Image pickup apparatus control method thereof and image pickup system

An image-pickup apparatus (1) includes a light projection part (32, 33) projecting light to an object, a focus detection part (26) detecting a focus state, a light-source detection part 31 detecting information relating to a light source. When a focus detection is performed without lighting of the light projection part, a controller (100) generates information used for focusing control based on a focus state detection result and the information relating to the light source. When the focus detection is performed with lighting of the light projection part, the controller generates the information used for the focusing control based on the focus state detection result and correction information depending on a wavelength of the light projected from the light projection part without using the information relating to the light source. Thus, a highly-accurate AF control can be performed under various light sources including an AF assist light.

TECHNICAL FIELD

The present invention relates to an image-pickup apparatus performing focusing control. More particularly, the present invention relates to an image-pickup apparatus that performs the focusing control depending on a determination result of a light source.

BACKGROUND ART

As an auto focusing (AF) method for an image-pickup apparatus such as a digital single-lens reflex camera, a so-called Through The Lens (TTL) phase-difference detection method has been known. In a camera using the TTL phase-difference detection method, light coming through an image-pickup lens is separated by a light-separating member such as a mirror and transmitted light is guided to an image-pickup system and reflected light is guided to a focus detection system.

As described above, in the camera using the TTL phase-difference detection method, the image-pickup system and the focus detection system are separately provided. This causes a problem as described below.

In the case of a general silver halide film, the image-pickup system generally has the highest spectral sensitivity characteristics to light of about 400 to 650 nm in order to provide the color reproducibility suitable for characteristics of human eyes.

On the other hand, silicon photo diode constituting an image-pickup device such as a CMOS sensor used for the image-pickup system generally has a sensitivity peak of about 800 nm and has the sensitivity up to about 1100 nm at the long-wavelength side.

However, in order to place importance on color reproducibility, light having a wavelength beyond the frequency range is blocked, causing some sacrifice in the sensitivity.

In the case of a photoelectric conversion device using the phase-difference detection method that is a sensor performing a focus detection, the sensitivity is generally up to about 1100 nm.

However, many photoelectric conversion devices have the sensitivity higher than 1100 nm by 100 nm in order to perform the focus detection even to a low luminance object and to allow a camera to project AF assist light in a near-infrared region (about 700 nm) under a low luminance to an object to perform an accurate focus detection.

FIG. 9shows light-dividing sensitivities of various light sources, the image-pickup device, and the assist light. The horizontal axis represents a wavelength and the vertical axis represents a relative focal point depending on chromatic aberration of relative energy or lens.

InFIG. 9, C denotes the chromatic aberration of the image-pickup lens and B, G, and R denote light-dividing sensitivities of a blue pixel, a green pixel, and a red pixel of a primary-color-type image pickup device, respectively. F denotes a fluorescent light. L denotes a photoflood lamp. A denotes the light-dividing sensitivity of the above-described assist light.

As can be seen fromFIG. 9, while the wavelength component of the fluorescent light includes substantially no wavelength components longer than 620 nm, the photoflood lamp shows a higher relative sensitivity toward the longer wavelength side.

On the other hand, the chromatic aberration C of the lens shows a different focal point depending on the wavelength and a longer focal length toward the longer wavelength side.

Thus, when the focus detection sensor having the highest sensitivity at 700 nm is used, the fluorescent light and the photoflood lamp having less long wavelength components cause a difference in detected focal points, causing a focal shift in the image-pickup device.

With regard to the problem described above in which the focal point detected by the focus detection system is shifted depending on the light-dividing sensitivity of the light source, a camera correcting the focal point is disclosed in Japanese Patent Laid-Open No. 2000-275512.

This camera compares outputs of two types of sensors having different light-dividing sensitivities to determine the type of the light source to correct the focal point to correct the focal shift due to the light-dividing characteristic.

Japanese Patent Laid-Open No. 62-174710 discloses a method in which the chromatic aberration amount of an interchangeable lens is stored in a memory in the lens and the defocus correction amount is calculated by multiplying a predetermined coefficient with the lens chromatic aberration amount based on the determination result of the type of the light source.

However, in the case of the auto-focusing cameras disclosed in Japanese Patent Laid-Open No. 2000-275512 and Japanese Patent Laid-Open No. S62-174710, a problem is caused where, when the type of the light source is determined while projecting the AF assist light, the focal point may be corrected in a wrong manner.

The focal shift due to the light-dividing wavelength when the AF assist light is projected will be described with reference toFIG. 10andFIG. 11.FIG. 10shows a relationship between a contrast pattern of the AF assist light and a position of the view field of the AF sensor (AF view field).

FIG. 11shows pixel information obtained by the AF sensor when the AF assist light ofFIG. 10is projected. The horizontal axis represents a pixel position and the vertical axis represents the signal intensity of a pixel.

It is assumed that there is no contrast of an object and there is no contrast of pixel information only due to ambient light. The ambient light is assumed as light other than illumination light (AF assist light) from the camera side.

The AF assist light projects a predetermined contrast pattern light on ambient light and thus the AF assist light forms a contrast in pixel information. AF is performed based on this contrast.

In other words, when there is no object contrast or a low object contrast, the detection of a defocus amount is performed based on the contrast by the AF assist light. Thus, a focal shift due to the wavelength of only the AF assist light is caused.

Thus, in the case described above in which there is no object contrast or a low object contrast and the AF assist light is projected, the determination of the type of the light source must be subjected to the correction based on the wavelength of only the AF assist light except for the ambient light.

However, in the case of the auto-focusing cameras disclosed in Japanese Patent Laid-Open No. 2000-275512 and Japanese Patent Laid-Open No. S62-174710, the operation for the determination of the light source when the AF assist light is projected is not taken into consideration.

Furthermore, the auto-focusing cameras also cause, when the type of the light source is determined while projecting the AF assist light, the light source mixed with not only the AF assist light but also the ambient light to be determined, causing a wrong focal point correction.

The present invention provides an image-pickup apparatus, an image-pickup system, and a method for controlling an image-pickup apparatus by which a highly-accurate AF control can be performed under various light sources including the AF assist light.

DISCLOSURE OF INVENTION

An image-pickup apparatus as one aspect of the present invention includes a light projection part projecting light to an object, a focus detection part detecting a focus state of an image-pickup optical system, a light-source detection part detecting information relating to a light source, and a controller generating information used for focusing control of the image-pickup optical system.

When a focus detection is performed without lighting of the light projection part, the controller generates the information used for the focusing control based on a detection result of the focus state and the information relating to the light source, when the focus detection is performed with lighting of the light projection part, the controller generates the information used for the focusing control based on the detection result of the focus state and correction information depending on a wavelength of the light projected from the light projection part without using the information relating to the light source.

An image-pickup system including the image-pickup apparatus and an interchangeable lens that can be attached to and detached from the image-pickup apparatus also constitutes another aspect of the present invention.

Another aspect of the present invention is a method for controlling an image-pickup apparatus having a light projection part projecting light to an object, a focus detection part detecting a focus state of an image-pickup optical system, and a light-source detection part detecting information relating to a light source. The method includes a first step of performing a focus detection without lighting of the light projection part and a second step of performing the focus detection with lighting of the light projection part. The first step generates information used for the focusing control based on a detection result of the focus state and the information relating to the light source. The second step generates the information used for the focusing control based on the detection result of the focus state and correction information depending on a wavelength of the light projected from the light projection part without using the information relating to the light source.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1shows a single-lens reflex camera system (image-pickup system) that is Embodiment 1 of the present invention. This camera system is constituted by a single-lens reflex camera (image-pickup apparatus)1and an interchangeable lens (lens apparatus)11detachably attached to the camera1.

InFIG. 1, the camera1stores therein an optical component, a mechanical component, an electric circuit, and an image-pickup device (or a film) for example so that an image (or a photograph) can be picked up.

Reference numeral2denotes a main mirror. The main mirror2is obliquely placed in an image-pickup optical path in a finder observation state and is retracted out of the image-pickup optical path in a photographing state.

The main mirror2serves as a half mirror. The main mirror2allows about a half of light flux from the object to be transmitted to a focus detection optical system (which will be described later) when being placed in the image-pickup optical path.

Reference numeral3denotes a focusing screen. The focusing screen3constitutes a part of a finder optical system and is placed at a predetermined image-forming plane of an image-pickup optical system (which will be described later).

Reference numeral4denotes a pentagonal prism for changing a finder light path. Reference numeral5denotes an eye piece. A photographer can observe the focusing screen3through a window of this eye piece to observe an object image.

Reference numerals6and7denote the first image-forming lens and a photometry sensor for measuring the object luminance within a finder observation screen. Reference numerals30and31denote the second image-forming lens and a light-source detection sensor for measuring the object luminance within the finder observation screen.

Reference numeral8denotes a focal-plane shutter. Reference numeral9denotes an image-pickup device and is constituted by a CCD sensor or a CMOS sensor.

Reference numeral25denotes a sub mirror. The sub mirror25is obliquely placed together with the main mirror2in the image-pickup optical path in a finder observation state and is evacuated out of the image-pickup optical path in an image pickup state.

This sub mirror25bends the light flux transmitted through the main mirror2placed within the image-pickup optical path in the lower direction to guide the light flux to a focus detection unit (which will be described later).

Reference numeral26denotes the focus detection unit. The focus detection unit26is constituted by the secondary image-forming mirror27, the secondary image-forming lens28, and a focus detection sensor29.

The secondary image-forming mirror27and the secondary image-forming lens28constitute the focus detection optical system and form the secondary imaging surface of the image-pickup optical system on the focus detection sensor29.

The focus detection unit26uses the so-called phase-difference detection method to detect the focus state of the image-pickup optical system (pixel information having a phase difference) to transmit the detection result to a camera microcomputer.

Reference numerals32and33denote a projection lens and an AF assist light source constituting a light projection part. Lighting the AF assist light source33causes the AF assist light having the contrast pattern to be projected to the object.

Reference numeral10denotes a mount contact point group that serves as a communication interface between the camera1and the interchangeable lens11.

Reference numerals12to14denote lens units. The first lens unit (hereinafter referred to as focus lens)12is moved on an optical axis to perform focusing. The second lens unit13is moved on the optical axis to change the focal length of the image-pickup optical system to vary the magnification.

Reference numeral18denotes a distance encoder. The sliding of a brush19attached to the focus lens12on the distance encoder18reads the position of the focus lens12to generate a signal corresponding to the position information.

Next, with reference toFIG. 2, the electric circuit architecture of the camera system will be described. InFIG. 2, the same components as those ofFIG. 1are denoted with the same reference numerals.

First, the circuit configuration in the camera1will be described. A camera microcomputer100is connected with the focus detection sensor29, a photometry sensor7, the light-source detection sensor31, a shutter control circuit107, a motor control circuit108, and a liquid-crystal-display circuit111.

The camera microcomputer100communicates with a lens microcomputer150placed in the interchangeable lens11via a mount contact point10.

The light-source detection sensor31has two sensors of a visible light sensor311and an infrared light sensor312having different light-dividing wavelengths.

The light-source detection sensor31performs a charge accumulation control and a charge readout control to the visible light sensor311and the infrared light sensor312based on the signal from the camera microcomputer100. Then, the light-source detection sensor31outputs luminance information obtained from the respective sensors311and312to the camera microcomputer100.

The camera microcomputer100subjects the luminance information to an A/D conversion to generate a ratio between luminance values (luminance ratio) detected by the visible light sensor311and the infrared light sensor312as the information relating to the light source. This operation is also called as the light source detection operation.

The focus detection sensor29is constituted by a pair or a plurality of pairs of CCD line sensors and performs the charge accumulation control and the charge readout control of the line sensors in accordance with the signal from the camera microcomputer100.

Then, the focus detection sensor29outputs the pixel information (information representing two images formed on the pair of line sensors) from the respective line sensors to the camera microcomputer100.

The camera microcomputer100subjects the pixel information to the A/D conversion and detects the phase difference of the pixel information. Then, the camera microcomputer100calculates the defocus amount of the image-pickup optical system (i.e., the information used for the focusing control) based on the phase difference.

Then, the camera microcomputer100performs, as required, the correction depending on the light source of the defocus amount or the AF assist light as will be described later in detail.

Then, based on the defocus amount and the focus sensitivity information of the image-pickup optical system for example, the camera microcomputer100calculates the driving amount of the focus lens12(the driving amount of the focus driving motor16) for obtaining an in-focus state.

The driving amount information of the focus lens12is transmitted to the lens microcomputer150. The lens microcomputer150controls the focus driving motor16in accordance with the received driving amount information. As a result, the AF control in the interchangeable lens11is performed and the in-focus state is obtained.

The AF assist light source33projects the AF assist light having a specific contrast pattern to the object based on the signal from the camera microcomputer100. This contrast pattern light provides an easier focus detection even when the object is dark or when there is no contrast.

The shutter control circuit107performs the energization control of a shutter front curtain driving magnet MG-1and a shutter rear curtain driving magnet MG-2constituting a focal-plane shutter8based on the signal from the camera microcomputer100. As a result, the front curtain and the rear curtain of the shutter are run and an image-pickup device9(or a film) is exposed.

The motor control circuit108controls a mirror driving motor M based on the signal from the camera microcomputer100. As a result, the up and down operations of the main mirror2and the charge operation of the focal-plane shutter8for example are performed.

SW1denotes a switch that is turned on by the first stroke (halfway depression) operation of a not-shown release button to start the photometry and the AF.

SW2denotes a switch that is turned on by the second stroke (full depression) operation of the release button to start the shutter running (i.e., exposure operation).

The camera microcomputer100reads not only the states of the switches SW1and SW2but also the states of not-shown operation members such as an ISO sensitivity setting switch, an aperture stop setting switch, and a shutter speed setting switch.

The liquid-crystal-display circuit111controls an in-finder indicator24and an external indicator42based on the signal from the camera microcomputer100.

Next, the electric circuit architecture in the interchangeable lens11will be described. As described above, the interchangeable lens11and the camera1are electrically connected to each other via the mount contact point10.

This mount contact point10includes a contact point L0that is a power source contact point for the focus driving motor16and an aperture stop driving motor17in the interchangeable lens11, a power source contact point L1of the lens microcomputer150, and a clock contact point L2for performing serial data communication.

The mount contact point10also includes a data transmission contact point L3from the camera1to the interchangeable lens11, a data transmission contact point L4from the interchangeable lens11to the camera1, a motor ground contact point L5to a motor power source, and a ground contact point L6to a power source for the lens microcomputer150.

The lens microcomputer150is connected to the camera microcomputer100via the mount contact point10and controls the focus driving motor16and the aperture stop driving motor17based on the signal from the camera microcomputer100. Thus, focusing and light amount adjustment are performed.

Reference numerals50and51denote a light detector and a pulse plate. The pulse plate51is rotated by the focus driving motor16. When the pulse plate51is rotated, the light detector50intermittently receives detection light to output pulse signals.

The lens microcomputer150counts the pulse number from the light detector50to obtain the position information of the focus lens12during the focusing.

The lens microcomputer150controls the focus driving motor16so that the position information of the focus lens12corresponds to the driving amount of the focus lens12for obtaining an in-focus state, which has been transmitted from the camera microcomputer100, thereby performing focusing.

Reference numeral18denotes the above-described distance encoder. The position information of the focus lens12read by the distance encoder18is input to the lens microcomputer150. The lens microcomputer150converts the position information to object distance information to send the object distance information to the camera microcomputer100.

Next, with reference toFIG. 3, the light-dividing characteristics of the visible light sensor311and the infrared light sensor312will be described. InFIG. 3, the horizontal axis represents a wavelength (nm) and the vertical axis represents the intensity. A denotes the light-dividing sensitivity characteristic of the visible light sensor311and B denotes the light-dividing sensitivity characteristic of the infrared light sensor312.

As can be seen fromFIG. 3, the visible light sensor311mainly detects light in a visible light region and the infrared light sensor312mainly has a peak sensitivity in a near-infrared region to detect light in a long wavelength region.

Next, the AF operation of the camera system of the embodiment will be described with reference to a flowchart ofFIG. 4. The AF operation is mainly executed by the camera microcomputer100as a controller based on a computer program.

When the SW1of the camera1shown inFIG. 2is turned on, the operation is started with Step101(shown as S in the drawings). The camera microcomputer100causes the charge accumulation by the focus detection sensor29to be performed and causes the pixel information depending on the focus state of the image-pickup optical system to be generated.

In Step102, the camera microcomputer100calculates the defocus amount of the image-pickup optical system based on the obtained displacement of the pixel information (phase difference).

In Step103, the camera microcomputer100calculates a reliability evaluation value of the pixel information obtained in Step101to determine the reliability of the detection result of the defocus amount calculated in Step102.

When the calculated reliability evaluation value is equal to or higher than a predetermined value, the camera microcomputer100determines that the detection result has a high reliability to proceed to Step104.

On the other hand, when the reliability evaluation value is lower than the predetermined value, the camera microcomputer100determines that the detection result has a low reliability to proceed to Step109to perform the AF operation by projecting the AF assist light.

The reliability evaluation value can be a difference between the detected maximum value and minimum values of the pixel information (amplitude of the pixel information) or an integration value obtained by the integration of differences in the level of neighboring pixel signals (the contrast of the pixel information).

In Step104, the camera microcomputer100requests the lens microcomputer150to transmit the chromatic aberration amount data unique to the interchangeable lens (the image-pickup optical system). This request is transmitted to the lens microcomputer150via serial communication lines LCK, LDO, and LDI shown inFIG. 2.

On receiving the request, the lens microcomputer150firstly analyzes the contents of the request (communication).

When the request is the request for the transmission of the chromatic aberration amount data, the lens microcomputer150reads the chromatic aberration amount data depending on the current focal length and focus lens position of the image-pickup optical system from a not shown ROM table in the lens microcomputer150.

The chromatic aberration amount data is previously measured to correspond to the focal length and focus lens position for each interchangeable lens and is stored in the ROM table. The lens microcomputer150returns the chromatic aberration amount data to the camera microcomputer100via the serial communication lines LCK, LDO, and LDI.

In Step105and106, the camera microcomputer100drives the light-source detection sensor31and reads the luminance information from the visible light sensor311and the infrared light sensor312.

Then, the camera microcomputer100calculates the ratio of pieces of the luminance information from the visible light sensor311and the infrared light sensor312(i.e., luminance ratio) to read the correction coefficient from the table shown inFIG. 7in accordance with the luminance ratio (infrared light/visible light).

In Step107, the camera microcomputer100multiplies the chromatic aberration amount data obtained in Step104with the correction coefficient calculated in Step106to calculate the first correction amount (the first correction information) that is the chromatic aberration amount data after the light source correction.

In Step108, the camera microcomputer100adds the multiplication result (the first correction amount) in Step107to the defocus amount calculated in Step102to correct the defocus amount to calculate the defocus amount after the light source correction (hereinafter referred to as a light-source-corrected defocus amount).

To correct the defocus amount is to generate a new defocus amount (the light-source-corrected defocus amount). In this context, to correct the defocus amount in this embodiment can be restated to generate the defocus amount.

On the other hand, in Steps109,110, and111, the camera microcomputer100drives the AF assist light source33and projects the AF assist light having the contrast pattern to a not shown object.

Then, the camera microcomputer100causes the charge accumulation by the focus detection sensor29to be performed and causes the pixel information depending on the focus state of the image-pickup optical system to be generated. Thereafter, the camera microcomputer100stops the driving of the AF assist light source33.

In Step112, the camera microcomputer100calculates the defocus amount of the image-pickup optical system based on the obtained displacement of the pixel information (phase difference).

In Step113, the camera microcomputer100calculates the reliability evaluation value of the pixel information obtained in Step110to determine the reliability of the detection result of defocus amount calculated in Step112.

When the calculated reliability evaluation value is equal to or higher than the predetermined value, the camera microcomputer100determines that the detection result has a high reliability to proceed to Step114.

On the other hand, when the reliability evaluation value is lower than the predetermined value, the camera microcomputer100determines that the detection result has a low reliability to set AF-NG and then completes the AF operation.

In Step114, the camera microcomputer100requests the lens microcomputer150to transmit the chromatic aberration amount data unique to the interchangeable lens (the image-pickup optical system). This request is transmitted to the lens microcomputer150via the serial communication lines LCK, LDO, and LDI shown inFIG. 2.

On receiving the request, the lens microcomputer150firstly analyzes the contents of the request (communication).

When the request is a request for the transmission of the chromatic aberration amount data, the lens microcomputer150reads the chromatic aberration amount data depending on the current focal length and focus lens position of the image-pickup optical system from a not shown ROM table in the lens microcomputer150.

The lens microcomputer150returns the chromatic aberration amount data to the camera microcomputer100via the serial communication lines LCK, LDO, and LDI.

In Step115, the camera microcomputer100multiplies the chromatic aberration amount data obtained in Step114with the correction coefficient in accordance with the wavelength of the AF assist light to calculate the second correction amount as the chromatic aberration amount data after the assist light correction (the second correction information).

The wavelength of the AF assist light is previously measured and the wavelength is stored in a not shown ROM table in the camera microcomputer100. Then, the camera microcomputer100reads the correction coefficient table (the same table as the one ofFIG. 7) depending on the wavelength to use the correction coefficient table. This can provide an appropriate defocus amount correction without causing an influence by the ambient light.

In Step116, the camera microcomputer100adds the multiplication result (the second correction amount) in Step115to the defocus amount calculated in Step112to generate the corrected defocus amount by the AF assist light (hereinafter referred to as an assist-light-corrected defocus amount). Then, the camera microcomputer100proceeds to Step117.

In Step117, the camera microcomputer100determines whether the light-source-corrected defocus amount calculated in Step108or the assist-light-corrected defocus amount calculated in Step116is within a specific range or not.

When the light-source-corrected defocus amount calculated in Step108or the assist-light-corrected defocus amount calculated in Step116is within the specific range, the camera microcomputer100determines that an in-focus state is achieved and then proceeds to Step119.

When the corrected defocus amount is larger than the specific range, the camera microcomputer100proceeds to Step118to calculate the driving amount of the focus lens12for obtaining an in-focus state based on the corrected defocus amount.

Then, the camera microcomputer100transmits the driving amount information to the lens microcomputer150via the above-described serial communication lines LCK, LDO, and LDI.

On receiving the driving amount information, the lens microcomputer150decides the driving direction of the focus driving motor16in accordance with the driving amount information to drive the focus driving motor16.

Then, the processing returns to Step101. The camera microcomputer100repeats the operations of the above-described respective steps until an in-focus state is determined in Step117.

In Step119, the camera microcomputer100determines whether SW2is ON or not. When SW2is ON, the camera microcomputer100proceeds to Step201shown inFIG. 5to perform an image-pickup operation. When SW2is OFF, the camera microcomputer100completes the processing of the AF operation.

Next, with reference toFIG. 5, the image-pickup operation will be described. When SW2is ON after the completion of the AF operation, the camera microcomputer100in Step201calculates an object luminance BV based on a photometry value from a photometry sensor7that measures the luminance of an object luminance.

Then, the camera microcomputer100adds the object luminance BV to a set ISO sensitivity SV to calculate an exposure value EV to calculate an aperture stop value AV and a shutter speed TV based on the exposure value EV.

In Step202, the camera microcomputer100subjects the main mirror2to an up operation to evacuate the main mirror2from an image-pickup optical path.

At the same time, the camera microcomputer100instructs the lens microcomputer150to set the aperture stop15to the aperture stop value AV decided in Step202. On receiving the instruction, the lens microcomputer150drives the aperture stop driving motor17.

Thereafter, when the main mirror2is completely retracted from the image-pickup optical path, the camera microcomputer100in Step203energizes the shutter front curtain driving magnet MG-1to start the releasing operation of the focal-plane shutter8.

When the predetermined shutter-released time has elapsed, the camera microcomputer100proceeds to Step204to energize the shutter rear curtain driving magnet MG-2to close the rear curtain of the focal-plane shutter8. This completes the exposure of the image-pickup device9.

In Step205, the camera microcomputer100subjects the main mirror2to a down operation to place the main mirror2in the image-pickup optical path, thereby completing the image-pickup operation.

As described above, according to this embodiment, when the contrast pattern light like the AF assist light is projected to the object to perform AF, the light source detection operation is prohibited and the correction coefficient depending on the wavelength of the AF assist light is used to correct the defocus amount.

This can provide an appropriate defocus amount correction without causing an influence by the ambient light.

FIG. 6is a flowchart showing the AF operation in a camera system that is Embodiment 2 of the present invention. The camera system of the embodiment has the same structure as that of the camera system of Embodiment 1. Thus, the same components in this embodiment as those of Embodiment 1 are denoted with the same reference numerals of Embodiment 1.

When a switch SW1of the camera1is turned on inFIG. 6, the camera microcomputer100starts the operation from Step301. In Step301, the camera microcomputer100causes the charge accumulation by the focus detection sensor29to be performed and causes the pixel information depending on the focus state of the image-pickup optical system to be generated.

In Step302, the camera microcomputer100calculates the defocus amount of the image-pickup optical system based on the obtained displacement of the pixel information (phase difference).

In Step303, the camera microcomputer100calculates the first contrast value (the first contrast information) owned by the pixel information calculated in Step301. The first contrast value is obtained by calculating an integration value of differences in the level of neighboring pixel signals.

In Step304, the camera microcomputer100requests the lens microcomputer150to transmit the chromatic aberration amount data unique to the interchangeable lens (the image-pickup optical system). This request is transmitted to the lens microcomputer150via the serial communication lines LCK, LDO, and LDI shown inFIG. 2.

On receiving the request, the lens microcomputer150firstly analyzes the contents of the request (communication).

When the request is a request for the transmission of the chromatic aberration amount data, the lens microcomputer150reads the chromatic aberration amount data depending on the current focal length and focus lens position of the image-pickup optical system from a not-shown ROM table in the lens microcomputer150.

The chromatic aberration amount data is previously measured to correspond to the focal length and the focus lens position for each interchangeable lens and is stored in the ROM table. The lens microcomputer150returns the chromatic aberration amount data to the camera microcomputer100via the serial communication lines LCK, LDO, and LDI.

In Step305and Step306, the camera microcomputer100drives the light-source detection sensor31to read the luminance information from the visible light sensor311and the infrared light sensor312.

Then, the camera microcomputer100calculates the ratio of pieces of the luminance information from the visible light sensor311and the infrared light sensor312(i.e., the luminance ratio) to read the correction coefficient from the table shown inFIG. 7in accordance with the luminance ratio (infrared light/visible light).

In Step307, the camera microcomputer100multiplies the chromatic aberration amount data obtained in Step304with the correction coefficient calculated in Step305to calculate the first correction amount (the first correction information) that is the light-source-corrected chromatic aberration amount data.

In Step308, the camera microcomputer100determines the reliability of the detection result of the defocus amount calculated in Step302by calculating the reliability evaluation value based on the pixel information obtained in Step301to determine that the detection result has the reliability when the reliability evaluation value is equal to or higher than the predetermined value to proceed to Step309.

On the other hand, when the reliability evaluation value is lower than the predetermined value, the camera microcomputer100determines that the detection result has no reliability to proceed to Step310to perform the AF operation by the AF assist light.

The reliability evaluation value can be a difference between the detected maximum value and minimum values of the pixel information (amplitude of the pixel information) or the first contrast value calculated in Step303.

In Step309, the camera microcomputer100adds the first correction amount calculated in Step307to the defocus amount calculated in Step302to correct the defocus amount to calculate the defocus amount after the light source correction (hereinafter referred to as the light-source-corrected defocus amount). Then, the camera microcomputer100proceeds to Step319.

On the other hand, in Step310,311and312, the camera microcomputer100drives the AF assist light source33to project the AF assist light having the contrast pattern to a not-shown object.

Then, the camera microcomputer100causes the charge accumulation by the focus detection sensor29to be performed and causes the pixel information depending on the focus state of the image-pickup optical system to be generated. Thereafter, the camera microcomputer100stops the driving of the AF assist light source33.

In Step313, the camera microcomputer100calculates the defocus amount of the image-pickup optical system based on the obtained displacement of the pixel information (phase difference).

In Step314, the camera microcomputer100calculates the second contrast value owned by the pixel information obtained in Step311(the second contrast information).

In Step315, the camera microcomputer100determines the reliability of the detection result of the defocus amount calculated in Step313by calculating the reliability evaluation value based on the pixel information obtained in Step311to determine that the detection result has the reliability when the reliability evaluation value is equal to or higher than the predetermined value to proceed to Step316.

On the other hand, when the reliability evaluation value is lower than the predetermined value, the camera microcomputer100determines that the detection result has no reliability to set AF-NG and then completes the AF operation.

The reliability evaluation value can be a difference between the detected maximum value and minimum values of the pixel information (i.e., the amplitude of the pixel information) or the second contrast value calculated in Step314.

In Step316, the camera microcomputer100multiplies the chromatic aberration amount data obtained in Step304with the correction coefficient depending on the wavelength of the AF assist light to calculate the second correction amount that is the chromatic aberration amount data after the assist light correction (the second correction information).

As in Embodiment 1, the wavelength of the AF assist light is previously measured and is stored in a not-shown ROM table in the camera microcomputer100. Then, the camera microcomputer100reads the correction coefficient from the correction coefficient table in accordance with the wavelength (the similar table as that inFIG. 7).

In Step317and318, the camera microcomputer100uses the first contrast value and the second contrast value calculated in Step303and314to decide a weighting amount to the first correction amount and the second correction amount calculated in Step307and Step316.

Then, based on the decided weighting amount, the camera microcomputer100calculates the third correction amount finally used for the defocus amount correction (the third correction information).

A method for calculating the third correction amount will be described with reference toFIG. 8AandFIG. 8B.FIG. 8Ashows when no AF assist light is projected (i.e., the pixel information obtained through the accumulation operation of Step301).

The horizontal axis represents the pixel position and the vertical axis represents the signal intensity of a pixel. Since no AF assist light is projected, a contrast only by the ambient light is formed.

FIG. 8Bshows when the AF assist light is projected (i.e., the pixel information obtained in the accumulation operation of Step311). This provides an image signal obtained by adding the contrast by the contrast pattern of the AF assist light to the contrast formed by the ambient light.

The defocus amount (the defocus amount before the light source correction) detected based on this pixel information includes two components of a defocus component by the ambient light and a defocus component by the AF assist light.

An influence by these defocus components changes depending on a ratio of the contrast by the ambient light to the contrast by the AF assist light.

First, the camera microcomputer100calculates the third contrast value only by the contrast pattern of the AF assist light. The third contrast value is obtained by deducting the first contrast value calculated in Step303(the contrast by the ambient light) from the second contrast value calculated in Step314(the ambient light+the contrast by the AF assist light).

Then, in accordance with the ratio between the first contrast value and the third contrast value (the contrast only by the AF assist light), the camera microcomputer100decides the weighting amounts of the first correction amount and the second correction amount calculated in Step307and Step316to calculate the third correction amount.

When assuming that the first contrast value is CNT1, the third contrast value is CNT3, the first correction amount is COR1, and the second correction amount is COR2, the third correction amount COR3is calculated by the following expression:
COR3=COR1×CNT1/(CNT1+CNT3)+COR2×CNT3/(CNT1+CNT3)

Next, in Step318, the camera microcomputer100adds the third correction amount calculated in Step317to the defocus amount calculated in Step313to correct the defocus amount to calculate the defocus amount after the correction by the AF assist light (hereinafter referred to as the assist-light-corrected defocus amount).

In Step319, the camera microcomputer100determines whether the light-source-corrected defocus amount calculated in Step309or the assist-light-corrected defocus amount calculated in Step318is within the specific range or not.

When the light-source-corrected defocus amount calculated in Step309or the assist-light-corrected defocus amount calculated in Step318is within the specific range, the camera microcomputer100determines that an in-focus state is achieved and then proceeds to Step321.

When the corrected defocus amount exceeds the specific range, the camera microcomputer100proceeds to Step320to calculate the driving amount of the focus lens12for obtaining an in-focus state based on the corrected defocus amount.

Then, the camera microcomputer100transmits the driving amount information to the lens microcomputer150via the above-described serial communication lines LCK, LDO, and LDI.

On receiving the driving amount information, the lens microcomputer150decides the driving direction of the focus driving motor16in accordance with the driving amount information to drive the focus driving motor16. Then, the processing returns to Step301to repeat the operations of the respective steps until an in-focus state is determined in Step319.

In Step321, the camera microcomputer100determines whether SW2is on or not. When SW2is on, the camera microcomputer100proceeds to Step201shown inFIG. 5to perform the image-pickup operation. When SW2is off, the camera microcomputer100completes the processing of the AF operation.

As described above, according to this embodiment, when the AF assist light is projected to the object to perform the AF, the light source detection operation is prohibited and the defocus amount is corrected based on the correction information depending on the wavelength of the AF assist light and the correction information depending on the wavelength of an environment light source in the state where the AF assist light is not projected.

Further, the defocus amount is corrected based on the contrast of the pixel information obtained by projecting the AF assist light and the contrast of the pixel information obtained without projecting the AF assist light.

This can provide an appropriate defocus amount correction even when both of the contrast by the AF assist light and the contrast by the ambient light exist.

According to the respective embodiments, when the light from the light projection part is projected to the object to perform the focus detection, the information relating to the focusing control using the detection result of the information relating to the light source is not generated and the correction information depending on the wavelength of projected light is used to generate the information relating to the focusing control.

This can provide an appropriate focusing control without causing an influence by the ambient light. This can reduce the focal shift under various light sources including the projected light such as the AF assist light.

Although the respective embodiments described the single-lens reflex camera, the present invention can also be applied to a video camera that performs the AF based on the phase-difference detection method.

FIELD OF INDUSTRIAL APPLICATION

The present invention provides an image-pickup apparatus in which a highly-accurate AF control can be performed under various light sources.