JPH0789172B2 - Automatic focus detection device - Google Patents

Description

The present invention relates to an automatic focus detection device used in a movie camera or the like and capable of adjusting a dead zone width.

[Prior Art] In an active automatic focus detection device, focus adjustment is performed based on an output difference from a pair of light receiving elements,
It is already well known to provide a dead zone in order to stabilize the autofocus operation and prevent hunting, and to expand the dead zone width in order to stabilize the operation after once focusing.

However, if, for example, the method of expanding the dead zone width after focusing once is adopted, it works correctly under the advantageous conditions of the active autofocus method where the reflectance of the subject is high and the distance is short, and it is highly accurate and stable. It is possible to make the both compatible. However, under the opposite condition, that is, when the object reflectance is low and the distance is long, which is disadvantageous to the active method, the S /
Since the N ratio is poor, the dead band width is expanded before the true focusing point is reached by the false focusing signal due to noise before the true focusing signal is obtained, and high stability is obtained but accuracy is high. Has the drawback that it becomes worse. Further, if autofocusing is performed without changing the size of the dead zone width as in the conventional case, accuracy is improved, but noise causes unstable movement of the taking lens.

[Object of the Invention] An object of the present invention is to eliminate the above-mentioned drawbacks and consider a true focus signal only when the focus signal is continuously output a predetermined number of times.
The dead zone width is expanded to ensure the stability of the taking lens, and if the non-focus signal is output before the focus signal continues for the specified number of times, the focus signal is output again for the specified number of times in succession. An object of the present invention is to provide a highly accurate and highly stable automatic focus detection device by not changing the dead zone width.

[Summary of the Invention] The gist of the present invention for achieving the above-mentioned object is to provide an automatic focus detection device that controls an in-focus state by moving a taking lens according to an output from a focus calculation unit. Has a counting means for counting the number of times the focusing signal is output from, and a dead zone width varying means for varying the dead zone width by the output from the counting means, and the counting means is reset by the non-focusing signal. Then, the dead band width expanding signal is output to the dead band width varying means after counting a predetermined number of signals by the focusing signal, and the dead band width reducing signal is output after being reset by the non-focus signal. An automatic focus detection device, comprising:

Embodiments of the Invention The present invention will be described in detail based on the illustrated embodiments.

FIG. 1 is a block circuit configuration diagram, in which the focus calculation section 1 obtains an input signal from a light receiving element or the like (not shown) to perform calculation, and outputs a signal based on the result of the distance measurement from terminals 1a to 1d. The pulse-shaped focusing signal a, which is calculated by the focusing calculator 1 at predetermined time intervals and is output from the terminal 1a, is connected to the input terminal of the 2-input AND gate 2, and the output of the AND gate 2 is a counting circuit. 3 is input to the CLK terminal, and the counting circuit 3 counts the number of times the focus signal a is output. Further, the non-focus signal b from the terminal 1b of the focus calculation unit 1 is input to the RESET terminal of the counting circuit 3. The output Q of the counting circuit 3 is input to the AND gate 2 via the inverter 4 and also to the dead band width varying means 5. The output of the dead zone width varying means 5 is input to the terminal 1e of the focus calculation section 1, and the size of the dead zone width is changed based on the output from the counting circuit 3. Furthermore, the terminals 1c and 1d of the focus calculation unit 1
From this, a forward signal c and a backward signal d for moving an unillustrated taking lens are output to the AF motor.

2 and 3 show the timings of the output signals of the terminals 1a to 1d of the focus calculation section 1, the output Q of the counting circuit 3, and the signal e input from the dead zone width varying means 5 to the terminal 1e of the focus calculation section 1. FIG. 2 is a chart, and FIG. 2 shows a case where the focusing signal a is continuously output a predetermined number of times, and FIG. 3 is a non-focusing signal b is output before the focusing signal a continues a predetermined number of times. It is a timing chart figure in a case.

When the taking lens is in the front focus state, the forward movement signal c from the terminal 1c of the focusing calculation unit 1 becomes H level, the backward movement signal d of the terminal 1d becomes L level, and the AF motor (not shown) is rotated to bring the focusing lens into focus. Move the taking lens forward until the condition is reached. In the focused state, as shown in FIG. 2, the focus signal a of the focus calculation unit 1 changes from the L level to the H level, the non-focus signal b changes from the H level to the L level, and the forward signal The AF motor stops when c goes from the H level to the L level and the reverse signal d remains at the L level. At this time, since the RESET terminal of the counting circuit 3 has just changed from the H level to the L level, the output Q of the counting circuit 3 is at the L level.
The output Q is inverted by the inverter 4 and H is applied to the AND gate 2.
Supply level. Therefore, the counting circuit 3 is ready to start counting, and counts the number of times the focusing signal a of the focusing calculator 1 is generated. The in-focus signal a is configured to be output in one pulse for each in-angle measurement cycle when in-focus, and maintains the L level state when out of focus.

When the focus signal a is continuously output n times in accordance with the predetermined number of distance measurement cycles, the output Q of the counting circuit 3 changes from L level to H level. At this time, the AND gate 2 has a counting circuit 3
An L level signal obtained by inverting the H level of the output Q of is output by the inverter 4, and the counting of the focus signal a thereafter is prohibited, so that the output Q maintains the H level state. The H level signal of the output Q is applied to the dead band width varying means 5, so that the dead band width becomes VD as shown in FIG.
To VD '(VD'> VD).

Further, FIG. 3 is a timing chart when the focusing signal a is not continuously output, and the operation is almost the same as the case of FIG. 2. Therefore, a brief description will be given. In FIG. After a false focusing signal a is output by
The out-of-focus signal b is generated again. Due to the first false focus signal a, the non-focus signal b from the focus calculation unit 1 is temporarily set to H.
From the level to the L level and the forward signal c changes from the H level to the L level, the AF motor is stopped, and the counting circuit 3 is also in focus calculation unit 1
When the focus signal a of the signal changes from the L level to the H level, the step proceeds. However, the counter circuit 3 is reset when the non-focus signal b of the focus calculation unit 1 changes from L level to H level in the next distance measurement cycle. Further, when the forward movement signal c of the focus calculation unit 1 changes from the L level to the H level again, the AF motor rotates again in the far direction. When the true focusing signal a is output in the next cycle, the dead band width varying means 5 detects the number of times the focusing signal a continues for a predetermined number of times by the same operation as in FIG. To expand.

FIG. 4 is a circuit configuration diagram of the dead zone width varying means 5, 11 to
Reference numeral 16 is a resistor, 17 and 18 are transistors, and 19 is a comparator, and the output Q of the counting circuit 3 is connected to the input terminal q in FIG. Input signal Q to increase the dead band width
Changes from L level to H level, transistor 17
The base current flows to the ON state. When the transistor 17 is turned on, the base current also flows through the transistor 18, and the transistor 18 is also turned on. Transistor 18
Is turned on, which means that the resistor 14 is connected in parallel with the resistor 15, and the negative input terminal of the comparator 19 has a constant voltage V0 divided by the resistors 15 and 16 from the voltage VD,
The constant voltage V0 is divided by the parallel combined resistance of the resistors 14 and 15, and the voltage VD 'is applied. To the plus input terminal of the comparator 19, the calculation signal | A−B | from the two light receiving elements A and B output from the focus calculation unit 1 is input, and | A−B | <VD ′ When it is determined to be in focus, the comparator
The output of 19 becomes L level. Before reaching the in-focus state, the input signal Q is at the L level and the dead band width is the resistances 15 and 16.
It is the VD determined by the division ratio of.

Further, the present invention can be applied not only to the active type autofocus described in the embodiments but also to the passive type autofocus.

[Advantages of the Invention] As described above, according to the automatic focus detection device of the present invention, by adjusting the dead zone width, it is possible to secure high accuracy and high stability even under bad distance measuring conditions. .

[Brief description of drawings]

The drawings show an embodiment of an automatic focus detection device according to the present invention,
FIG. 1 is a block circuit configuration diagram thereof, FIGS. 2 and 3 are timing charts of outputs of a focus calculation unit terminal, a counting circuit, and a dead band width varying circuit, and FIG. 4 is a circuit configuration of dead band width varying means. It is a figure. Reference numeral 1 is a focusing calculator, 2 is an AND gate, 3 is a counting circuit, 4 is an inverter, and 5 is a dead band width variable circuit.

Claims (1)

[Claims] 1. A count for counting the number of times a focus signal is output from the focus calculation section in an automatic focus detection device that controls the photographing lens by moving the photographing lens according to the output from the focus calculation section. Means, and dead band width changing means for changing the dead band width by the output from the counting means, wherein the counting means is reset by a non-focus signal, stepped by a focus signal, and a predetermined number of signals. And a control means for controlling so as to output a dead band width expansion signal to the dead band width changing means and output a dead band width reduction signal after being reset by a non-focus signal. Focus detection device.