly performed without performing a wobbling operation (Patent Document 1). In this method, the subject light is divided into first and second subject lights using the light splitting means, and two imaging sensors for individually imaging the first and second subject lights are provided, and up to two imaging sensors. The focus control means controls the in-focus position of the taking lens so that the position of the optical path length in the middle of the optical path length becomes the best imaging position, and the image for reproduction is acquired from the two imaging sensors by the focus correction means. The focus position is corrected so that the position of the imaging sensor for achieving the best imaging position.
JP 2005-62237 A

  However, in the invention described in Patent Document 1, only two contrast values having a difference in optical path length can be detected by a single distance measurement. Therefore, in order to detect a contrast peak, a plurality of values can be detected while moving the lens. It is necessary to measure the distance once. Further, since two expensive image sensors are used, the cost increases.

  In view of such circumstances, an object of the present invention is to provide an autofocus device capable of quickly detecting a contrast peak without moving a focusing lens as much as possible, and a camera using the same. A second object is to provide at low cost.

  In the present invention, an imaging sensor for imaging subject light passing through the photographic lens; provided between the photographic lens and the imaging sensor, shifted in a direction perpendicular to the optical axis of the photographic lens, and A spectroscopic element that splits light into at least three subject lights having different optical path lengths from the photographing lens to the imaging plane of the imaging sensor; and an image obtained from each ranging area of the imaging plane on which the at least three subject lights are incident At least three contrast detecting means for simultaneously detecting at least three contrast values by detecting high-frequency components of the signal respectively; and determining the contrast peak based on at least three contrast values simultaneously obtained from the contrast detecting means to perform the photographing Focusing position specifying means for specifying the focusing position of the lens; and moving the photographing lens to the focusing position That a focus driving means; those with a.

  The imaging sensor may be for acquiring a recording image. In this case, an optical element is provided on the optical axis of the photographic lens so that the optical element can freely enter and exit, and when a moving image is acquired by the imaging sensor, the spectroscopic element is retracted from the optical axis, and autofocusing is performed. What is necessary is just to insert on the said optical axis when performing.

  As the spectroscopic element, a mask layer provided on the entrance surface in a state where a part is exposed by the slit, a half mirror layer provided on the exit surface, and provided between the mask layer and the half mirror layer A parallel plate that splits the subject light incident from the slit into at least three subject lights having an optical path length difference according to the number of internal reflections between the mask layer and the half mirror layer; It may be a thing.

  By the way, since at least three subject lights dispersed by the spectroscopic element are produced by using internal reflection, the light quantity of the subject light having a longer optical path length decreases. Therefore, it is preferable to change the reflectance of the half mirror layer at a position on the exit surface that transmits each subject light so that the amount of light of at least three subject lights incident on the imaging surface is the same. .

  By forming the mask layer with the entire reflection mirror layer, the object light can be reflected by the entire reflection mirror layer at the insertion position. You may comprise a finder optical system using this.

  According to the present invention, since at least three contrast values can be obtained simultaneously by one distance measurement, a contrast peak can be quickly detected.

  As shown in FIGS. 1 and 2, the main part of the electronic camera 10 using the present invention is a single-lens reflex type structure, that is, performs distance measurement and photometry in response to half-pressing operation of the shutter button. In response to the pressing operation, the flip-up mirror 11 is flipped up and the subject light passing through the photographing lens 12 is imaged by the imaging sensor 13.

  The mirror 11 is supported so as to be rotatable between an insertion position and a retracted position around the shaft 14, and is rotated by driving obtained from the moving mechanism 15. The mirror 11 is normally set at the insertion position, and in the insertion position, the mirror 11 is in an attitude of approximately 45 degrees with respect to the photographing optical axis 16, and the subject light passing through the photographing lens 12 is used for a finder located above. An image is formed on the focusing screen 17. The subject light imaged on the focusing screen 17 is re-imaged into an erect image by a pentaprism (or penta roof mirror) 18, and the image re-imaged through the eyepiece lens 19 is viewed through the eyepiece window 20. When in the retracted position, subject light that is retracted from the photographing optical axis 16 and passes through the photographing lens 12 is incident on the imaging surface 13a of the image sensor 13.

  The mirror 11 is a total reflection mirror in which a total reflection coating is applied to the front surface (incident surface) of a parallel plane plate (hereinafter referred to as “parallel plate”) 21. The total reflection mirror 11 is formed with a narrow and wide slit 22 at a position corresponding to a focus area set at an arbitrary position within the photographing range, and part of the incident surface 21a is exposed. A half mirror 23 is coated on the exit surface (rear surface) 21 b of the parallel plate 21.

  The total reflection mirror 11, the slit 22, the parallel plate 21, and the half mirror 23 constitute the spectroscopic element 24 of the present invention. At least three optical path length differences, in the present embodiment, five optical path length differences are provided. Spectroscopy the subject light.

  The spectroscopic element 24 refracts the subject light incident inside from the slit 22 at the insertion position, and divides the light into the first reflected light and the first transmitted light at the exit surface 21b. The first transmitted light constitutes the first subject light 25 that is refracted by the exit surface 21b, exits to the outside, and enters the imaging surface 13a.

  The first reflected light is again internally reflected at the incident surface 21a by the coating of the total reflection mirror 11, travels toward the exit surface 21b, and branches into the second reflected light and the second transmission at the exit surface 21b. The second transmitted light constitutes second subject light 26 that is refracted at the exit surface 21b and exits to the outside and enters the imaging surface 13a. The second reflected light is again internally reflected at the incident surface 21a and travels toward the exit surface 21b, and branches into third reflected light and third transmission at the exit surface 21b. The third transmitted light constitutes third subject light 27 that is refracted at the exit surface 21b, exits to the outside, and enters the imaging surface 13a. Similarly, five subject lights 25 to 29 having different optical path length differences are produced by internal reflection.

  As shown in FIG. 3, the first to fifth subject light beams 25 to 29 are incident on five distance measuring areas 30 to 34 that are shifted in the vertical direction on the imaging plane 13a. In the five ranging areas 30 to 34, the first ranging area 30 where the first subject light 25 enters, the second ranging area 31 where the second subject light 26 enters, and the third subject light 27 enter in order from the bottom. The third ranging area 32, the fourth ranging area 33 where the fourth subject light 28 enters, and the fifth ranging area 34 where the fifth subject light 29 enters. And the width | variety of the slit 22 is determined so that each ranging area 30-34 may not overlap. Therefore, the size of each ranging area 30 to 34 is determined by the size of the slit 22 and the position (posture) of the slit. Further, the vertical interval between the distance measuring areas 30 to 34 is determined by the thickness and the inclination angle of the parallel plate 21.

  When the first to fifth ranging areas 30 to 34 are virtually represented on the photographing optical axis 16, as shown in FIG. 4, the optical path length from the principal point of the photographing lens 12 to the imaging plane 13a is shown. The optical path length difference is gradually increased in proportion to the number of internal reflections. The orientation of the spectral element insertion position is not limited to 45 degrees, and may be any inclination angle. Further, the spectroscopic element 24 is not limited to the parallel plate 21, and for example, an optical member having a curved surface in parallel so as to correct the spherical aberration of the photographing lens 12 may be used.

  In addition, as the spectroscopic element 24 described above, the internal reflection at the incident surface 21a of the flat plate 21 is performed by the total reflection mirror 11. The reflection may be performed only. In this case, the total reflection mirror 11 is provided on the front surface of the parallel plate 21 as a mask function. An air layer may be provided between the total reflection mirror 11 and the parallel plate 21. The reason for providing the air layer is that the light that is internally reflected by the total reflection mirror 11 is not used. In this case as well, the total reflection mirror 11 may have a function of reflecting subject light to the finder optical system.

  As shown in FIG. 5, the electronic camera 10 includes a photographing lens 12, an aperture 36, a mechanical shutter 37, an image sensor 13, an analog front end (AFE) 38, a digital signal processing circuit 39, an AF circuit 40, a CPU 41, a TG 42, and a V. The driver 43, the compression / decompression processing circuit 44, the recording unit 45, the LCD driver 46, the LCD 47, the ROM 48, the photometry circuit 49, the operation unit 50, and the like are included. The operation unit 50 includes a shutter button, a zoom operation unit, a playback button, and the like. Various programs are stored in the ROM 48 in advance. The photometry circuit 49 is built in the finder optical system. The mechanical shutter 37 is disposed between the spectroscopic element 24 and the image sensor 13, and is normally closed. The mechanical shutter 37 is fully opened in response to a half-pressing operation of the shutter button, and subject light for distance measurement is incident on the image sensor 13. Let As the image sensor 13, a CCD or a COMS can be used.

  The photographic lens 12 is a movable lens group, a focusing lens (group) 12a moved in the direction of the photographic optical axis 16 for focusing, and a photographic optical axis 16 for changing the image magnification (focal length). A zoom lens (group) 12b and the like that are moved in the direction are arranged. The aperture 36 is driven to open and close to change the aperture value. The focusing lens 12a, the zooming lens 12b, and the diaphragm 36 are connected to a focusing motor 55, a zooming motor 56, and a diaphragm motor 57, respectively.

  The motors 55 to 57 are connected to the drivers 58 to 60, respectively. When a drive signal is given from the CPU 41 to the drivers 58 to 60, the motors 55 to 57 are driven by a voltage or current corresponding to the drive signal. (Rotation speed and direction) are controlled. Although not shown, a motor and a driver are also connected to the mechanical shutter 37, and the drive is controlled by the CPU 41. In addition, position information indicating the current positions of the focusing lens 12a, the zoom lens 12b, and the aperture 36 is sent from the position detector to the CPU 41 via the A / D converter.

  The AFE 38 includes a CDS (correlated double sampling) 62, an AGC (automatic gain adjustment amplifier) 63, and an A / D converter 64, and an image signal obtained from the imaging sensor 13 is digitized by the AFE 38 and is connected to the AF circuit 40. To the digital signal processing circuit 65. The AGC 63 can change the gain amount, and the CPU 41 sets the AGC gain amount. The timing generator (TG) 42 supplies pulses to the AFE 38 and the V driver 43 to drive them synchronously.

  In response to the half-pressing operation of the shutter button, the AF circuit 40 receives an image signal. The AF circuit 40 has five processing circuits 66 to 70 in order to obtain contrast values of the five distance measuring areas 30 to 34. The processing circuits 66 to 70 are circuits that generate a focus evaluation value indicating the level of contrast of the image from the image signal (luminance signal) obtained from the imaging sensor 13. Since these processing circuits 66 to 70 have the same processing content for each image signal, only the processing circuit 66 will be described below.

  The processing circuit 66 includes a digital filter 71, a gate circuit 72, and an adder circuit 73. The digital filter 71 extracts only the high frequency component signal from the image signal. The gate circuit 72 receives a gate opening signal from the CPU 41, and thus, a signal corresponding to a predetermined focus area, in this case, the first ranging area 30 set within the photographing range from the extracted high frequency component signal. Is extracted. The adder circuit 73 integrates the signals extracted by the gate circuit 72 for each image (for one field in an interlaced image signal). The signal obtained by the integration of the adder circuit 73 is a value indicating the degree of focus on the subject in the focus area (contrast level), and these values are read by the peak detector 74.

  The peak detector 74 determines the contrast peak value based on the five contrast values obtained from the processing circuits 66 to 70. When the contrast peak value corresponds to one of the five contrast values, the contrast value may be handled as the peak value. Also, for example, when there is a peak value between the obtained contrast values, an interpolating operation is performed using an approximate value curve or a peak function to calculate a peak value in between. Information on the in-focus position corresponding to this peak value is sent to the CPU 41. The CPU 41 has lens position correction means 75, and the lens position correction means 75 corrects the position of the focusing lens 12a based on the information on the focus position so that the position of the imaging surface 13a becomes the focus position. Thus, the focus motor driver 58 is controlled.

  The CPU 41 extracts subject luminance information by the photometry circuit 49 and controls the adjustment of the diaphragm 36 based on the information. The image signal captured for recording is input to the digital signal processing circuit 65. The digital signal processing circuit 65 is provided with a Y / C processing circuit, an auto white balance circuit, an image processing circuit, and the like. The image data for one frame is recorded in the RAM 76 and processed while being read out again. The Y / C processing circuit generates a luminance signal and a color difference signal. The generated luminance signal and color difference signal are sent to the compression / decompression processing circuit 44, where they are encoded into a predetermined compression format, and the encoded image data is stored in a recording medium such as a card memory by the recording unit 45 as one file format. To be recorded.

  At the time of reproduction, the image recorded in the recording unit 45 is sent to the compression / decompression processing circuit 44, where it is decoded into a predetermined decompression format, and the decoded image data is sent to the LCD driver 46, where an LCD display drive signal is sent. Is converted to Thereby, the reproduced image is displayed on the LCD 47. The screen of the LCD 47 is provided outside the electronic camera 10, for example, on the back surface.

  As shown in FIG. 6, the peak detector 74 calculates a contrast peak value based on the five contrast values simultaneously obtained from the processing circuits 66 to 70. As a method for calculating the peak value, for example, an approximate value curve may be created based on five contrast values, and the peak value of the contrast may be calculated from the curve, or the peak value may be obtained using a peak function. Good. As the contrast value is closer to the in-focus position, an image with a clear outline is obtained, the high frequency component increases, and the contrast value increases. Before the distance measurement, the focusing lens 12a is set to a predetermined initial position (for example, the closest position or the infinity position, or a predetermined position therebetween). Here, an approximate value curve is created on the basis of the five contrast values to identify the peak value of contrast. The defocus amount (Xd) corresponding to this peak value is such that the focus position for the subject at that time is defocused in the closest direction with respect to the focus position corresponding to the lens position of the focus lens 12a at that time. It shows that it is shifted by the amount (Xd). Therefore, if the amount by which the in-focus position with respect to the lens position of the in-focus lens 12a moves in the closest direction by the defocus amount (Xd) is calculated and the in-focus lens 12a is driven by that amount, the subject at that time Is in focus.

  For a moving subject, continuing the half-press operation only results in the peak value shown in FIG. 6, for example, moving either to the nearest or infinity, so focusing can be performed quickly. Can continue to. For a subject moving at high speed, the in-focus position after a predetermined time can be predicted by calculating the amount of movement of the peak value.

  In addition, as shown in FIG. 7, when the peak value of contrast cannot be detected, it becomes an inclined substantially straight line. From this inclination, the direction of the peak, that is, the moving direction of the focusing lens 12a may be determined, and the distance measuring operation may be performed again after moving in that direction by a predetermined amount. Thus, since five contrast values can be obtained by one distance measurement operation, the peak of contrast can be obtained quickly, and the operation of driving the focusing lens can be reduced as much as possible as compared with the prior art. As a result, the AF operation becomes faster.

  By the way, when the reflectance at the exit surface 21b of the spectroscopic element 24, that is, the reflectance of the half mirror 23 is constant, the amount of light is attenuated each time reflection is repeated. For this reason, the amount of light reaching the imaging sensor 13 gradually decreases toward the first distance measurement area 30 to the fifth distance measurement area 34. Therefore, it is preferable to make the light amounts of the first to fifth subject lights 25 to 29 constant by changing the reflectance for each reflection position.

  For example, as shown in FIG. 8, the reflected light amounts of the first to fifth subject lights 25 to 29 are constant at the reflection positions A to E that reflect the first to fifth subject lights 25 to 29 in the half mirror 23. Change the reflectivity so that In the example shown in the figure, the reflectance is changed so as to emit 1/5 of the original light amount. Assuming that the original light amount is “1”, the reflectance is 80% and the transmitted light amount is 0.2 at the reflection position A that is reflected for the first time with respect to the exit surface 21b. At the second reflection position B, the reflectance is 75%, so the amount of reflected light is 1 × 0.8 × 0.75 = 0.6, and the amount of transmitted light is 0.8−0.6 = 0.2. It becomes. Hereinafter, the amount of reflected light can be made constant at “0.2” in order. By changing the film thickness of the half mirror 23 and the multilayer film configuration based on this curve, the reflectance is gradually changed based on the curve shown in FIG. In addition, you may make it a reflectance change in steps for every range including each reflective position AE.

  The operation of the above configuration will be described. As shown in FIG. 9, when the power of the electronic camera 10 is turned on, it is checked whether or not the spectroscopic element 24 is in the insertion position, and if it is not the insertion position, it moves to the insertion position. In this state, the mechanical shutter 37 is closed, and no subject light is incident on the image sensor 13. Further, it is assumed that the subject image is visually recognized from the eyepiece window 20 out of focus.

  When the shutter button is half-pressed, the CPU 41 activates the photometry circuit 49. Thereafter, the mechanical shutter 37 is fully opened, and a distance measuring operation for operating the AF circuit 40 is performed. The CPU 41 calculates the opening / closing time of the mechanical shutter 37 and the aperture value so that an appropriate exposure is obtained based on the subject brightness obtained from the photometry circuit 49.

  Before the distance measuring operation, the focusing lens 12a is first moved to a predetermined position, and then the distance measuring operation is performed. In the distance measuring operation, a contrast value is extracted based on the image signals obtained from the first to fifth distance measuring areas 30 to 34, and the peak value is calculated from the five contrast values by the peak detector 74. When the peak value is detected by one distance measurement, the in-focus position can be determined immediately. Then, the lens position correcting means 75 corrects the position of the focusing lens 12a so that the position of the imaging surface 13a becomes the best imaging position based on the in-focus position. If the peak value cannot be detected, the focusing lens 12a is moved by a predetermined amount in the direction of the peak value from the inclination, and the distance measuring operation is executed again. Note that the focusing lens 12a may not be moved to a predetermined position before the distance measuring operation. In this case, the focusing lens 12a may be moved from the position at that time.

  When the shutter button is fully pressed, the spectroscopic element 24 is moved to the retracted position and the mechanical shutter 37 is once closed. In conjunction with the movement of the spectroscopic element 24 to the retracted position, the diaphragm 36 is set to a diaphragm aperture diameter corresponding to the subject brightness, and then the mechanical shutter 37 is opened and closed for a time corresponding to the subject brightness. During this time, an image for recording is picked up by the image sensor 13. After imaging, the mechanical shutter 37 is kept closed, and the spectroscopic element 24 is moved to the insertion position. In conjunction with this movement, the aperture 36 is fully opened. Thereafter, the focus adjustment is performed in response to the half-pressing operation of the shutter button as described above. Note that the distance measurement operation is repeated by continuing the half-press operation of the shutter button.

  In the above embodiment, the TTL type finder optical system is provided, but this may be omitted and a through image may be displayed on the LCD 47 provided on the back surface of the electronic camera 10. In this case, the spectroscopic element 24 is always moved to the retracted position, and moved to the insertion position in response to the half-pressing operation of the shutter button. In this state, the AF circuit 40 is operated to take in five contrast values and adjust the focus of the focusing lens 12a. Then, in response to the completion of the focus adjustment, the spectroscopic element 24 is moved to the retracted position. Thereafter, an image for recording is taken in response to the full pressing operation of the shutter button. In this case, an AE circuit is provided in the digital signal processing circuit 65, and the diaphragm 36 may be controlled based on the subject brightness obtained based on the image signal for the through image immediately before the half-press operation. The mechanical shutter 37 may be fully opened during live view display, closed once in conjunction with the full-pressing operation, opened and closed for a time corresponding to the subject brightness, and fully opened again after imaging. In addition, although the aperture 36 and the mechanical shutter 37 are provided, a single aperture / shutter may be used.

  In the above embodiment, although the spectroscopic element 24 is moved to the retracted position in response to the completion of the focus adjustment, the spectroscopic element 24 is moved to the insertion position in response to the half-pressing operation of the shutter button to perform the focus adjustment. Only when the live view is not displayed. Therefore, as shown in FIG. 10, a light dividing means 81 such as a half mirror is provided to divide the subject light incident on the photographing lens 80 into first and second subject light, and a recording image is obtained. The first imaging sensor 82 for imaging the first subject light, and the second imaging light is imaged by the second imaging sensor 83 provided at a position different from the first imaging sensor 82. A spectroscopic element 84 that splits the second subject light into five subject lights may be provided in front of the second imaging sensor 83.

  In this configuration, the AF circuit 85 simultaneously obtains five contrast values from the five distance measuring areas of the second image sensor 83, and the AF circuit 85 calculates the contrast peak based on the five contrast values and corresponds to the peak. Information on the focus position to be sent is sent to the focus control circuit 86. The focus control circuit 86 corrects the current position of the photographic lens 80 to be the focus position based on the received focus position information. According to this, since the subject light can always be imaged by the first imaging sensor 82, a mechanism for inserting and removing the spectroscopic element 84 with respect to the optical axis is not required. In addition, since focus adjustment can always be performed regardless of half-pressing operation of the shutter button, a through image in focus can be displayed on a display unit such as an LCD.

  In each of the embodiments described above, a parallel plane plate is used as the spectroscopic element 24. Alternatively, a prism joined may be used. Further, as the spectroscopic element 24, the subject light transmitted through the photographing lens is split into five subject lights. However, in the present invention, it is not limited to five and may be any element that splits into at least three.

  In the embodiment described with reference to FIG. 1, a single image sensor 13 that captures a color image is described as a so-called single-plate electronic camera 10, but red (R), green (G), blue ( The present invention can also be used for a so-called three-plate camera in which a color image is picked up by three image pickup devices for each B). In this case, three image sensors for R, G, and B at optically equivalent distances are used, and the subject light that has passed through the photographing lens is split into R, G, and B light by the color separation optical system. In this configuration, subject light that has been split into wavelengths of each color by the color separation optical system is incident on the imaging surface of each imaging device. A spectroscopic element may be provided in front of any one of the three imaging elements. Therefore, in the case of the three-plate type, the luminance signal of one subject light out of the three colors of subject light may be obtained from any one of the three image sensors.

  In addition, in a single-lens reflex type camera, a lens is attached to the camera body in a replaceable manner. Therefore, the spectroscopic elements 24 and 84 described in the above embodiments may be provided on the camera body or on the interchangeable lens side.

  In addition, an imaging sensor is provided on the lens barrel having the photographic lens, and an operation unit and a recording unit are provided on the camera body to which the lens barrel is replaceable, and image data and signals are exchanged between the lens barrel and the camera body. A system for performing the above at high speed is known from Japanese Patent Application Laid-Open No. 8-172561. The present invention may be adopted in such a system. In this case, the spectroscopic element of the present invention may be incorporated in the lens barrel.

  The present invention can be applied not only to an electronic camera but also to a photographic camera and a television camera.

It is explanatory drawing which shows the outline of this invention, and has shown the state which moved the spectroscopic element to the insertion position. It is explanatory drawing which shows the state which moved the spectroscopic element to the retracted position. It is explanatory drawing which shows the ranging area which images five object light. It is explanatory drawing which shows roughly the optical path length difference to five ranging areas. It is a block diagram which shows the outline of an electrical structure of an electronic camera. It is a graph which shows a focus evaluation value in case a contrast peak is obtained by one distance measurement. It is a graph which shows a focus evaluation value when the peak of contrast is not obtained by one distance measurement. It is a graph which shows the reflectance of the half mirror coating of the back surface of the spectroscopic element which made constant the light quantity of each subject light disperse | distributed with a spectroscopic element. It is a follow chart figure which shows operation | movement of the electronic camera demonstrated in FIG. FIG. 10 is an explanatory diagram illustrating another embodiment in which focusing is performed during through image display.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electronic camera 11 Total reflection mirror 12 Shooting lens 14 Axis 22 Slit 23 Half mirror 24 Spectroscopic element 25-29 1st-5th subject light 30-34 1st-5th ranging area 40 AF circuit

Claims (5)

An imaging sensor for imaging subject light passing through the taking lens;
Provided between the photographic lens and the imaging sensor, shifted in a direction perpendicular to the optical axis of the photographic lens, and the optical path length from the photographic lens to the imaging plane of the imaging sensor is different. A spectroscopic element that splits light into at least three subject lights;
Contrast detection means for detecting a high-frequency component of an image signal obtained from each ranging area of the imaging plane on which each subject light is incident for each ranging area and simultaneously obtaining a contrast value for each ranging area;
A focus position specifying means for determining a focus position of the photographing lens by determining a contrast peak based on at least three or more contrast values obtained simultaneously from the contrast detection means;
Focus control means for moving the photographic lens to the in-focus position;
An autofocus device characterized by comprising:   The imaging sensor is for acquiring a recording image, and the optical element is provided so as to freely enter and exit on the optical axis of the photographing lens, and acquires an image for recording by the imaging sensor. 2. The autofocus device according to claim 1, further comprising a moving means for retracting the spectroscopic element from the optical axis and inserting the spectroscopic element on the optical axis when performing autofocus.   The spectroscopic element includes a mask layer that is provided on the incident surface and masks the remaining part in a state of being exposed by the slit, a half mirror layer provided on the exit surface, and the mask layer and the half mirror layer between the mask layer and the half mirror layer. A parallel plate that splits subject light incident from the slit into at least three subject lights having optical path length differences according to the number of internal reflections between the mask layer and the half mirror layer. The autofocus device according to claim 1, wherein the autofocus device is provided.   The half mirror layer is provided with a different reflectance at a position where the subject light is transmitted so that the amount of light of at least three subject lights incident on the imaging surface is the same. The autofocus device according to claim 3.   4. The camera using the autofocus device according to claim 3, wherein the mask layer is made of a full reflection mirror layer, and uses subject light reflected by the full reflection mirror layer at the insertion position. A camera comprising a finder optical system for visually recognizing a shooting range.

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