JPH07140377A - Camera provided with range-finding device - Google Patents

Abstract

PURPOSE:To decide the distance from a subject and the lowering of reflectance based on a received light quantity and to selectively switch a battery and the main capacitor of a stroboscope based on the decided result lest range-finding accuracy in AF should by deteriorated by always performing stable light projection for AF without being affected by battery voltage. CONSTITUTION:A power source switching part 13 selectively switches either the battery 10 or the main capacitor of a stroboscopic light emission part 12. A decision part 14 decides, based on a subject luminance decision signal from the outside, which of the battery 10 and the main capacitor is to be supplied to a light projection part 15. The light projection part 15 receives output from the switching part 13 switched and selected by the decision of the decision part 14 and allows an infrared light LED to emit light with the power source selected by the switching part 13 as a driving source according to a control signal outputted from a range-finding arithmetic part 16. Then, range-finding is performed by receiving reflected light from the subject by a light receiving part 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera having a distance measuring device that uses a part of the circuit configuration of a strobe light emitting device of the camera as a power source of the distance measuring device.

[0002]

2. Description of the Related Art While the size and weight of cameras used today, especially compact cameras, are being pursued, their functions are being promoted. As a result, an automatic exposure device, automatic focusing device, automatic film winding device, automatic strobe light emitting device, etc. were built in a small camera body, and the photographer's camera operation was very easy and it was possible to take photographs without failure. It was

However, on the other hand, the power supply load for operating the above-mentioned mechanical device is becoming heavier. In particular,
Recently, even when a lithium battery with a high energy density (single cell nominal value: 3V, 1200mAh) is used as the system power supply (usually 1 to 2), when a strobe is charged with a heavy load, film is wound, or automatically. When the infrared LED flashes for focus (active AF), the terminal voltage of the battery greatly fluctuates (drops). Therefore, most sequences are usually arranged in chronological order in order to avoid heavy load duplication. Further, by sharing a part of the function, it is devised to suppress the number of times of occurrence of load (fluctuation of power supply voltage).

For example, the one disclosed in Japanese Utility Model Laid-Open No. 55-71331 shares the power source of the automatic focusing device with a strobe boosting circuit. That is, the secondary coil of the booster circuit is provided with a center tap, and the boosted voltage is supplied to the regulator to obtain a stable power supply voltage.

Further, in Japanese Patent Laid-Open No. 57-135936, a power source for an automatic exposure device and an automatic focusing device is provided with a dedicated booster circuit in addition to a booster circuit for a strobe, and a heavy load (strobe charge) is provided. Shooting can be resumed immediately without waiting for the battery to fully recover immediately after film winding. Further, the output voltage of the booster circuit is supplied to the power supply capacitor of the infrared projection LED of the automatic focusing device.

Further, Japanese Patent Application No. 4-2 by the applicant of the present patent application
No. 29974 is an infrared emitting LED for automatic focusing
There is described a technique in which the power source is supplied from a main capacitor for stroboscopic light emission when the subject brightness is large (the brightness-dependent noise is large).

[0007]

However, in the case of Japanese Utility Model Laid-Open No. 55-71331, the strobe booster circuit must be activated at all times when operating the automatic focusing device. Therefore, the current consumption at the time of starting the booster circuit tends to be larger than the current consumption of the automatic focus adjustment device. Further, since the booster circuit operates during the autofocus (AF) operation, there is a risk that noise may enter the distance measuring circuit of the automatic focusing apparatus that handles a minute signal depending on the mounting state such as wiring.

On the other hand, in the case of Japanese Unexamined Patent Publication No. 54-135936, since the power supply system of the system is very strong because of the dedicated booster circuit, the number of parts is increased and the system is complicated as a result. ing.

As described above, a reliable AF operation (distance measuring accuracy) cannot be obtained simply by also using the strobe booster circuit. Also,
A system with high feasibility cannot be expected simply by installing a dedicated booster circuit.

Further, in the case of Japanese Patent Application No. 4-229974,
Although the distance measurement accuracy can be improved for a high-brightness subject, improvement of the distance measurement accuracy cannot be expected when the subject is at a long distance or when the infrared reflectance of the subject is low. Considering the actual shooting conditions of today's long-focus cameras, especially compact cameras, rather than shooting high-brightness subjects,
Since a subject having a long distance and a low reflectance is often photographed, this is a problem in improving the distance measurement accuracy.

The present invention has been made in view of the above problems, and by using a power supply circuit that is not influenced by the battery voltage, stable infrared projection of AF is always performed, and the ranging accuracy of AF is not deteriorated. An object of the present invention is to provide a camera having a range finder that does not complicate the system.

[0012]

That is, according to the present invention, a light projecting element and light reflected from a subject of the light projecting element are converted into a photoelectric conversion signal, and the distance to the subject is calculated based on the photoelectric conversion signal. In a camera having a distance measuring device for calculation, a power supply battery and a strobe voltage charging means for boosting and charging the voltage of the power supply battery in order to cause a strobe light emitting tube to emit light, and projecting light toward a subject. Receives the reflected light,
A light emitting and receiving means for outputting a light receiving signal according to the received light amount,
Switching means for selectively switching the voltage supplied to the light emitting element of the distance measuring device to either the power supply battery or the output voltage of the strobe voltage charging means based on the light receiving signal output from the light emitting and receiving means. And is provided.

The present invention also includes at least a light projecting element,
In a camera having a distance measuring device that converts the reflected light from the subject of the light projecting element into a photoelectric conversion signal and calculates the distance to the subject based on this photoelectric conversion signal, the focal length of the taking lens is detected. Based on the focal length detected by the focal length detection means, the power supply battery, and the strobe voltage charging means for boosting and charging the voltage of the power supply battery to cause the strobe light emitting tube to emit light. A switching means for selectively switching the voltage supplied to the light projecting element of the distance measuring device to either the power supply battery or the output voltage of the strobe voltage charging means.

[0014]

In the camera having the distance measuring device of the present invention, the power source for driving the infrared emitting LED of the AF is directly fed from the main capacitor of the strobe. As a result, it is possible to eliminate the influence of the S / N ratio during distance measurement on the load change of the battery. Further, by determining the amount of light received by the preliminary light emission, the drive power source for the infrared emitting LED of the AF is switched to the main capacitor of the strobe when the amount of received light is small, and to the battery when the amount of received light is large. ing.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing a concept of a power supply circuit of a camera having a distance measuring device according to a first embodiment of the present invention. In the figure, the output of the battery 10 is connected to the power source switching unit 13 together with the output from the strobe boosting circuit 11 via the strobe light emitting unit 12. The power supply switching unit 13 supplies a switching output to the light projecting unit 15 according to the determination output from the determination unit 14. Further, the distance measuring calculation unit 16 is connected to the light projecting unit 15. Furthermore, the distance measurement calculation unit 16
The light receiving unit 17 is connected.

The battery 10 is composed of an ordinary manganese battery, a lithium battery or the like, and the strobe booster circuit 11 and the strobe light emitting section 12 have a basic constitution which is generally used in a conventional strobe control circuit. For example, the strobe booster circuit 11 is composed of a self-excited inverter circuit including a blocking oscillator circuit. The strobe light emitting section 12 is composed of a light emission control circuit including main components such as a xenon tube, a main capacitor, and a trigger transformer. Here, since the strobe control circuit itself is not directly related to the present invention, detailed description thereof will be omitted.

The power source switching unit 13 selectively switches either the battery 10 or the main capacitor in the strobe light emitting unit 12. Although not particularly shown in FIG. 1, which of the battery 10 or the stroboscopic light emitting unit 12 (main capacitor thereof) is supplied to the light projecting unit 15 based on an external control signal (subject brightness determination signal). The determination unit 14 determines.

The output of the power source switching unit 13 which is switched and selected by the determination of the determination unit 14 is supplied to the light projecting unit 15 which is a control circuit for driving the infrared emitting LED of the AF.
Then, in accordance with a control signal output from the distance measurement calculation unit 16, the infrared light emitting LED is caused to emit light by using the power source selected by the power source switching unit 13 as a driving source, and the reflected light from the subject is received by the light receiving unit 17 for measurement. Make a distance.

Next, a second embodiment of the present invention will be described. FIG. 2 is a block diagram showing a power supply circuit of a camera in a second embodiment according to the present invention, and specifically expresses the above-mentioned first embodiment.

A strobe boosting circuit 11 and an AF distance measuring circuit 20 are connected via a switching circuit 19 to a plus terminal of a battery 18 supplied as a driving source. The strobe booster circuit 11 is connected to a strobe light emitting circuit 22, a xenon tube 23, and a main capacitor 24 of the illustrated polarity via a diode 21 of the illustrated polarity.

The strobe booster circuit 11 charges the main capacitor 24 to a predetermined set voltage (for example, 300 [V]) during strobe charging. The diode 21 is for rectifying the secondary coil output of the boosting transformer included in the strobe boosting circuit 11. Further, the strobe light emission circuit 22 is a trigger circuit for exciting the xenon tube 23. Then, the strobe boosting circuit 12, the diode 21, the strobe light emitting circuit 22,
The xenon tube 23 and the main capacitor 24 are the main parts constituting the strobe control circuit.

The switching circuit 19 includes resistors 25 and 2
6 and a switch 27 having two contacts in one circuit. The switching circuit 19 is supplied with power from the battery 18 to the resistor 25 and a switching signal from the outside. Then, as shown in the figure, when the switch 27 is closed to the contact b, the main capacitor 24 connected through the resistor 26 is selected, and when it is closed to the contact a, the battery 18 is connected. You have selected.

The switch 27 of the switching circuit 19 is provided with an NPN transistor 29 having the polarity shown in the figure via the infrared light emitting LED 28.
It is connected to the. The i _F (forward current) of the infrared emitting LED 28 is limited by the resistors 25 and 26.
The infrared emitting LED 28 has a PSD 30
It is turned on / off (light emission / non-light emission) by the NPN transistor 29 which switches in synchronization with the drive signal output from the F distance measuring circuit 20.

Further, infrared light emission L radiated on the subject 31
The pulsed light of the ED 28 forms an image on the PSD surface of the AF distance measuring circuit 20, and the distance measurement calculation is performed. The infrared emitting LED 2
8, NPN transistor 29, PSD 30, distance measuring circuit 2
0 and the subject 31 are the basic configuration of active AF.

FIG. 3 is a diagram showing another configuration example of the switching circuit of FIG. In the figure, the switching circuit 32 is shown in FIG.
The switch 27 is replaced with a PNP transistor 33 and a PNP transistor 34 so as to be electrically switched.

The emitter of the PNP transistor 34 is connected to the plus terminal of the main capacitor 24 provided in the xenon tube 23 of the strobe control circuit. Further, inverters 36 and 37 are connected in series to the base of the PNP transistor 34 via a resistor 35 for limiting the base current. And the inverter 37
By inputting the switching signal of "L (low)" to
The PNP transistor 34 is turned on.

On the other hand, the PNP transistor 33 has its emitter connected to the positive terminal of the battery 18 in FIG. 2, and its collector connected to the PN via resistors 38 and 39.
It is connected to the collector of the P-transistor 34. An inverter 41 is connected to the base of the PNP transistor 33 via a base current limiting resistor 40. The PNP transistor 33 is turned on by inputting a switching signal of "H (high)" to the inverter 41. The resistors 38 and 39 are used for the infrared light emitting LED 28.
I _F limiting resistance of, and has a resistance value corresponding to each supply voltage in order to obtain a predetermined i _F value.

As described above, the switching circuit 19 shown in FIG.
Can be replaced with the switching circuit 32 as it is. The switching signal is normally set to "H" in consideration of the fail safe of the circuit itself of FIG. Also, PN
AF infrared LE input to the base of P-transistor 29
The D emission signal is also normally set to "L".

FIG. 4 is a diagram showing still another configuration example of the switching circuit of FIG. 2, in which the PNP transistor 33 and the PNP transistor 34 of the switching circuit 32 of FIG. Abbreviated as)
Is replaced with.

In FIG. 4, the N-MO in the switching circuit 42 is
The SFET 43 and the N-MOSFET 44 are the inverter 4
By inputting a switching signal of "L" or "H" to the inverter 46 connected in series with 5, only one of them can be turned on. For example, when selecting the main capacitor 24 provided along with the xenon tube 23, the switching signal may be set to "H". Resistance 4
The roles and functions of the resistor 7, the resistor 48, the infrared light emitting LED 28, and the PNP transistor 29 have already been described with reference to FIG.

FIG. 5 is a basic block diagram of a camera having an automatic focusing device and a stroboscopic light emitting device according to a third embodiment of the present invention. The CPU 49
The AF distance measuring circuit 20 and the strobe control circuit 50, which are the basic blocks of the camera shown in the figure, are comprehensively controlled (sequential control, numerical operation, etc.).

For example, when measuring the subject distance, C
The PU 49 outputs an AF control signal to the AF distance measuring circuit 20. Then, the AF distance measuring circuit 20 having the infrared light emitting LED 28 and the PSD 30 starts the distance measurement, and the distance measurement result is displayed as CP.
Output to U49. Then, the CPU 49 converts this output value into a digital value by A / D conversion or the like, and performs distance measurement calculation. Thus, the role of the CPU 49 is to operate each block as needed.

Next, the operation of the third embodiment will be described with reference to the flow charts of FIGS. Usually, the camera is provided with a power switch (SW) (or another SW having exactly the same function).
By turning on, all the functions of the camera are activated. FIG. 6 is a flowchart showing this state. The actual operation in the explanation of the flowchart of FIG. 6 is performed between the CPU 49 and the strobe control circuit 50 in FIG.

First, when the power SW is turned on in step S1, the process proceeds to step S2 to start charging the strobe. That is, the main capacitor of the strobe is fully charged by using the short time immediately before the release so that a subject with low brightness can be photographed. Then, when the charging is completed in step S3, the process proceeds to step S4 and waits for release (1st. Release).

Here, 1st. Release input (1s
t. When the release SW is turned on, the process proceeds to step S5 and the release processing subroutine is immediately executed.
Then, 1st. When the release is not input and when the release process is completed, the process proceeds to step S6, and it is determined whether the power SW is on. Here, if it is ON, the process returns to step S4 and the 1st. The release status is determined. If it is off, the process returns to step S1.

Next, referring to the flowchart of FIG.
1st. The operation of the release process after the release will be described. In the release process, photometry is first executed in step S11. Here, photometry is performed by an AE photometric circuit having a photometric element such as a photodiode that receives a photometric start signal from the CPU 49. Then, the photometric result is A / D converted and taken into the CPU 49 as a digital value, and the exposure calculation is performed by the CPU 49. When the photometry is completed, the process proceeds to step S12 and AF
Distance measurement is started. Incidentally, in the same embodiment, the active AF
Is assumed.

When the distance measuring subroutine is completed, the operation proceeds to step S13 to execute the AF calculation. Then, in step S14, 2nd. The camera is waiting for release. Here, 2nd. If the release is not input, the process proceeds to step S15 and 1st. It is determined whether or not the release is input. 1st. If the release is input, the process returns to step S14. On the other hand, 1st. When the release is turned off, the process immediately returns to the main flowchart.

In step S14, 2nd. When the release is input, a series of sequences required for the fully automatic camera is executed. That is, lens driving (step S1
6), shutter driving (step S17) and film winding (step S18) are executed, and then the process returns to the main flowchart.

Next, referring to the flowchart of FIG.
The operation of distance measurement will be described. Preliminary light emission is executed first in step 21 after shifting to the distance measuring subroutine. This preliminary light projection is performed using a battery as a power source for emitting light from the infrared emitting LED. Next, in step S22, the received light amount Vres by the preliminary light projection in step S21 is obtained. Then, in the next step S23, Vre
It is determined whether s is larger or smaller than the predetermined value V. That is, here, it is determined whether the subject distance is far or near, and whether the infrared reflectance of the subject is low or high, based on the amount of received light.

Normally, when the subject distance is long or the infrared reflectance is low, the amount of signal light received by the light receiving section of the AF is small, and the effects of stationary light noise, circuit noise, etc. are large. That is, the S / N ratio becomes worse. In order to improve this S / N ratio, the amount of signal is increased and the amount of noise is decreased, that is, the infrared emission LE.
It is sufficient to increase the light emission output of D and reduce the noise component accompanying light emission.

Therefore, in the present embodiment, the power supplied to the infrared emitting LED is switched depending on the amount of light received by the above-mentioned preliminary light emission, and S / when the distance measuring condition is bad (long distance, low reflectance). The N ratio is improved.

In step S23, if the projected light amount Vres by the preliminary light projection is larger than the predetermined value V, the process proceeds to step S24, and the infrared light emission L is performed using the battery voltage as it is.
Make the ED emit light. On the other hand, when Vres is smaller than V, the power source of the infrared light emitting LED is switched to the strobe light emitting main capacitor to emit light.

The switching signal based on the above determination is directly output from the CPU 49 to the strobe control circuit 50. The switching circuit 32 or 42 of FIG. 3 or 4 selects the power source of either the main capacitor 24 or the battery 18. After the power source is selected, the infrared emitting LED 28 emits light according to the AF infrared LED emitting signal of the AF distance measuring circuit 20. Then, in step S26, the predetermined active A
The distance measurement operation of F is executed and the subject distance is obtained.

Next, the reason why the main condenser of the strobe is used as the power source when the subject distance is long or the reflectance is low, that is, the received light amount is small will be described. Figure 9
FIG. 6 is a circuit diagram illustrating an operation when the power source of the embodiment is switched to the main capacitor.

In the figure, C ₁ is the electrostatic capacity of the main capacitor, V _C is the initial charging voltage of the main capacitor, and R
₁ represents the i _F limiting resistance value, and i _F represents the forward current of the infrared light emitting LED (D ₁ ). Further, V _R and V _F are the terminal voltage of the infrared light emitting LED (D ₁ ) and the i _F limiting resistance generated when the forward current i _F flows. First, NPN
The energy E _C stored in the main capacitor C ₁ when the transistor (Q ₁ ) is off (initial state) is
It is expressed as in equation (1).

[0046]

[Equation 1]

Here, if A, as shown in FIG.
When the F infrared LED light emission signal is input to the base side of the NPN transistor (Q ₁ ), the main capacitor C after light emission
The residual energy E _C ′ of ₁ is expressed by the equation (2).

[0048]

[Equation 2]

Assuming that C ₁ = 280 [μF] and V _C = 30
0 [V], R ₁ = 1.1 [kΩ], t _ON = 150 [μ
S], r _P = 128 [times], the relational expression of Formula 3 is obtained.

[0050]

[Equation 3]

That is, in the circuit of the above constants, the energy of the main capacitor C ₁ consumed by one light emission is expressed as a percentage ρ _C , with respect to the initial energy,
ρ _C = 1.39 / 122.6 × 100 = 11 [%]. By the way, the residual voltage V _C of the main capacitor C ₁ after the light emission is expressed by the relational expression (4).

[0052]

[Equation 4]

Further, the i _F value which fluctuates during one emission is expressed as a percentage ρ _i , and ρ _i =
(1-282 / 300) × 100 = 6 [%] reduction.
This value (p ₁ ) is 1/2 to 1/3 smaller than the fluctuation rate of the battery voltage with respect to heavy load. In particular, the lower the battery voltage (3 [V] system), the more the infrared emission LE becomes.
Voltage fluctuations easily occur during D drive. Therefore, the light emission efficiency is lowered and the distance measurement accuracy is adversely affected. In this sense, the higher power supply voltage is more advantageous.

Further, the influence of the forward voltage V _{F of} the infrared light emitting LED (D ₁ ) and the collector-emitter saturation voltage V _CE of the NPN transistor (Q ₁ ) is also advantageous when the power supply voltage is high (main capacitor C 1 [%] or less) as compared with the _first charging voltage.

As described above, when the main capacitor is used as the power source, when the distance measuring condition is relatively bad (the subject distance is long,
Alternatively, even when the infrared reflectance is low), the emission efficiency of the infrared light emitting LED can be improved in a timely manner. At the same time, the battery voltage is stable (there is no drive noise when driving the conventional infrared emitting LED), so that the distance measurement accuracy is improved (S
/ N ratio improvement).

However, in this case, when the shooting condition requires the flash light emission, the flash light amount may be insufficient. Therefore, the capacity of the main capacitor may be increased or the charging voltage may be set higher. It is necessary to take measures such as putting it down.

By the way, the received light amount Vres by the preliminary light projection
Is larger than the predetermined value V, the signal light received by the light receiving unit of the AF is large, and the deterioration of the S / N ratio is small. Therefore, a battery is selected as the power source of the infrared emitting LED. Further, by doing so, the electric charge of the main capacitor can be saved.

Here, the actual infrared emission L including the switching circuit
The drive circuit of the ED will be described in more detail. In general, infrared light emitting LEDs are driven by a constant current in most cases in order to reduce the influence of fluctuations in power supply voltage. Figure 11
Is a modification of the circuit of FIG. 3 so that the infrared emitting LED can be driven with a constant current.

In FIG. 11, the PNP in the switching circuit 51.
Transistors 52 and 53, resistor 54, inverter 55
And 56, resistor 57, and inverter 58 are respectively shown in FIG.
Of the PNP transistors 33 and 34, the resistor 35, the inverters 36 and 37, the resistor 40, and the inverter 41.

A load resistor 60 is connected in series to the emitter side of the NPN transistor 59, and the load resistor 60 is connected to the negative input of the operational amplifier 61 built in the AF distance measuring circuit 20.
The terminal voltage of is fed back. The operational amplifier 61 always refers to the positive input V _ref value and the negative input feedback value to ensure that the infrared emitting LED 2
In order to keep the value of the forward current i _F flowing through 8 constant,
The base current of the NPN transistor 59 is controlled.

By making the constant current in this way, the i _F limiting resistors 38 and 39 of FIG. 3 are unnecessary, and a simple structure like the switching circuit 51 of FIG. 11 is obtained. If the resistance value of the load resistor 60 is R _S , the forward current i _F is
It is expressed by equation (3). i _F = V _ref / R _S (3) Further, as shown in FIG. 4, the changeover switch is an N-MO.
Even if it is composed of SFETs, the constant current circuit of FIG. 11 can be applied without any inconvenience. Particularly in the case of the embodiment, the effect is exhibited when the switching circuit 51 selects the battery.

Next explained is the fourth embodiment of the invention. In the fourth embodiment, in the third embodiment described above, the infrared light emission LE is changed depending on the amount of received light to be preliminarily projected.
The power source of D is switched, but it is switched according to the focal length of the photographing lens of the camera having the zoom lens.

FIG. 12 is a block diagram showing the basic structure of the fourth embodiment. In the figure, the CPU 49
PI detected by the position of zoom encoder and shooting lens
Infrared emission L is obtained by taking in focal length information from the photographing lens focal length detection circuit 62 such as output of (photo interrupter).
It is determined whether the battery is used as the power source of the ED or the main capacitor for strobe emission is used. as a result,
A switching signal is output to the strobe control circuit 50. Other configurations are the same as the block diagram shown in FIG.
The description is omitted here.

Next, the operation of the fourth embodiment will be described with reference to the flow chart of the distance measuring subroutine of FIG.
First, in step S31, information about the focal length f _TL of the photographing lens at the time of photographing is taken into the CPU 49 by the output of the zoom encoder, the PI for detecting the position of the photographing lens, and the like. Then, in step S32, the above f _TL is compared with the predetermined value f.

Here, if f _TL is smaller than f, that is, if f _TL is wider than f, the process proceeds to step S33, and the infrared emitting LED emits light at the battery voltage. On the other hand, f _TL
Is larger than f, that is, if f _TL is on the tele side of f, the process proceeds to step S34, and the main capacitor for stroboscopic light emission is used as the power source of the infrared light emitting LED to emit light.

Next, in step S35, a predetermined active AF distance measuring operation is executed to obtain the subject distance. The other operations are similar to those of the above-described third embodiment, and therefore the description thereof is omitted here.

The infrared light emitting LED is caused to emit light by the battery voltage when the focal length of the photographing lens is on the wide side and is caused to charge by the charge of the main condenser when the focal length of the photographing lens is on the wide side. Normally, photographing is performed at the wide focal length. In this case, the subject is at a short distance, and in the case of the telephoto side, it is often at a long distance. Further, the need for preliminary light emission is eliminated, so that the distance measurement time can be shortened.

Next explained is the fifth embodiment of the invention. The fifth embodiment is obtained by adding the subject brightness as a power source switching determination element to the above-described fourth embodiment.

FIG. 14 is a block diagram showing the basic structure of the fifth embodiment. The CPU 49 uses the AE photometric circuit 6
3. Object brightness information and photographing lens focal length information are fetched from the photographing lens focal length detection circuit 62 such as a zoom encoder. Then, it is determined whether the battery is used as the power source of the infrared emitting LED or the main capacitor for strobe light emission is used, and a switching signal is output to the strobe control circuit 50. The AE photometric circuit 63 is used for the infrared emitting LED 2
It has a photodiode 64 that receives the light projected from 8 and reflected by the subject 31.

Since the other structure is the same as the block diagrams shown in FIGS. 5 and 12, the description thereof is omitted here. Next, referring to the flowchart of FIG.
The operation of the fifth embodiment will be described.

First, in step S41, the focal length f _TL of the taking lens is detected. Then, in step S42,
It is determined whether f _TL is larger than the predetermined value f. Here, when f _TL is larger than the predetermined value f, that is, when f _TL is on the tele side, the process proceeds to step S46, and the main capacitor for strobe light emission is used as the power source of the infrared light emitting LED to perform light emission. On the other hand, in step S42, f
_{When TL} is smaller than f, that is, when f _TL is on the wide side, the process proceeds to step S43, the subject brightness BVacs is obtained from the photometric result in step S11 of FIG. 7, and the process proceeds to step S44.

In step S44, BVacs is compared with the predetermined value BV. Here, when BVacs is larger than BV (bright), the process proceeds to step S46, and the main capacitor 11 is used as the power source of the infrared emitting LED, and light emission is performed. On the other hand, when BVacs is smaller than BV (dark), the process proceeds to step S45, and the infrared light emitting LED is driven by the battery voltage.
Is emitted. Then, from the result of light reception by light emission using either the battery or the main capacitor as a power source, step S
The subject distance is obtained at 47.

The other operations are the same as those of the above-mentioned third and fourth embodiments, and therefore the description thereof is omitted here. With the above configuration, the AF accuracy can be improved not only for a long-distance and low-infrared reflectance subject but also for a high-luminance subject.

In the fifth embodiment, the power source switching is determined by the focal length of the taking lens and the subject brightness. However, as in the third embodiment described above, the amount of light received by the preliminary light projection and the subject brightness are determined. The power switching may be determined by.

Further, the switching circuit is constructed as shown in FIG. 16, and depending on the power source used, the switching circuit shown in FIGS.
Input a switching signal such as shown in to the switching circuit 65,
It goes without saying that changes and applications can be made without departing from the scope of the present invention, such as using the switching circuit 32 as a drive circuit for an infrared emitting LED.

[0076]

As described above, according to the present invention, the infrared emitting LED of the AF can be used in accordance with the amount of light received by the preliminary light projection, the focal length of the photographing lens, and the subject brightness without complicating the system.
By switching the driving power source, it is possible to improve the AF brightness of a subject such as a long distance, low infrared reflectance, high brightness, etc., which are conditions that have been unfavorable for conventional active AF.

Further, since one power source is also used as the main condenser of the strobe, the photographer can take a photograph without any inconvenience such as an increase in the volume of the camera body.

[Brief description of drawings]

FIG. 1 is a block diagram showing a concept of a power supply circuit of a camera having a distance measuring device in a first embodiment of the present invention.

FIG. 2 is a block diagram showing a power supply circuit of a camera in a second embodiment according to the present invention.

FIG. 3 is a diagram showing another configuration example of the switching circuit of FIG.

FIG. 4 is a diagram showing still another configuration example of the switching circuit of FIG.

FIG. 5 is a basic block diagram of a camera having an automatic focus adjustment device, an automatic exposure control device, and a stroboscopic light emission device according to a third embodiment of the present invention.

FIG. 6 is a flowchart illustrating the operation of the third embodiment.

FIG. 7: 1st. It is a subroutine for explaining the operation of the release process after the release.

FIG. 8 is a subroutine for explaining a distance measuring operation.

FIG. 9 is a circuit diagram illustrating an operation when the power source of the third embodiment is switched to the main capacitor.

FIG. 10 is a time chart illustrating the operation of the circuit of FIG.

FIG. 11 is a modification of the circuit of FIG. 3 and shows infrared light emission L at a constant current.
It is the figure which made it possible to drive ED.

FIG. 12 is a block diagram showing a fourth embodiment according to the present invention.

FIG. 13 is a flowchart illustrating a distance measuring operation according to a fourth embodiment.

FIG. 14 is a block diagram showing a basic configuration of a fifth embodiment according to the present invention.

FIG. 15 is a flowchart illustrating the operation of the fifth embodiment.

16 is a circuit diagram showing a modified example of the switching circuit of FIG.

17 is a switching signal A input to the switching circuit of FIG.
It is the figure which showed the example of B.

[Explanation of symbols]

10, 18 ... Battery, 11 ... Strobe booster circuit, 12 ... Strobe light emitting section, 13 ... Power switching section, 14 ... Judgment section, 15
... Projector, 16 ... Distance calculator, 17 ... Receiver, 19, 3
2, 42, 51, 65 ... Switching circuit, 20 ... AF distance measuring circuit, 21 ... Diode, 22 ... Strobe light emitting circuit, 23
… Xenon tubes, 24… Main capacitors, 25, 26…
Resistance, 27 ... Switch, 28 ... Infrared emitting LED, 29 ...
NPN transistor, 30 ... PSD, 31 ... Subject, 4
9 ... CPU, 50 ... Strobe control circuit, 62 ... Shooting lens focus detection circuit, 63 ... AE photometry circuit.

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Claims (2)

[Claims] 1. A camera having a light projecting element and a distance measuring device for converting light reflected from a subject of the light projecting element into a photoelectric conversion signal and calculating a distance to the subject based on the photoelectric conversion signal. At this time, the power supply battery and strobe voltage charging means for boosting and charging the voltage of the power supply battery in order to cause the strobe light emitting tube to emit light, and projecting light toward the subject and receiving the reflected light, And a light emitting / receiving means for outputting a light receiving signal according to the above, and a voltage to be supplied to the light emitting element of the distance measuring device based on the light receiving signal output from the light emitting / receiving means. And a switching means for selectively switching to one of the output voltages of the camera. 2. A camera having at least a light projecting element and a distance measuring device for converting reflected light from a subject of the light projecting element into a photoelectric conversion signal and calculating a distance to the object based on the photoelectric conversion signal. , A focal length detecting means for detecting the focal length of the photographing lens, a power supply battery, and a strobe voltage charging means for boosting and charging the voltage of the power supply battery in order to make the strobe arc tube emit light, and the focal length. Based on the focal length detected by the detection means, the voltage supplied to the light projecting element of the distance measuring device,
A camera having a distance measuring device, comprising: switching means for selectively switching to either the power supply battery or the output voltage of the strobe voltage charging means.