JPS5932762B2 - focus detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device for an optical device such as a camera.

Photoelectrically detecting the focus of optical equipment is significant because it eliminates individual differences in pit alignment and improves accuracy, and it also streamlines pit alignment operations, and its completion is awaited. Ta.

However, most of the devices that have been proposed in the past are highly dependent on the contrast and brightness of the subject, and require complex electronic circuits and power sources to extend the lens. The disadvantage is that it becomes larger and its power consumption increases. Such drawbacks are particularly fatal for optical equipment such as cameras, which are used for photographing a wide variety of subjects and require small size and low power consumption. A conventionally known focus detection method uses a photoconductive element such as CdS as a focus signal detection element, and its photoresistance changes in response to changes in the contrast of the subject image and shows an extreme value at the in-focus position. Many methods utilize the dip effect.

In this type of method, the extreme value due to this dip effect changes greatly depending on the brightness, contrast, and spatial frequency of the subject image, but in particular cameras and the like, because the brightness range and spatial frequency of the subject cover a wide range, , this amount of change is extremely large. Therefore, when displaying and observing the detected voltage value due to this dip effect with a meter such as a voltmeter, it is necessary to use a meter that has a wide dynamic range and has a significantly different focusing sensitivity depending on the subject. It has disadvantages such as having to be used. Therefore, the focus detection device of the present invention employs an electronic circuit means to suppress the significant fluctuation of the maximum value due to such a dip effect and to always detect this extreme value at the focal plane as the minimum value of zero potential. .

Furthermore, the range in which the in-focus signal is displayed is limited to the vicinity of the focal point, and a constant positive voltage is always maintained at the defocus position far away from the focal plane. As such electronic circuit means, a comparator circuit or an amplitude limiting circuit is used, and the operation thereof will be described later. In this way, the detection signal at the in-focus point is always held at zero, and the display range of the in-focus signal is limited to the vicinity of the focus, so the LED is turned on only in a very narrow in-focus range corresponding to the depth of focus, and the in-focus point is can be displayed and observed, and even in the case of a meter display, the deflection of the pointer is always within a certain range regardless of the brightness and contrast of the subject, and the focus is always displayed as zero.

Still another object of the focus detection device according to the present invention is to provide a means for removing false focus signals caused by sudden sudden shaking of the subject or camera, which is different from conventional focus detection devices. This is an advantage that cannot be found.

Thus, the purpose of the present invention is, firstly, to always obtain a focusing signal with a constant amplitude without being affected by subject brightness, contrast, and spatial frequency, and furthermore, to always detect the true focusing signal at the minimum value of zero potential. Second, it has a compact and low-profile electronic circuit that eliminates false focusing signals caused by sudden movement of the subject or camera shake, and always obtains a stable focusing signal. An object of the present invention is to provide a focus detection device that operates using power consumption.

An embodiment of the focus detection device according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a conventional focus detection device that utilizes this dip effect.

Further, FIG. 2 shows a dip signal based on a change in contrast of an optical image. In the example shown in Figure 1, the light beam from lens 1 is divided into optical paths by Fumira 12, and film 3 and CdS5 are placed on the two expected image formation planes, and then CdS5 is installed.
The light beam traveling to the dS5 is divided into optical paths by a half mirror 4, and a diffusing plate 7 is placed on another planned imaging plane obtained thereby, and a CdS6 is placed immediately after it. If the outputs of the CdSs 5 and 6 are subjected to differential amplification or bridge detection in such an optical system, a chevron-shaped dip signal having an extreme value as shown in FIG. 2 can be obtained in response to a change in the contrast of the object image. Here, the horizontal axis d is the distance between the lens 1 and the CdS5, and the vertical axis V is the output voltage of the differential amplifier or bridge detection corresponding to the photoresistance change of the photoconductive element, F
is the intended imaging plane, Vp is the extreme value or peak voltage of the dip signal, and v is the dip voltage at any location of the dip signal. The conventional method detects that the position of the optical image coincides with the planned imaging plane F by detecting the peak value of the dip signal obtained in this manner.

However, the height, peak voltage (in this case is designated as Vp'), and slope of this dip signal vary greatly depending on the illuminance, contrast, and spatial frequency of the subject image, as shown by the broken line in the figure. It is. Therefore, for example, in order to digitally detect the planned imaging plane F, if a dip signal is processed using a comparator having a reference voltage Vref as shown by the dashed line in FIG. Although the imaging plane F is detected, it is not detectable in the case shown by the broken line.

As described above, in the conventional method, a situation occurred in which focus detection became impossible depending on the subject, which was extremely inconvenient. A possible solution to this drawback is to vary the reference voltage Vref depending on the subject, but this is not appropriate because it complicates the detection operation and at the same time makes the detection accuracy unstable. There is another well-known method that attempts to solve the above drawback by periodically vibrating the light-receiving element in the planned image plane, but this requires a vibrating device such as an electric motor, which makes the device complicated and consumes a lot of power. This is unsuitable for small devices such as cameras because an increase in the amount of noise is unavoidable. Furthermore, even when the intended image plane F is detected in analog form using a meter or the like, the above-mentioned fluctuations in the dip signal bring about extremely inconvenient results.

In other words, a phenomenon occurs in which the meter pointer oscillates greatly when photographing certain objects, while the oscillation is small when photographing other objects.This is a nuisance when observing the meter, and the meter itself is required to have a wide dynamic range. This is inconvenient. The present invention easily solves these drawbacks without using an electric motor, performs stable focus detection regardless of the subject situation, and displays digital or analog information.
FIG. 3 shows an embodiment of the present invention.

This embodiment is intended for digital display; as shown in FIG. 3, a bridge circuit is constructed of CdSs 5 and 6, resistors 8 and 9, and a power supply E, and the output thereof is amplified by an amplifier 10.

Here, the CdSs 5 and 6 are arranged as shown in FIG.
The output of the amplifier 10 is connected to a storage capacitor 12 through a forward-connected discharge prevention diode 11. A switch 13 for setting a lever is installed on the capacitor 12. The anode terminal of the capacitor 12 is connected to the positive input terminal of a differential amplifier 15 through a buffer amplifier 14 having a high input impedance. The output of the amplifier 10 is directly connected to the negative terminal of the differential amplifier 15. The output of the differential amplifier 15 is connected to a comparator 16 having a reference voltage Vref, and a light emitting diode 18 connected in series with a load resistor 19 is connected to the comparator 16 via an inverter 17. Next, the operation of this circuit will be explained. Generally, in pit alignment operations performed by the human eye, the vicinity of the focal point must be observed back and forth many times. That is, by performing back-and-forth observation, the best optical image is obtained by comparing the peak contrast value of the optical image stored by the photographer with the contrast of the optical image on the reticle. The present invention utilizes this principle. First, the reset switch 13 is short-circuited to discharge the voltage stored in the storage capacitor 12. Next, the switch 13 is opened to move the lens 1 in FIG. At this time, the position of the lens 1 before movement can be anywhere, and the movement direction is also free. For simplicity, it is assumed that the optical image of the lens 1 is now on the left slope of the dip signal in FIG. If the photographer turns the pit link from this state and moves the lens 1 in the direction of arrow 5 in FIG.
A dip signal as shown in FIG. 2 is output to the amplifier 10. At this stage, the peak voltage V of the dip signal is stored in the storage capacitor 12 without being discharged by the discharge prevention diode 11 and buffer amplifier 14. Next, if the photographer moves the lens 1 in the direction of arrow 8 in Fig. 1 according to his pit alignment habits,
The amplifier 10 receives the same dip signal as before. At this time, focusing on the input terminal of the differential amplifier 15, the peak voltage Vp stored in the capacitor 12 by the previous operation is input to the positive input terminal, and the negative terminal corresponds to the position d. The dip voltage v is input. Therefore, if the gain of the differential amplifier 15 is G, its output will be G(Vp-v). Here, when the position of the optical image formed by lens 1 coincides with the planned image forming plane F, Vp-v
Therefore, when the optical image is before and after F, Vp>v. FIG. 4 shows the output of the differential amplifier 15 in FIG. 3. Planned imaging plane F as shown by the solid line in Figure 4
The voltage becomes zero volts, and the voltage becomes positive before and after that. Therefore, if the lens 1 is stopped at a position where the output of the differential amplifier 15 is zero volts, the optical image will be focused on the intended image plane F. Next, let us consider a case where the subject changes and a dip signal as shown by the broken line in FIG. 2 is obtained (its peak voltage is V and the dip voltage at an arbitrary location is V5). Here, prior to pit alignment, the reset switch 13 discharges the voltage stored in the capacitor 12. This switch 1
If you make 3 work in conjunction with the shutter button,
Conveniently, the memory of the capacitor 12 is erased each time a photograph is completed. Next, if the switch 13 is opened and the lens 1 is moved, the first four
By moving the lens in this direction, Vp' is stored in the capacitor 12, and by subsequently moving the lens in the five directions, G (V, Norde) is output from the differential amplifier 15 as described above. In this case as well, the expected image plane F is Vp'-zo, and the area before and after F is V〆〉v, so the output of the differential amplifier 15 is as shown by the broken line in FIG. It shows a valley shape with zero port on the imaging plane F. As described above, according to the present invention, regardless of the subject, the output of the differential amplifier 15 is always zero volts at the intended image plane F, making it easy to process the dip signal by the subsequent electronic circuit. The output of the differential amplifier 15, thus aligned to zero volts at the predetermined imaging plane F, is input to a comparator 16 having a reference voltage as indicated by Vref in FIG.

FIG. 5 shows the output of the comparator 16, and VH and VL indicate the high level and low level of the output of the comparator 16, respectively. As is well known, a comparator maintains a low level VL for an input signal below its reference voltage Vref, and a high level VH for an input signal above Vref, so the dip signal shown in FIG. It is processed by the controller 16 and becomes as shown in FIG. Therefore, if the output of the comparator 16 is inverted by the inverter 17 and inputted to the light emitting diode 18 connected in series with the resistor 19, the focus can be displayed by lighting the light emitting diode 18. Here, the signal input to the comparator 16 is always zero volts at the planned imaging plane F, regardless of the subject, so that a situation where focus detection becomes impossible as in the conventional case does not occur. Although a light emitting diode is used here as a display element, it is clear that it may be a miniature light bulb or a liquid crystal display device. During the first stage of movement in the direction (a) in FIG. 1, the output of the differential amplifier is initially 0, and becomes a positive potential after the peak value of the dip signal is held in the capacitor 12.

Therefore, while the output of the differential amplifier is O, the light emitting diode 18 is lit by the focusing signal.

At this time, the photographer confirms that the light-emitting diode installed on the side of the viewfinder is lit, but does not recognize this as a focus signal and returns the lens to direction (b) until the light-emitting diode lights up again. Stop moving the lens and check the focus signal. In this way, in the focusing operation of the present invention, the reciprocating operation of extending the lens constitutes one cycle. In order to distinguish between the first stage false focus signal and the second correct focus signal,
For example, an appropriate logic circuit may be provided after the inverter 17 in FIG. 3 to select the second focusing signal. Although the above embodiments were intended to perform focus detection display digitally, an embodiment aimed at analog display will now be described.

FIG. 6 shows another embodiment aimed at analog display. As mentioned earlier, dip signals vary greatly depending on the subject, but displaying such dip signals as they are in analog form on a meter, etc. not only requires a meter with a wide dynamic range; The amplitude of the meter varies depending on the subject, and the display performance changes, which is extremely inconvenient. The present invention ameliorates these drawbacks in analog display. The circuit up to the differential amplifier 15 is the same as the previous embodiment;
For example, an amplitude limiting circuit 20 such as a limit circuit or a saturation amplifier circuit is connected to. The output of the amplitude limiting circuit 20 is guided to a meter 22 via an inverter 21. Next, the operation of this embodiment will be explained with reference to FIGS. 6 and 7.

FIG. 7 shows the output of the amplitude limiting circuit in FIG. 6. Since the output of the differential amplifier 15 changes as shown in FIG. 4, if it is expressed in analog form as it is, the above-mentioned problems will occur. The dip signal as shown in FIG. 4 is processed by an amplitude limiting circuit 20 having an amplitude limiting level Vc to become as shown in FIG. 7. That is, the planned imaging plane F
The dip signal is limited to a constant value Vc in the out-of-focus region except in the vicinity of . As is clear from the figure, the dynamic range of the dip signal is set to the amplitude limit level Vc by the amplitude limit circuit 20. Here, the amplitude limit level Vc is set to an appropriate value in consideration of the dynamic range of the subsequent meter 22. If the dip signal whose dynamic range is made constant in this way is displayed on the meter 22 via the inverter 21, the focus detection display will be performed based on the maximum value of the deflection of the meter 22, and the vibration amplitude of the meter 22 due to fluctuations in the dip signal will be detected. There is no change, which is extremely convenient.
Further, the maximum amplitude of the meter 22 corresponds to the voltage of the intended imaging plane F in FIG. 7, that is, zero volts, and is always a constant value regardless of the subject, which is very convenient. If the inverter 21 is not inserted here, focus detection will be performed based on the minimum value of the deflection of the meter 22. In the above embodiments, basic application examples of the present invention have been described, but since the present invention utilizes a memory function such as a capacitor, the following problems arise.

That is, during pit alignment, for example, if an object crosses the front of the lens, or if the shooting target suddenly changes from one subject to another, the intensity of the optical image changes suddenly, causing the image signal to change. A large signal is generated in the bridge circuit, which is the detection section, and is stored in the capacitor 12, which may cause malfunction. FIG. 8 shows an embodiment that solves the problem caused by sudden changes in optical image intensity. The amplifier 1
The output of 0 is input to the differentiating circuit 24 via the capacitor 23. A transistor 27 is connected to the AC amplifier 24 via a resistor 25. A resistor 26 is connected between the emitter and base of the transistor 27. Further, the collector of the transistor 27 is connected to the power source E via a relay 29 connected in parallel with a diode 28 for suppressing the intag tape pulse. Both terminals of the break contact of the relay 29 are connected to both terminals of the memory capacitor 12. Next, the operation of this embodiment will be explained.

When there is no sudden change in the optical image intensity as described above, the output of the amplifier 10 is a DC signal, so the input to the differentiating circuit 24 is blocked by the capacitor 23. At this time, transistor 27 is in a cut-off state and no collector current flows, so the break contact of relay 29 is open. The switch 13 is also open. Now, if the optical image intensity suddenly changes due to the reasons mentioned above,
The signal is detected by the bridge circuit and the amplifier 10
The peak voltage reaches the storage capacitor 12 as described above. At this time, since the signal based on the sudden change in optical image intensity is an alternating current signal, it simultaneously passes through the capacitor 23 and is amplified by the differentiating circuit 24. When the output voltage of the differentiating circuit 24 rises, the base voltage of the transistor 27 connected to the amplifier 24 through the resistor 25 also rises, and a collector current begins to flow correspondingly. When the same current exceeds the emotional current of relay 29, relay 29
operates and the break contact of the relay 29 closes. Therefore, the signal reaching the storage capacitor 12 is not stored, but is discharged through this break contact, thereby preventing malfunction. Although a relay is used as the switching element in this embodiment, it is obvious that similar effects can be obtained by using other suitable switching elements, such as semiconductor switching elements.

Furthermore, if a holding circuit having an appropriate holding time is attached to the relay circuit of this embodiment and the operating time of the relay 29 is made long enough, the voltage stored in the capacitor 12 can be completely discharged, making it more effective. be. As described above, this embodiment is effective in preventing malfunctions caused by sudden changes in optical image intensity and fully demonstrating the features of the present invention.

As has been made clear from the above description, the present invention provides an output that is obtained by differentially amplifying the peak voltage stored in the memory element and the output of the light receiving element, regardless of the subject when the planned image plane and the optical image plane coincide. By taking advantage of the fact that the value is always zero, the inconveniences of the conventional method were easily solved.

This is an electronic version of the principle of pit alignment with the naked eye, and can be said to be extremely rational. Furthermore, by utilizing these features of the present invention to limit the amplitude of the differential amplification output in the out-of-focus region, the dynamic range can be made constant;
It also has the feature of providing extremely stable analog display of focus detection. As described above, the present invention enables digital or analog display, is inexpensive, has good operability, is small in size, and has low power consumption, which is an extremely practical feature. There is. The advantages of the present invention in that it is not subject dependent, is compact, and has low power consumption makes it possible to incorporate a focus detection device into a general hand-held camera, which has been difficult in the past. Therefore, it is possible to solve the conventional problems of individual differences in pit alignment and the difficulty of pit alignment in dark environments such as when shooting using a telephoto lens or at night, and in this sense, the effects of the present invention are extremely significant. It is.

[Brief explanation of the drawing]

FIG. 1 shows a conventional focus detection device. 1: Lens, 2: Half mirror, 3: Film, 4: Half mirror, 5, 6: CdSl7: Diffusion plate, arrows 5, 8
: Movement direction of lens 1. FIG. 2 shows a dip signal based on a change in contrast of an optical image. Horizontal axis d: distance between lens 1 and CdS 5 or diffuser plate 7,
Vertical axis V: Differential amplifier or bridge detection output, F: Planned imaging plane, Vp: Peak voltage of the solid line dip signal, Vp!
: Peak voltage of dip signal indicated by broken line, v: Arbitrary distance d
dip voltage, Vref: reference voltage of the comparator. FIG. 3 shows an embodiment of the present invention. 8, 9: Resistor configuring the bridge circuit, E: Power supply, 10
: Amplifier, 11: Diode, 12: Capacitor 1, 1
3: Switch, 14: Buffer, 15: Differential amplifier,
16: Comparator 17: Inverter, 18: Light emitting diode, 19: Resistor. FIG. 4 shows the output of the differential amplifier 15 in FIG. 3. FIG. 5 similarly shows the output of the comparator 16, and VH and VL indicate the high level and low level, which are the outputs of the emparator 16, respectively.
FIG. 6 shows another embodiment aimed at analog display. 20: amplitude limiting circuit, 21: inverter,
22: Meter. FIG. 7 shows the output of the amplitude limiting circuit in FIG. 6. VO: Amplitude limit level of the circuit. FIG. 8 shows an embodiment that solves the problem caused by sudden changes in optical image intensity. 23: Capacitor 1, 24: Differential circuit, 25, 26: Resistor, 27: Transistor 1, 28: Diode, 29:
Lilly one.

Claims (1)

[Claims] 1. In a focusing optical system of an optical device such as a camera, a half mirror 2 provided in an intermediate optical path between a photographing lens 1 and a film surface 3.
, a half mirror 4 that divides the luminous flux from the subject reflected by this half mirror 2 into two, and this half mirror 4
photoelectric elements 5 and 6, which are transmitted or reflected by each other and are provided at positions coextensive with the film surface; a diffuser plate 7 provided immediately before one of the photoelectric elements 6; and a bridge circuit including these photoelectric elements 5 and 6. , an amplifier 10 that receives the output from this bridge circuit, circuits 11, 12, 13, and 14 that store the maximum value of the focusing signal output from the amplifier 10, and circuits 11, 12, 13, and 14 that store the maximum value of the focusing signal output from the amplifier 10, and A differential amplifier 15 that outputs the difference from the focused signal, a comparator 16 that compares the output of the differential amplifier 15 with a reference voltage, and a focus display means such as a light emitting diode that displays the output of the comparator 16. A focus detection device consisting of. 2. A half mirror 2 provided in the intermediate optical path between the photographing lens 1 and the film surface 3, a half mirror 4 that divides the luminous flux from the subject reflected by the half mirror 2 into two, and light transmitted or reflected by the half mirror 4, respectively. In addition, photoelectric elements 5 and 6 are provided at positions coextensive with the film surface, a diffusion plate 7 is provided immediately before one of the photoelectric elements 6, and these photoelectric elements 5
, 6, an amplifier 10 receiving the output from the bridge circuit, and circuits 11, 12, 13, 1 for storing the maximum value of the focusing signal output from the amplifier 10.
4, a differential amplifier 15 that outputs the difference between this maximum value and a focusing signal output from the amplifier 10;
a comparator 16 that compares the output of the output with a reference voltage;
In a focus detection device for an optical device such as a camera, which is comprised of a focus display means such as a light emitting diode that displays the output of the comparator 16, the output terminal of the amplifier 10 detects a change due to sudden movement of the subject or the camera. and memory circuits 11, 12, 1 by the output of the differentiating circuit.
A focus detection device connected to a switching circuit for resetting 3 and 14. 3 In a focusing optical system of an optical device such as a camera, a half mirror 2 provided in the intermediate optical path between the photographing lens 1 and the film surface 3
, a half mirror 4 that divides the luminous flux from the subject reflected by this half mirror 2 into two, and this half mirror 4
photoelectric elements 5 and 6, which are transmitted or reflected by each other and are provided at positions coextensive with the film surface; a diffuser plate 7 provided immediately before the photoelectric element 6; a bridge circuit including these photoelectric elements 5 and 6; Amplifier 1 receiving the output from the bridge circuit
0, circuits 11, 12, 13, and 14 that store the maximum value of the focusing signal output from the amplifier 10 when the photographing lens 1 is moved in one direction on the optical axis, and this maximum value and the photographing lens. When amplifier 1 is returned to the opposite direction to the above-mentioned direction, amplifier 1
a differential amplifier 15 that outputs the difference between the focus signal outputted from 0 and an amplitude limiting circuit 20 that limits the output of the differential amplifier 15 to a constant amplitude level; A focus detection device consisting of a meter 22.