Auxiliary Light Source for Camera Having Automatic Focusing Device

1. Field of the Invention

This invention relates to an auxiliary illumination device to be mounted on a photographic camera for illuminating an object to be photographed and, more particularly, to an illumination device adapted for distance measurement by a camera automatic focusing device when the brightness of the object is low.

2. Description of the Prior Art

Heretofore, there have been proposed various kinds of cameras of the type using a device for automatic focusing (hereinafter called AF). However, the distance measuring power of such AF devices is generally limited. It is particularly difficult to have them perform an AF action on an object of low brightness. To solve this problem, there have also been proposed various improvements. None of these proposed improvements, however, has been satisfactory. In one of these prior art methods, the camera is equipped with an auxiliary illumination device and an object, at the distance which is to be measured, is illuminated, if necessary, from the camera. In other words, a light beam is emitted from the camera in the direction of the optical axis thereof. FIGS. 1, 2 and 3 of the accompanying drawings show some examples of the prior art methods for equipping a camera with such an auxiliary illumination devices for AF. In FIG. 1, an auxiliary illumination device is disposed in front of a pentaprism. This arrangement, however, makes the size of the pentaprism larger and it is not suitable for a camera which must be of a compact size. Besides, in the case of a single lens reflex camera, there is the possibility that an auxiliary light thus obtained might be eclipsed or shade by a lens barrel, as shown in FIG. 2, when a large aperture lens such as a telephoto lens or the like is mounted on the camera. A method of arranging the auxiliary illumination device in the neighborhood of a camera lens, as shown in FIG. 3, not only results in an increased camera size but also incurs the fear of having the auxiliary light eclipsed when a telephoto lens of a large aperture is mounted on the camera. Furthermore, the method of FIG. 3 has another disadvantage in respect to operability as it imposes some restriction on the manner in which the camera can be hand held during photography. As will be understood from the above, is is inevitable that the camera size be greater with an auxiliary illumination device provided on the camera body, in accordance with the methods of the prior art.

The AF camera using an auxiliary illumination device of the above stated type further presents the following problem. While the AF mechanism of the camera is in operation, if either the brightness of the object to be photographed is measured or an aperture or shutter speed is computed concurrently, illumination with auxiliary light would give an erroneous brightness measurement and thus would result in an inadequate exposure. To solve this problem, there is a method of using an auxiliary light that is outside the photosensitive spectrum range for a light sensitive element, such as near infrared rays. However, it is impossible to completely remove infrared rays with any photometric infrared cutting filters that are presently available. Furthermore, when this auxiliary illumination light is emitted during photography, the film would be affected by undesirable illumination if film that is sensitive to the auxiliary light is used.

It is an object of this invention to provide a compact and lightweight auxiliary illumination device which is discretely arranged as an attachment or an accessory to be attachable to and detachable from the camera. With the auxiliary illumination device attachable to the camera as an accessory thereof, the device can be easily positioned away from the photo-taking optical axis, so that the above problem of having the auxiliary light flux eclipsed by a lens barrel, when a telephoto lens of a large aperture is mounted on the camera, can be effectively solved.

It is another object of the invention to provide an auxiliary illumination device which is not only an attachment to a camera but is also an adapter to permit a flash device to be mounted thereon, so that flash photography can be accomplished even with the auxiliary illumination device attached to the camera.

It is a further object of the invention to provide an auxiliary illumination device for distance measurement which becomes inoperative during the light measuring or photo-taking operation of a camera and which also inhibits the light measuring operation during the auxiliary light emitting action of the device, so that the above-mentioned problem of inaccurate light measurement can be solved.

It is a further object of the invention to provide an auxiliary illumination device which intermittently emits an auxiliary light when the device is in operation, so that power consumption can be reduced and the load on a power source lessened.

It is still a further object of the invention to provide an auxiliary illumination device which is rendered operative only when a storage type AF sensor such as a CCD sensor is in the process of a storing action and when the brightness of an object to be photographed is low when such a sensor is used.

These and further objects and features of the invention will become apparent from the following detailed description of embodiments thereof taken in conjunction with the accompanying drawings.

FIG. 1 is a front view showing by way of example a conventional method for mounting an auxiliary illumination device.

FIG. 2 is a side view of the camera shown in FIG. 1.

FIG. 3 is a front view showing another conventional mounting method.

FIG. 4 is an oblique view showing a method for mounting an auxiliary illumination device on a camera in an embodiment of the present invention.

FIG. 5 is a sectional schematic illustration showing the optical system of a single lens reflex camera equipped with an AF device.

FIG. 6 is a circuit diagram showing an embodiment of the circuit arrangement of an AF camera which permits an auxiliary illumination device of the invention to be mounted thereon.

Referring to FIG. 1 which is an oblique view showing an auxiliary illumination device as an embodiment of the invention, reference numeral 1 indicates a camera body. A photo-taking lens 2 is mounted on a mount 9 of the camera body 1 by a known method. On the fore end of a lens barrel of the photo-taking lens 2 is provided an accessory shoe 5e for mounting an auxiliary illumination device 4. The auxiliary illumination device 47 in accordance with the invention serves as auxiliary light adapter and is provided with a mount part 5b attached to an accessory shoe 5a of the camera body 1 and another mount part 5c which permits other accessories such as a flash device, a remote control relese device, etc., to be mounted on the auxiliary illumination device 4. In this embodiment as illustrated in FIG. 4, the mount part 5a also serves as the conventional accessory shoe. However, the mount part 5a may be separate from the conventional accessory shoe. The auxiliary illumination device or auxiliary light adapter 4 is provided with an auxiliary light emitting part 6, which has an auxiliary light beam emitted in the direction of an optical axis by means of a light emitting element or a flash device toward an object to be photographed. The mount part 5a of the camera body 1 is provided with a signal pin 7a for controlling the light emission of the auxiliary light adapter 4 or for controlling other accessories. The signal pin 7a conductively connects with a contact which is not shown but is provided on the mount part 5b of the auxiliary light adapter 4 in such a way as to effect signal exchange therewith. The mount part 5c of the auxiliary light adapter 4 is provided with a signal pin 7b which effects signal exchange with other accessories for controlling them, when they are mounted on the adapter 4. Another signal pin 7d, which performs a similar function, is provided on the accessory shoe 5e disposed at the fore end part of the photo-taking lens. Meanwhile, a mount 9 of the camera body 1 is provided with signal pins 7c which effect control signal exchange with signals pins of the lens barrel through contacts provided on the lens 2 side. A reference numeral 8 indicates a known flash device which is attachable either to the accessory shoe 5a of the camera body 1 or to the mount part 5c of the auxiliary light adapter 4.

Referring to FIG. 5, which is a sectional view of a single lens reflex camera, the camera includes a pentaprism 10, a condenser lens 11, a reticle 12, an eyepiece 13 and a main mirror 14 which is either partially or entirely composed of a half mirror. These parts constitute a known viewfinder optical system. Behind the main mirror 14 is disposed an auxiliary mirror 15. A sensor 16 for automatic focusing is disposed in a conjugate position relative to the reticle 12 of the camera. A focusing state is detected through a light flux which passes through the half mirror part of the main mirror 14 and is reflected by the auxiliary mirror 15 to be received by the sensor 16 which is in the conjugate position with the reticle 12 of the camera. Both the main mirror 14 and the auxiliary mirrors 15 are moved upward by a known quick return mechanism during a photo-taking process. Through-the-lens (TTL) light measurement is accomplished with a light sensitive element which is provided for exposure control. As shown in FIG. 4, the auxiliary light adapter 4 is mountable either on the camera body 1, on the lens 2 or on the flash device 8. With the flash device 8 mounted on the camera body 1, the auxiliary light adapter 4 can be mounted on top of the flash device 8. Conversely, the flash device 8 can be mounted on top of the auxiliary light adapter 4 after the latter has been mounted on the camera body 1.

FIG. 6 is a circuit diagram showing by way of example the circuit arrangement of an automatic focusing type camera which permits mounting of the auxiliary illumination device 4 according to the present invention. The circuit arrangement of FIG. 6 and the operation thereof are as described below.

Referring to FIG. 6, the circuit includes a light measuring light sensitive element SPC; an amplifier MOS which is of a high input impedance and which has its output logarithmically suppressed by a diode D1; a constant voltage source, which is not shown, impresses a constant voltage on the amplifier MOS; and an A-D converter which converts a light measurement analog signal from the amplifier MOS into a digital signal. The converter includes a comparator CP1, an operational amplifier OP1; an up-down counter 120; a ladder resistor 119; an AND gate AND 1 and a resistor R5. This is an A-D converter of known arrangement using a D-A converter. With the input signal A-D converted, a digital value thus obtained is kept in the form of a binary code at the up-down counter 120. Clock pulses produced from a clock pulse generator, which is not shown, is supplied to the up-down counter 120 through the AND gate AND 1. The digital value which is produced from the up-down counter 120, which represents the brightness of an object to be photographed, is supplied to one input terminal of a comparator 103. The other input terminal of the comparator 103 has a resistor 104' connected thereto. At the resistor 104', there is set a predetermined digital value which corresponds to a brightness value limit of the object whose brightness is too low to be detectable by a light sensitive element for automatic focusing (such as CCD). Such being the arrangement, a light brightness warning value is constantly supplied to the comparator 103. When the light measurement value of the up-down counter 120 becomes lower than this low brightness value, the output level UNDER of the comparator 103 becomes high.

The output of the up-down counter 120 is also supplied to one of the input terminals of a digital adder 104. The other input terminal of the digital adder 104 receives a digital output corresponding to a set film sensitivity value from a film sensitivity setting member 110 which is composed of, for example, a digital code plate, etc., which is responsive to a film sensitivity setting dial. The brightness Bv which is set as a digital value from the up-down counter 120 and film sensitivity Sv which is set as a digital value from the film sensitivity setting member 110 are subjected to an A.P.E.X. computation (addition) to obtain an exposure value Ev (Bv+Sv) as the output of the adder 104. The output of the adder 104 is supplied to one of the input terminals of a subtractor 105. Meanwhile, the other input terminal of the subtractor 105 receives a digital value which corresponds to a preset aperture value Av and is produced from a switch member 111, which is responsive to the diaphragm of the lens 2. An A.P.E.X. computation of EV-Av is performed by the subtractor 105. The output, Ev-Av=Tv which is a shutter time value, of the subtractor 105 is then supplied to a changeover circuit 107. The changeover circuit 107 is formed by a data selector and is arranged in the following manner. A signal produced at the camera upon completion of a charging process on a main capacitor of a flash device is detected by a detector 112 which is, for example, formed by a comparator. In response to the output of the detector 112, the changeover circuit 107 shifts the output mode thereof from the output mode of the subtractor 105 to that of a setting member 106, composed of a resistor which includes a digital value corresponding to a shutter time value for flash photography, such as 1/60 sec. The digital value output of the setting member 106 is produced by the changeover circuit 107. This output of the changeover circuit 107 is applied to a decoder 108 to change the logarithmically suppressed binary value into an expanded value. This value is then supplied to a comparator 109. While the expanded value is supplied to one of the input terminals of the comparator 109, the output of the up-down counter 120 is supplied to the other input terminal. The reset terminal of the up-down counter 120 is connected to a switch SW4 which is interlocked with the leading curtain of a camera shutter. The switch SW4 turns off when the leading shutter curtain begins to travel. With the switch SW4 thus turning off, the up-down counter 120 begins to count clock pulses CLK. The output level of the comparator 109 becomes high when the count value thus obtained agrees with the expanded value of the decoder 108. The signal thus produced from the comparator 109 is supplied to the reset terminal R of a flip-flop FF.

The set terminal S of this flip-flop FF is connected to a release button switch SW2 of the camera through an inverter I1. When a release action begins, the switch SW2 turns on, setting the flip-flop FF. The flip-flop FF is reset by the output signal of the comparator 109. The output terminal Q of the flip-flop FF is connected to a driver 118 to control a magnet MG3 for a trailing curtain of the shutter and to thereby define a shutter time.

Further included in the ciruit arrangement are a battery BAT, a transistor TR; and a power supply switch SW1 which turns on, for example, in response to the first stroke on a shutter release button. With the SW1 turned on, the transistor TR produces a voltage Vcc and the whole circuit is supplied with the power source voltage. The output signal of the flip-flop FF is at a high level during the shutter release control. With the output signal of the flip-flop FF at a high level, the transistor TR is turned on through an inverter I2. During the release control, therefore, the voltage is continuously supplied to the circuit even after the release button is released.

The circuit arrangement further includes a light sensitive element 115, such as CCD, and an AP circuit 113 which computes and processes the output of an A-D converter 114, which A-D converts a picture image produced from a light sensitive element 115 and a control circuit arranged to control the light sensitive element 115. The AF circuit 113 uses the clock pulsed CLK as basic clock and produces clock pulses CCLK which control the light sensitive element (CCD) 115. The circuit 113 further produces a signal INT which renders the CCD of the light sensitive element 115 charged. Upon completion of a charging process of the CCD, the light sensitive element 115 transmits a signal END to the circuit 113 to make the signal INT low level at that time. With the charging process of the CCD completed, the accumulated electric charge thus obtained is transferred by means of the clock pulses CCLK, one after another. Each charge thus transferred is A-D converted by the A-D converter 114. Then, the digital value thus obtained is supplied as a signal to the circuit 113. The AF circuit 113 computes the signal by a known operation method to detect a focal point. The output of the circuit 113, which is thus produced, is transmitted to a motor driver 116 which drives a lens. In response, the motor driver 116 controls a focusing motor 117 which is provided to shift the focal point of the lens. The AF circuit 113 thus performs a control action always bringing the lens 2 into an in-focus position. The AF circuit 113, the light sensitive element (CCD) 115, the A-D converter 114, the motor driver 116 and the motor 117 jointly form an AF action control circuit. However, this AF action control circuit is known. Therefore, the details are omitted from the description herein. The terminal EN of the motor driver 16 is connected to the output terminal Q of the flip-flop FF. The motor driver 116 thus becomes operative only when the output Q of the flip-flop is high (i.e., before shutter release). During shutter control, therefore, the focusing motor remains inoperative. The output Q of the flip-flop FF is supplied to a NOR circuit NOR 1. During shutter control, the clock pulses CLK are not allowed by the AND gate 1 to be supplied to the counter 120 and light measurement information is stored there.

A low brightness signal from the comparator 103, the output of the inverter I2 and the signal INT from the control circuit 113 are supplied to an AND circuit AND 3. The output level of the AND circuit AND 3 becomes high only when the CCD of the light sensitive element 115 is being charged and the brightness of an object to be photographed is low while no shutter release action has been initiated as yet. This output signal of the AND circuit AND 3 is supplied through a resistor R4, a terminal AF1 of a hot shoe 121 and a terminal AF2 disposed at the mount part of the auxiliary light adapter to a light emitting element 122 which is disposed within the auxiliary light adapter. The element 122 thus emits a light by this output signal of the AND circuit AND 3. Meanwhile, the output of the AND circuit AND 3 is also supplied to the NOR gate NOR 1 to inhibit the clock pulse input of the up-down counter 120 for the purpose of lessening the adverse effect of the auxiliary light on the brightness of the object to be photographed.

Such being the arrangement, the A-D converter ADC is rendered inoperative to inhibit any light measuring action during an auxiliary light emitting action. Conversely, the auxiliary light emitting action is inhibited during the light measuring action.

The auxiliary light adapter is provided with an accessory shoe 300, which permits a flash device 301 to be mounted thereon. With the flash device 301 mounted on this shoe 300, a synchronizing switch SWX is connected to a trigger circuit of the flash device through a terminal X1 of the hot shoe 121 of the camera, a terminal X2 of the mount part of the auxiliary light adapter, a terminal X3 of the shoe part of the adapter and a terminal X4 of the amount part of the flash device. Furthermore, the synchronizing switch SWX is also connected to a charge completion detection circuit disposed within the flash device through terminals cc and cc'. The arrangement permits the adapter to be mounted on the camera and further permits the flash device to be mounted on the adapter, so that an AF action and flash photography can be accomplished employing the auxiliary illumination device 4.

When the auxiliary light adapter or the auxiliary illumination device 4 is mounted on the shoe 302 of the flash device 301 with the flash device 301 mounted on the shoe of the camera, the light emitting element 122 of the adapter is connected to the AND gate AND 3 of the camera through the terminal AF1 of the shoe of the camera, the terminal AF3 of the flash device 4, the terminal AF4 of the shoe part of the flash device 4 and the terminal AF2 of the adapter. Therefore, this permits an AF action and flash photography with auxiliary illumination effected by mounting the adapter on top of the flash device 4.

In accordance with the invention, a mount part 5e for the auxiliary light adapter may be provided at the fore end part 2 of a photo-taking lens 2, as shown in FIG. 4. This arrangement permits mounting of a ring light device for close-up photography, etc. The signal pin 7d provided at the mount part 5e permits mounting without any cord for ease of handling.

The above arrangement has the auxiliary light device 4 attachable to and detachable from the camera without increasing the size of the camera. The device 4 can be mounted on the camera as an auxiliary light adapter only when it is required. A conventional accessory shoe, which is provided on the camera, may also be utilized as a mount part for mounting the adapter without providing any additional mount part. It is another advantage of the invention that the auxiliary light device 4 can easily be away from the photo-taking optical axis to prevent the auxiliary light flux from being eclipsed or shaded by the photo-taking lens 2.

This advantage can be more effectively attained by providing a mount part at the fore end of the photo-taking lens 2. Besides, this mount part and the signal pin also provided there can be used for other accessories such as a ring flash device, etc.

Furthermore, in accordance with the invention, the automatic focusing action and the light measuring action can be accomplished in a time seriated manner to prevent erroneous light measurement. Meanwhile, the automatic focusing and light measuring actions can be performed with the same ease of operation as the conventional camera without necessitating any additional operation by the photographer for enlarging the detectable range of the object's brightness while carrying out automatic focusing.

In the embodiment described above, priority is given to the automatic focusing mechanism 4 and, during the charging process thereof, the light measurement action is inhibited only during illumination by the auxiliary light. However, the invention is, of course, not limited to this and it is to be understood that modifications will be apparent to those skilled in the art without departing from the spirit of the invention. For example, where light measurement is to be carried out through A-D conversion of the double integration type, the AF sensor may be charged while it is separated from the light measurement output during the process of reverse integration. Furthermore, arrangement for circuit shifting such as light measurement AF--light measurement--AF, one after the other, can be made without difficulty in accordance with the invention.