JPH073500B2 - Automatic focus adjustment device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an automatic focus adjustment device used in a camera or the like.

(Prior Art) FIG. 8 shows an optical system of an automatic focus adjusting device by a general correlation method in a camera. In this optical system, the taking lens 1
Of light passing through the condenser lens 2 through the imaging lens
An image is formed on the right side sensor array section A and the left side sensor array section B of the focus detection light receiving section 5 composed of a charge-coupled device by 3 and 4. In the figure, F indicates a surface equivalent to the film surface. In the automatic focusing device by the correlation method, the shift amount δ from the in-focus position of the subject image on the charge coupled device 5 is calculated from the video signals from the right side sensor array unit A and the left side sensor array unit B of the charge imaging device 5. Then, the photographic lens 1 is moved to the in-focus position by obtaining the differential focus amount Δ from the displacement amount δ using the linear approximation relationship between the displacement amount δ and the differential focus amount Δ of the capturing lens 1.

However, in this automatic focus adjusting device, the relationship between the shift weight δ and the focus amount Δ can be approximated to a straight line within a range displaced by ± 3 to 5 mm from the in-focus position, but basically the following ( Since there is a hyperbolic relationship like equation (1), In the linear approximation, the distance measurement error increases as the defocus amount Δ increases. For example, as shown in FIG. 9, when the taking lens 1 is driven by the result of the first distance measurement, the linear approximation δ
Distance measurement error due to the difference between-△ characteristic and δ- △ characteristic of hyperbola x
However, the taking lens 1 stops at a position that is too far from the in-focus position. Here, the distance is measured again to check whether or not the taking lens is at the in-focus position. If the taking lens is at the in-focus position, the process proceeds to the next process such as release prohibition release. If it is not in the in-focus position, driving of the taking lens, stopping, and distance measurement are performed again. That is, if the distance measurement error x becomes large, the steps of distance measurement → driving lens drive → stop increase, and the time from the start of automatic focus adjustment by turning on the release switch to the end of automatic focus adjustment becomes longer. The phenomenon occurs. This is considerably negative as the commercial value of a camera using this automatic focusing device.

(Object) It is an object of the present invention to provide an automatic focus adjusting device which is capable of improving the above-mentioned drawbacks and having a good distance measuring accuracy even if the amount of defocus is large and shortening the automatic focus adjusting time.

(Structure) The present invention has a focus detection light receiving unit 11 and a calculation unit 12 as shown in FIG. 1, and the calculation unit 12 uses the data from the light receiving unit 11 to combine a subject image on the surface of the light receiving unit 11. Deviation amount from focal position δ
Then, the defocus amount Δ of the lens is obtained from the deviation amount δ and the constants A ₁ and A _{2 by the} calculation Δ = A ₂ / (δ + A ₁ ) −A ₂ / A ₁ .

Next, an embodiment of the present invention will be described.

Considering the constants A ₁ , A ₂ , and A ₃ of the hyperbolic function of the equation (1), when the defocus amount Δ = 0, the deviation amount δ =
0 Therefore, in reality, it is only necessary to consider two of A ₁ , A ₂ , and A ₃ . As shown in FIG. 2, in the above optical system, the distance from the surface F equivalent to the film surface to the principal point position of the condenser lens 2 is L ₁ , and the principal point of the condenser lens 2 is the principal point of the imaging lenses 3 and 4. The distance to the position is L ₂ , the distance from the principal point position of the imaging lenses 3 and 4 to the light receiving surface of the charge-coupled device 5 is L ₃ , and the focal length of the condenser lens 2 is
f ₁ , focal length f ₂ of imaging lenses 3 and 4, condenser lens 2
When the optical axis distance between the lens and the imaging lenses 3 and 4 is h _T , A ₁ = hM A ₂ = LhM. here And also Therefore, A ₁ , A ₂ , and A ₃ are constants obtained by design. Therefore, in this embodiment, the distance measurement accuracy is improved by obtaining the shift amount δ from the output signal of the charge-coupled device 5 and obtaining the defocus amount Δ by the equation (1).

FIG. 3 shows the configuration of this embodiment.

This embodiment uses the optical system described above, and the charge-coupled device 5 is used.
Are driven by the driver 13. The structure of the charge-coupled device 5 is as shown in FIG. 4, and includes photodiode arrays A and B arranged in a row in the left-right direction and a pair of monitoring photodiodes 14 and 15 arranged in parallel with the photodiode arrays A and B. Have. The photodiode arrays A and B are bisected into the right side portion A and the left side portion B on the optical axes of the lenses 1 and 2, and the monitoring photodiodes 14 and 15 are provided on one side portion thereof. When the reset pulse φR from the driver 13 is at a high level, the field effect transistors 16 and 17 are turned on, the capacitors 18 and 19 are charged from the power source V _DD , and the storage electrode 20 is reset. When the reset pulse φR becomes low level,
A photocurrent corresponding to the brightness distribution of the subject image flows into the photodiode arrays A and B, and electric charges are stored in the storage electrode 20. At the same time, a photocurrent also flows through the monitor photodiodes 14 and 15 in accordance with the brightness distribution of the subject image, and the photocurrent lowers the potentials of the capacitors 18 and 19. The potentials of the capacitors 18 and 19 are output to the driver 13 via the buffer amplifiers 21 and 22. When the transfer pulse φT is input from the driver 13, the shift gate 23 opens and the electric charge stored in the storage electrode 20 is transferred to the analog shift register 24, and the driver 13
Field-effect transistor 25 by pulses φ1 and φ2 from
The video signal V _OUT is sequentially output via the capacitor 26 and the buffer amplifier 27.

The driver 13 is a buffer amplifier 2 in the charge coupled device 5.
It includes a circuit as shown in FIG. 5 for processing the output signal V _AGC1, A _{AGC 2} of 1, 22. The signal V _AGC1, A _{AGC 2} is an operational amplifier 30 and 31 via a buffer amplifier 29, the diode 3
The absolute value of the difference is taken by an absolute value amplifier composed of 2, 33 and resistors 34 to 41, and sampled and held by a sample and hold circuit 42. When the reset pulse φR becomes low level and integration of the charge coupled device 5 (accumulation of the storage electrode 20 and discharge of the capacitors 18 and 19) is started for a predetermined time, for example, 10 mS, A sample hold pulse is applied from an adjusting microcomputer (hereinafter referred to as CPU) 43 (see FIG. 2) to sample and hold an input signal. Also buffer amplifier 28,29
The output signal of the buffer amplifier 46 is added by resistors 44 and 45.
And is compared with the comparison voltage of the comparison voltage source 48 by the comparator 47. When the output signal of the buffer amplifier 46 becomes equal to the comparison voltage, the φT generating circuit 49 outputs the pulse φT to the charge coupled device 5. The output signals a and b of the buffer amplifiers 28 and 29 and the output signal f of the buffer amplifier 46, after the integration of the charge-coupled device 5 is started, are inclined according to the amount of light received by the monitoring photodiodes 14 and 15 as shown in FIG. As shown in FIG. 6, the output signal c of the absolute value amplifier increases with an absolute value of the difference in the amount of light received by the monitoring photodiodes 14 and 15, that is, with a slope corresponding to the contrast of the subject image.

As shown in FIG. 3, the video signal V _OUT from the buffer amplifier 27 in the charge-coupled device 5 is amplified by the scaling amplifier 50 via the multiplexer 53 to be converted into an analog / digital converter.
It is converted into a digital signal in 51 and input to the CPU 43 via the interface 52. The output signal of the sample hold circuit 42 in the driver 13 is converted into a digital signal by the analog / digital converter 51 via the multiplexer 53 and input to the CPU 43 via the interface 52. C
The PU 43 adjusts the gain of the variable power amplifier 50 via the multiplexer 54 according to the output signal of the sample-hold circuit 42 before the video signal from the charge-coupled device 5 is fetched, and the video signal from the charge-coupled device 5 is converted into a subject image. The defocus amount Δ is calculated with high accuracy by taking in what has been amplified by the variable power amplifier 50 at a magnification according to the contrast of. The focal length Fφ and the set position Siφ of the photographing lens 1 are input from the circuits 55 and 56 for detecting them to the CPU 43 through the multiplexer 53, the analog / digital converter 51 and the interface 52, and the encoder 57 outputs pulses and switches 58 to 58. The signal from 60 is input to the CPU 43. The encoder 57 constitutes a rotation detector that detects the rotation of the photographing lens 1 driving motor 61, and the switches 58 to 60 are manually operated switches. The switch 58 performs automatic focus adjustment in the manual mode or automatically. Set whether to perform in mode. The switch 59 is a power switch consisting of a release switch that turns on when the release button is pressed to perform automatic focus adjustment.
60 sets a mode for adjusting the above constants A ₁ , A ₂ , and A ₃ .
The manual distance setting circuit 62 is a circuit that generates a signal for manually rotating the motor 61, and when the CPU 43 sets the automatic mode by the switch 58, the CPU 43 causes the motor drive circuit 63 to rotate the motor 61 by the calculated defocus amount Δ. When the manual mode is set by the switch 58, the motor drive circuit 63 is caused to rotate the motor 61 by the output signal of the manual distance setting circuit 62. Further, when the subject is dark, the CPU 43 turns on the projector 64 to emit auxiliary light to the subject, and causes the display device 65 to display the focus, the front focus, the rear focus, and the distance measurement impossible, and the F value circuit 66. The open F value of the taking lens 1 from is used for the calculation of the differential focus amount Δ.

FIG. 7 shows a processing flow of the CPU 43.

The CPU 43 starts by turning on the switch 59, resets each part in step S1 to an initial state, and outputs a release prohibition signal to the sequence control part of the camera in step S2 to prohibit release. Next, in step S3, the signal from the switch 60 is checked, and when the switch 60 is on, the adjustment mode of the constants A ₁ , A ₂ , and A ₃ is entered. This mode is set at the time of assembly or service, and the constants A ₁ , A ₂ and A ₃ are adjusted. If the switch 60 is off, the process proceeds to step S4, where the number Viφ, the integration flag,
The low brightness flag is reset and the charge coupled device 5 is initialized. Next, in step S5, the reset pulse φR is driven
Then, in step S6, the reset pulse φR is turned off to integrate the charge-coupled device 5 and simultaneously start the timer. Next, in step S7, the low-brightness flag is checked, and since it is reset, the process proceeds to step S8, in which the slope (change) of the output signal of the comparator 47 in the driver 13, that is, the brightness of the subject image is measured, and in step S9 the slope is determined. It is determined whether or not the subject image has low brightness by determining whether or not the value is equal to or less than a predetermined value. If the subject image is not of low brightness, the process proceeds to the next step S10, but if the subject image is of low brightness, the low brightness flag is set in step S11, the projector 64 is turned on in step S12, and then the process proceeds to step S10. . In step S10, it is determined whether or not the output signal of the comparator 47 has become zero, thereby determining whether or not the integration of the charge-coupled device 5 has been completed, and even if the output signal of the comparator 47 does not become zero, When the timer times out, it is determined that the integration of the charge coupled device 5 is completed. When the integration of the charge-coupled device 5 is not completed, the process returns to step S6 and steps S6 to S10 are repeated, but the subject image has low brightness and the projector 64
When is turned on, the process jumps from step S7 to step S10. After that, when the integration of the charge-coupled device 5 is completed, the process proceeds to step S13, the driver 13 outputs the transfer pulse φT to the charge-coupled device 5, the random access memory (RAM) is cleared in step S14, and the analog / digital operation is performed in step S15. Cause the converter 51 to start analog / digital conversion of the video signal from the charge coupled device 5. Next, in step S16, the low brightness flag is checked, and if it is not set, the process proceeds to step S18. If the low brightness flag is set, in step S17 the projector 64 is turned off by the completion of charge accumulation in the charge coupled device 5. Go to step S18. Step S18
Now measure the output signal of the comparator 47 and perform step S19.
Then, it is determined from the signal whether or not the subject image has low brightness. If the subject image has low brightness, the process proceeds to step S21. If the subject image has low brightness, the gain of the variable power amplifier 50 is changed to a large value according to the output signal of the sample hold circuit 42, and the process proceeds to step S21. In step S21, the video signal from the charge-coupled device 5 is converted into a digital signal by the analog / digital converter 51, and the captured signal is taken into RAM in step S22.
Then, in step S23, the lens information siφ and Fφ from the detection circuits 55 and 56 are fetched and the number Nr is set to 20.

Next, in step S24, the focal length Fφ of the taking lens 1 is 75 mm.
If the focal length Fφ is 75 mm or less, the process proceeds to step S25 to determine whether the first distance measurement after the switch 59 is turned on is the first time. When the distance measurement is the first time, the set position siφ of the lens 1 is set to 11 and the number Nr is set to 32 in step S26. This number Nr is a photodiode array in which the charge coupled device 5 is bisected up and down along the optical axis of the lens 1.
This is the number of photodiodes within the range when comparing the images on A and B by a certain range to find how much the image interval has changed from the time of focusing. Then, the number of pitches (integer) of the photodiode is calculated, and the fractional part calculation is used to calculate the number (fractional) less than one pitch of the photodiode. Next, in step S27, the integer part calculation is performed to find the maximum value Viφ of the number of photodiodes within the matched range by comparing the constant ranges (Nr) of the images on the photodiode arrays A and B, and The amount of change (integer) M (1) is obtained, and it is determined in step S28 whether the maximum value Viφ is 4 or less. When the maximum value Viφ is 4 or less, it is determined that distance measurement is impossible, and the fact is displayed on the display device 65. If the maximum value Viφ is not 4 or less, step S2
The fractional part calculation of 9 is performed to calculate the fractional part Cφ
Find φ.

In the second and subsequent distance measurements, steps S25 to S30
In step S29, the lens set position Siφ is set to 11, the integer part M (1) of the image interval change amount is set to 11, and the integer part calculation is not performed. Next, in step S31, it is determined whether or not the number Nφ of the video signals from the charge-coupled device 5 which has a large contrast and can be used for the data comparison in the fractional part calculation is 2 or less, and when the number Nφ is 2 or less. Determines that distance measurement is impossible and causes the display device 65 to display that fact. If the number Nφ is not 2 or less, the amount of deviation Df ₁ from the in-focus position of the image on the charge coupled device 5 is calculated as Df ₁ = {(Siφ−M (1)) × 64−Cφφφ} × kd in step S32. in calculated, determined by the calculation of the lens 1 in the defocus amount Df2 the _{Df2 = a 2 / (Df 1} + a 1) + a 3 becomes hyperbolic function in step S33. Next, in step S34, it is determined whether or not the absolute value of the defocus amount Df2 is equal to or less than a predetermined value Kφ · Fφ, and the absolute value of the defocus amount is a predetermined value Kφ.
When Fφ or less, the lens 1 is determined to be at the in-focus position and the release prohibition signal to the sequence control unit is released to enable the release.

If the absolute value of the differential focus amount is not less than or equal to the predetermined value Kφ · Fφ, it is determined in step S35 whether or not the motor 61 should be rotated in the normal direction to move the lens 1 to the in-focus position from the sign of the differential focus amount. If 61 should be rotated in the normal direction, it is determined in step S36 whether the lens 1 is at the infinite position. Since the motor 61 moves the lens 1 to the far side in the forward rotation and moves the lens 1 to the near side in the reverse rotation, if the lens 1 is at the infinity position, it is determined that the distance cannot be determined in step S3, and that fact is displayed. This is displayed on the device 65, and the motor 61 is stopped in step S38. If the lens 1 is not at the infinity position in step S36, the process proceeds to step S39 to start the timer, and in step S40, the motor 61 is rotated in the normal direction to step S40.
41 counts pulses from encoder 57. Next, at steps S42 to S44, whether the timer has timed up, whether the lens 1 has reached the infinity position, the encoder
It is determined whether or not the absolute value | Df2-Np | of the difference between the count value Np of the pulses from 57 and the defocus amount Df2 has become equal to or less than a predetermined value Npφ. If none of the three conditions that the timer has timed up, that the lens 1 has reached the infinite position, and that | Df2-Np | Npφ has been reached, the process returns to step S40 and the motor 61 rotates normally. If any one of the three conditions is satisfied, the motor 61 is stopped in step S45 and the number of times the motor 61 is driven is 4 in step S6.
Judge whether the number of times has been reached. The number of times the motor 61 is driven is 4
If the number of times has been reached, it is determined that distance measurement is impossible and the fact is displayed on the display device 65, but if not, the process returns to step S4.

If it is determined in step S35 that the motor 61 should be rotated in the reverse direction, it is determined in step S47 whether or not the lens 1 is in the closest position, and if lens 1 is not in the closest position, the timer is started in step S48. Then, in step S49, the motor 61 is rotated in the reverse direction. Next, in step S50, the number of pulses from the encoder 57 is counted, and in steps S51 to S53, it is determined whether or not the timer has timed out and whether or not the lens 1 has reached the closest position, | Df2-Np | Npφ. Determine whether or not. If none of the three conditions that the timer has timed up, that the lens 1 has reached the closest position, and that | Df2-Np | Npφ have been reached, the process returns to step S49 to continue the reverse rotation of the motor 61. However, if any of the three conditions is satisfied, the process proceeds to step S54 and the motor 61 is stopped. Next, in step S55, it is determined whether or not the number of driving times of the lens 1 has reached four times. If the number of times the lens 1 has been driven reaches four times, it is determined that distance measurement is impossible and the fact is displayed on the display device 65. If not, the process returns to step S4.

When the lens 1 is located at the closest position in step S47, it is determined in step S56 whether the defocus amount Df2 is equal to or less than a predetermined value. If the defocus amount is less than or equal to the predetermined value, the macro device is displayed in step S57, and the motor 61 is stopped at step T58.If the defocus amount is not less than or equal to the predetermined value, distance measurement is impossible in step S59. Is displayed on the display device 65 and the motor 61 is stopped in step S60.

If the focal length Fφ of the lens 1 is not equal to or less than 75 mm in step S24, the process proceeds to step S61, and it is determined whether or not the number of times only the integer part calculation (fractional part calculation is not performed) is one or more. When the number of times only the integer part is calculated is set once or more, Siφ = 11, Nr = 32 is set in step S64, and the integer part is calculated in step S63. Determines in step S62 whether the fractional part calculation has been performed once. If the fractional part calculation does not reach once, step S63
The integer part is calculated with. Next, in step S65, it is determined whether or not the maximum value Viφ of the matched numbers is 4 or less in the data comparison in the integer part calculation. If the maximum value Viφ is 4 or less, it is impossible to measure the distance on the display device 65. Make the display. Maximum value
If Viφ is not less than 4, N ₁ = Siφ-M in step S66
N ₁ in step S67 is set to (1) it is determined whether a predetermined value or less, Si in the step S68, if N ₁ is a predetermined value or less
φ = 11, M (1) = Siφ−N ₁ is set, and the fractional part calculation is performed in step S69. Next, in step S70, it is determined whether or not the number of data Nφ used for data comparison in the fractional part calculation is 2 or less, and if Nφ3, the display device 65 displays that distance measurement is impossible. Then, the image shift amount Df ₁ is obtained by the calculation of Df ₁ = (N ₁ × 64−Cφφφ) × kd. If N ₁ is not less than or equal to the predetermined value in step S67, Cφφφ is set to 0 in step S72 and the process proceeds to step S71. If the fractional part operation reaches one in step S62, Siφ = 11, M (1) = 11
And proceed to step S69.

Steps S74 to S101 are the same as steps S33 to S60.

(Effect) As described above, according to the present invention, the light receiving unit for focus detection that measures the subject image that has passed through the lens, and the focus position of the subject image on the surface of the light receiving unit based on the data from the light receiving unit. From the deviation amount δ and the constants A ₁ and A _{2 are used} to calculate the defocus amount Δ of the lens by a calculation of Δ = A ₂ / (δ + A ₁ ) −A ₂ / A _1. Since it is provided, the distance measurement accuracy is high and the automatic focusing time can be shortened even when the differential focus amount is large.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a diagram for explaining the present invention, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG. 4 is a charge in the same embodiment. FIG. 5 is a circuit diagram showing a configuration of a coupling element, FIG. 5 is a circuit diagram showing a part of a driver in the same embodiment, FIG. 6 is a diagram showing signal waveforms of respective parts of the driver, and FIG. FIG. 8 is a flowchart showing a processing flow, FIG. 8 is a diagram showing an example of an optical system in the automatic focus adjusting device, and FIG. 9 is a characteristic curve diagram for explaining a conventional automatic focus adjusting device. 11: Focus detection light-receiving part, 12: Calculation means.

Front Page Continuation (72) Inventor Daisuke Hata 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Takayuki Hatase 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Kazumasa Aoki 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd.

Claims (1)

[Claims] 1. A light receiving portion for focus detection for measuring a subject image that has passed through a lens, and a shift amount δ from a focus position of the subject image on the surface of the light receiving portion is obtained from data from the light receiving portion. An automatic focus adjusting device comprising a calculation means for calculating a defocus amount Δ of the lens from a shift amount δ and constants A ₁ and A ₂ by a calculation of Δ = A ₂ / (δ + A ₁ ) −A ₂ / A ₁ .