JPS6318172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus detection device for a camera or the like that repeatedly outputs a focus position information signal according to the focus adjustment state of a photographic lens. Although various types of focus detection devices have been proposed in the past, the focus position is often misidentified due to false focus position information signals. Reasons for this include fluctuations in the output signal level of the photometric circuit, changes in the object due to noise, obstacles entering the distance measurement zone, and the like.

An object of the present invention is to provide an automatic focus detection device that eliminates misidentification of the focus adjustment state of a photographic lens due to this false focus position information signal.

Hereinafter, the present invention will be explained based on the drawings. 1st
The figure is a block diagram showing an embodiment of the present invention. FIG. 2 shows a timing chart of this embodiment, and the various waveforms in the block diagram are given the same reference numerals as in FIG. First, the configuration of the automatic focusing device that is the basis of the present invention and the influence of the false focus position information signal on the automatic focusing operation will be described.

In FIG. 1, the focal length detection lens 11 is
A force from a drive mechanism 12 including a motor etc. causes it to reciprocate in the optical axis _O1 direction between, for example, a subject distance of 1 m and infinity. On the other hand, the clock pulse generation circuit 13 has a detection lens 11 with a subject distance of 1 m.
A pulse output a corresponding to the subject distance is generated each time the subject moves from to infinity. Furthermore, the drive mechanism 12
includes a cam means for moving the detection lens 11 by a predetermined amount by constant rotation of the motor.
Now, the object light transmitted through the reciprocating detection lens 11 is measured by the photometry circuit 14 including the light receiving element 14a. The photometric circuit 14 generates a photometric output b having a peak value corresponding to a high-contrast portion of the subject. This photometric output b has a plurality of peak values corresponding to the presence of a plurality of objects having relatively high contrast at different distances within the screen.

A peak detection circuit 15 including a sample and hold circuit receives the photometric output b and detects the peak of its fluctuation components. In other words, when the output is increasing, pulses are continuously output, and when the output is decreasing relative to the hold value, the pulse output is stopped, and as a result, the final stop of this pulse increases the maximum output. A peak detection pulse c indicating the peak value is output. The counter 16 receives the clock pulse output a as a count input, and receives the peak detection output c as a reset input. Therefore,
Until the detection lens 11 moves from a subject distance of 1 m toward infinity and detects the maximum peak value, that is, the counter 16 counts up when the peak detection output pulse c stops, and continues counting up when the peak detection output pulse c occurs. 16 is reset.
When the application of the peak detection pulse output c finally stops, the number of clock pulses is counted until the detection lens 11 reaches infinity. This count result indicates the position of the detection lens 11 at the time when the maximum peak value is detected, and the focal position information signal of the subject to be focused can be obtained from that position.

The digital count output of the counter 16 is stored by the latch circuit 17 when the detection lens 11 moves back. The storage output of the latch circuit 17 is converted into an analog voltage by the D/A conversion circuit 18. A photographing lens 19 of a camera or the like is configured to be moved in the direction of the optical axis _O2 by a drive mechanism ₂₀ including a motor M2. The resistor 21 indicates information about the position of the photographing lens 19, that is, the distance to the in-focus subject by a change in resistance value, and by supplying current to the resistor 21, this is extracted as a voltage pressure.
The servo amplifier 22 drives the motor _M2 so that the output voltage of the D/A conversion circuit 18 and the output voltage of the resistor 21 have a predetermined relationship. That is, servo control is performed using the output of the D/A conversion circuit 18 corresponding to the maximum peak value as a reference voltage and the output generated by the resistor 21 depending on the position of the photographic lens 19 as a feedback voltage.

By the way, with the above configuration, automatic focus detection (D/A
The output of the conversion circuit 18 is a focus position information signal of the subject to be focused. ), the pulse generation stop point of the peak detection pulse output c changes due to level fluctuations or noise of the photometric output b, and the photographing lens moves for focusing for each scan, so the motor M ₂ The current consumption of
This causes problems such as the focal position changing, resulting in photographs that are not accurately focused.

The present invention solves this problem. Now, returning to FIG. 1, in each scanning period, the timing circuit 31 performs distance measurement with a constant pulse width when the detection lens 11 moves forward from the object distance of 1 m to infinity and returns to 1 m. A termination pulse d is generated. When the memory circuit 32 which inputs the count output of the counter 16 receives the distance measurement end pulse d,
The count output of the counter 16 is stored. The storage output of the memory circuit 32 is digitally compared with the count output of the counter 16 in the next scanning cycle by the coincidence circuit 33, and when the two outputs coincide with the period of the ranging end pulse d, the coincidence circuit 33 activates the latch. circuit 17
Instructs to read and store the counting output of the counter 16.

Therefore, only when the count output of the counter 16 is the same twice in a row due to multiple scans,
Since the latch circuit 17 stores the counting output, the maximum peak value can be detected more reliably, and misidentification of the focal position due to a false focal position information signal can be eliminated.

FIG. 3 shows the memory circuit 32 and the coincidence circuit 33.
and an embodiment of the latch circuit 17. In the figure, the distance measurement end pulse d is delayed by a delay circuit 51 for a certain period of time and is applied to a latch circuit 52.
This causes the latch circuit 52 to store the count output of the counter 16. Delay circuit 51 and latch circuit 5
2 constitutes a memory circuit. exclusive
The OR gates 53 to 57 input the storage output of the latch circuit 52 and the count output of the counter 16. Noah Gate 58 is exclusive or gate 5
3 to 57, and applies the output as the other input to an AND gate 59 which has the distance measurement end pulse d as one input. The output of the AND gate 59 serves as an output for instructing the latch circuit 17 to read. The matching circuit 33 is configured in the above manner.

In the embodiment, the control means of the present invention includes the memory circuit 3
2 and matching circuit 33 and latch circuit 17 and D/
It corresponds to the A conversion circuit 18 and the servo amplifier 22.

Now, in a certain scanning period, the distance measurement end pulse d
When d is applied, the delay circuit 51 applies the pulse d to the latch circuit 52 with a time delay longer than the pulse width of the ranging end pulse. As a result, the latch circuit 52 stores the count output of the counter 16, so at this point, all the inputs of the exclusive OR gates 53 to 57 match and output a logic value of "0".

Therefore, the output of the NOR gate 58 has a logical value of "1".
It is. However, due to the action of the delay circuit 51,
Distance measurement end pulse d input to AND gate 59
has already disappeared (logical value "0"), the AND gate 59 outputs the logical value "0". As a result, the latch circuit 17 does not read the count output of the counter 16.

In the next scanning period, when the distance measurement end pulse d is applied, one input of the AND gate 59 becomes a logical value "1". If the count output of the counter 16 at this time is the same as the storage output of the latch circuit 52, the outputs of the exclusive OR gates 53 to 57 will have a logic value of "0", and therefore the NOR gate 58
The output of is a logic "1". As a result, the AND gate 59 outputs a logical value of "1" and instructs the latch circuit 17 to read the counting output of the counter 16. By the way, it goes without saying that when the output of the latch circuit 52 and the output of the counter 16 do not match when the distance measurement end pulse d is applied twice, the latch circuit 17 does not perform reading.

In this embodiment, for example, a circuit that divides the distance measurement end pulse by 1/2 is provided, and the
The above judgment operation may be performed, and the operation of the matching circuit may be analog comparison instead of digital comparison, and the operation and effect are the same. Furthermore, the detection lens 11 and the photographing lens 19 may be used to perform so-called TTL distance measurement.

According to the present embodiment described above, since fluctuations in the output of the latch circuit 17 are suppressed, motor current consumption during automatic focusing control can be reduced, and fluctuations in the focus position of the camera can be eliminated.

As described above, according to the present invention, the control means outputs the control signal according to the past focus position information signal and the newly output focus position information signal, so that the photographing lens is not affected by the false focus position information signal. It is possible to eliminate misidentification of the detection adjustment state, and to obtain an appropriate control signal for operating the driven means (for example, the driving means for the photographing lens, the display means for indicating the focus detection state, etc.). Therefore, even if an obstacle or the like crosses in front of the subject, a stable control signal can be obtained without transiently responding to the obstacle, and a highly accurate automatic focus detection device can be obtained. can.

According to the embodiment, among the focus position information signals (photometry output) that are periodically output, the latest focus position information signal (peak value of photometry output) and the focus position information signal (photometry output) output immediately before are used. output peak value)
When it detects that the two images match (that is, when the peak value of the focus position information signal is output for a certain period of time), the photographing lens is driven to the focus position, so there is no obstruction in front of the subject. Even when an object or the like crosses the camera, the photographing lens does not respond sensitively and operate, resulting in a good photographic feel, which is convenient for photographing. In addition, this focus position information signal may be used to indicate the focus adjustment status of the photographic lens in the viewfinder of the camera, thereby making the display of the focus detection status in the viewfinder stable, less flickering, and easier to see. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a timing chart of the first illustrated embodiment, and FIG. 3 is a circuit diagram showing a specific example of a determination circuit according to the present invention. Explanation of symbols of main parts, 11, 12, 13, 1
4, 15, 16... focus detection means, 20, 21,
22...driving means, 32...storage means, 17,3
3... Control means.

Claims (1)

[Claims] 1. Focus detection means that repeatedly performs a focus detection operation and generates a focus position information signal for each focus detection operation, and drives a photographing lens to a focus position based on the focus position information signal. Driving means: Storage means for storing and storing the focal position information signal while sequentially updating the focal position information signal; Comparing the focal position information signal stored in the storage means and the next newly generated focal position information signal, Preventing the drive means from responding to the newly output focus position information signal if the position information signals are not substantially equal; An automatic focus detection device comprising: a control means for controlling the driving means to drive the photographing lens to a focus position based on the newly generated focus position information signal.