JPH0477290B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention forms a subject image on a light-integrating type light-receiving element using a light flux that passes through a lens and enters the lens, and integrates the light amount to form a subject image on a light-receiving element of the light-integrating type. The present invention relates to an automatic focusing device for a camera that determines the amount of defocus for a subject.

[Prior Art] In cameras that require high-precision focusing, such as single-lens reflex cameras, so-called TTL focus detection is used to detect the amount of defocus based on the state of the image formed by the light flux that passes through the lens. This method is often used as an autofocus AF method.

Defocus amount is the lens extension amount conversion coefficient
It is converted into a drive pulse for the AF motor using Kval.

In this specification, Kval is defined as the amount of lens extension per unit amount of image plane movement, but it can also be defined in the opposite way, that is, as the amount of image plane movement per unit amount of lens extension. In this case, the magnitude relationship described later is reversed.

Note that Kval takes a different value for each focal length in a zoom lens, so it is
Stored in ROM as variable information.

By the way, Kval generally takes a smaller value as the focal length is longer and a larger value as the focal length becomes shorter.
It is expressed by a curve as shown by the broken line in the figure. Note that since the focal length of the lens cannot be directly detected, the graph shows the position of the zoom ring as a variable corresponding to the focal length.

In conventional zoom lenses, Kval is determined based on the zoom code detected by the sliding contact between the brush and the code plate provided on the zoom ring and fixed ring of the lens barrel. 1st
As shown by the solid line in Figure 3, the data was managed as intermittent data that took one value within the zoom code section.

This similarly applies to detecting the focal length as shown in FIG. In addition, in FIG. 14, in order to distinguish between the actual focal length and the focal length detected from the zoom code plate, the latter is shown as the detected focal length.

[Problems to be Solved by the Invention] However, in the configuration in which the data in the lens ROM is addressed based on the zoom code detected from the zoom code board as described above, the Kval
The problem was that the AF control was rough and accurate AF control could not be performed.

This invention was made in view of the above problems, and by detecting the drive amount of the zoom motor that performs zooming,
The purpose of this invention is to provide an automatic focusing device for a camera that can more accurately calculate Kval.

[Means for Solving the Problems] As shown in FIG. 1, an automatic focusing device according to the present invention includes a zoom motor for zooming a photographic lens, a focus motor for focusing the photographic lens, and a focus motor. a zoom motor drive amount detection means for detecting the drive amount of the zoom motor; a focal length detection means for dividing and detecting the focal length of the photographic lens into a plurality of sections; A defocus amount detection means for detecting a defocus amount; and a reference coefficient output means for outputting a reference value of a lens extension amount conversion coefficient for converting the defocus amount into a focus lens drive amount in accordance with the output of the focal length detection means. , correction coefficient output means for outputting the rate of change of the conversion coefficient within the interval, and managing the conversion coefficient within the same interval of the focal length detection means as a linear function from the output and change rate of the reference coefficient and the zoom motor drive amount detection means. The present invention is characterized by comprising a conversion coefficient calculating means and a driving amount calculating means for calculating the driving amount to be transmitted to the motor driving means from the conversion coefficient and the differential focus amount.

[Operation] According to this invention, the lens extension amount conversion coefficient
Kval can be successively determined in more detail based on the focal length information detected by the drive amount of the zoom motor. Furthermore, it is only necessary to manage two values for the coefficient Kval within the zoom code section while using the conventionally used zoom code board.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 2 is a block diagram schematically showing a camera system equipped with an automatic focusing device according to the present invention.

The body 1 is equipped with two CPUs: a main CPU 10 that processes various information for shooting, and a display CPU 11 that mainly inputs information using a switch, exchanges information with the shooting lens 2, and displays it.
Display various information centered on these CPUs
LCD panel 12, printed on the cartridge
A Dx code input circuit 13 that inputs the ISO sensitivity of the film used from the Dx code, a light receiving element 14 that measures the brightness of the subject from the light flux incident through the photographic lens, and A that converts the output of this light receiving element from A/D. /D circuit 15, an exposure control circuit 16 that controls the shutter based on various input shooting conditions, an AF CCD 17 that receives a subject image formed by a flux of light incident through the shooting lens,
A CCD processing circuit 18 is provided for detecting the amount of defocus of the photographing lens from the output of the AF CCD 17.

In addition, an autofocus AF motor 19 for performing lens focusing is installed inside the lens.
This is an AF motor control circuit that transmits driving force to the photographic lens side via the coupler 19a when a photographic lens without a motor is attached, and drives the AF motor 19 by calculating the output of the CCD processing circuit 18. 20, is provided together with an AF pulser 21 that detects the drive amount of the AF motor 19 as a pulse.

The battery 22 not only supplies power to each of the active elements in the camera body described above, but also supplies power to the motor and CPU in the photographic lens, which will be described later.

On the other hand, lens 2 has an AF motor 60 inside the lens.
and power zoom PZ motor 61 and automatic aperture control AE
It has three built-in motors, including a motor 62, and is configured so that focusing, zooming, and aperture control can all be performed by the driving force within the lens.

The lens 2 has a conventional cam mechanism that performs focusing and zooming by moving each lens group relative to each other in the optical axis direction by rotating a cam ring, and the AF motor 60 and PZ motor 61 described above are used for focusing and zooming.
and drive the cam rings to rotate.

Each motor is configured to be controlled by a lens CPU 66 as calculation means via an AF motor drive section 63, a PZ motor drive section 64, and an AE motor drive section 65.

Information input means for the lens CPU 66 include a lens ROM 67 as a storage means for storing lens-specific information, an AF pulser 68, a PZ pulser 69, an AE pulser 70 that converts the drive amount of each motor into pulses and detects the pulses, and a zooming system. It has a zoom code plate 71 and a distance code plate 72 for detecting the rotational positions of the cam ring for use and the cam ring for focusing, respectively.

Note that the code plate is actually composed of a combination of a code plate fixed to the cam ring and a plurality of brushes attached to the fixed ring and in sliding contact with the code plate. Although the configuration is such that the rotational position is detected by dividing it into a plurality of regions, these are collectively referred to as a code plate for convenience's sake.

In addition to being connected to the control target and input means described above, the lens CPU 66 is also capable of communicating with the body 1 side through a group of electrical contacts provided at the mount opening. In response to the detected amount of def focus, the lens ROM6
The function calculates the driving amount while referring to the data of 7, and drives the AF motor 60 while detecting the driving amount with the AF pulser 68, or the driving amount is calculated with the AE pulser 70 based on the aperture value determined on the body side. It has a function of rotationally driving the AE motor 62 while detecting it.

In addition, depending on the situation, the lens may have a
AF coupler 73 for driving the focus lens so that focusing is also possible with the AF motor.
Also provided.

The lens CPU 66 uses information from the lens ROM,
Alternatively, each motor drive circuit within the lens is controlled based on information transferred from the body, and setting data is transferred to the body side.

The lens ROM 67 stores information specific to the photographic lens, such as the maximum aperture F number, the minimum aperture F number, and the amount of change in Kval associated with zooming, and is controlled by the lens CPU 66 or the CPU on the body side. Send data.
In a zoom lens as in this example, the upper address of the lens ROM is designated based on the zoom code detected from the zoom code board, and the lower address is created internally by counting input clocks.

By the way, as mentioned above, Kval is a value that changes depending on the focal length of the lens, and generally, the longer the focal length is, the smaller it is, and the shorter the focal length is, the larger it is. This system calculates Kval by dividing the same zoom code area detected from the zoom code plate into finer steps using the PZ pulse output from the PZ pulser, enabling more accurate AF control. It is said that

In other words, Kval originally changes smoothly as shown by the broken line in Figure 3, but with this lens, Kval changes smoothly at the top of one set corresponding to one zoom code area.
Read KvalKh, Kval correction coefficient Kc, and number of leading pulses Ph from the lens ROM, and use these values and the absolute number of pulses Ps from the wide end of the current zoom lens using the PZ pulser to calculate the number of pulses within one zoom code area. Changes in Kval are managed as a linear function like an equation.

Kval=Kh+Kc ^* (Ps-Ph)... Note that the leading KvalKh and the leading pulse number Ph are the Kval and pulse number at the wide end in one focal length area detected from the zoom code board, respectively, and are C in the figure. It refers to the value from point to point G. Further, the Kval correction coefficient Kc refers to the slope of a straight line connecting each leading Kval. In this embodiment, Kval is managed as a linear function within the same section of the zoom code plate, but it is also possible to store Kval in correspondence only to the absolute number of pulses Ps.

Further, in this system, the detection focal length f is also managed in the same manner as shown in the equation (see FIG. 4).

f=fh+fc ^* (Ps-Ph)... fh: Leading focal length fc: Focal length correction coefficient This allows constant image magnification control to be performed with high precision. Furthermore, constant image magnification control is
In a camera capable of power zooming using a zoom motor, this refers to changing the focal length of the lens so that the size of the subject image on the image plane remains constant even when the distance between the subject and the camera changes.

In cameras that use the focus detection method for autofocus, such as single-lens reflex cameras, this control calculates the change in focal length corresponding to the change in magnification from the amount of defocus after the subject moves once in focus. This is done by converting the change into a drive pulse for the zoom motor and controlling it.

Furthermore, in this camera system, in order to achieve accurate AF even if the focal length of the photographing lens changes during AF operation, the Kval at the start and end of CCD integration is input and the drive is activated based on both. Calculating pulses.

This configuration will be explained below.

5 to 8 are graphs showing an example of the interrelationship between the focal length of the lens, the amount of defocusing, and the number of driving pulses for the focusing lens.

In Figure 5, the x-axis is the focal length of the lens, and the y-axis is
The number of AF drive pulses, the z-axis shows the amount of defocus, and the focal lengths from wide end to tele end are f1 to f7. For example, the focal length for the differential focus amount z ₁
The number of drive pulses until focus at f3 is represented by _y1 .

FIG. 6 shows the operation when focusing the lens at the defocus amount z2 while performing zooming at focal lengths f2 to f6. The upper curve of the plane S, which is a projection of a cross section parallel to the z-axis onto the yz plane, shows a decrease in the amount of defocus as the lens is driven.

Similarly, Figure 7 shows the operation of zooming from wide end f1 to tele end f7 until the lens is brought into focus when the def focus amount is z3. - This figure shows the operation of zooming at the wide end _f1 until the lens is brought into focus when the lens is in the state of the defocus amount z4. The above three cases are cases in which the number of drive pulses is the same, although the amount of defocus is different.

As can be understood from the projection diagrams of FIGS. 6 to 8, the process of decreasing the amount of defocus differs when zooming from the wide side to the telephoto side and when zooming from the telephoto side to the wide side. When performing overlap integration while driving the lens for focusing, more accurate AF control can be performed by taking the above process into consideration.

First, the overlap integral will be explained based on FIG. 9. P1 is the drive pulse from the stop position to the start of CCD integration, P2 is the drive pulse until the end of integration, P3 is the number of pulses until the end of the calculation that detects the defocus amount from the CCD output and converts it into a drive pulse, and the target Let P4 be the number of pulses until the desired in-focus position.

According to a simple calculation, the number of pulses obtained by the above calculation corresponds to the amount of defocus when the lens is located at the intermediate position between the start and end of integration, the number of pulses (P1 + P2) / 2. Become. However, the actual lens position at the end of the calculation is
It is located at a point closer to the target by α pulse than the intermediate point, and according to the simple calculation above, the α pulse will overlap in the drive amount, so AF
During driving, the driving pulse is determined by subtracting α from the calculation result.

Next, calculate the overlap integral during zooming as the first
This will be explained in detail based on Figure 0.

FIG. 10 is an enlarged view of a part of the process shown in FIGS. 6 and 7 in which overlap integration is performed while zooming from the wide side to the telephoto side.

The amount of defocus determined by overlap integration is the average value between the start and end of the integration, that is, (d1 + d2)/2, but the approximate Kval for finding the number of pulses corresponding to this defocus amount is Kval (K1) at the start and at the end
It can be determined by the average value (K1+K2)/2 of Kval (K2).

Then, the number of drive pulses found using Kval based on this average value is (P1 + P2)/2,
Number of drive pulses corresponding to the actual amount of focus
It will take a value larger than P5. Therefore,
In this system, Kval used for pulse calculation is subtracted by n% when performing overlap integration while zooming from the wide side to the telephoto side, so that it is possible to calculate a value close to the number of pulses starting from P5. It consists of

On the other hand, when performing overlap integration while zooming from the telephoto side to the wide side, the defocus pulse curve curves downward as can be seen from Figure 8, so it is necessary to use it for calculations.
The configuration is such that Kval is increased by n%. In addition,
n% is a value calculated based on Kval at the start and end of integration.

Hereinafter, the operation of the system configured as described above will be explained based on FIGS. 11 and 12.

FIG. 11 is a flowchart for calculating the AF drive pulse. In step (hereinafter referred to as S.) 1, CCD integration is started, and in S. 2, Kval at the starting focal length is calculated.

This Kval calculation is performed according to the flow shown in FIG. This process inputs the current zoom code from the zoom code board in S.20,
Leading KvalKh corresponding to this zoom code in S.21
etc. are input from the lens ROM.

In S.22, input the current number of zoom lens driving pulses counted from the wide end from the counter that counts the pulses output from the PZ pulser, and the Ps detected in S.23 is It is determined whether the number is between the first pulse Ph and the number obtained by adding the pulse width Pw of the code area. When the pulsar is operating normally, Ps is within this range, so if it is out of this range, it is assumed that there is a problem with the pulsar or counter, and error processing is entered to stop further calculations.

If Ps is within the predetermined range, Kval is determined according to the above-mentioned formula in S.24, and the process returns to the flow of FIG. 11.

Now, when Kval is calculated in S.2, in S.3 this is set as Kval (K1) at the time of starting the integration. Next, in S.4, wait until the CCD integration is completed, and in S.5 and 6, calculate Kval (K2) at the end of the integration, and in S.7, calculate the amount of defocus.

During AF driving, that is, when performing overlap integration, proceed from S.8 to S.9, set the average value of K1 and K2 to Kval, and determine whether the PZ motor is being driven in S.10. However, when zooming from the wide side to the tele side, the Kval set in S.9 is changed to n%.
If you are zooming from the tele side to the wide side, add n% to Kval.

Subsequently, the drive pulse Px is calculated from the above-mentioned Kval and the defocus amount dx, and in S.15, the overlap amount α is subtracted to calculate the final drive pulse.

If it is determined in S.8 of Figure 11 that AF is not in operation, proceed to S.16 and
Find the drive pulse based on Kval and K2.

The lens CPU 66 manages the output of the AF pulser 68 based on the drive pulse obtained by the above calculation, and controls the AF motor drive section 63 to perform AF operation.
The motor 60 is driven. As a result, focusing is performed and the lens can be brought into focus on the subject.

In the above embodiment, only a camera using a silver-lead film was described, but the scope of application of the present invention is not limited thereto, and for example, a so-called electronic still camera that uses a photoelectric conversion element such as a two-dimensional CCD as an imaging means. The same applies to systems where lenses can be replaced.

[Effect] As explained above, according to the camera automatic focusing device according to the present invention, the lens extension amount conversion coefficient that changes with zooming can be accurately managed using the drive amount of the zoom motor. Therefore, accurate AF control can be performed.

[Brief explanation of drawings]

FIG. 1 is a diagram corresponding to claims of the automatic focusing device for a camera according to the present invention. Fig. 2 is a block diagram showing an embodiment of a camera including the device according to the present invention, and Figs. 3 and 4 show focal length and Kval in the device according to the invention, detected from the focal length and zoom code plate, etc. Graphs showing the relationship with the detected focal length; FIGS. 5 to 8 are graphs showing the relationship between the focal length and the amount of defocus and the amount of drive of the focus lens; FIG. 9 is an explanatory diagram showing the principle of overlap integral; FIG. 10 is an explanatory diagram showing the principle of overlap integration during zooming, FIGS. 11 and 12 are flowcharts showing the operation of the focus detection device according to the present invention, and FIGS. 2 is a graph showing the relationship between the focal length and Kval in a focusing device, and the focal length and a detected focal length detected from a zoom code plate or the like. 1... Camera body, 2... Shooting lens, 1
0, 11, 66...Main CPU, display CPU,
Lens CPU (conversion coefficient calculation means, drive amount calculation means), 17... CCD for AF (defocus amount detection means), 60... AF motor (focus motor),
61...PZ motor (zoom motor), 63...
AF motor drive unit (motor drive means), 69...
PZ pulser (zoom motor drive amount detection means), 6
6... Lens ROM (reference coefficient output means, correction coefficient output means), 71... Zoom code plate (focal length detection means).

Claims (1)

[Claims] 1. A zoom motor for zooming a photographic lens, a focus motor for focusing the photographic lens, a motor driving means for driving the focus motor, and a zoom motor driving amount detecting means for detecting the driving amount of the zoom motor. a focal length detecting means for detecting the focal length of the photographing lens by dividing it into a plurality of sections; a defocus amount detecting means for detecting the amount of focus of the photographing lens relative to the subject; and a means for detecting the amount of defocus for detecting the amount of focus of the photographic lens with respect to the subject; a reference coefficient output means for outputting a reference value of a conversion coefficient for a lens extension amount corresponding to the output of the focal length detection means; a correction coefficient output means for outputting a rate of change of the conversion coefficient within the interval; conversion coefficient calculation means for managing the conversion coefficient within the same section of the focal length detection means as a linear function from the reference coefficient, the output of the zoom motor drive amount detection means, and the rate of change;
An automatic focusing device for a camera, comprising: drive amount calculation means for calculating a drive amount to be transmitted to the motor drive means from the conversion coefficient and the defocus amount.