JPH05107452A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To surely predict a distance from a subject after a predetermined time has passed without affected by a focal distance of a lens and to surely focus on the moving subject by predicting movement of the subject based on change in a defocusing amount and a photographing lens position. CONSTITUTION:A defocusing amount of a photographing optical system is detected, the defocusing amount after a predetermined time has passed is predicted by change in the detected defocusing amount and a driving amount of the photographing lens is obtained by the detected defocusing amount. And a calculating means calculates the defocusing amounts at a first point of time and a second point of time after a first predetermined time has passed, respectively (B1, B2), and a detecting means detects a total delivery amount of the photographing lens from an infinite far position (B3). A predicting and calculating means predicts the defocusing amount at a third point of time after a second predetermined time has passed in continuation from the first predetermined time from the defocusing amounts at the first and the second points of time and the delivery amount (B6).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device used for a camera or the like, and more particularly to an automatic focusing device which detects movement of a subject and focuses on the moving subject.

[0002]

2. Description of the Related Art Conventionally, many devices have been proposed which detect the movement of a subject and focus on the moving subject. For example, in Japanese Unexamined Patent Publication No. 60-214325, in predicting the movement of a subject from the change in the detected defocus amount, a linear expression of the detected defocus amount and time is used. That is, when the time is t and the defocus amount is ΔD, Equation 1 is obtained.

[0003]

[Equation 1] The coefficients a ₀ and b ₀ are obtained from the defocus amounts ΔD ₀ and ΔD ₁ detected at the time t ₀ and the time t ₁ to obtain the defocus amount after a predetermined time. For example, JP-A-1-107224
No. 2 predicts a quadratic equation of the detected defocus amount and time as shown in Formula 2.

[0004]

[Equation 2] ΔD of the defocus amount detected at times t ₀ , t ₁ and t _2.
The coefficients a ₁ , b ₁ and c ₁ are obtained from ₀ , ΔD ₁ and ΔD ₂ to obtain the defocus amount after a predetermined time.

[0005]

The change of the defocus amount when the object is moving at a constant speed in the optical axis direction is first described.
Shown in the figure.

In FIG. 9, the optical image of the subject image I is formed as a subject image I'in the vicinity of the film surface F by the taking lens unit L. The equivalent focal length of the taking lens unit L is f,
When the equivalent thickness is C and the distance from the film surface F to the imaged subject image I ′, that is, the defocus amount is ΔD, the distance R from the film surface to the subject is as shown in Formula 3.

[0007]

[Equation 3] Therefore, Equation 4 is obtained.

[0008]

[Equation 4] Considering with the lens fixed, R-1-2f-C = D + ΔD =
Since k can be set, Equation 5 is required.

[0009]

[Equation 5] If the subject is moving at a constant velocity v in the optical axis direction,
Equation 6 is obtained with l = vt + l ₀ .

[0010]

[Equation 6] Now, focal length f = 100 mm, subject distance l ₀ = 10
Table 1 shows changes in the defocus amount from the in-focus state (ΔD = 0) at m, subject speed v = 50 km / h. Table 1 shows the change in the predicted value and the error between the conventional example in which the defocus amount is predicted by a linear expression and the conventional example in which it is predicted by a quadratic expression.

[0011]

[Table 1] Table 1 shows the distance measured every 0.1 sec and the position predicted every 0.1 sec. When predicting with a linear expression, time t ₀ =
From the distance measurement data of 0 sec and t ₁ = 0.1 sec, time t =
The position of 0.2 sec to 0.5 sec is predicted. When predicting with a quadratic equation, time t ₃ = 0 sec; t ₁ = 0.1 se
From the distance measurement data of c, t ₂ = 0.2 sec, time t = 0.3
The position of ~ 0.5sec is predicted.

As can be seen from Table 1, in the conventional example, the error increases as the prediction time increases, and the correct focus position cannot be obtained.

In FIG. 10, focal length f = 100 mm, subject distance l ₀ = 10 m, 8 m, 6 m, subject velocity v = 5.
The change of the defocus amount from the focused state (ΔD = 0) is shown at 0 km / h. When l ₀ = 10 m, 8 m, and 6 m, the value of k is set as ΔD = 0 from equation (6), and k = 1 mm, 1.25 mm,
It will be 1.67 mm. According to the figure, as the subject distance becomes shorter and the prediction time becomes longer, the conventional 1
It can be seen that there is a large error in the approximation curves of the following equations and quadratic equations.

The present invention has been made in view of the above-mentioned problems, and by using an expression having a high prediction accuracy again from the conventional prediction expression, an automatic focusing operation can be performed accurately for a moving object. The purpose is to provide a device.

[0015]

That is, the present invention detects the defocus amount of a photographing optical system, predicts the defocus amount after a predetermined time from changes in the detected defocus amount, and calculates the defocus amount from the predicted defocus amount. In an automatic focusing device for obtaining the driving amount of a photographing lens, a calculating means for calculating a defocus amount at a first time point and a second time point after a first predetermined time from this point, and an infinity position of the photographing lens. From the defocus amount at the first time point and the defocus amount and the feed amount at the second time point, the second predetermined time following the first predetermined time. And a predictive calculation means for predicting a defocus amount at a third time point after the elapse of time.

[0016]

The automatic focusing device of the present invention detects the defocus amount of the photographing optical system, predicts the defocus amount after a predetermined time from the change in the detected defocus amount, and determines the defocus amount of the photographing lens from the predicted defocus amount. The drive amount is obtained. Then, the defocus amount of each of the first time point and the second time point after the first predetermined time from this time point is calculated by the calculation means, and the detection means calculates the extension amount of the photographing lens from the infinity position. To be detected. Then, based on the defocus amount and the feed amount at the first and second time points, the predictive calculation means calculates the defocus amount at the third time point after the second predetermined time period following the first predetermined time period. Predict.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

First, the principle of the present invention will be described. According to the present invention, the relational expression between the defocus amount and the time is obtained by the equation 7 obtained by modifying the equation 6.

[0019]

[Equation 7] Here, k is D + ΔD in FIG. 9 as described above, and this corresponds to the amount of extension of the taking lens from the infinite position. Coefficient alpha, beta, as shown in Equation 8 and Equation 9, and [Delta] D ₁ of the defocus amount at time t _1, obtained from the defocus amount [Delta] D ₂ at time t _2. However, it is assumed here that the lens position does not change.

[0020]

[Equation 8]

[0021]

[Equation 9] Therefore, the equations 10 and 11 are obtained.

[0022]

[Equation 10]

[0023]

[Equation 11] Here, the relationship between the above equations 7 and 6 is as follows. That is, it becomes as shown in Expression 12.

[0024]

[Equation 12] On the other hand, as shown in FIG. 1, the subject I is I from time t ₀ to t _2.
Assuming that the vehicle travels from ₀ to I ₃ at the speed v, the following equations, equations 13 and 14, hold at the time t _{1 and} the time t ₂ .

[0025]

[Equation 13]

[0026]

[Equation 14] Then, when l ₀ is deleted from the _equations 13 and 14, the _equation 1
5 is required.

[0027]

[Equation 15] Furthermore, if f ² is erased from Equations 13 and 14, Equation 16 is obtained.
Is established.

[0028]

[Equation 16] By the way, it is possible to accurately predict the defocus amount after a predetermined time by the above-mentioned formula 7 based on the defocus amount and the photographing lens position detected at two different times. When the lens position changes at time t ₁ and time t ₂ , that is, when the lens position is detected while driving the lens, it can be similarly obtained by approximating Formula 7 to a formula such as Formula 17.

[0029]

[Equation 17] Here, k ₁ is the lens position at time t ₁ , and k ₂ is time t
_This is the lens position at ₂ . Next, an explanation will be given according to an example in which the present invention is applied to a camera having a built-in zoom lens mechanism.

FIG. 2 shows a ray diagram of a camera incorporating the zoom lens mechanism to which the automatic focusing device of the present invention is applied. In the figure, the subject ray is
It passes through a photographing lens 101 including five lens groups and a photographing diaphragm, and enters a main mirror 102. The taking lens 101 has a focusing function in the first and second groups, and a third group
The fifth and fifth groups in which the fourth group and the fourth group perform zooming operations are fixed. When zooming, move the 3rd and 4th groups while
The first and second groups are driven by a cam structure to prevent out of focus during zooming.

The main mirror 102 is a half mirror, and 2/3 of the amount of incident light is in the finder optical system 10.
It is reflected in 3. The remaining 1/3 of the amount of incident light is transmitted through the main mirror, reflected by the sub mirror 104, and guided to the AF optical system 105. The AF optical system 105 includes a field stop 1
06, infrared cut filter 107, condenser lens 1
08, a mirror 109, a re-imaging diaphragm 110, a re-imaging lens 111, and an AFIC 112.

The field stop 106 determines the field of view for AF detection from the photographing screen so that the two light images divided by the re-imaging lens 111 do not interfere with each other.
The infrared cut filter 107 cuts infrared light unnecessary for AF detection and prevents aberration shift due to infrared light. The condenser lens 108 is installed in the image formation plane of the subject light image by the taking lens 101, that is, in the vicinity of the film equivalent plane, and the subject light image formed near the film equivalent plane in the AFIC 112 together with the re-imaging lens 111. Reimage.
Further, the re-imaging diaphragm 110 is symmetrical with respect to the optical axis and makes a pair, and selects and passes two light beams from the subject light beams that have passed through the condenser lens 108. The two light fluxes that have passed through the re-imaging diaphragm are re-imaged on the two photoelectric conversion element arrays on the AFIC 112.

The finder optical system 103 is composed of a focusing screen 113, a condenser lens 114, a prism 115, a mold roof mirror 116, and an eyepiece lens 117. The subject light image that has passed through the taking lens 101 is formed on the focusing screen 113. Then, the formed image can be observed by the photographer through the condenser lens 114 and the eyepiece lens 117.

Main mirror 102 and sub mirror 104
Is the position of the dotted line in the figure during film exposure (shown by the arrow G
Direction). Then, the subject light that has passed through the taking lens 101 is exposed on the film 119 from the time when the front curtain of the shutter 118 opens to the time when the rear curtain closes.

FIG. 3 is a block diagram of the camera of this embodiment. In the camera system in the embodiment, C
PU201, interface IC202, power supply unit 203, flash unit 204, mirror shutter unit 205, winding unit 206, lens unit 207, finder unit 208, display unit 2
09, the AF unit 210, and the like.

The CPU 201 controls the entire camera system, and via the serial communication line 211,
Interface IC202, LCDIC235, AF
It transmits and receives data to and from the IC 240 and the E ² PROM 237. In addition, the CPU 201 and the interface IC 202
There is another communication line between and, and various analog signals are input and signals after PI waveform shaping are input. The analog signal is input to the A / D conversion input terminal of the CPU 201 and digitally converted. Further, the CPU 201 has various calculation units, a data storage unit, and a time measurement unit.

The interface IC 202 is a digital
A Bi-CMOS IC with a mixture of analog circuits, an analog processing unit such as a motor, a drive of a magnet, photometry, a battery check, a lighting circuit of a backlight LED and an auxiliary light LED, a waveform shaping circuit of a photo interrupter, and a switch (SW). It is composed of a digital processing unit such as input serial communication data conversion.

The power supply unit 203 supplies power of two systems. One is a power source used for a driver that requires power such as a motor and a magnet, and the voltage of the battery 212 is constantly supplied. The other one is DC / DC converter 213.
Is a small signal power source stabilized by
01 is controlled through the interface 202.

The strobe unit 204 comprises a strobe charging circuit 214, a main capacitor 215, a strobe light emitting circuit 216, a strobe light emitting tube 217 and the like. When flash emission is required in low brightness or backlight condition, CPU2
The control signal of 01 causes the strobe charging circuit 214 to boost the battery voltage and charge the main capacitor 215 via the interface IC 202. At the same time, the charging voltage divided from the strobe charging circuit 214 is applied to the CPU 20.
1 is input to the A / D conversion input terminal. This gives C
The PU 201 controls the charging voltage. When the charging voltage reaches a predetermined level, the CPU 201 transmits a charging stop signal to the strobe charging circuit 214 via the interface IC 202, and the charging of the main capacitor 215 is stopped. The CPU 201 controls the start and stop of light emission of the strobe light emitting tube 217 via the strobe light emitting circuit 216 at a predetermined timing during film exposure.

The flash emission timing is as follows. Front curtain light emission that is emitted by the input of a shutter front curtain travel completion switch 244, which will be described later, rear curtain light emission that is emitted immediately before the rear curtain starts traveling, at equal time intervals from the completion of the front curtain traveling to immediately before the rear curtain traveling, etc. For example, multi-emission in which light is emitted multiple times according to the amount of light.

The mirror shutter unit 205 is composed of a mirror shutter motor 218, two shutter magnets 219 for controlling the traveling of the front curtain and the rear curtain, and a front curtain traveling completion switch included in the sequence switch group 244. The mirror shutter motor 218 includes a CPU 201, an interface IC 202, and a motor driver 241.
The main mirror 10 is controlled by the forward rotation.
2 up and down, narrowing down the shooting aperture, and charging the open shutter (closing the front curtain and opening the rear curtain).

The shutter magnet 219 is controlled by the CPU 201 via the interface IC 202. At the start of exposure, first, the mirror shutter motor 218 immediately retracts the main mirror and narrows down the photographing aperture. Next, the shutter magnet 219
At the same time when the exposure for attracting the magnet is started, the shutter magnet 219 of the front curtain is released from the attraction, so that the front curtain is opened. When the attraction of the shutter magnet 219 of the trailing curtain is released after the desired exposure time has elapsed from the input of the leading curtain leading end switch 244,
The trailing curtain is closed. Thus, the film is exposed between the opening of the front curtain and the closing of the rear curtain. Next, the shutter motor 218
The forward rotation causes the mirror to go down and the photographic aperture to open. At the same time, the shutter is charged.

The shutter motor 218 rewinds the film by reversing it.

The winding unit 206 includes a winding motor 220 and a film detecting photo interrupter 221.
Etc. The hoisting motor 220 is C through the interface IC 202 and the motor driver 241.
It is controlled by the PU 201. The output of the film detection PI 221 is waveform-shaped by the interface IC 201, and C
It is transmitted to the PU 201 to generate a winding amount feedback pulse. The CPU 201 controls the winding amount for one frame by counting the number of pulses.

The lens unit 207 includes the taking lens 22.
2, zoom motor 223, zoom gear train 224, AF motor 225, AF gear train 226, AFPI 227, zoom encoder 228, diaphragm PI 229, diaphragm magnet 230, and the like. The zoom motor 223 and the AF motor 225 are controlled by the CPU 201 via the interface 202 and the motor driver 241. The rotation of the zoom motor 223 is decelerated by the zoom gear train 224, which drives the zoom system of the taking lens 222. In addition, the zoom encoder 228 is used by the taking lens 2
It is an encoder consisting of 6 switches installed around the lens frame that supports 22.
The FF data is input to the CPU 201, and the absolute position of the zoom lens is detected.

The CPU 201 obtains the focal length from the absolute position of the zoom lens and stores it in the focal length storage unit 247. The rotation of the AF motor 225 is decelerated by the AF gear train 226, which drives the focus system lens of the taking lens 222. On the other hand, the output of the AF photo interrupter 227 is taken out from the middle of the AF gear train 226. The output of AFPI227 is the interface IC2.
The waveform is shaped in 01 and transmitted to the CPU 201 to generate an AF lens drive amount feedback pulse. CPU2
01 controls the drive amount of the AF lens by counting the number of pulses. The ejection amount from the mechanical stopper of the AF lens or the infinite reference position is AFPI2.
The integrated pulse amount of 27 is stored in the lens ejection amount storage unit 246 in the CPU 201.

The diaphragm magnet 230 is controlled by the CPU 201 via the interface IC 202. Simultaneously with the start of mirror up, current is applied and the magnet is attracted. At the same time as the mirror-up operation of the mirror shutter motor 218 of the mirror shutter unit 205 described above, the photographing diaphragm is mechanically started to be narrowed by a spring. Then, when the desired aperture value is reached, the attraction of the aperture magnet 230 is released, and the aperture operation is stopped to set. Aperture PI22
The output of 9 is waveform-shaped by the interface IC 202 and is transmitted to the CPU 201 to generate a reduction amount feedback pulse. The CPU 201 controls the amount of narrowing down of the photographing aperture by counting the number of pulses.

The finder unit 208 includes an in-finder LCD panel 231 and a backlight LED 232.
And a photometric 8-division photodiode element 233 and the like. The in-viewfinder LCD panel 231 is made of a transmissive liquid crystal, and the display is controlled by the LCDIC 235 according to the display content sent from the CPU 201 to the LCDIC 235. The backlight LED 232 is the CPU 20.
1 controls the lighting via the interface IC 202 to illuminate the in-finder LCD panel 231.

The photometric element 233 is controlled by the CPU 201 via the interface IC 202. The photocurrent generated by the photometric element 233 is sent to the interface IC 202 every eight elements, and current / voltage conversion is performed therein. Then, only the output of the element designated by the CPU 201 is transferred from the interface IC 202 to the CPU 20.
It is sent to the A / D input conversion terminal 1 and is digitally converted for use in photometric calculation.

The display unit 209 comprises an external LCD panel 234, an LCDIC 235, a key switch (SW) group (1) 236 and the like. The LCD panel 234 is a reflective liquid crystal, and the display is controlled by the LCDIC 235 according to the display content sent from the CPU 201 to the LCDIC 235. The key switch group (1) 236 is mainly for setting the mode of the camera, and is a switch such as an AF mode selection switch, a camera exposure mode selection switch, a strobe mode selection switch, an AF / PF switching switch, and a macro mode switch. Is included. The state of each of these switches is read into the CPU 201 via the LCDIC 235, and the respective modes are set thereby.

The AF unit 210 includes the E ² PROM 23
7, condenser lens 238, separator lens 239,
The AFIC 240 and the like are used.

A part of the optical image of the subject is formed by the condenser lens 2.
38, divided into two images by the re-imaging lens 239, A
The two photoelectric conversion element arrays on the FIC 240 receive the light.
The AFIC 240 generates a digital output according to the light intensity for each element, which is sent to the CPU 201 and stored in the element output storage unit 245 in the CPU 201.

The CPU 201 calculates the image interval between the two divided images or the movement amount of each image after a predetermined time based on the stored element output by the internal correlation calculation circuit 248.
Further, the CPU 201 controls the photoelectric conversion operation of the AFIC 240. In the E ² PROM 237, various non-uniformity correction data for photoelectric conversion element output, which will be described later, and various adjustment data such as an interval between two images at the time of focusing are written, for example, at the time of factory shipment. During the operation of the camera, the data such as the number of film frames that needs to be stored is written even when the power is turned off.

The motor driver 241 is a driver for controlling a large current of the mirror shutter motor 218, the winding motor 220, the zoom motor 223, the AF motor 225, etc. described above.

The auxiliary light LED 242 is an LED for illuminating a subject when the luminance is low. This auxiliary light LED 24
Reference numeral 2 is for turning on the AFIC 240 when the photoelectric conversion is not completed within a predetermined time and the image interval between the two images cannot be detected, so that the AFIC 240 can perform photoelectric conversion of the subject image by the illumination light.

The key switch (SW) group (2) 243 is
It is a switch group that controls the operation of the camera. This includes
Release switch first stroke signal (1R), second
A stroke signal (2R), a switch for driving the zoom lens to the long focal side, a switch for driving the short focal side, a switch for storing a spot photometric value, and the like are included. The states of these switches are read by the CPU 201 via the interface IC 202, and the camera operation is controlled.

The sequence switch (SW) group 244 is
It detects the state of the camera. This includes a switch for detecting the raised position of the mirror, a switch for detecting completion of shutter charging, a switch for detecting completion of traveling of the shutter front curtain, a power switch, and a switch for detecting a strobe pop-up state.

The buzzer 245 also displays a sound when the AF is in focus, out of focus, when the power is turned on, and when a hand shake is warned.

Next, the AF optical system will be described.

As shown in FIG. 4, the AF optical system 105 includes a condenser lens 123 located in the vicinity of the image forming surface 122 of the taking lens 121 and a pair of re-imaging lenses 1.
It is composed of 24L and 124R. Shooting lens 1
21 is focused on the image plane 122, the subject image 125
Is imaged. The subject image 125 is re-formed by the condenser lens 123 and the pair of re-imaging lenses 124L and 124R on the secondary imaging surface 127 (photoelectric conversion element array) perpendicular to the optical axis 126. , A first subject image 128L and a second subject image 128R.

When the subject lens 129 is formed in front of the photographing lens 121, that is, in front of the image forming surface 122, the subject images 129 are close to the optical axis 126 and are relative to the optical axis 126. Are vertically re-imaged to form a first subject image 130L and a second subject image 130R. Further, when the photographing lens 121 is rear-focused, that is, when the subject image 131 is formed behind the image plane 122, the subject images 131 are perpendicular to the optical axis 126 at positions apart from each other. Are re-imaged into a first subject image 132L and a second subject image 132R. The first subject image and the second subject image are oriented in the same direction, and the focus state of the photographing lens 121 is set to the front focus or the rear focus by detecting the interval between the portions corresponding to each other in both the images. Etc. can be detected.

FIG. 5 shows the principle of the photoelectric conversion element. In the figure, first, the reset transistor 1
By turning on 42, the potential of the point 141 becomes V
Set to ₀ . Next, when the reset transistor 142 is turned off, the photodiode 143 sends a photocurrent i corresponding to the intensity of the received light, and the photodiode 143.
Stored in the junction capacitor 144 of As a result, the potential at the point 141 gradually increases. Point 141
When the potential of V exceeds the reference voltage V _REF , the comparator 145
Output is inverted, a latch signal is generated in the latch 146, and the value (8 bits) of the counter 147 is latched.

On the other hand, the clock generator 148 generates a clock that expands with time. The sensor OR signal (OR) 149 is generated from the element that reaches the reference voltage V _REF earliest in the photoelectric conversion element array, and the switch 150 is closed. Since the switch 150 is closed, the counter 147 counts the clock of the clock generator 148. Therefore, the counter output “0” is latched in the latch 146 of the element that receives the strongest light in the photoelectric conversion element array. In other elements, the time until reaching V _REF is delayed depending on the intensity of light received by that element, so the counter output corresponding to the delayed time is latched.

When the time at which the output of the brightest element reaches V _REF is t ₀ , the time t at which the output of the other element reaches V _REF is t.
It is known that relations of number 18 is established in _(I) and latched by counter output D _(I).

[0065]

[Equation 18] Since t _(I) changes according to the light intensity received by the element,
A subject image signal can be obtained by reading the counter output D _(I) . The counter 147 stops counting when it counts 8 bits. Therefore,
The element output having a weak light intensity and t _(I) longer than a predetermined time is fixed at "255".

Next, non-uniformity correction is performed on the obtained subject image signal.

This is for correcting uneven illuminance due to the re-imaging optical system and uneven sensitivity of the light receiving element. The correction coefficient calculated from the output of each element with respect to the uniform light source is stored in the storage device, and is corrected each time the subject image signal is input.

The correction coefficient is obtained as follows.

Assuming that the output of the photoelectric conversion element of the uniform light source is D ₀ (I), the response time t _(I) of this element is expressed by the above equation 18. Here, t ₀ is the response time of the element that responded fastest in the photoelectric conversion element array, and it is desirable that the response time of all the elements be t ₀ in a uniform light source. When the element output of an arbitrary subject is D (I) and the corrected element output is D '(I), and is corrected from the response time, Equation 19 is obtained.

[0070]

[Formula 19] The correction coefficient H _(I) is transformed into a form that can be easily stored in the storage device, and is expressed by the formula 20.

[0071]

[Equation 20] Here, k is a compression coefficient for effectively storing the correction range within the capacity of the storage device, and is 104, for example. When the correction coefficient H _(I) is used, the above correction formula becomes as shown in the equation ₍ 21 ₎ .

[0072]

[Equation 21] Therefore, Equation 22 is obtained.

[0073]

[Equation 22] Here, α is an offset value for preventing the value of D ' _(I) from becoming negative. This correction is effective only for the element output that has been photoelectrically converted correctly, and as described above, the element output that latched the content that the count of the counter was stopped due to the low light intensity or was forced from the outside. No correction is made for the element output in which the accumulated charge does not reach the reference voltage when the detection operation is stopped.

Next, the correlation calculation is performed on the two subject image signals.

For convenience, the first object image is image L, the first object image signal is L _(I) , the second object image is image R, and the second object image is L _(I) .
The subject image signal of is R _(I) . I is an element number, which is 1, 2, 3, ..., 64 from the left in this embodiment. That is, each element array has 64 elements.

Description will be made with reference to the flowchart of FIG. First, the variables SL, SR, and J are set to 5, 3 as initial values.
7 and 8 are set (step A1, step A
2). SL is a variable for storing the leading number of the small block element array for correlation detection from the subject image signal L _(I) ,
Similarly, SR is a variable for storing the leading number of the small block element array for correlation detection from the subject image signal R _(I) , and J is a variable for counting the number of times of movement of the small block in the subject image signal L _(I). is there. Then, the correlation output F _{(S) according} to the equation 19
Is calculated (step A3).

[0077]

[Equation 23] In this case, the number of elements in the small block is 27. The number of elements of the small block is determined by the size of the distance measuring frame displayed on the finder and the magnification of the detection optical system.

Next, the minimum value of the correlation output F _(S) is detected (step A4). Ie, F _{(S) is} compared with F _MIN, Wakashi F _(S) if is less than F _MIN F _MIN to F _(S)
Is stored, the SL and SR at that time are stored in the SLM and SRM (step A5), and the process proceeds to step A6. If F _(S) is larger than F _{MIN in} step A4, the process directly proceeds to step A6.

At step A6, 1 is subtracted from SR and 1 is subtracted from J. Then, if J is not 0 (step A7), the correlation equation of Expression 19 is repeated. That is, the small block position in the image L is fixed, and the small block position in the image R is shifted by one element, and the correlation is obtained. J is 0
Then, 4 is added to SL, 3 is added to SR, and correlation is continued (step A8). That is, the correlation is repeated while shifting the small block positions in the image L by four elements.
When the value of SL reaches 29, the correlation calculation is finished (step A
9).

As described above, the correlation calculation can be performed efficiently and the minimum value of the correlation output can be detected. The position of the small block showing the minimum value of the correlation output shows the positional relationship of the image signals having the highest positive correlation.

Next, the correlation of the detected image signal of the block having the highest correlation is determined. First, in step A10, as shown by the equations 24 and 25, F
Calculate the values of _M and F _P.

[0082]

[Equation 24]

[0083]

[Equation 25] That is, with respect to the subject image R, the correlation output when the block position showing the minimum correlation output is shifted by ± 1 element is calculated. At this time, F _M , F _MIN , and F _P have the relationship shown in FIG. If the image interval detected here has a high correlation, the correlation output F _(S) becomes ₀ at the point S ₀ as shown in FIG. 7A. On the other hand, if the correlation is low, it does not become 0 as shown in FIG.

Here, the layer-relatedness index S _k as in the equations 26 and 27 is _obtained (step A11).

[0085]

[Equation 26]

[0086]

[Equation 27] As shown in FIG. 7, the correlation index S _k is S _k = 1 when the correlation is high, and S _k > 1 when the correlation is low.
Becomes Therefore, based on the value of the correlation index S _k , it can be determined whether or not the detected image shift amount is reliable (step A12). Actually, due to variations in optical system, noise of photoelectric conversion element, conversion error, etc.
Since the non-coincidence component of the second subject image is generated, the correlation index S
_k cannot be 1. Therefore, when S _k ≤α, it is determined that there is a correlation, and the image shift amount is obtained (step A13). S _k
When> α, it is determined that there is no correlation and AF detection is impossible (step A14).

The value of the judgment value α is about 2 to 3, but it is stored as an adjustment value for each product because it varies depending on the product.

Further, if a dark current is generated in the photoelectric conversion element, the correlation is deteriorated and the probability of AF detection being unsatisfactory increases. Therefore, the judgment value is increased depending on the magnitude of the dark current or the integration time, or the temperature and the integration time. To do. When the auxiliary light is turned on, the correlation is deteriorated due to the influence of the color of the auxiliary light, the aberration, and the like. Therefore, the determination value is increased to prevent AF detection from becoming difficult. If there is a correlation, the image shift amount S ₀ is obtained from the relationship of FIG.

[0089]

[Equation 28]

[0090]

[Equation 29] The image shift amount ΔZ from the in-focus state is obtained as in Expression 30.

[0091]

[Equation 30] Here, ΔZ ₀ is an image shift amount at the time of focusing, which is measured for each product and stored in the storage device. C is the temperature coefficient, T is the temperature detected by the temperature detecting means, T ₀ is the temperature when ΔZ ₀ is measured, and C × (T−T ₀ ) is the image shift amount during focusing due to the temperature change of the optical system. Perform the temperature correction of. Further, the defocus amount ΔD on the optical axis based on the image shift amount ΔZ can be obtained by Expression 31.

[0092]

[Equation 31] Since many methods for obtaining the lens driving amount from the defocus amount ΔD on the optical axis have been proposed in the related art, detailed description thereof will not be given here. For example, in the method disclosed in Japanese Patent Application Laid-Open No. 64-54409 filed by the applicant of the present invention, the value can be calculated as in the following formula 32.

[0093]

[Equation 32] Further, if the movement of the subject, which will be described later, is not taken into consideration, it can be brought into a focused state by driving the taking lens by ΔL.

Next, the feeding amount ΔL of the above-mentioned photographing lens
Calculation of will be described with reference to the flowchart of FIG.

At time t ₁ and time t ₂ , the defocus amounts ΔD ₁ and ΔD ₂ are detected, respectively (step B1 and step B2). Then, the lens extension amount k is detected (step B3). Then, whether the subject is moving from the defocus amounts ΔD ₁ and D ₂ is first determined by the equation 33.

[0096]

[Expression 33] The focus detection device includes error factors such as quantization error, electric noise, and dark output as described above, and the detected defocus amount slightly changes. If the minute change is judged as the movement of the subject and the defocus amount is predicted, the lens is driven to the wrong position. In order to prevent this, it is first confirmed that the change in the detected defocus amount is larger than the possible change in the detected value. The determination value ε is determined by the subject brightness, the focal length, the subject contrast, the above-mentioned correlation index, and the like.

If it is determined in step B4 that the above expression 33 is satisfied and the subject is moving, the process proceeds to step B5, and the change rate of the detected defocus amount is determined by expression 34.

[0098]

[Equation 34] In step B5, when the change rate of the equation 34 is smaller than the predetermined value ε ₁ , the moving speed of the subject is sufficiently small with respect to the magnification of the optical system, and it is necessary to predict the movement of the subject and correct the defocus amount. It is determined that there is no. If the rate of change is greater than the predetermined value ε _2, it means that the moving speed of the subject is too fast, or that the defocus amount is detected for different subjects at time t ₁ and time t ₂ There is no prediction of quantity.

If the above expressions 33 and 34 are satisfied in steps B4 and B5, respectively, it is determined that the subject is moving, and time t after a predetermined time has elapsed.
_The defocus amount at ₃ is predicted (step B6).

Predicted defocus amount ΔD at time t _3
3 is obtained by the equations 35, 36 and 37 as described above.

[0101]

[Equation 35]

[0102]

[Equation 36]

[0103]

[Equation 37] Here, k is the photographing lens position at time t ₁ and time t ₂ , and is calculated from the integrated value of AFPI pulses from the infinite reference position. Here, it is assumed that the photographing lens position does not change between time t ₁ and time t ₂ .

Then, from the predicted defocus amount ΔD ₃ obtained in step B6, the equation 32 is obtained from the equation 32.

[0105]

[Equation 38] The lens drive amount ΔL ₃ is obtained as shown in (step B7). Thus, by driving ΔL ₃ , the photographing optical system can be brought into the in-focus state at the time t ₃ .

Next, a method of obtaining the time t ₃ for determining at which position the shutter should be turned on will be described.

As a first method of obtaining, a time t at which a focused state is obtained at the end of lens driving as shown in the equation 39.
Ask for ₃ .

[0108]

[Formula 39] Here, t _a is the time from the time t ₂ until the lens drive is started. This includes the correlation calculation time, the lens drive amount calculation time, camera LCD display, switch input determination, photometry, and strobe control. Etc. time is included. k _a is a coefficient for obtaining the drive time proportional to the lens drive amount, and is stored for each lens type and focal length. Further, t _b is a coefficient for correcting the loss time that occurs regardless of the lens driving amount such as acceleration and deceleration when driving the lens, and a fixed value is stored.

Further, k _b is a coefficient set by the power supply voltage, the attitude of the camera, the change in the lens weight due to the mounting of the conversion lens, and the like. The driving time becomes longer because the motor torque becomes smaller such as the power supply voltage becomes smaller. When I try to eject the lens with the camera facing up,
The driving time becomes long due to the weight of the lens. On the other hand, when the lens is driven with the camera facing upward, the driving time becomes shorter due to the weight of the lens. When a conversion lens or the like is attached and the weight of the lens becomes large, the driving time becomes long. That is, the above k _b is a coefficient for correcting these influences, and is calculated by the power supply voltage by the power supply voltage detection means, the camera attitude by the camera attitude detection means and the lens driving direction coefficient calculation means, and the output of the attachment detection means such as a conversion lens. Is set.

However, when the lens is driven at a constant speed, the coefficient k _b is unnecessary. For example, when there is no movement of the subject image, when there is no movement in the optical axis direction, or when the subject image is not predicted, the lens is driven at full speed and the image predicted by detecting the movement of the subject image. When the lens is driven by the amount of deviation, the coefficient k _b is unnecessary in a camera that drives the lens at a relatively low constant speed that is determined according to changes in the power supply voltage, the camera posture, the lens weight of the conversion lens, and the like. ..

Note that t _c is a processing time after the lens driving is completed, and includes a motor braking time and a photo interrupter ending processing time.

By solving the above equations 31, 34 and 35, it is possible to obtain the time t ₃ at which the lens is brought into the separated state at the end of driving. However, since the calculation formula becomes complicated and the calculation time is required, the time t ₃ is generally obtained by the formula 40.

[0113]

[Formula 40] Here, t _d is given by t _a + t _b × k _b + t _c in Equation 36,
This is a constant that takes into account the error component of Equation 40. Also, k
_c is a conversion coefficient for obtaining the lens drive time proportional to the defocus amount, and is corrected to a value stored for each lens type and focal length by the power supply voltage, camera posture, and mounting of a conversion lens.

Next, as a second method, the time t ₃ from the release switch on to the exposure start is calculated.

The time t _{3 in} this case is obtained by the equation 41 in the same manner as the equation 40.

[0116]

[Formula 41] t _d and k _c are the same as in the equation 40. t _e is the time from the end of lens driving to the start of exposure after the shutter curtain is released, and includes time for LCD display of the camera, switch input determination, photometry, strobe control, mirror up, and the like.

Further, as a third method of obtaining, time t ₃ until the strobe light emission is obtained. This is because when the flash fires, the image at the flash firing time mainly starts from the exposure start time when the shutter curtain is opened, so in the flash firing mode it is better to predict the subject image position at the flash firing time for a more focused picture. This is because it can be obtained.

In this case, the time t ₃ is calculated by the following formula 38 from formula 38.

[0119]

[Equation 42] Note that t _d , k _c , and t _e are the same as in Eq. t _f is the time from the start of exposure to strobe light emission, which is 1 to 2 msec when the so-called front curtain synchronized light emission is performed immediately after the opening of the shutter curtain at the start of exposure. Further, when the rear curtain synchro flash is emitted immediately before the shutter curtain is closed immediately before the end of exposure, the value becomes a value obtained by subtracting a predetermined time from the exposure time.
In the multi-flash mode in which a predetermined amount of light is repeatedly emitted at a predetermined interval, the value of t _f is set to the time from the start of exposure to the first flash (first curtain synchronized multi flash) or the time of the last flash from the start of exposure (( 2nd curtain synchro multi emission) allows you to take pictures with different effects.

[0120]

As described above, according to the present invention, an automatic focusing device capable of accurately performing a focusing operation on a moving subject by using a formula with high prediction accuracy in addition to the conventional prediction formula. Can be provided.

[Brief description of drawings]

FIG. 1 is times t ₀ and t for explaining the principle of the present invention.
FIG. 3 is a diagram showing a positional relationship between a subject and a subject image at ₁ and t ₂ .

FIG. 2 is a diagram to which the autofocus device of the present invention is applied,
It is a ray diagram of a camera incorporating a zoom lens mechanism.

FIG. 3 is a block diagram of the camera of this embodiment.

4 is a diagram showing an arrangement of the AF optical system of FIG.

FIG. 5 is a diagram showing a principle of a photoelectric conversion element.

FIG. 6 is a flowchart for explaining a correlation calculation between a first subject image and a second subject image.

FIG. 7 is a diagram illustrating a relationship among correlation outputs F _M , F _MIN , and F _P.

FIG. 8 is a flow chart for explaining calculation of a moving-out amount of a photographing lens.

FIG. 9 is a diagram showing a relationship among a subject, a taking lens, a subject image, and the like.

FIG. 10 is a diagram showing a conventional relationship between time and defocus amount.

[Explanation of symbols]

101 ... Photographic lens, 102 ... Main mirror, 103 ...
Viewfinder optical system, 105 ... AF optical system, 201 ... CP
U, 202 ... Interface CPU, 203 ... Power supply unit, 204 ... Strobe unit, 205 ... Mirror shutter unit, 206 ... Winding unit, 207
... lens unit, 208 ... viewfinder unit, 20
9 ... Display unit, 210 ... AF unit, 245 ... Element output storage section, 246 ... Lens ejection amount storage section, 247
... focal length storage unit, 248 ... Correlation calculation circuit.

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[Procedure amendment]

[Submission date] July 31, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

[0022]

[Equation 10]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

[0023]

[Equation 11] Here, the relationship between the above equations 7 and 6 is as follows. That is, it becomes as shown in Expression 12.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0089

[Correction method] Change

[Correction content]

[0089]

[Equation 28]

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0090

[Correction method] Change

[Correction content]

[0090]

[Equation 29] The image shift amount ΔZ from the in-focus is obtained as in Expression 30.

[Procedure Amendment 5]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction content]

[Figure 7]

[Procedure correction 6]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 18

[Correction method] Change

[Correction content]

[Figure 8]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 5/232 A 9187-5C 7811-2K G03B 3/00 A

Claims (1)

[Claims] 1. A defocus amount of a photographing optical system is detected,
In the automatic focusing device that predicts the defocus amount after a predetermined time based on the change in the detected defocus amount and obtains the driving amount of the photographing lens from the predicted defocus amount, the first time point and the first predetermined time A second calculation means for calculating the defocus amount at each subsequent second time point, a detection means for detecting an amount of the taking lens from the infinite position, and a defocus amount at the first time point and the second And a predictive calculation means for predicting the defocus amount at the third time point after the second predetermined time period following the first predetermined time period from the defocus amount and the feed amount at the time point. Characteristic autofocus device.