Patent Description:
Typical camera systems have been available which perform automatic focus (AF) control. In this automatic focus control, a camera detects the in-focus state of a subject and generates a driving command to drive a focus unit including lenses which move to adjust the in-focus state. A lens apparatus is utilized to move the focus unit based on the driving command. The driving command is generated based on the correspondence relation between the current position of the focus unit and the defocus amount obtained in advance by the camera.

Although many typical lens apparatuses have one focus unit, lens apparatuses having a plurality of focus units, such as the lens apparatus discussed in <CIT>, have been proposed.

In an interchangeable-lens camera system in which both a lens apparatus having one focus unit and a lens apparatus having a plurality of focus units are attached to a camera, the camera needs to suitably issue driving commands to the lens apparatus regardless of the number of focus units.

As one method, it is assumed that the driving command for the focus unit to be transmitted from the camera to the lens apparatus is changed depending on the number of focus units included in the attached lens apparatus. For example, if the lens apparatus has one focus unit, the camera transmits one driving command to the lens apparatus. If the lens apparatus has two focus units, the camera transmits two driving commands to the lens apparatus. However, this method requires the update of a typical camera program capable of generating and transmitting only one driving command to a program capable of generating and transmitting driving commands depending on the number of focus units included in the attached lens apparatus. In addition, errors may be likely to occur in the camera system because of complicated control and communication.

As another method, only a driving command for one focus unit is generated and transmitted even if a lens apparatus having a plurality of focus units is attached to the camera. In such a case, the position of one of the focus unit of the plurality of focus units is associated with the positions of the other focus units of the plurality of focus units on a one-to-one basis in the lens apparatus, and only the driving command related to any one of the focus units is handled between the lens apparatus and the camera. However, if the movement of any one of the focus units lags behind the others, this control method will collapse the correspondence relation between the focus unit position and the defocus amount subjected to the driving command. Particularly in control (continuous AF) in which the defocus amount detection and the driving command generation are repeated before image capturing and in automatic focus control during moving image capturing, a suitable driving command cannot be generated because of the lag in the movement of a focus unit. This may make it difficult to accurately perform automatic focus control.

<CIT> discloses a camera system that is provided with the interchangeable lens having: an imaging optical system that includes first and second focus lenses independently movable in an optical axis direction for a focus adjustment; lens position detection means that detects positions of the first and second focus lenses on the optical axis; lens drive amount computation means that, when receiving an instruction of a drive amount of the focus lens from a body side upon adjusting a focus of the imaging optical system, determines drive amounts of the first and second focus lenses, respectively from the instructed drive amount and positions of the first and second lenses in order to attain a movement amount of an imaging plane corresponding to the instructed drive amount; lens drive means that drives the first and second focus lenses; distance computation means that computes a photographing distance to a subject; and display means that displays the photographing distance calculated by the distance computation means.

The present invention has been devised in view of the above-described issue, and is directed to offering a lens apparatus for accurately performing automatic focus control by using a plurality of focus units, a camera, a camera system, and a control method.

According to a first aspect of the present invention, there is provided a lens apparatus as specified in claims <NUM> to <NUM>. According to a second aspect of the present invention, there is provided a camera system as specified in claim <NUM>. According to a third aspect of the present invention, there is provided a control method as specified in claim <NUM>.

A lens apparatus, a camera, a camera system, and a method for controlling focus units according to exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the following drawings, identical components are assigned the same reference numerals, and duplicated descriptions thereof will be omitted.

A first exemplary embodiment of the present invention will be described below. <FIG> illustrates a configuration of a camera system <NUM> according to the present exemplary embodiment. The camera system <NUM> is an interchangeable-lens camera system. Both a lens apparatus having one focus unit and a lens apparatus having a plurality of focus units are used as a lens apparatus attachable to and detachable from a camera body <NUM>.

In the present specification, a "focus unit" refers to a lens unit including one or a plurality of lenses moving along the same locus in focusing. If a lens that does not move or a lens that moves along a locus in focusing is disposed between two lenses moving along the same another locus, the two lenses belong to different focus units.

<FIG> illustrates a lens apparatus <NUM> having a plurality of focus units. The lens apparatus <NUM> includes an optical system <NUM> capable of forming a subject image on an image sensor <NUM> of the camera body <NUM>. According to the first exemplary embodiment, the optical system <NUM> is a fixed focal length lens.

The optical system <NUM> includes a first focus unit (first lens unit) <NUM> and a second focus unit (second lens unit) <NUM> moving along the optical axis of the optical system <NUM> in adjusting the in-focus state of the subject image. Although, in the first exemplary embodiment, mainly the first focus unit <NUM> is moved to adjust in-focus state, and the second focus unit <NUM> is moved to make fine adjustment of aberration correction and in-focus state, the role of each individual focus unit is not limited thereto.

A lens control unit (acquisition unit, control unit, communication unit, and determination unit) <NUM> is a computer including a central processing unit (CPU). The lens control unit <NUM> is electrically connected to a memory <NUM>, a diaphragm drive unit <NUM>, a first drive unit <NUM>, a second drive unit <NUM>, a first detection unit <NUM>, and a second detection unit <NUM>.

The lens control unit <NUM> functions as a control unit for controlling the positions of the first focus unit <NUM> and the second focus unit <NUM> via the first drive unit <NUM> and the second drive unit <NUM>. The lens control unit <NUM> functions as an acquisition unit for acquiring position information about a single position representing the positions of the first focus unit <NUM> and the second focus unit <NUM> corresponding to the current in-focus position. The position information about the single position is position information for a composite focus unit when a virtual focus unit representing the first focus unit <NUM> and the second focus unit <NUM> is assumed as a composite focus unit. In addition, the lens control unit <NUM> functions as a communication unit for communicating necessary information with the camera control unit <NUM> in automatic focus control. For example, the lens control unit <NUM> transmits information about the position of the composite focus unit (also referred to as composite focus unit position), the focus sensitivity of the composite focus unit, and the pulse conversion coefficient required to generate a driving command, and receives a command to drive the composite focus unit. These pieces of information and the functions of the lens control unit <NUM> will be described in detail below.

The lens control unit <NUM> reads a program for automatic focus control from the memory <NUM> and executes the program. The lens control unit <NUM> also reads information to be transmitted to the camera control unit <NUM> and information necessary for the calculation from the memory <NUM>.

The memory <NUM> includes a read only memory (ROM) and a random access memory (RAM), and serves as a storage unit for storing information. The memory <NUM> prestores information indicating the relation between each of the positions of the first focus unit <NUM> and the second focus unit <NUM> and the subject distance (first relational information), and information indicating the relation between the position of the composite focus unit and the subject distance (second relational information). The memory <NUM> stores the focus sensitivity of the first focus unit <NUM> and the focus sensitivity of the second focus unit <NUM>. The memory <NUM> stores the composite focus sensitivity corresponding to the combination of the positions of the first focus unit <NUM> and the second focus unit <NUM> (focus sensitivity information). The memory <NUM> also stores the program of the flowchart for the lens side processing illustrated in <FIG> (described below) and information necessary for automatic exposure and automatic light adjustment which is performed by the camera body <NUM>.

The diaphragm drive unit <NUM> adjusts the aperture diameter of an aperture diaphragm <NUM> included in the optical system <NUM> based on a command from the lens control unit <NUM>.

The first drive unit <NUM> moves the first focus unit <NUM> based on a command from the lens control unit <NUM>, and the second drive unit <NUM> moves the second focus unit <NUM> based on a command from the lens control unit <NUM>.

Movement control for the first focus unit <NUM> will be described below with reference to <FIG>. To the first drive unit <NUM> as a stepping motor, a lead screw <NUM> is coupled. The first focus unit <NUM> is coupled to the lead screw <NUM> via a rack <NUM>.

When the first drive unit <NUM> is driven based on a command from the lens control unit <NUM>, the lead screw <NUM> rotates, and the first focus unit <NUM> moves along the shaft of the lead screw <NUM> together with the rack <NUM>. The first drive unit <NUM> is controlled based on the number of pulses indicating the target absolute position for the first focus unit <NUM>.

The lens apparatus <NUM> includes the first detection unit <NUM> and the second detection unit <NUM> as detection units for detecting the respective positions of the plurality of focus units.

The first detection unit <NUM> detects the position of the first focus unit <NUM> and outputs the detection result to the lens control unit <NUM>. With the position of a photo-interrupter <NUM> as the reference position, the first detection unit <NUM> resets the count of the number of pulses and counts the number of pulses required to move the first focus unit <NUM> from the reference position to the current position, thus detecting the absolute position of the first focus unit <NUM>.

Movement control for the second focus unit <NUM> is similar to movement control for the first focus unit <NUM>. As in the first detection unit <NUM>, the second detection unit <NUM> detects the position of the second focus unit <NUM> and outputs a detection result to the lens control unit <NUM>.

The first drive unit <NUM> and the second drive unit <NUM> may be actuators other than stepping motors, such as ultrasonic motors and voice coil motors. In such a case, the configurations of the first detection unit <NUM> and the second detection unit <NUM> are not limited to the present exemplary embodiment.

Referring back to <FIG>, the camera body <NUM> includes the image sensor <NUM>, a signal processing unit <NUM>, a recording processing unit <NUM>, an electronic viewfinder <NUM>, a display unit <NUM>, a defocus detection unit <NUM>, the camera control unit <NUM>, and a memory <NUM>.

The image sensor <NUM> receives the light from the optical system <NUM>, generates an electrical signal through photoelectric conversion, and outputs the signal to the signal processing unit <NUM>. The image sensor <NUM> includes pixels for in-focus position detection (not illustrated) in addition to image pickup pixels.

The signal processing unit <NUM> performs various processing, such as the amplification, noise rejection, and color correction on the input electrical signal and outputs the processed signal to the recording processing unit <NUM>. The recording processing unit <NUM> records an input image and displays the image on the electronic viewfinder <NUM> and the display unit <NUM>.

The defocus detection unit (in-focus position detection unit) <NUM> detects the in-focus state of the subject image by using the image sensor <NUM>. The camera system <NUM> according to the present exemplary embodiment detects the defocus amount based on the phase difference detection method. The defocus detection unit <NUM> detects the phase difference between a pair of subject image signals obtained from the light incident via a micro lens for performing pupil division on focus detection pixels of the image sensor <NUM>, determines the defocus amount corresponding to the phase difference, and outputs the defocus amount to the camera control unit <NUM>.

The camera control unit <NUM>, a computer including a central processing unit (CPU), is electrically connected to the defocus detection unit <NUM>, the recording processing unit <NUM>, and the memory <NUM>.

The camera control unit <NUM> reads a program stored in the memory <NUM> and then executes the program. The camera control unit <NUM> also communicates necessary information with the lens control unit <NUM> in automatic focus control. The camera control unit <NUM> further generates a driving command to drive the focus unit based on the detection result from the defocus detection unit <NUM> and the current position of the focus unit acquired from the attached lens apparatus <NUM>. In a case where the lens apparatus <NUM> is attached to the camera body <NUM>, the position of the focus unit corresponds to the position of the composite focus unit, and the driving command to be generated is one directed for the composite focus unit. The camera control unit <NUM> repetitively detects the defocus amount and determines the movement amount of the focus unit from when a command for automatic focus control is issued by the user by when a predetermined in-focus state is obtained (until the defocus amount falls at or below a predetermined value).

The focus sensitivity will be described below with reference to <FIG>, <FIG>, and <FIG>. <FIG> illustrates the definition of the focus sensitivity.

In the optical system having a focus unit <NUM> and a fixed unit <NUM>, the relation d = L * S is satisfied, where L denotes a movement amount from a position <NUM> of the focus unit <NUM> to the current position of the focus unit <NUM> in the in-focus state, d denotes the defocus amount, and S denotes the focus sensitivity. More specifically, the focus sensitivity S denotes a variation of the defocus amount d in a unit of the movement amount of the focus unit <NUM>. The defocus amount d is the distance on the optical axis from a light receiving surface <NUM> of the image sensor <NUM> to the in-focus position as illustrated in <FIG>.

<FIG> illustrates the relation between the movement amount L and the defocus amount d. <FIG> illustrates the relation between the focus sensitivity S and the defocus amount d.

In a case where the focus sensitivity S remains unchanged with the movement of the focus unit <NUM>, the relation between the defocus amount d and the movement amount L is proportional, as indicated by the solid line, i.e., the focus sensitivity S is constant.

In a case where the focus sensitivity S changes with the movement of the focus unit <NUM>, the focus sensitivity S is represented as a function of the defocus amount d, i.e., S = f(d). When the function f(d) is Talor-expanded, Expansion (<NUM>) results. The movement amount L of the focus unit <NUM> is represented by Expansion (<NUM>). These relations are represented by the broken lines illustrated in <FIG>. <MAT> <MAT>.

For the comparison with the lens apparatus <NUM>, focus control in a case where the lens apparatus <NUM> having one focus unit is attached to the camera body <NUM> will be described below. In the focus unit of this lens apparatus <NUM>, the focus sensitivity S is assumed to change with the position of the focus unit.

In the camera system <NUM> according to the present exemplary embodiment, the driving command to drive the focus unit indicates the absolute position (hereinafter also referred to as a target position) equivalent to the distance from the photo-interrupter <NUM> as the reference position to the target position. The absolute position is represented not by the unit of length but by the above-described number of pulses. The number of pulses P corresponding to the defocus amount is represented by Equation <NUM> where S denotes the focus sensitivity and h denotes the pulse conversion coefficient (movement amount [mm/pulse] of the focus unit per pulse).

The focus sensitivity S and the pulse conversion coefficient h are values specific to the lens apparatus <NUM>. Thus, to calculate a driving command indicating the target position, it is necessary to add the number of pulses P corresponding to the defocus amount to the current position. Accordingly, the lens apparatus <NUM> needs to transmit the number of pulses indicating the current position of the focus unit, the focus sensitivity S corresponding to the current position of the focus unit, and the pulse conversion coefficient h to the camera body <NUM>. The camera control unit <NUM> generates the driving command based on the above-described pieces of information acquired and the defocus amount output from the defocus detection unit <NUM>.

In this case, the number of pulses calculated by Equation <NUM> may be corrected in consideration of the focus variation accompanying the diaphragm drive and the optical path length between a phase difference sensor and the image pickup surface.

The lens apparatus <NUM> moves the focusing lens to the target position based on the driving command generated by the camera control unit <NUM>. The lens apparatus <NUM> repeats the above-described control until by when the defocus amount falls at or below a predetermined value, after moving the focus unit, thus finally focusing the subject.

The lens apparatus <NUM> may transmit the information indicating the relation between the position of the focus unit and the focus sensitivity to the camera body <NUM> in advance, and then, the camera control unit <NUM> may acquire the focus sensitivity S according to the current positions of the focus units.

A description will be provided of focus control in a case where the lens apparatus <NUM> having a plurality of focus units is attached to the camera body <NUM> that generates the driving command as described above.

As described above, to reduce the risk of error occurrence due to the system complexity, it is demanded that the camera body <NUM> is capable of generating the driving command in a similar procedure regardless of the number of focus units included in the lens apparatus <NUM>. Even if the positional relation between the plurality of lens units collapses because any one of the plurality of lens units lags with respect to the target position, it is demanded that the camera system is capable of compensating for the defocus amount variation due to the collapse.

For this reason, the lens apparatus <NUM> according to the present exemplary embodiment introduces a concept of "composite focus unit". The composite focus unit refers to a single virtual focus unit in which information about the first focus unit <NUM> and information about the second focus unit <NUM> are integrated into one. Instead of communicating driving commands to drive the plurality of focus units, the respective positions of the plurality of focus units, and the respective focus sensitivities of the plurality of focus units, the lens apparatus <NUM> communicates a driving command to drive the composite focus unit, the position of the composite focus unit, and the focus sensitivity of the composite focus unit. More specifically, the lens apparatus <NUM> has a function of operating, for the camera body <NUM>, as if the lens apparatus <NUM> has only one focus unit.

The position of the composite focus unit will be described below with reference to <FIG>, and <FIG>.

<FIG> illustrate information indicating the relations between the position of a focus unit and the subject distance stored in memory <NUM>. <FIG> illustrates the relation between the position of the first focus unit <NUM> and the subject distance (first relational information). <FIG> illustrates the relation between the position of the second focus unit <NUM> and the subject distance (second relational information). The horizontal axis represents the subject distance, and the vertical axis represents the positions of the first focus unit <NUM> in <FIG> and the second focus unit <NUM> in <FIG>. The positions of the first focus unit <NUM> and the second focus unit <NUM> may be represented by the distance [mm] from the reference position or by the number of pulses corresponding to the position viewed from the reference position.

The target positions for the first focus unit <NUM> and the second focus unit <NUM> to obtain a predetermined subject distance are associated with each other on a one-to-one basis. The subject is focused by the first focus unit <NUM> and the second focus unit <NUM> being moved to the positions corresponding to respective predetermined subject distances.

<FIG> illustrates the relation between the position of the composite focus unit and the subject distance stored in the memory <NUM>. The horizontal axis represents the subject distance, and the vertical axis represents the composite focus unit position.

A description will be provided of an example case of changing the state where the subject distance at infinity is in focus to the state where a subject distance of <NUM> is in focus. To simplify descriptions, a case where the movement of the second focus unit <NUM> lags behind the first focus unit <NUM> will be described below. For example, the lag in movement is caused by a control response lag.

Referring back to <FIG>, the open circles (o) represent the positions of the first focus unit <NUM> and the second focus unit <NUM> when the subject distance is infinity. The filled circles (•) represent the positions of the first focus unit <NUM> and the second focus unit <NUM> with a subject distance of <NUM>. The open triangles represent the current positions of the first focus unit <NUM> and the second focus unit <NUM>. Referring to <FIG>, the open circle (o) represents the position of the composite focus unit when the first focus unit <NUM> and the second focus unit <NUM> are positioned at the open circles (o) illustrated in <FIG>, respectively. The filled circle (•) represents the position of the composite focus unit when the first focus unit <NUM> and the second focus unit <NUM> are positioned at the filled circles (•) illustrated in <FIG>, respectively.

More specifically, <FIG> illustrates a state where the current position of the first focus unit <NUM> has reached the position corresponding to a target subject distance of <NUM>, while <FIG> illustrates a state where the current position of the second focus unit <NUM> is the position corresponding to a subject distance of <NUM>. In a case where the second focus unit <NUM> lags by ΔL, as illustrated in <FIG>, the subject at a subject distance of <NUM> is not in focus because of the lag by ΔL. In practice, the focus is at a subject distance of αm. Referring to <FIG>, Fα represents the position of the composite focus unit corresponding to the current subject distance (αm).

If all of the plurality of focus units are movable without lagging behind, the lens control unit <NUM> can transmit the current position of one focus unit (e.g., the first focus unit <NUM>) without change, to the camera control unit <NUM>, as in the lens apparatus <NUM> having one focus unit. However, since the camera control unit <NUM> detects the actual defocus amount, the camera control unit <NUM> recognizes the necessity of a driving command for reducing a deviation Δα between a subject distance of <NUM> and a subject distance of αm. Accordingly, if the lens control unit <NUM> simply transmits the current position of the first focus unit <NUM> without taking the lag ΔL into consideration, the camera control unit <NUM> will further generate a driving command to drive the first focus unit <NUM> with a position closer to the shortest distance than the target position as the target position, although the first focus unit <NUM> has already reached the target position.

According to the present exemplary embodiment, the lens control unit <NUM> acquires the composite focus unit position Fα corresponding to the actual subject distance (αm) as the focus unit position in the lens apparatus <NUM> in consideration of the lag of the second focus unit <NUM>. More specifically, the composite focus unit position Fα is position information determined in consideration of the current positions of the first focus unit <NUM> and the second focus unit <NUM>, and is equivalent to the position information about a single position representing the respective positions of the first focus unit <NUM> and the second focus unit <NUM>. The lens control unit <NUM> transmits the composite focus unit position Fα to the camera control unit <NUM>.

This configuration enables the camera control unit <NUM> to generate a driving command with F1 as an absolute position of the target position for the composite focus unit, based on the composite focus unit position Fα and a position lag ΔL' corresponding to the subject distance deviation Δα. The lens control unit <NUM> that has received the driving command moves each of the first focus unit <NUM> and the second focus unit <NUM> with the position corresponding to a subject distance of <NUM> corresponding to the target absolute position F1 set as the target position. This eliminates the concern that the first focus unit <NUM> is moved more than necessary, thus enabling only the second focus unit <NUM> that is lagging behind to be moved to the position corresponding to a subject distance of <NUM>.

The lens control unit <NUM> calculates the composite focus unit position Fα as follows. Let the focus sensitivity of the second focus unit <NUM>, at the current position, stored in the memory <NUM> be S2. Let the focus sensitivity of the composite focus unit, at the current position, stored in the memory <NUM> be St. The composite focus sensitivity St is determined by the combination of the positions of the first focus unit <NUM> and the second focus unit <NUM>. Thus, even with the same subject distance, the composite focus sensitivity may have a different value depending on the combination of the positions of the first focus unit <NUM> and the second focus unit <NUM>. In such a case, the position Fα is represented by Equation <NUM>.

In Equation (<NUM>), (ΔL * S2) is an image plane conversion value at the in-focus position resulting from the lag of the second focus unit <NUM>. This is equivalent to the deviation Δα illustrated in <FIG>. Dividing (ΔL * S2) by the composite focus sensitivity St obtains a deviation amount ΔL' from the target position F1 for the composite focus unit. The lens control unit <NUM> can calculate the position Fα based on the calculated (ΔL * S2)/St and the position F1.

Since the composite focus unit position is determined in this way, the composite focus unit position can be freely set only by determining the composite focus unit position based on a predetermined definition.

Desirably, the composite focus unit position at a certain subject distance is equalized to the position of one focus unit out of the plurality of focus units with the same subject distance. More desirably, the one focus unit is set to the focus unit having the largest movement amount in focusing from infinity to the shortest distance, out of the plurality of focus units.

For example, according to the present exemplary embodiment, the movement amount of the first focus unit <NUM> is larger than that of the second focus unit <NUM>, the vertical axis scale indicating the position of the first focus unit <NUM> illustrated in <FIG> is equalized to the vertical axis scale indicating the composite focus unit position illustrated in <FIG>. More specifically, if the position of the first focus unit <NUM> at a subject distance of <NUM> is represented by <NUM> pulses in <FIG>, the composite focus unit position at a subject distance of <NUM> is also represented by <NUM> pulses. Similarly, if the position of the first focus unit <NUM> at a subject distance at infinity is represented by <NUM> pulses, the composite focus unit position at a subject distance of <NUM> is also represented by <NUM> pulses.

These settings enable the lens control unit <NUM> to treats the driving command for the composite focus unit (F1 = <NUM> pulses) received from the camera control unit <NUM> as a driving command for the first focus unit <NUM> without change. More specifically, the target position for the first focus unit <NUM> can be set to the position of <NUM> pulses. This means that the lens control unit <NUM> needs to determine only the driving command for the second focus unit <NUM> by using the information illustrated in <FIG>, thus reducing the calculation load.

The resolution of the driving command for the composite focus unit can be ensured by setting the position of the focus unit having the largest movement amount as the composite focus unit position.

In addition, the composite focus unit position at a certain subject distance may be set to a predetermined multiple of the position of a certain focus unit at the same subject distance. An example case will be described in which the vertical axis scale illustrated in <FIG> is <NUM>/<NUM> times the vertical axis scale illustrated in <FIG>. In this case, when the position of the first focus unit <NUM> at a subject distance of <NUM> is represented by <NUM> pulses, the composite focus unit position at a subject distance of <NUM> is represented by <NUM> pulses. Similarly, if the position of the first focus unit <NUM> at a subject distance at infinity is represented by <NUM> pulses, the composite focus unit position at a subject distance at infinity is represented by <NUM> pulses. If <NUM> pulses are received as a driving command indicating the target position for the composite focus unit, the lens control unit <NUM> can recognize the position of <NUM> * <NUM> = <NUM> pulses as the target position for the first focus unit <NUM>.

Although, in the above-described example case, the first focus unit <NUM> does not lag during movement and only the second focus unit <NUM> lags during movement, the above-described method is applicable even if both the first focus unit <NUM> and the second focus unit <NUM> lag. For example, there arises no problem even if the first focus unit <NUM> is positioned at the position of <NUM> pulses, at a subject distance of <NUM>, for a target subject distance of <NUM>. Assume that the composite focus unit position Fα corresponding to the current subject distance is represented by <NUM> pulses, and that the movement amount ΔL' of the composite focus unit for zeroing the defocus amount is calculated as <NUM> pulses. In such a case, the camera control unit <NUM> calculates a driving command indicating the target position for the composite focus unit as <NUM> pulses. Accordingly, the target position for the first focus unit <NUM> is set to <NUM> pulses, and thus, the lens control unit <NUM> further moves the target position by <NUM> pulses from the current position of <NUM> pulses in the direction of the shortest distance.

Detailed focus control according to the present exemplary embodiment will be described below. The driving command indicating the position and the target position is represented by the number of pulses, and the composite focus unit position and the position of the first focus unit <NUM> at the same subject distance are assumed to be equal in the present exemplary embodiment.

<FIG> is a flowchart illustrating automatic focus control according to the first exemplary embodiment. The lens control unit <NUM> performs the lens side processing illustrated on the left-hand side of <FIG> according to a program read from the memory <NUM>. The camera control unit <NUM> performs the camera side processing illustrated on the right-hand side of <FIG> according to a program read from the memory <NUM>. In the flowcharts and descriptions thereof, the position of the composite focus unit is referred to as a composite focus position, and the focus sensitivity of the composite focus unit is referred to as a composite focus sensitivity. The composite focus sensitivity has been described above.

In step S101, the lens control unit <NUM> calculates the composite focus position. The calculation method will be described below with reference to <FIG>.

In step S201, the defocus detection unit <NUM> detects the defocus amount based on a command from the camera control unit <NUM>.

In step S102, the lens control unit <NUM> transmits the calculated composite focus position to the camera control unit <NUM>. In step S202, the camera control unit <NUM> receives the composite focus position.

In step S103, the lens control unit <NUM> reads the composite focus sensitivity from the memory <NUM> and transmits the composite focus sensitivity to the camera control unit <NUM>. In step S203, the camera control unit <NUM> receives the composite focus sensitivity.

In step S104, the lens control unit <NUM> reads the pulse conversion coefficient from the memory <NUM> and transmits the pulse conversion coefficient to the camera control unit <NUM>. In step S204, the camera control unit <NUM> receives the pulse conversion coefficient.

In step S205, the camera control unit <NUM> generates a driving command indicating the target absolute position for the composite focus unit based on the defocus amount detected by the defocus detection unit <NUM>, the composite focus position, the composite focus sensitivity, and the pulse conversion coefficient.

In step S206, the camera control unit <NUM> transmits the driving command generated in step S205 to the lens control unit <NUM>. In step S105, the lens control unit <NUM> receives the driving command. Since the received driving command is only one driving command for the composite focus unit, the lens control unit <NUM> cannot control the positions of the first focus unit <NUM> and the second focus unit <NUM> with the driving command unchanged.

Thus, in step S106, the lens control unit <NUM> generates a driving command for each of the first focus unit <NUM> and the second focus unit <NUM> based on the driving command for the composite focus unit received in step S <NUM>. In such a case, according to the present exemplary embodiment, since the composite focus unit position and the position of the first focus unit <NUM> at the same subject distance are equal, the absolute position indicated by the driving command for the composite focus unit serves as the target absolute position for a driving command for the first focus unit <NUM>. The position of the second focus unit <NUM> at the subject distance corresponding to the driving command for the composite focus unit (driving command for the first focus unit <NUM>) serves as the target absolute position for the driving command for the second focus unit <NUM>.

In step S107, the lens control unit <NUM> drives the first drive unit <NUM> and the second drive unit <NUM> based on the two driving commands generated in step S106. Thus, the lens control unit <NUM> performs a focusing operation by the movement of the first focus unit <NUM> and the second focus unit <NUM>.

As described above, the lens side processing and the camera side processing in focus control are performed. The operations in steps S101 to S107 and operations steps S201 to S206 are repetitively executed until a result of the defocus amount detection falls at or below a predetermined value.

The order in which the lens control unit <NUM> transmits the composite focus position, the composite focus sensitivity, and the pulse conversion coefficient to the camera control unit <NUM> is not limited to the transmission order illustrated in the flowchart illustrated in <FIG>.

The operation in step S101 illustrated in <FIG> will be described in detail below with reference to <FIG> is a flowchart illustrating the method for calculating the composite focus position according to the first exemplary embodiment. This flowchart illustrates the calculation process of the above-described Equation <NUM>. The lens control unit <NUM> reads a program for executing the processing of the flowchart from the memory <NUM> and then executes the program.

In step S1011, the lens control unit <NUM> acquires the current position of the first focus unit <NUM> with the first detection unit <NUM>.

In step S1012, the lens control unit <NUM> calculates the subject distance corresponding to the current position by using the information illustrated in <FIG> based on the current position of the first focus unit <NUM> acquired in step S1011.

In step S1013, the lens control unit <NUM> calculates the ideal position of the second focus unit <NUM> at the subject distance calculated in step S1012 by using the information illustrated in <FIG>.

In step S1014, the lens control unit <NUM> acquires the current position of the second focus unit <NUM> with the second detection unit <NUM>.

In step S1015, the lens control unit <NUM> calculates the lag amount of the position of the second focus unit <NUM>. The lag amount is equivalent to a difference between the ideal position of the second focus unit <NUM> calculated in step S1013 and the current position of the second focus unit <NUM> acquired in step S1014.

In step S1016, the lens control unit <NUM> calculates an image plane conversion value corresponding to the lag amount calculated in step S1015. The image plane conversion value corresponding to the lag amount is equivalent to a difference between the in-focus position when the second focus unit <NUM> does not lag and the in-focus position when the second focus unit 104lags. In other words, the image plane conversion value is equivalent to the above-described subject distance deviation Δα. Here, the lens control unit <NUM> calculates the image plane conversion value corresponding to the lag amount by multiplying the lag amount calculated in step S1015 by the focus sensitivity of the second focus unit <NUM> alone.

In step S1017, the lens control unit <NUM> calculates the composite focus position based on the image plane conversion value calculated in step S1016, the composite focus sensitivity, and the position of the first focus unit <NUM> acquired in step S1011.

This completes the description of the method for calculating the composite focus position. The operation of the processing in step S1014 needs to be performed before the operation in step S1015 and is not limited to the timing in the flowchart illustrated in <FIG>.

Thus, the lens control unit <NUM> acquires the composite focus unit position as a result of combining the positions of the plurality of focus units into one, and controls the positions of the plurality of focus units based on the driving command determined based on the composite focus unit position. The lens control unit <NUM> and the camera control unit <NUM> handle only information about the composite focus unit. This enables the camera control unit <NUM> to generate a driving command without changing the calculation processing depending on the number of focus units included in the lens apparatus <NUM> attached to the camera body <NUM>. Restraining the complexity in calculation processing and communication provides the camera system <NUM> in which errors are less likely to occur.

In addition, the lens control unit <NUM> calculates the composite focus unit position corresponding to the current in-focus position as the composite focus unit position required for the camera control unit <NUM> to generate a driving command. Even if the movement of the first focus unit <NUM> and/or the second focus unit <NUM> lags, the above-described calculation controls the positions thereof based on driving commands with the lag compensated.

A second exemplary embodiment of the present invention will be described below. <FIG> illustrates a configuration of a camera system <NUM> according to the present exemplary embodiment. Unlike the optical system <NUM> of the camera system <NUM> as a fixed focal length lens, the optical system <NUM> of the camera system <NUM> is a zoom lens having a lens unit that moves in zooming.

The lens unit is mechanically connected to an operation unit (not illustrated) provided on the lens apparatus <NUM>, and moves along the optical axis of the optical system <NUM> according to the operation amount and operation direction performed on the operation unit.

The lens apparatus <NUM> includes a zoom position detection unit <NUM> for detecting the position of the lens unit to grasp the zoom position (the focal distance of the optical system <NUM>). The zoom position detection unit <NUM> outputs the detected position of the lens unit to the lens control unit <NUM>.

The memory <NUM> stores information indicating the relation between the zoom position and the focus unit position for each subject distance (described below with reference to <FIG>). The memory <NUM> further stores information indicating the relation between the zoom position and the composite focus unit position for each subject distance (described below with reference to <FIG>), and information for normalizing the zoom positions for the information.

The focus sensitivity S changes not only by the focus unit position but also by the zoom position. Thus, the memory <NUM> stores the focus sensitivity of the composite focus unit for the respective positions of the first focus unit <NUM> and the second focus unit <NUM> for each zoom position. The memory <NUM> stores the focus sensitivity for each zoom position and for each position of the first focus unit <NUM>, and the focus sensitivity for each zoom position and each position of the second focus unit <NUM>.

Other configurations of the camera system <NUM> are similar to those of the camera system <NUM>, and duplicated descriptions thereof will be omitted.

The optical system <NUM> is capable of maintaining the in-focus state on a certain subject by changing the positions of the first focus unit <NUM> and the second focus unit <NUM> with a change in the zoom position.

<FIG> illustrate the relations between the zoom position, the focus unit positions, and the subject distance. <FIG> illustrates the relation for the first focus unit <NUM>, and <FIG> illustrates the relation for the second focus unit <NUM>. The horizontal axis is assigned the zoom position, and the vertical axis is assigned each focus unit position. The curve drawn by a single solid line represents the relation between the zoom position and each focus unit position required to maintain the same subject distance. The memory <NUM> stores the curves corresponding to the plurality of representative subject distances. The curve related to a subject distance other than infinity, <NUM>, <NUM>, and <NUM> can be calculated by internally dividing the interval between the two curves corresponding to the subject distance closest to the subject distance according to the subject distance of the curve to be obtained. The target position for each focus unit at each zoom position can be calculated based on the obtained curve. While an example using a curve is described here, the memory <NUM> may store data about representative points with which these curves can be drawn through approximation.

A control method using a plurality of focus units will be described below for a case of a target subject distance of <NUM>, with reference to <FIG>, <FIG>.

In the lens apparatus <NUM>, the lens control unit <NUM> communicates information about the composite focus unit position, the composite focus sensitivity, and a driving command for the composite focus unit with the camera control unit <NUM>, as in the first exemplary embodiment. More specifically, the lens apparatus <NUM> has the function of operating, for the camera body <NUM>, as if the lens apparatus <NUM> has one focus unit.

<FIG> illustrate the relations between the zoom position and the composite focus position for each subject distance. <FIG> illustrates a case where the zoom positions are not normalized, and <FIG> illustrates a case where the zoom positions are normalized. In a case where zooming is performed while the camera control unit <NUM> is generating a driving command, the camera control unit <NUM> cannot grasp the zoom position variation. Thus, the camera control unit <NUM> cannot grasp the movement of the first focus unit <NUM> and the second focus unit <NUM> accompanying the zooming. Thus, for the lens control unit <NUM> to behave as if the first focus unit <NUM> and the second focus unit <NUM> remain unchanged according to change in the zoom position, the zoom positions are normalized as illustrated in <FIG>. To simplify the description, a case will be described where the zoom positions are normalized at the positions where the composite focus unit positions are at TELE (telephoto end). The zoom position normalization is discussed in detail in <CIT>.

The zoom position normalization is not limited to a case where the zoom positions are normalized at the composite focus unit positions when the zoom positions are at TELE. If the normalized composite focus unit position can be calculated backwards to the original composite focus unit position, the zoom positions may be normalized at the composite focus unit positions when the zoom positions are at WIDE (wide-angle end) or at intermediate positions, or by using other methods.

Referring now to <FIG>, the filled circles (•) indicate the target positions for the first focus unit <NUM> and the second focus unit <NUM> for focusing on a subject distance of <NUM> at the zoom position X, respectively. The open triangles indicate the current positions for focusing on the first focus unit <NUM> and the second focus unit <NUM>, respectively. Referring to <FIG>, the filled circles (•) indicate the target positions for the composite focus unit for focusing on a subject distance of <NUM> at the zoom position X. The open triangles indicate the current positions of the composite focus unit.

In the lens apparatus <NUM>, the lens control unit <NUM> calculates the current subject distance based on the current positions of the first focus unit <NUM> and the second focus unit <NUM> and calculates the composite focus unit position corresponding to the calculated subject distance. The camera control unit <NUM> then generates a driving command for causing the composite focus unit to reach a subject distance of <NUM> by using the composite focus unit position, the focus sensitivity of the composite focus unit, and the pulse conversion coefficient acquired from the lens apparatus <NUM>. According to the second exemplary embodiment, the camera control unit <NUM> generates the number of pulses indicating the target absolute position for the composite focus unit as a driving command, as in the first exemplary embodiment.

An automatic focus control method according to the second exemplary embodiment will be described in detail below with reference to <FIG> and <FIG>.

<FIG> is a flowchart illustrating the automatic focus control according to the second exemplary embodiment. The lens control unit <NUM> performs the lens side processing illustrated on the left-hand side of <FIG> according to a program read from the memory <NUM>. The camera control unit <NUM> performs the camera side processing illustrated on the right-hand side of <FIG> according to a program read from the memory <NUM>.

Operations in steps S111 to S115 correspond to operations in steps S101 to S105, respectively, and operations in steps S211 to S216 correspond to operations in steps S201 to S206, respectively.

These operations differ from those according to the first exemplary embodiment in that the composite focus position is handled as a value when the zoom positions are normalized, and the composite focus sensitivity is handled as the focus sensitivity corresponding to the composite focus position when the zoom positions are normalized. In addition, the information transmitted from the camera control unit <NUM> in step S216 and then received by the lens control unit <NUM> in step S115 is a driving command for the composite focusing lens unit when the zoom positions are normalized.

In step S116, the lens control unit <NUM> generates a driving command for the first focus unit <NUM> and a driving command for the second focus unit <NUM>. To generate a driving command for each of the first focus unit <NUM> and the second focus unit <NUM>, based on the information received in step S115, the lens control unit <NUM> generates a driving command for the first focus unit <NUM> and a driving command for the second focus unit <NUM> in a state where the zoom positions are normalized. The lens control unit <NUM> then converts the driving commands into the positions corresponding to the current zoom position, thus generating a driving command for the first focus unit <NUM> and a driving command for the second focus unit <NUM>.

For example, a case will be described where <position of the first focus unit <NUM> at zoom position X with a subject distance of <NUM>>/<position of the first focus unit <NUM> at TELE> is <NUM>/<NUM> in <FIG>. In such a case, the lens control unit <NUM> multiplies the number of pulses as a driving command for the first focus unit <NUM> when the zoom positions are normalized, by <NUM>/<NUM>, thus obtaining the target absolute position for the first focus unit <NUM> at the current zoom position.

In step S117, the lens control unit <NUM> drives the first drive unit <NUM> and the second drive unit <NUM> based on the two driving commands generated in step S116, thus performing a focusing operation by the first focus unit <NUM> and the second focus unit <NUM>.

The lens side processing and the camera side processing in the focus control are performed in this way.

The order in which the lens control unit <NUM> transmits the composite focus position, the composite focus sensitivity, and the pulse conversion coefficient to the camera control unit <NUM> is not limited to the transmission order described in the flowchart illustrated in <FIG>.

The processing in step S111 illustrated in <FIG> will be described in detail below with reference to <FIG> is a flowchart illustrating the method for calculating the composite focus position according to the second exemplary embodiment. The lens control unit <NUM> reads a program for executing the processing of the flowchart from the memory <NUM> and then executes the program.

In step S1111, the lens control unit <NUM> acquires the current zoom position with the zoom position detection unit <NUM>.

In step S1112, the lens control unit <NUM> acquires the current focus position of the first focus unit <NUM> via the first detection unit <NUM>.

In step S1113, based on the current zoom position acquired in step S1111 and the current position of the first focus unit <NUM> acquired in step S1112, the lens control unit <NUM> calculates the subject distance corresponding to the current position by using the information illustrated in <FIG>.

Operations in steps S1114 to S1118 are almost similar to the above-described operations in steps S1013 to S1017, respectively, and detailed descriptions thereof will be omitted. However, unlike the first exemplary embodiment, in step S113, the lens control unit <NUM> transmits, as the focus sensitivity, the focus sensitivity corresponding to the zoom position normalization to the camera control unit <NUM>.

In step S1119, the lens control unit <NUM> calculates the composite focus unit position when the zoom positions are normalized, based on the composite focus unit position calculated in step S1118. In such a case, the lens control unit <NUM> normalizes the composite focus unit position in the entire zoom range in terms of the composite focus position at TELE (telephoto end) for the same subject distance. This completes the description of the processing included in step S111.

The present exemplary embodiment produces effects similar to the first exemplary embodiment. More specifically, the camera control unit <NUM> can generate a driving command without changing the calculation processing depending on the number of focus units included in the lens apparatus <NUM> attached to the camera body <NUM>, making it possible to configure the camera system <NUM> in which error are less likely to occur.

Even in a case where the movement of a certain focus unit lags, the lens control unit <NUM> can control the positions based on a driving command with the lag compensated, by calculating the composite focus unit position corresponding to the current in-focus position.

In addition, in a case where the lens apparatus <NUM> is a zoom lens, the lens control unit <NUM> applies normalization processing to the zoom positions. Thus, even if the camera control unit <NUM> cannot grasp the zoom position, the camera control unit <NUM> can perform focus control without changing the calculation processing according to the type of the optical system <NUM> (fixed focal length lens or zoom lens).

A third exemplary embodiment of the present invention will be described below. The first and the second exemplary embodiments have been described above centering on a case where the driving command specifies the number of pulses indicating the target absolute position. In the present exemplary embodiment, the driving command specifies the number of pulses indicating a movement amount required for a movement from the current position to the target position. In other words, the driving command according to the third exemplary embodiment specifies the number of pulses indicating a relative position with reference to the current position.

Differences from the processing according to the first exemplary embodiment illustrated in <FIG> will be described below.

In step S101, the lens control unit <NUM> calculates the composite focus position through processing similar to the first exemplary embodiment. The composite focus position calculated here is to be used by the lens control unit <NUM> to perform calculation afterwards, and therefore does not need to be transmitted to the camera control unit <NUM> as in step S102. According to the third exemplary embodiment, the information to be transmitted from the lens control unit <NUM> to the camera control unit <NUM> may include only the composite focus sensitivity and the pulse conversion coefficient.

The third exemplary embodiment differs from the first exemplary embodiment in the operations in steps S205 and S <NUM>.

In step S205, the camera control unit <NUM> calculates a driving command based on the defocus amount detected by the defocus detection unit <NUM> and the composite focus sensitivity and the pulse conversion coefficient acquired from the lens control unit <NUM>. The driving command to be calculated here specifies the number of pulses indicating the movement amount of the composite focus unit required to zero the defocus amount, more specifically, the number of pulses indicating a relative position with respect to the current position. In step S206, the camera control unit <NUM> transmits this driving command. In step S105, the lens control unit <NUM> receives the driving command.

In step S106, the lens control unit <NUM> controls the positions of the first focus unit <NUM> and the second focus unit <NUM> based on the received driving command and the composite focus position calculated in step S101.

In this case, the lens control unit <NUM> determines the number of pulses indicating the target absolute position for the composite focus unit from the received driving command. For example, assume that the composite focus unit position corresponding to the current subject distance (αm) is represented by <NUM> pulses, and the lens control unit <NUM> has received -<NUM> pulses as a driving command from the camera control unit <NUM>. In such a case, the target absolute position for the composite focus unit is calculated as <NUM> - <NUM> = <NUM> pulses.

After calculating the target absolute position, the lens control unit <NUM> calculates the number of pulses indicating the target absolute positions for the first focus unit <NUM> and the second focus unit <NUM> by using the information illustrated in <FIG>, and <FIG> and then executes step S107, as in the first exemplary embodiment.

In this way, the present invention produces effects similar to the first exemplary embodiment even in a case where a driving command indicates the movement amount required to reach the target absolute position.

If the driving command includes information indicating whether the driving command is the target position or the movement amount to reach the target position, a driving command of a different type may be transmitted at a different timing depending on the status of the camera control unit <NUM>.

A fourth exemplary embodiment of the present invention will be described below. According to the first exemplary embodiment, the defocus detection unit <NUM> detects the defocus amount based on the phase difference detection method. According to the present exemplary embodiment, the defocus detection unit <NUM> detects a contrast value based on image signals generated by the image sensor <NUM> and the signal processing unit <NUM>. Automatic focus control by detecting the contrast value is referred to as contrast automatic focusing (AF). In contrast AF, the defocus detection unit <NUM> detects the contrast value while moving the focus unit at a constant speed from end to end of the movable range and detects the focus unit position when the contrast value reaches the peak as the position in the in-focus state. The lens control unit <NUM> then moves again the focus unit having reached the end of the movable range, with the position in the in-focus state as the target absolute position, to perform focusing.

In contrast AF, the fourth exemplary embodiment differs from the first exemplary embodiment also in the calculation processing which is performed by the camera control unit <NUM> to generate a driving command. Other configurations are similar to those of the camera system <NUM>, and detailed descriptions thereof will be omitted.

In contrast AF, the camera control unit <NUM> transmits the driving command to the lens control unit <NUM>, and the lens control unit <NUM> moves the first focus unit <NUM> and the second focus unit <NUM> at predetermined speeds over the entire movable range. While the first focus unit <NUM> and the second focus unit <NUM> are being scanned, the defocus detection unit <NUM> outputs a contrast value to the camera control unit <NUM> at a fixed timing. The lens control unit <NUM> transmits the composite focus position to the camera control unit <NUM> at predetermined intervals.

The camera control unit <NUM> determines the composite focus unit position where the contrast value peaks, based on the output from defocus detection unit <NUM>. The peak may be determined by interpolation. The camera control unit <NUM> then determines the composite focus unit position when the current contrast value peaks, as a driving command for the composite focus unit, and transmits the driving command to the lens control unit <NUM>. The method through which the lens control unit <NUM> determines the composite focus unit position and the processing in which the lens control unit <NUM> receives a driving command are similar to those according to the first exemplary embodiment.

The present exemplary embodiment produces effects similar to those of the first and the second exemplary embodiments even in a case where the driving command for the composite focus unit is generated based on a result of the contrast detection.

As other exemplary embodiments, the following modifications may be applied to the first to the fourth exemplary embodiments.

While the number of pulses corresponding to the target position is used as the driving command in the above-described exemplary embodiments, the method for representing the driving command according to the present invention is not limited thereto. For example, the distance [mm] from the reference position and the movement amount [mm] from the current position to the target position may be used as a driving command. Alternatively, an electrical signal to be applied to an actuator by when the target position is reached may be used as a driving command. The information about the composite focus unit position generated by the lens control unit <NUM> is not limited to the number of pulses, and may be represented by the distance from the reference position.

The number of focus units included in the lens apparatus <NUM> is not limited to two, and may be three or more. Even when the lens apparatus <NUM> includes three or more focus units, the lens control unit <NUM> is capable of calculating one composite focus unit position based on the respective positions and the respective focus sensitivities of all focus units. The lens apparatus <NUM> transmits the composite focus position and the composite focus sensitivity to the camera control unit <NUM>, and thus, the camera control unit <NUM> can generate a driving command for the composite focus unit.

The information to be transmitted from the lens control unit <NUM> to the camera control unit <NUM> is not limited to the focus sensitivity of the composite focus unit, and may be other information as long as the information is focus sensitivity information with which the focus sensitivity can be calculated by the camera control unit <NUM>. For example, if the camera control unit <NUM> recognizes that the focus sensitivity is represented by Expansion (<NUM>), the lens control unit <NUM> may transmit the coefficient for each term (S<NUM>, S<NUM>,. ) as the focus sensitivity information to the camera control unit <NUM>. However, one set of coefficients for calculating one focus sensitivity is treated as one piece of focus sensitivity information.

While the present invention has specifically been described based on the above-described exemplary embodiments, the present invention is not limited thereto but can be modified and changed in diverse ways within the ambit of the appended claims.

Claim 1:
A lens apparatus attachable to and detachable from a camera body (<NUM>), the lens apparatus comprising:
an optical system (<NUM>) including a plurality of lens units (<NUM>, <NUM>) configured to move in adjusting an in-focus state of a subject image;
detection means (<NUM>, <NUM>) configured to detect a position of each of the plurality of lens units (<NUM>, <NUM>);
acquisition means (<NUM>) configured to acquire position information regarding a single position representing a position of a virtual composite lens unit, that integrates the plurality of lens units (<NUM>, <NUM>) into one, corresponding to a current subject distance, based on:
the positions of the plurality of lens units (<NUM>, <NUM>) detected by the detection means (<NUM>, <NUM>),
first relational information indicating a relation between a position of each of the plurality of lens units (<NUM>, <NUM>) and a subject distance, and
second relational information indicating a relation between the subject distance and a position of the virtual composite lens unit; and
control means (<NUM>) configured to control the positions of the plurality of lens units (<NUM>, <NUM>) based on the position information,
wherein the acquisition means (<NUM>) is configured to calculate a deviation in the position of the virtual composite lens from a target position of the virtual composite lens corresponding to a target subject distance resulting from a lag in movement of at least one but not all of the plurality of lens units (<NUM>, <NUM>) such that at least one but not all of the lens units (<NUM>, <NUM>) are at their target position, and to determine the current subject distance based on the deviation.