JPH0812316B2 - Automatic focus adjustment device - Google Patents

Description

The present invention relates to an automatic focus adjustment device used for movie cameras and the like and capable of adjusting a dead zone width.

[Prior Art] In an active type automatic focus adjusting device, focus adjustment is performed based on an output difference from a pair of light receiving elements,
It is already known that a dead zone is provided in order to stabilize the autofocus operation and prevent hunting, and that the dead zone width can be prevented in order to stabilize the operation once the focus is achieved.

Then, for example, if a method of expanding the dead band width after once focusing is adopted, it works properly under the conditions advantageous for the active auto focus method where the reflectance of the subject is high and the distance is short, and it is highly accurate and stable. It becomes possible to make the both compatible. However, under the opposite condition, that is, when the subject has a low reflectance and a long distance, which is unfavorable to the active method, the electric signal S / N ratio obtained is poor, and therefore, before the true focusing signal is obtained. In addition, the dead band width is expanded due to a false focusing signal due to noise. It has a drawback that accuracy is deteriorated although stability is obtained.
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 after autofocus operates to approach an in-focus state from an out-of-focus state, after the first focus signal is output from the focus detection calculation unit. Providing an automatic focusing device that can achieve high accuracy and stability by expanding the dead band width after continuing the distance measurement with a predetermined dead band width regardless of whether it is in focus or not for a predetermined distance measurement cycle period To do.

[Summary of the Invention] The gist of the present invention for achieving the above-described object is to provide an automatic focusing apparatus for controlling an in-focus state by moving an imaging lens so that focusing is performed for each ranging cycle that repeats ranging. A focus calculation means for outputting a signal or a non-focus signal, a counting means for counting the number of distance measurement cycles from the output of the focus signal from the focus calculation means to the output of the non-focus signal, and the counting means. Dead band width changing means for changing the dead band width by the output from the means, and the counting means starts counting the number of distance measuring cycles, counts a predetermined number of distance measuring cycles, and then the dead zone widening signal to the dead band width varying means. And a dead band is expanded, and the counting unit is reset by a non-focus signal after the dead band, and a dead band reduction signal is output to the dead band width varying unit to control the dead band width. Equipped with It is an automatic focusing device characterized by the above.

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 of an embodiment of the present invention, and FIG.
The figure is a signal and a timing chart. The focus signal a output from the terminal 1a of the focus calculator 1 that calculates the output signal from the light receiving element is connected to the terminal S of the RS flip-flop 2, and the non-focus signal c output from the terminal 1c is It is connected to the terminal R of the RS flip-flop 2 via the 2-input AND gate 3. The output from the terminal Q of the RS flip-flop 2 is the distance measurement cycle signal b from the terminal 1b of the focus calculation unit 1.
Also, it is connected to a 3-input AND gate 4, and the output of the AND gate 4 is connected to the CLK terminal of the counting circuit 5. Further, the output of the counting circuit 5 is supplied to the dead band width variable circuit 6 and the AND gate 3, and further to the AND gate 4 via the inverter 7.
It is connected to the. The output of the AND gate 3 is also connected to the RESET terminal of the counting circuit 5, and the dead band width variable circuit 6
Is connected to the terminal 1f of the focus calculation unit 1. It should be noted that the far signal d is output from the terminal 1d of the focus calculation unit 1 and the near signal e is output from the terminal 1e.

The focus calculation unit 1 outputs a signal based on the distance measurement result from the terminals 1a to 1e. When the focus signal a is output from terminal 1a, RS
The flip-flop 2 stores that the focus signal a has been output, and changes the output of its terminal Q from L level to H level. The output of the RS flip-flop 2 is input to the 3-input AND gate 4. Further, the output of the inverter 7 and the distance measurement cycle signal b from the terminal 1b of the focus calculation unit 1 are also input to the AND gate 4, so that the output of the RS flip-flop 2 is at the H level and the output of the inverter 7 is at the H level. At the level, one pulse is output for each one ranging cycle. The distance measurement cycle signal b from the terminal 1b of the focus calculation unit 1 is input to the CLK terminal of the counting circuit 5 as the output of the AND gate 4, and the counting circuit 5 starts counting. And the counting circuit 5
When n pulses of a predetermined circuit are input to the CLK terminal of the, the output Q of the counting circuit 5 changes from the L level to the H level and is input to the dead band width varying circuit 6. This dead band width changing circuit 6
Output f is input to the terminal 1f of the focus calculation unit 1, and the size of the dead zone width is changed.

The output Q of the counting circuit 5 is also input to the inverter 7 and the 2-input AND gate 3, and the output of the inverter 7 is L when the counting circuit 5 counts a predetermined number of times n times. H from level to H level
From the level to the L level, the output of the AND gate 4 becomes L
The level is set and the counting circuit 5 stops counting. The AND gate 3 has an output Q of the counting circuit 5 and a terminal 1c of the focus calculation unit 1.
From the terminal 1c of the focus calculation unit 1 after the counter circuit counts n times and the output Q of the counter circuit 5 changes from L level to H level. Focus signal c
Is output, the output of the AND gate 3 is input to the terminal R of the RS flip-flop 2 and the RESET terminal of the counting circuit 5 to reset the RS flip-flop 2 and the counting circuit 5 to the initial state. Furthermore, when the imaging lens is in the front focus state, the focus calculation unit 1 outputs an H level from the terminal 1d that outputs a far signal and an L level from the terminal 1e that outputs a near signal. By driving, the imaging lens is moved to the focal point.

When the first focus signal a is output from the terminal 1a of the focus calculator 1 and input to the terminal S of the RS flip-flop 2,
The output of terminal Q of RS flip-flop 2 changes from L level to H
It becomes a level and is input to the AND gate 4. One distance measurement cycle signal b is output to the other input terminal of the AND gate 4 for each distance measurement cycle, and the number of distance measurement cycles after the first focus signal a is generated is calculated by the counting circuit 5. Input to the CLK pin to start counting. For example, when the focus signal a initially output is due to noise and is not the true focus signal a, the focus signal a is not stably output, and as shown in FIG. In the third and third distance measurement cycles, the in-focus signal a is not output and the out-of-focus signal c is output.

When the reason why the non-focus signal c is output is that the taking lens has not moved to the in-focus point sufficiently, H level is output from the terminal 1d and L level is output from the terminal 1e. To be done. When the taking lens reaches the true focusing point, a stable focusing signal a is output. When the counting circuit 5 counts the distance measurement cycle signal b a predetermined number of times n, the output Q of the counting circuit 5 becomes H level, and the dead band width varying circuit 6 causes VD to V as indicated by the dead band width control voltage.
It is changed to D'and the dead zone width is expanded.

By doing so, even under the condition that the S / N ratio is not so good, the stable and accurate autofocus operation can be performed. Further, as described above, the counting circuit 5 has a predetermined n
When counting the number of times, the counting is stopped, and when the non-focus signal c is input to the AND gate 3 from the terminal 1c due to the (n + 2) th movement of the subject as shown in FIG. 2, the RS flip-flop 2 Are reset, and the counting circuit 5 is also reset at the same time to be reset to the initial state, and thereafter, control is performed so that the in-focus state is achieved by the same operation as at the beginning.

Note that FIG. 3 is a circuit configuration diagram of the dead band width variable circuit 6, and the output Q of the counting circuit 5 is input to the terminal q in FIG. Here, 11 to 16 are resistors, 17 and 18 are transistors,
Reference numeral 19 is a comparator, and when the input signal to the terminal Q changes from L level to H level, a base current flows through the transistor 17 to turn it on. Then, the base current also flows through the transistor 18, and the transistor 18 is also turned on.
When the transistor 18 is turned on, the voltage applied to the negative input terminal of the comparator 19 is the constant voltage V0
The constant voltage V0 changes from the voltage VD divided by 15 and the resistor 16 to the voltage VD 'divided by the parallel combined resistance of the resistors 14 and 15 and the resistor 16. To the plus input terminal of the comparator 19, the calculation signals | A−B | of the outputs A and B of the two light receiving elements output from the focus calculation unit 1 are input, and when the transistor 18 is off, When A−B | <VD, it is determined that the focus state is achieved, and the output of the comparator 19 becomes L level. When the transistor 18 is on, if | AB | <VD ', it is determined to be in focus, and the output of the comparator 19 becomes L level. Thus, the dead band width can be changed by changing the input signal to the terminal Q.

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

[Advantages of the Invention] According to the automatic focus adjusting device of the present invention as described above, by adjusting the dead zone width, it is possible to secure high accuracy and high stability even when the ranging condition is bad. Become.

[Brief description of drawings]

The drawings show an embodiment of an automatic focus adjusting device according to the present invention. FIG. 1 is a block circuit configuration diagram thereof, FIG. 2 is a signal timing chart diagram, and FIG. 3 is a circuit diagram of a dead band width variable circuit. Is. Reference numeral 1 is a focusing calculator, 2 is an RS flip-flop, 3 and 4
Is an AND gate, 5 is a counting circuit, 6 is a dead zone variable circuit,
Reference numeral 7 is an inverter.

Claims (1)

[Claims] 1. An automatic focus adjusting device for controlling an in-focus state by moving an image pickup lens, and focusing calculation means for outputting a focusing signal or a non-focusing signal for each distance measurement cycle in which distance measurement is repeated. A counting means for counting the number of distance measurement cycles from the output of the focusing signal from the focusing calculation means to the output of the non-focusing signal; and a dead zone width varying means for changing the dead zone width by the output from the counting means. After the counting means starts counting the number of distance measurement cycles and counts a predetermined number of distance measurement cycles, a dead zone expansion signal is output to the dead zone width varying means to expand the dead zone, and a dead zone after the dead zone is detected. An automatic focus adjusting device, comprising: a control unit that resets the counting unit by a focus signal and outputs a dead band reduction signal to the dead band width changing unit to control the dead band width.