JPS6391612A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To secure high accuracy and high stability even when range finding conditions are inferior by adjusting the width of a blind sector. CONSTITUTION:A range finding cycle signal (b) from a terminal 1b of a focusing arithmetic part 1 is inputted to the CLK terminal of a counting circuit 5 as the output of an AND gate 4 and the counting circuit 5 begins to count. Then when a specific number (n) of pulses are inputted to the CLK terminal of the counting circuit 5, the output Q of the counting circuit 5 rises from an L level to an H level and is inputted to a blind sector width varying circuit 6. The output (f) of this blind sector width varying circuit 6 is inputted to a terminal 1f of a focusing arithmetic part 1 to vary the blind sector width. In this case, an autofocus mechanism operates to enter a nearly focusing state from a nonfocusing state and range finding operation is carried out with the specific blind sector width regardless of whether the lens is in focus or not for a specific range finding cycle period after a 1st focusing signal is outputted from a focus detecting arithmetic part. Then the blind sector width is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an automatic focus adjustment device that is used in movie cameras and the like and can adjust the width of a dead zone.

[Prior Art] In an active type automatic focus adjustment device, focus adjustment is performed based on the output difference from a pair of light receiving elements, and a dead zone is provided to stabilize the autofocus operation and prevent hunting. It is already known to widen the dead zone width to make the operation more stable after focusing.

For example, if you adopt a method of widening the dead zone width after focusing, it will function correctly in conditions that are advantageous for active autofocus methods, such as when the subject has high reflectance and is close to the subject, resulting in high precision and high accuracy. It becomes possible to achieve both stability. However, under the opposite conditions, which are disadvantageous to the active method, such as when the subject has low reflectance and is far away, a true in-focus signal cannot be obtained because the S/N ratio of the obtained electrical signal is poor. The dead zone width is expanded due to a false focusing signal due to noise, and although stability is obtained, accuracy is deteriorated. Furthermore, if autofocus is performed without changing the width of the dead zone as in the past, the accuracy will improve, but there is a drawback that the movement of the photographing lens will become unstable due to noise.

[Object of the Invention] An object of the present invention is to eliminate the above-mentioned drawbacks, and to solve the problem when the autofocus operates and approaches the in-focus state from the out-of-focus state, and after the first in-focus signal is output from the focus detection calculation section. Provided is an automatic focusing device that can achieve high accuracy and high stability by expanding the dead zone width after continuing distance measurement with a predetermined dead zone width regardless of whether the focus is in focus or out of focus during a predetermined distance measurement cycle period. It's about doing.

[Summary of the Invention] The gist of the present invention for achieving the above-mentioned object is to provide an automatic focus adjustment device that moves a photographic lens to a focused state using an output from a focus calculation unit, and provides a counting means for counting the number of distance measurement cycles after outputting a focusing signal from the counting means; a dead band width variable means for changing a dead band width according to an output from the counting means; After counting a predetermined number of ranging cycles, outputting a dead zone expansion signal to the dead zone width variable means to enlarge the dead zone, and resetting the counting means by the out-of-focus signal after expanding the dead zone; The automatic focus adjustment device is characterized by comprising a control means for outputting a dead zone reduction signal to the dead zone width variable means and controlling the dead zone width to be reduced.

[Embodiments of the invention] The present invention will be explained in detail based on illustrated embodiments.

FIG. 1 is a block circuit configuration diagram of an embodiment of the present invention, and FIG. 2 is a signal timing chart. The focus signal a output from the terminal 1a of the focus calculation section l that calculates the output signal from the light receiving element is as follows.

Connected to terminal S of RS flip-flop 2, terminal IC
The out-of-focus signal C output from the RS flip-flop 2 is connected to the terminal R of the RS flip-flop 2 via the two-man AND gate 3. The output from the terminal Q of the RS flip-flop 2 is 3 along with the distance measurement cycle signal from the terminal 1b of the focusing calculation section l.
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 connected to a variable dead band width circuit 6 and an AND gate 3, and further to an AND gate 4 via an inverter 7. Also, the output of the AND gate 3 is the counting circuit 5
The output of the variable dead band width circuit 6 is also connected to the terminal 1f of the focusing calculation section 1. Note that the far signal d is output from the terminal ld of the focus calculation s1, and the near signal e is output from the terminal 1e.

The focus calculation unit l sends signals based on the distance measurement results to terminals 1a to 1e.
Output from. When the focus signal a is output from the terminal 1a, the RS flip-flop 2 remembers that the focus signal a has been output, and changes the output of the terminal Q from the L level to the H level. The output of this RS flip-flop 2 is input to a three-man AND gate 4. Furthermore, the output of the inverter 7 and the ranging cycle signal from the terminal 1b of the focusing calculation section 1 are also input to the AND gate 4, so that the output of the RS flip-flop 2 is at H level and the output of the inverter 7 is at H level. At the level, the distance measurement cycle signal from the terminal 1b of the 0-focus calculation unit 1, which outputs one pulse for each distance measurement cycle, is output from the CL of the counting circuit 5 as the output of the AND gate 4.
The signal is input to the K terminal, and the counting circuit 5 starts counting. When a predetermined number of n pulses are input to the CLK terminal of the counting circuit 5, the output Q of the counting circuit 5 changes from the L level to the H level and is input to the variable dead band width circuit 6. The output f of this variable dead band width circuit 6 is inputted to a terminal if of a focusing calculation section l, and the size of the dead band width is changed.

Further, the output Q of the counting circuit 5 is also input to the inverter 7 and the two-person gate 3, and the output of the inverter 7 is outputted to the counting circuit 5 when the counting circuit 5 has counted a predetermined number of times.
As the output Q changes from L level to H level, it changes from H level to L level, and the output of AND gate 4 goes to L level, causing counting circuit 5 to stop counting. The AND gate 3 includes the output Q of the counting circuit 5 and the terminal IC of the focusing calculation section 1.
The out-of-focus signal C from n is input, and the counting circuit 5
After the output Q of the counting circuit 5 changes from the L level to the H level after counting the number of times, when the out-of-focus signal C is output from the terminal IC of the focus calculation section 1, the output of the AND gate 3 is output from the RS flip-flop. RS flip-flop 2 and counting circuit 5.
Furthermore, when the photographic lens is in the front focus state, the focus calculation unit 1 outputs an H level from the terminal 1d that outputs the far signal, and an L level from the terminal 1e that outputs the near signal. is output, which drives an AF motor (not shown) to move the photographic lens to the in-focus point.

When the first focusing signal a is output from the terminal 1a of the focusing calculation section l and inputted to the terminal S of the RS flip-flop 2, the output of the terminal Q of the RS flip-flop 2 changes from the L level to the H level. It is input to gate 4. One distance measurement cycle signal is outputted 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 focusing signal a is generated is determined by the counting circuit 5. C.L.
0 is input to the K terminal and counting starts. For example, if the initially output focus signal a is due to noise and is not the true focus signal a, the focus signal a is stably output. Therefore, as shown in FIG. 2, in the second and third distance measurement cycles, the focus signal a is not output, but the out-of-focus signal C is output.

If the reason why this out-of-focus signal C is output is that the photographic lens has not moved sufficiently to the in-focus point, an H level is output from terminal 1d and an L level is output from terminal 1e. be done. When the photographic lens reaches the true focus, the focus signal a is stably output. When the distance measurement cycle signal S is counted a predetermined number of times by the counting circuit 5, the output Q of the counting circuit 5 becomes H level, and the dead band width variable circuit 6 changes the range from VD to V as indicated by the dead band width control voltage.
D' and the dead zone width is expanded.

As a result, accurate and stable autofocus operation can be performed even under conditions where the S/N ratio is not very good. Further, as described above, the counting circuit 5 stops counting after counting a predetermined number of n times, and furthermore, as shown in FIG.
+2) When the out-of-focus signal C is input from the terminal IC to the AND gate 3 due to the subject moving for the second time, the RS flip-flop 2 is reset, and at the same time the counting circuit 5 is also reset to return to the initial state. The lens is reset, and from then on, control is performed to bring it into focus using the same operation as at the beginning.

Note that FIG. 3 is a circuit diagram of the variable dead band width 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, and 19 is a comparator. When the input signal to the terminal Q changes from the L level to the H level, a base current flows through the transistor 17 and turns 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 equal to the voltage VD obtained by dividing the constant voltage vO by the resistors 15 and 16.
Then, the constant voltage VO is divided by the parallel composite resistance of the resistor 14 and the resistor 15, and the resistor 16, which changes to the voltage ■D'. The plus input terminal of the comparator 19 receives the calculation signal lA of the outputs A and H of the two light receiving elements output from the focus calculation section 1.
-B1 is input and the transistor 18 is off, it is determined that IA-Bl<VD, the in-focus state is established, and the output of the comparator 19 becomes L level. When the transistor 18 is on, IA-Bl<V
In the case of D', it is determined that the focus is in focus, and the output of the comparator 19 becomes L level. In this way, 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 an active type autofocus method as described in the embodiments, but also to a passive type autofocus method.

[Effects of the Invention] According to the automatic focusing device according to the present invention as described above, by adjusting the dead zone width.

Even when distance measurement conditions are poor, it is possible to ensure high accuracy φ and high stability.

[Brief explanation of the drawing]

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

Claims (1)

[Claims] 1. In an automatic focus adjustment device that moves a photographing lens and controls it to a focused state based on an output from a focus calculation section, a system for counting the number of distance measurement cycles after outputting a focus signal from the focus calculation section; a counting means, a dead zone width variable means for changing the dead zone width based on an output from the counting means, and a dead zone width variable means for changing the dead zone width after the counting means starts counting in response to a focus signal and has counted a predetermined number of ranging cycles; outputting a dead zone expansion signal to the means to expand the dead zone, resetting the counting means with an out-of-focus signal after expanding the dead zone, and outputting a dead zone reduction signal to the dead zone width variable means to reduce the dead zone width; An automatic focus adjustment device characterized by comprising: control means for controlling.