JPS6227688B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a camera equipped with an automatic focus detection device that drives a photographing lens to a focus position based on focus detection information that detects the distance to a subject. Only when the focus detection information continues, the photographing lens is driven in the direction of the focus position, and when the focus detection information fluctuates within a short period of time, the photographing lens is driven based on this focus detection information. The present invention relates to a method for preventing unstable operation of an automatic focus detection device, which eliminates instability (twitching) of focusing operation caused by excessive response of the automatic focus detection device by setting the automatic focus detection device in an inactive state.

When an automatic focus detection device is applied to an 8mm cine camera, etc., conventionally, the photographic lens is immediately driven in the direction of the focus position according to the focus detection information repeatedly detected by the focus detection circuit, so the focus detection information is The photographing lens is driven in response to fluctuations in
Furthermore, since the magnification of the image changes, the image often becomes very unsightly. It is desirable to eliminate excessive responsiveness due to such short-time focus detection information in a cine camera using an automatic focus device, and in the present invention,
Only when constant focus detection information persists for a certain period of time, the photographing lens can be driven in the direction of the in-focus position. The object of the present invention is to obtain a method for preventing unstable operation of an automatic focus detection device that does not perform driving.

Conventionally, when adjusting the photographic lens to automatically focus on the subject, there was a proposal to use a timer to remove noise contained in the subject, for example in Japanese Patent Laid-Open No. 52
- This is done according to Publication No. 126225. This is because the subject has a three-dimensional spread, so an automatic focus detection device that detects the sharpness of the image can obtain multiple false focus signals from areas other than the targeted subject. In order to eliminate the signal, a timer is activated once a focus signal is received, and false signals are prohibited during the timer time corresponding to one focus detection time.

The present invention does not eliminate spurious signals that occur during one focus detection time, but rather removes false signals that occur during one focus detection time.
In order to prohibit lens drive and prevent lens twitching even if out-of-focus is determined at the next focus detection, out-of-focus is determined continuously after focusing by multiple focus detection operations. The lens was allowed to be driven only when this was done.

As a configuration of the present application to achieve the above object, a focus signal indicating that the focus position of the photographing lens is at the in-focus point by repeatedly detecting the focus state with respect to the in-focus point of the photographing lens, and a focus signal indicating that the focus position of the photographing lens is at the in-focus point; Repeat any one of at least three signals: a near-distance signal indicating that the lens is in a close-distance focus position, and a long-distance signal indicating that the taking lens is in a far-distance focus position with respect to the in-focus point. a focus detection means (corresponding to the PUC in FIG. 1) that outputs an output every time the focus state is detected; and one when the short distance signal is output in response to the output signal from the focus detection means. When the long-distance signal is output, the lens is rotated in the other direction to move the photographic lens from the short-distance focus position to the in-focus direction. A motor drive circuit including a motor that moves the lens toward the focal point and stops the photographing lens by prohibiting rotation when the focusing signal is output (example, Tr ₁ to Tr 6 , R ₁ to Tr ₆ in Fig. 3).
Corresponds to _R2 , _R5 to _R7 , and _R10 . ), the device enters a reset state in response to the focus signal, and when the signal from the focus detection means changes from a focus signal to a short-distance signal or a long-distance signal, the reset state is canceled and timekeeping starts. Timer circuit (example,
This corresponds to C ₁ , C ₂ , R ₃ , and R ₈ in FIG. ), and allow the motor drive circuit to respond to the short-range or long-distance signal when a short-range or long-range signal that has changed from the focus signal is continuously output for a predetermined time measured by the timer circuit. (corresponding to R ₄ , R ₉ , Tr ₇ , Tr ₈ in the embodiment, FIG. 3) is provided, and the focus state detection operation by the focus detection means is provided to allow the predetermined time period of the timer circuit to be set. is set to the time required for it to be repeated multiple times.

The present invention will be explained in detail below with reference to the drawings. FIG. 1 is a block diagram showing an example of the configuration of a focus detection device. In the figure, OPS is an optical block for focus detection consisting of mirrors, lenses, and prisms, and SP is
It is a solid-state image sensor such as CCD, and the object OB1, OB
The second image is formed on the solid-state image sensor SP via the optical block OPS.

The image IM1 on SP is a standard image, and IB1 and IB2 are reference images.The distance to the subject can be determined by detecting the relative position of the standard image IM1 and the reference images via the focus calculation control circuit PUC. Measure.

The focus detection information detected by the focus calculation control circuit PUC is sent to the control terminals MU1, MU2, MU3 and
The photographic lens drive circuit SMD and motor MT are driven via the MU4 to move the photographic lens LS to the in-focus position.

FIG. 2 is a block diagram showing an example in which the automatic focus detection device shown in FIG. 1 is installed in an 8 mm cine camera or a video camera. In the figure, G1 is a pinion gear installed on the rotating shaft of the motor MT, and G2
is the focus ring driving gear provided on the focus ring of the photographic lens LS, and GR is the focus ring of the photographic lens LS or linked to the focus ring, and the focus state of the photographic lens is sent to the focus calculation control circuit PUC. It is a gray code board or resistor for inputting information for transmission, and the focus information from GR and the image information for focus detection from SP are compared in the focus calculation control circuit PUC, and when they match, the control terminal MU1 ~The photographing lens LS is fixed (stopped) via the MU4.

Discrepancies between the standard image and reference image due to poor adjustment of the optical block for focus detection, uneven sensitivity of each pixel of the solid-state image sensor, camera shake, etc. may cause focus detection to differ for a short time even when the subject is at the same distance. It is an object of the present invention to provide a system that ignores this short-term focus detection information and drives the photographing lens only when constant focus detection information continues for a certain period of time or more. FIG. 3 is an embodiment of a detailed electric circuit of a photographing lens drive circuit SMD having a circuit for preventing unstable operation of an automatic focus detection device according to the present invention. In the figure, R1 to R10 are resistors, Tr1 and Tr2 are PNP transistors, Tr3 and Tr
4 is an NPN transistor, Tr1 to Tr4 constitute a bridge, and controls forward and reverse rotation of the motor MT for driving the photographing lens LS. D1, D
2 is a diode for improving the braking effect when the motor MT is stopped; Tr5 and Tr6 are transistors for controlling the transistors Tr1 and Tr2; and transistor Tr5 is a control transistor. The capacitors connected to the bases of transistors Tr5 and Tr6 form a time discrimination circuit together with transistors Tr5 and Tr6.
5. If constant focus detection information is not applied to the base of Tr6 for a predetermined period of time or more, transistors Tr5,
Tr6 is not turned on, that is, reception of the information is delayed for a certain period of time.

Transistors Tr7 and Tr8 are capacitor C
This circuit forms a control circuit for resetting the discriminating circuit, which instantaneously discharges the charges of the transistors Tr5 and C2, shortens the turn-off time of the transistors Tr5 and Tr6, and stably drives the photographing lens LS without jerking. Further, E is a power battery, and SW is a power switch.

If the subject is far away from the current position of the focus ring of the photographic lens LS, for example, MU1 and MU3 are at "H" level, MU2 and MU4 are
is at "L" level, and when the subject is close, MU2 and MU4 are at "H" level, MU1,
MU3 is inverted to "L" level, rotates motor MT forward or reverse, and drives photographic lens LS toward the focus position. When the photographing lens LS reaches the focus position, MU1 and MU2 go to "H" level, and MU3 and MU
4 is reversed to the "L" level, shorting both ends of the motor MT and instantly stopping the photographing lens LS.

Referring to the time chart in Figure 4 below,
The specific operation shown in the figure will be explained.

At times t ₁ , t ₂ , t ₃ ..., T ₅₁ , ..., focus detection information is repeatedly output via the control terminals M1 to M4 of the focus calculation control circuit PUC until the next focus detection information is output. held for a period of time. From time _t1 to time _t10 , MU1 and MU3 are at “H” level, MU2,
Since MU4 is at “L” level, the transistor
Tr3 and Tr2 are turned on, transistors Tr1 and Tr4 are turned off, and current flows to the motor MT via the transistors Tr2 and Tr3, driving the photographing lens LS toward infinity, for example. At time _t10 , MU2 is inverted to "H" level and MU3 is inverted to "L" level, so transistors Tr3 and Tr4 are turned on, transistors Tr1 and Tr2 are turned off, the motor MT is short-circuited, and the motor MT stops instantly. shooting lens
LS is fixed at the focus position.

At time _t12 , when focus detection information on the short distance side of the focus position is momentarily generated, if there is no unstable operation prevention circuit of the present invention, between time _t12 and _T13 , MU1, MU3 is “L” level, MU2, MU
4 is inverted to “H” level, so the transistor
Current flows to the motor via Tr1 and Tr4, driving the photographic lens in a short distance direction. If the same focus detection information as at time t ₁₁ occurs at time t ₁₃ , MU2 and MU4 are inverted to “L” level and MU1 and MU3 are inverted to “H” from time t ₁₃ to t ₁₄ . Therefore, the photographing lens LS is driven back toward the in-focus position at time _t11 . In other words, the photographing lens LS starts from time _t12 .
A reciprocating movement occurs during t ₁₄ , which not only blurs the photographic screen but also changes the photographic magnification, resulting in an extremely unsightly image.

When a time discrimination circuit and its reset control circuit are added as described above, for example, if focus detection information on the far side from the in-focus position is momentarily generated at time _t18 , the time difference between time _t18 and _t19 ,MU2,MU
4 is inverted to "L" level, and MU1, MU3 are inverted to "H" level, but transistors Tr7 and Tr8 are turned on from time _t14 to _t18 , and the charges in delay capacitors C1 and C2 for preventing unstable operation are discharged. By selecting the capacitance of C2 so that the terminal voltage of delay capacitor C2 does not reach the turn-on threshold VTH of transistor Tr6 between time _t18 and time _t19 , transistor Tr2 will not turn on. Focus detection information for a short period of time is ignored, the photographing lens does not move, and unstable operation does not occur. At time _t19 , MU2 is inverted to "H" level, so the charge in delay capacitor C2 is instantly discharged via transistor Tr8, and if a certain focus detection information does not continue for a certain period of time, there will be a delay. The terminal voltage of the capacitor for this purpose will not reach the threshold level for turning on the transistor.

Note that the resistors R3, R5, R8, and R10 are current limiting resistors, which are not necessarily required when constant current driving is performed from the focus calculation control circuit PUC via the control terminals MU1 to MU4. time
When shooting a close subject with _t50 , the MU
1. MU3 is inverted to "L" level, and MU2 and MU4 are inverted to "H" level, so the base potential of transistor Tr5 turns on at time _tN and reaches "L" level, transistor Tr1 is also turned on almost simultaneously, and the photograph is taken. Drive lens LS in the short distance direction.

As described above, the present invention is configured such that certain focus detection information continues and the photographing lens, etc. is driven only when a predetermined time has elapsed, and short-term continuous information is prohibited. It becomes insensitive to fluctuations in focus detection information within a short period of time, thus preventing unstable operation and performing stable focus detection. Note that in the above embodiment, the drive circuit is
Although we have explained an example of driving a photographic lens, the invention is not limited to lenses, and using well-known techniques, for example, we can drive an example corresponding to a photosensitive surface, such as a photosensitive film, an image pickup tube, etc., relative to the lens. Of course, it may be movable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the configuration of an automatic focus detection device, FIG. 2 is a block diagram showing an example of the automatic focus detection device of FIG. 1 installed in a cine camera or video camera, and FIG. FIG. 4 is a circuit connection diagram showing an embodiment of a photographic lens drive circuit having an unstable operation prevention circuit for an automatic focus detection device according to the present invention, and FIG. 4 is a curve diagram showing a timing chart of the circuit shown in FIG. OPS...Optical block for focus detection, SP...Solid-state image sensor, OB1, OB2...Subject, IM1...
...Reference image on SP, IB1, IB2...Reference image on SP, PUC...Focus calculation control circuit, MU1, MU
2, MU3, MU4...Control output terminal, SMD...
Photographing lens drive circuit, MT...Lens drive motor, LS...Photography lens, _C1 , _C2 ...Capacitors of the delay operation circuit, Tr7, Tr8...Transistors of the same circuit.

Claims (1)

[Claims] 1. A focus signal that repeatedly detects the focus state of the photographic lens with respect to the in-focus point and indicates that the focus position of the photographic lens is at the in-focus point. Output any one of at least three signals, a short-distance signal indicating that the photographing lens is at a focus position at a far distance with respect to the in-focus point, and a long-distance signal indicating that the photographing lens is at a focus position at a far distance with respect to the in-focus point each time the focus state is repeatedly detected. a focus detection means; in response to an output signal from the focus detection means, when the short distance signal is output, the photographing lens is rotated in one direction to move the photographing lens from the short distance focus position toward the in-focus point; When the long-distance signal is output, the camera rotates in the other direction to move the photographing lens from the long-distance focus position toward the in-focus point, and when the focus signal is output, the camera becomes prohibited from rotating and moves the photographic lens. A motor drive circuit including a motor that is brought into a stopped state; and a motor driving circuit that is brought into a reset state in response to the focus signal, and the signal from the focus detection means changes from a focus signal to a short-distance signal or a long-distance signal, thereby causing the reset. A timer circuit that starts timing when the state is released, and a short-distance or long-distance signal when a short-distance or long-distance signal that has changed from the focus signal is continuously output for more than a predetermined time measured by the timer circuit. furthermore, the predetermined clock time of the timer circuit is set to a time necessary for the focus state detection operation by the focus detection means to be repeated a plurality of times. An automatic focus adjustment device characterized by: