JP2006235353A - Focus detector and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detector capable of easily detecting image separation while suppressing a distance between a separation surface for separating a luminous flux in a specified wavelength region and an imaging device. <P>SOLUTION: A wavelength selecting reflection mirror 3 for reflecting the range-finding luminous flux in the specified wavelength region is arranged between a photographing lens 1 and the imaging device 5. The imaging luminous flux transmitted through the mirror 3 is projected on the imaging device 5. On the other hand, the range-finding luminous flux reflected by the mirror 3 is made incident on a split prism 7 as an image separating optical element, then, the image is separated in accordance with the focusing state of the photographing lens 1, then, the luminous flux is detected by a range-finding element 8. The wavelength selecting reflection mirror 3 has an action as a concave lens for the range-finding luminous flux, then, the image forming position extends toward the split prism 7, and also, the image is enlarged. Consequently, even when the distance between a prism block 4 and the imaging device is made short, the image can be formed outside the prism block 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a focus detection device and an imaging device including the same.

  Conventionally, as a focus detection device for a camera, an infrared component contained in a photographed light beam is separated by a prism having a separation surface (beam splitter), and the light beam component is detected by a phase difference detection type detection optical system to measure a distance. Is known (for example, see Patent Document 1). The visible light transmitted through the separation surface is imaged on the imaging surface of the camera, and the infrared light beam reflected by the separation surface passes through the prism and is guided to the detection optical system.

JP 2003-140246 A

  By the way, the above-described focus detection apparatus has a structure in which the infrared light beam reflected by the separation surface is guided through the prism block, then exits the prism block, and enters the detection optical system. In such a focus detection apparatus, if the distance between the imaging surface for photographing and the separation surface is set to be short in order to shorten the back focus, the infrared light beam is focused in the prism block. For this reason, it is necessary to lengthen the back focus so that the focal point is formed outside the prism block, which is a factor of increasing the size of the camera.

According to a first aspect of the present invention, a focus detection apparatus separates light in a specific wavelength range included in light that has passed through a photographic lens as a focus detection light beam, and transmits a photographic light beam outside the specific wavelength range, thereby taking a photographic image pickup surface The first optical element that has a negative refractive power with respect to the focus detection light beam and forms an enlarged image of the image by the focus detection light beam, and a position optically substantially equivalent to the imaging surface for photographing And a second optical element that separates the magnified image in a plurality of directions according to the focus adjustment state of the photographic lens, and a detection unit that detects the magnified image separated by the second optical element. Features.
According to a second aspect of the present invention, in the focus detection apparatus according to the first aspect, the first optical element and the waveguide that totally reflects the focus detection light beam and guides it to the second optical element are integrally formed. Provided with an optical block.
According to a third aspect of the present invention, in the focus detection apparatus according to the first or second aspect, the negative refractive power is set so that the separated focus detection light beam becomes substantially parallel light, and the first optical element and the first optical element And a lens that is disposed between the two optical elements and forms an image of a focus detection light beam that is substantially parallel light at a position optically substantially equivalent to the imaging surface for photographing.
According to a fourth aspect of the present invention, in the focus detection apparatus according to the third aspect of the present invention, a lens is integrally formed on the exit surface of the focus detection light beam in the optical block.
According to a fifth aspect of the present invention, in the focus detection device according to any one of the first to fourth aspects, the photographing light flux is photographed through a filter including filter elements having different spectral transmission characteristics. The first optical element is a hologram, and the hologram separates light in a wavelength region excluding the wavelength region near each transmittance peak of the filter element as a focus detection light beam.
An image pickup apparatus according to a sixth aspect of the invention includes the focus detection apparatus according to any one of the first to fifth aspects, and an image pickup element that picks up a subject image by a shooting light beam that has passed through the first optical element. It is characterized by.

  According to the present invention, since the focus detection light beam is separated by the first optical element having negative refractive power, the enlarged image can be separated while keeping the distance between the imaging element and the first optical element short. It can be easily detected. Furthermore, since a magnified image can be formed by the first optical element, focus detection accuracy can be improved.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining an embodiment of a focus detection apparatus according to the present invention, and shows a schematic configuration when the focus detection apparatus is applied to a camera. The focus detection apparatus includes a prism block 4 on which a wavelength selective reflecting mirror 3 is formed, a split prism 7 and a distance measuring element 8.

  The prism block 4 is disposed on the optical axis between the photographing lens 1 and the image pickup device 5, and the subject light beam condensed by the photographing lens 1 is incident thereon. As the image sensor 5, a CCD image sensor or the like is used. The wavelength selective reflecting mirror 3 formed in the prism block 4 is configured to reflect light in the near infrared region that is not used for imaging. For example, light in the wavelength region as shown by the curve 21 in FIG. A reflective dichroic film is used.

  FIG. 2 shows the wavelength range of the light reflected by the wavelength selective reflecting mirror 3 of the present embodiment, and the vertical axis represents the reflectance. In FIG. 2, a curve 21 is a curve showing the reflection characteristics of reflected light, and light in the near infrared region is reflected. Curves 18 to 20 shown as reference indicate the transmission characteristics of the RGB color filter provided in the image sensor 5, the curve 18 is the transmission characteristic of the R filter, the curve 19 is the transmission characteristic of the G filter, Curve 20 shows the transmission characteristics of the B filter. That is, the wavelength band used by the image sensor 5 for imaging is in the vicinity of 400 nm to 700 nm. For curves 18-20, the vertical axis represents the transmittance.

  The near-infrared luminous flux reflected by the wavelength selective reflecting mirror 3 enters a split prism 7 that is an image separation optical element. The split prism 7 is disposed at a position optically equivalent to the imaging surface of the imaging device 5. The split prism 7 separates the subject image according to the focus adjustment state of the photographing lens 1, and the separated image is detected by the distance measuring element 8. As will be described later, the wavelength selective reflecting mirror 3 reflects light of a specific wavelength and acts as a concave lens having negative refractive power on the reflected light.

Output signals from the image sensor 5 and the distance measuring element 8 are input to a control circuit 9 of the camera.
The control circuit 9 includes an interface circuit that controls the operation of the camera, an AF circuit that performs a distance measurement operation based on a signal from the distance measuring element 8, and an image process that performs image processing based on the image pickup signal from the image sensor 5. Circuits are included. The image data after image processing is stored in the memory 11. Reference numeral 12 denotes a display device that can sequentially display image data after image processing via the display circuit 10 or read and display image data in the memory 11. The control circuit 9 calculates the focus adjustment state from the image shift information of the distance measuring element 8 and drives the AF driving mechanism 2 to perform the focusing operation of the photographing lens 1.

  FIGS. 3A and 3B are diagrams for explaining an optical path. FIG. 3A shows an optical path of a light beam used for imaging, and FIG. 3B shows an optical path of a light beam used for distance measurement. In FIG. 3A, since the wavelength selective reflecting mirror 3 has no influence on the light flux, the illustration thereof is omitted. In FIG. 3B, the reflecting system including the reflecting mirror 3 is replaced with a refraction system equivalent to the reflecting system, and the wavelength selective reflecting mirror 3 is illustrated as a concave lens. As shown in FIG. 3A, the subject luminous flux is collected by the photographing lens 1 to form a subject image 13. The subject image 13 is captured by the image sensor 5.

  On the other hand, the wavelength selective reflecting mirror 3 disposed between the photographing lens 1 and the split prism 7 functions as a teleconverter of the photographing lens 1 because it functions as a concave lens having negative refractive power. As a result, an enlarged image 14 larger than the subject image 13 is formed in the vicinity of the split prism 7.

  FIG. 4 is a diagram for explaining the operation of the split prism 7, that is, the principle of distance measurement. The split prism 7 includes a pair of prisms 7R and 7L, and the distance measuring element 8 is provided with sensor rows 16R and 16L corresponding to the prisms 7R and 7L. FIG. 4A shows a front pin state. The light beam is focused on the photographing lens 1 side with respect to the split prism 7, and an image separation action by the split prism 7 occurs.

  In this case, the left light beam incident on the prism 7L is projected to the left side of the drawing from the center of the sensor row 16L. On the other hand, the right light beam incident on the prism 7R is projected to the right side of the center of the sensor row 16R. At this time, the signal waveforms output from the sensor arrays 16R and 16L are as shown by the curves 17R and 17L, respectively. If the relationship between the shift amount and the defocus amount of the two waveforms 17R and 17L is known, the defocus amount can be calculated from the image shift amount d1.

  FIG. 4B shows a focused state, and the light beam is focused on the slopes of the prisms 7R and 7L. In this case, the left and right light beams are incident on the sensor rows 16R and 16L without being deflected. At this time, the signal waveforms 17R and 17L output from the sensor arrays 16R and 16L match. That is, focusing is performed when the image shift amount d1 is d1 = 0. In FIG. 4B, the signal waveforms 17R and 17L are drawn slightly shifted so that they can be easily understood.

  FIG. 4C shows a rear pin state, and the light beam is focused on the sensor rows 16R and 16L side from the split prism 7. In this case, an image shift occurs in the direction opposite to the front pin state shown in FIG. 4A, and the focus adjustment state can be calculated from this image shift amount.

  In the present embodiment, since the wavelength selective separation mirror 3 has a negative refractive power, an image used for distance measurement can be enlarged and observed, so that the amount of image separation by the split prism 7 is enlarged and the focus detection accuracy is improved. Can be improved. In addition, since the optical axis distance and magnification of the magnified image 14 can be adjusted by changing the refractive power of the wavelength selective reflector 3, the wavelength from the wavelength selective reflector 3 to the split prism 7 can be sufficiently secured. It is possible to shorten the distance between the selective reflection mirror 3 and the image sensor 5. Therefore, the camera can be reduced in size without generating a useless space.

  In the embodiment described above, the light reflected by the wavelength selective reflecting mirror 3 has a wavelength in the near-infrared region, so that it hardly overlaps the wavelength used by the image sensor 5 indicated by the curves 18 to 20 in FIG. did. In the conventional digital camera, light in the infrared region is removed by an infrared cut filter integrated with the image pickup device 5, but the light in the near infrared region reflected by the wavelength selective reflecting mirror 3 is removed for imaging. It is included in the unused wavelength region. Therefore, even if a part of the light beam that has passed through the photographing lens 1 is used for distance measurement, the amount of light on the imaging side is not reduced.

  Instead of using a dichroic film having reflection characteristics as shown by the curve 21 in FIG. When a hologram is used instead of the wavelength selective reflecting mirror 3, light of a specific wavelength can be diffracted and separated and used as a distance measuring light beam. For example, as shown in FIG. 5, by using light 22 to 24 in the wavelength region excluding the valleys of the curves 18 to 20, that is, the wavelength regions in the vicinity of the transmittance peaks of the filters, visible light can be obtained. The influence on the luminous flux used for imaging can be reduced while using light for distance measurement. Of course, the distance measuring light beam diffracted and separated by the hologram is not limited to visible light but may be light in the infrared region.

  Furthermore, since a method of observing an image divided by the split prism 7 is adopted as a focus detection method, it is hardly affected by the pupil diameter or focal length of the photographing lens 1, and the present invention has a focal length of about several millimeters. This can also be applied to the photographic lens 1.

[Modification 1]
6 and 7 are diagrams showing a first modification of the above-described embodiment. 6A and 6B are diagrams showing the focus detection device mounted on the camera, where FIG. 6A is a cross-sectional view, and FIG. 6B is a plan view showing the image sensor 5 and the distance measuring element 8 mounted on a flexible substrate. It is. As shown in FIG. 6B, the distance measuring element 8 is mounted directly on the flexible substrate 25, and the image pickup device 5 is mounted on the flexible substrate 25 via a rigid image pickup substrate 27 on which electronic components for the image pickup device are mounted. ing. The flexible substrate 25 is connected to the control circuit 9 shown in FIG. Note that the distance measuring element 8 may also be connected to the flexible substrate 25 through a rigid substrate in the same manner as in the case of the imaging element 5 when there are a large number of electronic components related thereto.

  Reference numeral 26 denotes the above-described optical low-pass filter, which is disposed between the prism block 4 and the image sensor 5. The wavelength selective reflecting mirror 3 formed in the prism block 4 is composed of a dichroic film having a convex shape on the photographing lens 1 side, and has a negative refractive power similar to that of a concave lens by making the reflecting surface into such a convex shape. have. The distance measuring light beam reflected by the wavelength selective reflection mirror 3 in the diagonally lower left direction is totally reflected by the front surface 4a of the prism block 4 and changes its traveling direction in the diagonally lower right direction, and is emitted below the prism block 4. It is emitted from the surface.

  A converging exit surface lens 15 is integrally formed on the exit surface, and the split prism 7 and the distance measuring element 8 are disposed so as to face the exit surface lens 15. The light beam emitted from the exit surface lens 15 enters the distance measuring element 8 via the split prism 7. The image pickup element 5 and the prism block 4 may be separate bodies, but since the optical interface is reduced by integration (may be bonding), ghost, flare, reduction of transmitted light amount, etc. Can be suppressed. Note that the embodiment shown in FIG. 1 described above corresponds to a configuration in which the exit surface lens 15 is omitted in FIG.

  The split prism 7 is bonded to the front surface of the distance measuring element 8. The prism block 4, the optical low-pass filter 26, the image sensor 5, the split prism 7 and the distance measuring element 8 are integrated with the housing 6 to form one image unit. Thus, by integrating the components of the imaging device 5 and the focus detection device into the housing 6, the components can be manufactured within tolerances, so that the accuracy after assembly can be easily secured and the mass productivity can be ensured. Is excellent.

  Since the wavelength selective reflecting mirror 3 acts as a lens tilted obliquely with respect to the optical axis, the spherical aberration increases the aberration due to decentration. Therefore, in order to suppress such aberration to be small, it is preferable to have a free-form surface shape having a refractive power distribution that is rotationally asymmetric with respect to the optical axis. Further, the exit surface lens 15 formed in the prism block 4 may have an effect of correcting aberrations.

  FIG. 7 is an optical path diagram corresponding to FIG. 3B described above. In the first modification, the exit surface lens 15 is disposed between the wavelength selective reflecting mirror 3 and the split prism 7. The subject light beam is refracted so as to be condensed by the photographing lens 1, but the distance measuring light beam reflected by the wavelength selective reflecting mirror 3 is once made into a substantially parallel light beam by the concave lens action of the wavelength selective reflecting mirror 3. . Thereafter, the enlarged image 14 is formed by being condensed by the exit surface lens 15.

  The distance measuring light beam is guided in the prism block 4 from the wavelength selective reflecting mirror 3 to the exit surface lens 15. However, by making the light substantially parallel, the parallel plate-like prism block 4 is totally reflected. It becomes easy to guide. That is, it is possible to reduce the proportion of the light beam that does not satisfy the total reflection condition. As a result, the degree of freedom regarding the layout of the split prism 7 and the distance measuring element 8 is increased, and the optical path length of the distance measuring system can be set longer while shortening the distance between the wavelength selective reflecting mirror 3 and the imaging element 5. The magnified image 14 can be formed outside the prism block 4.

[Modification 2]
In the first modification, a dichroic film that reflects the near infrared region is used as the wavelength selective reflecting mirror 3, but in the second modified example shown in FIG. 8, the hologram 28 is used in the wavelength selective reflecting mirror 3. The hologram 28 has the characteristics as shown in FIG. 5 described above, and acts as a concave lens with respect to the distance measuring light beam to make it substantially parallel light. The reflection angle of the hologram 28 is set so that the distance measuring light beam used for distance measurement is totally reflected by the front surface of the parallel flat prism block 4. The distance measuring beam is guided downward in the prism block 4 while repeating total reflection, and is reflected to the back side by an end face reflecting mirror 29 provided obliquely at the lower end of the prism block 4. An exit surface lens 15 is provided on the lower back surface of the prism block 4, and the distance measuring light beam is condensed by the exit surface lens 15 to form an enlarged image.

  In the second modification, by adjusting the refractive power of the exit surface lens 15, the image surface of the transmitted light and the image surface of the reflected light of the wavelength selective reflecting mirror 3 can be formed on substantially the same plane. As a result, as shown in FIG. 8, it is possible to mount the image sensor 5 and the distance measuring element 8 on the same rigid board 27, and it is necessary to connect both with the flexible board 25 as shown in FIG. It is excellent in assembly and cost. Further, by using the lower part of the prism block 4 as the waveguide 41 by total reflection, an enlarged image can be formed outside the prism block 4 even if the prism block 4 is thinned. As a result, the thickness dimension of the imaging unit integrated by the housing 6 can be reduced, and the camera can be further downsized.

[Modification 3]
FIG. 9 is a diagram showing a third modification, in which the single-plate image pickup device 5 is replaced with RGB three-plate image pickup devices 5R, 5G, and 5B. In the prism block 4, a dichroic mirror 4G that reflects G light and a dichroic mirror 5B that reflects B light are formed in addition to the wavelength selective reflecting mirror 3 that reflects light in the near infrared region. The G light in the luminous flux is reflected by the dichroic mirror 4G and enters the G light image sensor 5G, and the B light reflected by the dichroic mirror 4B enters the B light image sensor 5B. The R light transmitted through the dichroic mirror 4B passes through the wavelength selective reflection mirror 3 and enters the imaging element 5R for R light. On the other hand, the reflected light reflected by the wavelength selective reflection mirror 3 is totally reflected by the dichroic mirror 4B and emitted to the split prism 7 via the emission surface lens 15.

  Although the camera has been described as an example in the above-described embodiment, the focus detection apparatus according to the present invention can be applied to various imaging apparatuses. In the correspondence between the embodiment described above and the elements of the claims, the wavelength selective reflecting mirror 3 and the hologram 28 are the first optical element, the split prism 7 is the second optical element, and the distance measuring element 8 is The exit surface lens 15 constitutes a lens, and the prism block 4 constitutes an optical block. The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims.

It is a figure explaining one Embodiment of the focus detection apparatus by this invention, and shows schematic structure at the time of applying a focus detection apparatus to a camera. It is a figure which shows the reflective characteristic of the wavelength selection reflective mirror. It is a figure explaining an optical path, (a) shows the optical path of the light beam used for an imaging, (b) shows the optical path of the light beam used for ranging. It is a figure explaining the effect | action of the split prism 7, (a) shows a front pin state, (b) shows an in-focus state, (c) shows a back pin state, respectively. It is a figure which shows the wavelength of the light beam for ranging at the time of using a hologram. It is a figure which shows the modification 1, (a) shows sectional drawing of the focus detection apparatus mounted in the flexible substrate 25, (b) shows a top view. 10 is an optical path diagram in Modification 1. FIG. It is sectional drawing which shows the modification 2. It is sectional drawing which shows the modification 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shooting lens 3 Wavelength selective reflection mirror 4 Prism block 5, 5R, 5G, 5B Image pick-up element 7 Split prism 7R, 7L Prism 8 Distance measuring element 9 Control circuit 15 Exit surface lens 16R, 16L Sensor array 26 Optical low-pass filter 28 Hologram 41 Waveguide

Claims (6)

The light of a specific wavelength range included in the light that has passed through the photographing lens is separated as a focus detection light beam, and the photographing light beam outside the specific wavelength range is transmitted to the imaging surface for photographing, and the focus detection light beam A first optical element having a negative refractive power and forming an enlarged image of the image by the focus detection light beam;
A second optical element that is disposed at a position that is optically substantially equivalent to the imaging surface for imaging, and that separates the magnified image in a plurality of directions according to a focus adjustment state of the imaging lens;
A focus detection apparatus comprising: a detection unit that detects the enlarged image separated by the second optical element. The focus detection apparatus according to claim 1,
A focus detection apparatus, comprising: an optical block in which the first optical element and a waveguide that totally reflects the focus detection light beam and guides it to the second optical element are integrally formed. The focus detection apparatus according to claim 1 or 2,
The negative refractive power is set so that the separated focus detection light beam becomes substantially parallel light,
The focus detection light beam, which is disposed between the first optical element and the second optical element and is substantially parallel light, forms an image at a position optically substantially equivalent to the imaging surface for photographing. A focus detection apparatus further comprising a lens. The focus detection apparatus according to claim 3,
The focus detection apparatus characterized in that the lens is integrally formed on an exit surface of the focus detection light beam in the optical block. In the focus detection apparatus in any one of Claims 1-4,
The photographing light flux is photographed through a filter composed of filter elements having different spectral transmission characteristics,
A focus detection apparatus, wherein the first optical element is a hologram, and the hologram separates light in a wavelength region excluding a wavelength region near each transmittance peak of the filter element as the focus detection light beam. A focus detection apparatus according to any one of claims 1 to 5,
An image pickup apparatus comprising: an image pickup element that picks up a subject image by a light beam for photographing that has passed through the first optical element.

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