JP2007033653A - Focus detection device and imaging apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a focus detection device in which the focus adjustment state of a photographic lens is detected highly precisely by using so called an image blurring method. <P>SOLUTION: The focus detection device has: a secondary imaging system which forms a plurality of light quantity distributions of an object image by using luminous fluxes which pass through different regions of a pupil of the photographic lens; a photoelectric converter element which is provided with a plurality of pixel rows composed of a plurality of pixels and detects the plurality of light quantity distributions of the object image formed by the secondary imaging system; and a first and a second focus detection systems which derive the focusing condition of the photographic lens from the relative positions of the plurality of light quantity distributions. The chromatic aberrations of the first and the second focus detection systems are different from each other. The nature of a light source for illuminating the object is discriminated by comparing the first and the second focused values derived by correcting a first and a second detected focus values measured by the first and a second focus detection systems by a first and second correction values, and the first and the second correction values for correcting the first and the second detected focus values are varied on the basis of the discriminated result. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a focus detection apparatus and an imaging apparatus using the same, and more particularly, to detect a focus adjustment state of a photographic lens (objective lens) using a so-called image shift method (phase difference detection method). It is suitable for imaging devices such as cameras, single-lens reflex electronic cameras, digital cameras, and video cameras.

  Many photographic cameras or video cameras have a built-in focus detection device for automatic focus adjustment. In a focus detection device that requires strict focus accuracy such as a single-lens reflex camera, a focus detection device using a phase difference detection method is generally used (for example, Patent Document 1). In the phase difference detection method, a plurality of light quantity distributions related to an object image (subject image) are formed on a pixel row (line sensor row) of a photoelectric conversion element by a paired secondary imaging lens (secondary imaging system). In this method, the focus adjustment state of the objective lens is detected from the relative positional relationship between the two light quantity distributions.

  In the focus detection device of the phase difference detection method, the focus position read by the focus detection device may differ from the actual focus position (true focus position) of the photographic lens due to the aberration of the photographic lens. For this reason, a correction value for complementing this is provided for each photographing lens.

  In general, the photographic lens is not corrected for aberrations in the infrared wavelength region outside the visible region. For this reason, shooting is performed under illumination light in a wide wavelength range such as natural light containing a lot of infrared light as illumination light of an object (object) or a light beam from an incandescent lamp, and narrow such as a fluorescent lamp containing almost no infrared light. When shooting is performed under illumination light in the wavelength range, the way in which the aberration of the shooting lens is different is different, and the correction value for focus detection must be different.

  Therefore, in order to perform focus detection with high accuracy, it is necessary to detect the spectral characteristic (type of light source) of the light beam illuminated by the subject and adjust the correction value.

  Patent Documents 2 and 3 propose focus detection apparatuses that detect the type of light source that illuminates a subject and perform focus detection.

  In Patent Document 2, two sensors, a sensor having sensitivity in the infrared part and a sensor having sensitivity in the visible part, are prepared, and the light source is a fluorescent lamp by comparing the intensity of the output signal from each sensor. Or not.

In Patent Document 3, the type of light source is determined by detecting a high-frequency component (flickering, flicker) of a fluorescent lamp.
JP 2001-66496 A JP 2001-337263 A JP 62-047017 A

  In the focus detection device proposed in Patent Document 2, a new unit must be prepared for detection of a fluorescent lamp, and a complicated device is required. As a result, the weight of the camera increases.

  The focus detection device detected in Patent Document 3 can use an existing photometric sensor or the like, but is insufficient in terms of focus detection accuracy. For example, since many fluorescent lamps in recent years have little flicker, there is a possibility that the light source is erroneously determined. In addition, illumination light from a fluorescent lamp and natural light exist together, and flicker is detected and the light source may be mistakenly determined even under a situation where natural light is dominant.

  In order to increase the focus detection accuracy, the difference in the spectral characteristics of the illumination light that illuminates the subject without complicating the apparatus is appropriately determined, that is, the type of the light source means is determined, and the focus correction value corresponding thereto is determined. It is important to use

  It is an object of the present invention to provide a focus detection device capable of improving focus detection accuracy and an imaging device using the focus detection device.

A focus detection apparatus according to a first aspect of the present invention includes a secondary imaging system that forms a plurality of light quantity distributions related to an object image using light beams that have passed through different areas of the pupil of the photographing lens,
A photoelectric conversion element including a plurality of pixel rows each including a plurality of pixels, which detects a plurality of light quantity distributions related to an object image formed by the secondary imaging system;
A first and second focus detection system for obtaining an imaging state of the photographing lens from a relative positional relationship of the plurality of light quantity distributions,
The chromatic aberrations of the first and second focus detection systems are different from each other,
A light source for illuminating an object by comparing the first and second focus values obtained by correcting the first and second focus detection values actually measured by the first and second focus detection systems with the first and second correction values. Determine the type
Based on the determination result, the first and second correction values for correcting the first and second focus detection values are changed.

  According to the present invention, it is possible to obtain a focus detection apparatus that can perform focus detection with high accuracy.

  FIG. 1 is a configuration diagram of Embodiment 1 in which the focus detection apparatus of the present invention is applied to a single-lens reflex camera. In FIG. 1, the inside of the paper is the vertical direction (vertical direction), and the direction perpendicular to the paper is the horizontal direction (horizontal direction).

  In FIG. 1, 21 is a photographic lens that can be attached to and detached from the camera body CB, 11 is a pupil of the photographic lens 21, and 11a is a pupil diameter.

  La is the optical axis of the taking lens 21. The light beam incident along the optical axis La reaches the quick return mirror 22 having a semi-transmissive portion, and is divided into two light beams of reflected light and transmitted light.

  On the reflection side, a focusing screen 23, a pentaprism 24, and an eyepiece lens 25 are arranged along the optical axis La, and these members constitute a finder system for visualizing a finder image formed on the focusing screen 23.

  On the other hand, on the transmission side of the quick return mirror 22, a movable sub mirror 26 and a phase difference type focus detection system (focus detection device) FD are arranged along the optical axis La. At the time of automatic focus detection, based on the output from the focus detection system FD, the focus portion of the photographic lens 21 is driven by a drive mechanism (not shown) to adjust the focus state.

  Details of the focus detection system FD will be described. Reference numeral 2 denotes a field mask having a horizontally long opening placed at or near the focal plane of the photographing lens 21.

  4 is an aperture having openings 4a and 4b, 5 is a secondary imaging system for forming a secondary image relating to the subject image, and 6 is a plurality of light sources for detecting the light quantity distribution (image shift) of the secondary image relating to the subject image. This is a photoelectric conversion element (sensor) composed of the above elements.

  Each element from the field mask 2 to the secondary imaging system 5 constitutes a secondary imaging system.

  In this embodiment, a secondary optical system 2 that forms a plurality of pairs of quantity distributions including two or more pairs in the horizontal direction with respect to a subject image using light beams that have passed through different regions 11b1 and 11b2 of the pupil 11 of the photographing lens 21. -5 and a plurality of pairs of photoelectric conversion elements 6 that respectively detect the relative positional relationship of the plurality of pairs of light quantity distributions, and the focal position of the photographic lens 21 is publicly known using signals from the photoelectric conversion elements 6 This is detected using the phase difference detection method.

  FIG. 2A is an explanatory diagram of a light beam range used by the focus detection device in a light beam range used by the photographing lens 21 at the exit pupil 11 of the photographing lens 21. FIG. 2B is an explanatory diagram showing the positions of the focal points corresponding to the respective light beams in FIG.

  In FIG. 1A, the maximum circle 11 a is the total luminous flux range that passes through the exit pupil 11 of the photographing lens 21, and is the luminous flux range that is used by the photographing lens 21.

  In FIG. 1B, the focal point P1 where the light beam passing through the regions 11b1 and 11b2 is condensed differs from the focal point Q1 where the light beam passing through the entire pupil 11a is condensed. The difference Δ at this time is caused by the aberration of the taking lens.

  The focus detection apparatus uses ranges 11b1 and 11b2 indicated by oblique lines in the exit pupil 11a. A photographic lens generally has spherical aberration. For this reason, in a focus detection apparatus that uses a light beam having a low height from the optical axis, a position different from the focus position of the photographing lens using all light beams is determined as the focus position (focus detection value). End up. In order to eliminate this difference, each photographing lens and the camera using the same store a correction value for correcting the focus error, and the focus value obtained by correcting the actually measured focus detection value with the correction value is stored. Used.

  In the focus detection operation, when the subject is dark in order to improve the focusing accuracy, light may be projected onto the subject from the camera side. The light used at this time uses infrared light outside the visible range (wavelength 700 to 800 nm), for example, infrared light from an infrared light emitting diode, in order to avoid an influence on the photographing composition. Therefore, the infrared cut filter used in the optical path of the focus detection device transmits infrared light having a longer wavelength than the infrared cut filter used on the light incident side of the imaging sensor.

  Various aberrations of the photographing lens are designed so as to be corrected in the visible region (wavelength 400 to 700 nm). For this reason, many aberrations remain in the infrared region. FIG. 3 is a conceptual diagram of spherical aberration of a photographic lens. SA1 is a spherical aberration in the visible region, and SA2 is a spherical aberration in the infrared region. As can be seen from FIG. 3, the spherical aberration in the visible region exists near the center of the coordinates (Gauss image plane), whereas the spherical aberration in the infrared region deviates greatly from the center. As described above, the difference between the focal position of the photographing lens and the focal position detected by the focus detection apparatus is mainly caused by aberration. For this reason, the focal position detected in the infrared region is greatly different from the focal position detected in the visible region.

  FIG. 4 is a graph showing the wavelength-dependent intensity of a typical light source and sunlight used for photographing. The horizontal axis represents wavelength, and the vertical axis represents light emission intensity.

  Each line is for the sun, an incandescent lamp or a fluorescent lamp. In view of the influence on the detection error of the focal position, a distinction should be made between the case where the light source contains a lot of infrared light and the case where it hardly contains the infrared light for the reasons described above. Here, natural light or light from an incandescent lamp is a light source that contains a lot of infrared light, and light from a fluorescent lamp is a light source that contains almost no infrared light. In the first embodiment, when the two types of light sources are discriminated at the time of photographing and the focal position is obtained, the difference in the focal position (focus detection error) due to the difference of the light sources is reduced by using a correction value corresponding to each section. is doing.

  FIG. 5 is a conceptual diagram of a part of a focus detection apparatus using a phase difference method.

  A primary imaging plane 3 that is optically equivalent to the imaging plane, a diaphragm 4 having two openings 4a and 4b that divide the light beam that has passed through the primary imaging plane 3 into two regions, and a diaphragm 4 The secondary image forming system 5 includes a pair of lenses 5a and 5b for forming an image of the secondary object images 6a and 6b based on the light passing through the apertures 4a and 4b on the line sensor 6.

  The focal position is determined by the interval (relative shift amount) between the two secondary object images 6a and 6b projected through the openings 4a and 4b of the stop 4 and projected onto the line sensor 6. For example, when the distance between the two secondary object images 6a and 6b is wider than a preset reference value, the rear pin is in focus (in a state where the subject is originally focused on), and when the distance is narrow, the front pin is (A state in which the subject is originally focused on and in focus).

  FIG. 6 is an explanatory diagram of one lens 5a of the secondary imaging system 5 for adjusting the chromatic aberration of the photographing lens during focus detection. The lens 5a of FIG. 6 is configured by arranging a prism 5a1 on the front surface (light incident side) and a lens 5a2 on the rear surface. The prism action is caused by the angle of the prism 5a1 and the eccentricity of the lens 5a2 in the vertical direction on the paper surface, and the imaging position on the line sensor 6 is changed depending on the wavelength.

  Here, the light beam 9 having a long wavelength is refracted inward and the light beam 8 having a short wavelength is refracted outward. When light having a long wavelength is incident on the secondary imaging system 5 in which chromatic aberration is generated by such a prism action, two secondary object images 6a, 6a, The interval of 6b becomes narrow and shows the tendency of a front pin more. On the other hand, when short-wavelength light is incident, the interval between the two secondary object images 6a and 6b is widened as opposed to when long-wavelength light is incident, and a tendency toward a rear pin is exhibited.

  FIG. 7 is a conceptual diagram of a part of the focus detection apparatus according to the first embodiment. In FIG. 6, the chromatic aberrations of the two focus detection systems 71 and 72 are different from each other, and the detected focal positions are different depending on the wavelength.

  Further, since the two focus detection systems 71 and 72 need to measure substantially the same distance (the same region of the object), the light rays taken into the line sensors 61 and 62 are almost the same place on the primary imaging plane 3. Each member is arranged to pass through.

  The prism action of the secondary imaging system 51 of the focus detection system 71 is larger than the prism action of the secondary imaging system 52 of the focus detection system 72.

  In this embodiment, the chromatic aberrations of the two focus detection systems 71 and 72 are made different.

  The two focus detection systems 71 and 72 according to the present embodiment have two different prisms depending on whether the light incident on the line sensors 61 and 62 includes many or almost no long wavelengths. The amount of focus deviation (focus signal) derived from the two focus detection systems 71 and 72 changes. As a result, the type of light source can be detected.

  Hereinafter, the flow of focus detection in this embodiment will be described based on the flow of FIG.

  When focus detection is performed, the focus shift amount (first focus detection value) output from one focus detection system 71 is output from AF1 and the other focus detection 72 having chromatic aberration different from that of the focus detection system 71. The amount of focus shift (second focus detection value) is AF2.

  Under a specific light source (reference light source), correction values for eliminating the difference between the output value and the actual focus value (true focus position) are first and second correction values C1 and C2, respectively. Adjustments are made under a reference light source and stored in storage means in the taking lens or in the camera body.

  This time, for example, sunlight containing a large amount of infrared light is used as a light source as a reference light source. Compared with the focus detection system 71 that outputs the first focus detection value AF1, the focus detection system 72 that outputs the second focus detection value AF2 has a prism action that bends the long wavelength closer to the optical axis (inward) than the short wavelength. (The amount of spherical aberration toward the infrared region is large).

  Next, a flow for determining whether or not the light source is the reference light source when actually performing focus detection (whether or not the spectral characteristic of the illumination light has the reference distribution) will be described. When the light source for photographing includes a lot of infrared light, a value obtained by adding the focus detection value AF1 and the correction value C1 (first focus value), and a value obtained by adding the focus detection value AF2 and the correction value C2. Since the (second focus value) is adjusted with a reference light source that contains a large amount of infrared light, the second focus value is approximately the same.

  On the other hand, if the light source at the time of photographing is a light source that hardly contains infrared light, for example, a fluorescent lamp, the first focus detection value AF1 is derived from the prism action difference between the first focus detection value AF1 and the second focus detection value AF2. And the value obtained by adding the correction value C1 (first focus value) is a rear pin (larger) than the value obtained by adding the second focus detection value AF2 and the second correction value C2 (second focus value). Indicates.

  Whether the light source is a fluorescent lamp or a light source close to the reference light source can be determined from determining whether the difference Δ between the first focus value and the second focus value is greater than or equal to a threshold value (δ).

  When photographing under a fluorescent lamp according to this determination, focus detection is performed using correction values C′1 and C′2 that are different from the correction values C1 and C2.

  A series of these operations is performed by a calculation means in the camera body. Then, the focusing operation is performed by driving the focusing lens using at least one of the first and second focusing values obtained from the two focus detection systems.

  In this embodiment, the number of threshold values (δ) is not limited to one, and several types of threshold values (δ) may be provided. According to this, a large number of light sources can be detected, and focus detection can be performed with high accuracy.

  As described above, in this embodiment, the first focus detection system that detects the focus by the phase difference detection method and the second focus detection system that detects the focus by the phase difference detection method to which chromatic aberration different from the first focus detection system is added. And using the outputs from the first and second focus detection systems, it is determined whether or not the illumination means for illuminating the subject is a light source including a large amount of infrared region, and the focus value corrected according to the determination is used. Thus, a highly accurate focusing operation is performed.

  As described above, according to the present embodiment, since the output from the focus detection system changes according to the difference in illumination means (light source), it is possible to detect natural light or light from a fluorescent lamp by determining the change. Is possible. After the illuminating means is determined, the focus value (focus position) is obtained using correction values depending on the illumination means, thereby enabling more accurate focus detection (ranging).

Explanatory drawing of the imaging device which has the focus detection apparatus of this invention (A) The conceptual diagram showing the difference of the light beam used for imaging | photography on an exit pupil surface, and the light beam (diagonal line) used by a focus detection system of a certain imaging lens. (B) The conceptual diagram showing the difference in the focus position in the light beam of a photographic lens and a focus detection system. The typical spherical aberration figure of a taking lens. Wavelength dependence of the intensity of luminous flux emitted from various light sources. The conceptual diagram of the focus detection apparatus using a phase difference detection system. The conceptual diagram showing the difference in the imaging position depending on the difference in wavelength. The conceptual diagram of the focus detection apparatus which performs light source detection in this invention. The figure showing the flow for performing light source detection and focus detection.

Explanation of symbols

SA1 Visible region aberration SA2 Infrared aberration 2 Field mask 3 Primary imaging plane 4 Aperture 5 Secondary imaging system 6 Sensors 71 and 72 Secondary imaging system 8 Long-wavelength light path 9 Short-wavelength light path Path 21 Photo lens

Claims (5)

A secondary imaging system that forms a plurality of light quantity distributions related to the object image using light beams that have passed through different areas of the pupil of the taking lens;
A photoelectric conversion element including a plurality of pixel rows each including a plurality of pixels, which detects a plurality of light quantity distributions related to an object image formed by the secondary imaging system;
A first and second focus detection system for obtaining an imaging state of the photographing lens from a relative positional relationship of the plurality of light quantity distributions,
The chromatic aberrations of the first and second focus detection systems are different from each other,
A light source for illuminating an object by comparing the first and second focus values obtained by correcting the first and second focus detection values actually measured by the first and second focus detection systems with the first and second correction values. Determine the type
A focus detection apparatus that changes values of first and second correction values for correcting the first and second focus detection values based on a determination result. The region of the object that performs focus detection in the first and second focus detection systems is the same,
The focus detection apparatus according to claim 1, wherein the first and second focus detection systems use light beams that pass through the same region of the pupil of the objective lens.   3. The focus detection apparatus according to claim 1, wherein the first and second focus detection systems are provided with prisms having different prism apex angles in the optical path.   An imaging apparatus comprising: the focus detection apparatus according to claim 1; and an in-focus lens of an objective lens that is driven based on a focus signal obtained by the focus detection apparatus. A secondary imaging system that forms a plurality of light quantity distributions related to the object image using light beams that have passed through different areas of the pupil of the taking lens;
A photoelectric conversion element including a plurality of pixel rows each including a plurality of pixels, which detects a plurality of light quantity distributions related to an object image formed by the secondary imaging system;
A first focus detection system and a second focus detection system for determining an imaging state of the photographing lens in the same region of the object from a relative positional relationship of the plurality of light quantity distributions;
The chromatic aberrations of the first and second focus detection systems are different from each other,
Having first and second correction values for correcting the first and second focus detection values actually measured in the first and second focus detection systems,
Comparing the first and second focus values obtained by correcting the first and second focus detection values with the first and second correction values to determine the type of illumination means on which the object is illuminated;
A focus detection system comprising: an arithmetic unit that changes values of the first and second correction values for correcting the first and second focus detection values based on a determination result.