Automatically controlled electronic flash device

An automatic electronic flash device for use with a camera includes a flash tube carried by a housing. A battery is carried by the housing as a source of electric supply. A capacitor is connected to the flash tube to fire it when discharged. A circuit is used to automatically adjust the amount of light emitted from said flash tube upon the firing of the tube. The circuit includes a light receiving element arranged to receive light reflected from a photographic object upon the firing of the tube. The information of distance from the camera to an object to be photographed is fed to the circuit as a function of the amount of light received. A switch is connected to the circuit to cause it to vary the amount of light emitted from the flash tube. A calculator enables calculation of a plurality of combinations of aperture settings and distance setting in response to a film speed setting, so that selection of a desired film speed will result in indication of a desired aperture setting and distance setting. Light emitting diodes are disposed adjacent to the calculator for indication of one of the combinations calculated by the calculator. Another switch connects one of the light emitting diodes to the battery for selective energization thereof in association with the switching of the above switch connected to the circuit.

BACKGROUND OF THE INVENTION 
The present invention relates generally to devices used with photographic 
equipment, and more specifically to an automatically controlled electronic 
flash device used as an artificial source of light necessary to illuminate 
photographic objects. 
Automatically controlled electronic flash devices have heretofore been used 
as a source of artificial light. In such prior devices a predetermined 
amount of light is produced from an electronic flash tube. The amount of 
light is automatically adjusted in accordance with the output of a light 
measuring device used to represent the distance from a camera to a 
photographic object. One such prior art device is for example shown in 
published Japanese Utility Model No. Sho 49-148052. The device disclosed 
in the Japanese publication relates to an automatically controlled 
electronic flash device which permits a selection between two aperture 
openings to be set on a camera for a film having a particular speed or 
sensitivity. The device is provided with a calculator having a pair of 
neon tubes used to indicate the aperture setting (f-number) which is 
representative of the aperture to be set on the camera, as well as the 
maximum permissable distance or range from the camera to the photographic 
object. In this prior device indicia is used to represent the distance 
between the camera and the object. Similarly indicia representing the 
f-number (aperture setting) is also used. The f-number indicia are movable 
with respect to the distance setting indicia and also movable relative to 
the two neon tubes depending upon the setting of a particular film speed 
or sensitivity. The neon tubes are selectively lit depending upon the 
position of a manual switching member. When the manual switching member is 
set to a first position and a certain film sensitivity or speed is set, a 
particular combination of aperture setting and maximum permissable 
distance between the camera and the object is indicated by one of the neon 
tubes being lit. When the manual switching member is set to a second 
position, with the same film speed or sensitivity being set, another 
combination of aperture setting and maximum permissible distance between 
the camera and the object is indicated by the other neon tube being lit. 
The use of the neon tubes or lamps provides the operator, or photographer, 
with the ability to see the selected aperture setting and maximum 
permissable distance between the camera and the object even when using the 
device in the dark. 
The disadvantage of this prior device, however, relates to the fact that 
the neon tubes are connected to opposite terminals of a capacitor used for 
storing electric charge to energize a flash tube. Accordingly, the neon 
lamps cannot be lit unless the potential across the capacitor reaches a 
level sufficient to allow the flash tube to emit a sufficient quantity of 
light. In other words, unless the capacitor is fully charged the 
combination of proper aperture setting to be chosen on the camera and the 
maximum permissable distance between the camera and the object for a 
particular film speed, cannot be indicated. Therefore, soon after the 
flash tube has reached a condition for emitting light, imaging using the 
flash as a source of artificial light may not be possible. 
It is accordingly an object of the present invention to provide an improved 
automatic electronic flash device which overcomes the disadvantages of the 
prior art. 
It is a more specific object of the present invention to provide an 
automatic electronic flash device which provides for the selection of a 
particular aperture size to be set on a camera for any selected film 
speed, and which, independent of the condition of charge on the capacitor 
used to fire the flash tube, indicate the aperture size to be set on the 
camera and the maximum permissable distance between the camera and the 
object which is available under the conditions for the selected film speed 
and a set aperture size. 
SUMMARY OF THE INVENTION 
In order to accomplish the foregoing objectives the automatic electronic 
flash device of the present invention is provided with means to 
automatically adjust the amount of illumination provided by the flash in 
accordance with the selected film speed and a camera-to-object distance. 
The device includes a light receiving element which receives light from an 
object to be photographed. The information of the distance is obtained as 
a function of the intensity of light which is received by the light 
receiving element during the firing of the flash tube. Manually operable 
first switch means is used to change the amount of flash illumination 
during firing of the flash tube, depending on the set position of the 
first switch means so that the flash device will allow a plurality of 
aperture sizes to be selectively set on a camera for a desired film speed. 
A calculator is provided on the housing of the flash device and includes 
indicia to represent film speed, f-numbers and the maximum permissable 
distance between the camera and the object. The various indicia are 
arranged with respect to each other such that designations or settings of 
a desired film speed will specify a combination of f-numbers (aperture 
settings) and the maximum permissable distance setting, which would be 
available for the preselected film speed. A plurality of light emitting 
elements are also provided on the housing adjacent the calculator. The 
light emitting elements are selectively connected to a battery for 
energization by second switch means interconnected with the first switch 
means. The light emitting elements are arranged so that when they are 
selectively energized a particular combination of f-number or aperture 
size settings for a predetermined film speed will be appropriately 
indicated. Thus, the proper indication will be made in response to the 
operation of the first switch means to change the amount of flash 
illumination, independent of whether or not the capacitor used to fire the 
flash tube has been charged to an adequate voltage level. 
The foregoing objects, advantages and features of the present invention 
will become more apparent from the following description of the invention 
taken in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates the external rear surface of the automatically 
controlled electronic flash device of the present invention. A flash 
device body 1 includes an upper flash portion 1a carrying an electronic 
flash tube (not shown). A manually operable switch member 2 is carried on 
the flash device body 1 and is used to operate a power source switch. An 
auto-manual switch member 3 (hereinafter referred to as the "A-M switch 
member") is also carried on the flash device body 1. The A-M switch member 
3 can be set to any position within two separate ranges, identified in the 
drawing as either the "A" range or the "M" range. When the A-M switch 
member 3 is set to the "A" range the device will be in an automatic mode 
so that the amount of light to be emitted from the flash tube for 
illuminating an object will be automatically controlled to provide an 
optimum exposure. When the A-M switch member 3 is set to the "M" range the 
device will be in a manual mode so that the flash device can emit light to 
full extent. Within the "A" range the A-M switch 3 can be moved between 
two positions A1 or A2. The aperture setting of the lens structure of the 
camera can therefore be selected in two different positions. A distance 
setting dial 4 carries indicia to indicate distance (illustrated in FIG. 
2b in units of meters), and aperture setting dial 5 carries indicia 
representative of aperture settings. Additionally, there is means for 
indicating selected film speeds as indicated by an ASA setting. Through 
the use of the film speed setting, the aperture setting dial and the 
distance setting dial an operator or photographer can determine the 
relationship between the desired aperture setting and the distance from 
the camera to the object for a particular chosen film speed. 
FIG. 2 illustrates the structure of the calculator shown in FIG. 1, which 
includes the distance setting dial 4 and the aperture setting dial 5. The 
distance setting dial 4 is attached to the flash device body 1 by set 
screw 6. The aperture setting dial is arranged below the distance setting 
dial 4 and is rotatably carried about a threaded portion 1b of the set 
screw 6. 
Indicia 4a to indicate distance settings, indicia 5a to indicate desired 
aperture settings and indicia 5b to indicate selected film speed are 
provided on the dials 4 and 5 in such a manner that when the aperture 
setting dial 5 is turned through a particular angle, which will be 
determined by the selected film speed indicated by the cut-out portion 4b 
on the distance setting dial 4 (shown for example as ASA setting 100 in 
FIG. 2b), the product of a distance setting with an aligned aperture 
setting 5a will correspond to a maximum guide number (for example, Guide 
No. 20) in the flash device. A potentiometer 25 is interconnected with 
dial 5 so that the resistance thereof varies with the selected film speed. 
Aperture setting indicating dial 5 is preferably made of a semi-transparent 
(for example, milky-white), synthetic resin, so that two of the aperture 
settings carried on the aperture indicating dial 5 will be selectively 
illuminated by light emitting diodes 7 and 8 which are disposed below the 
dial 5. 
Light emitting diodes 7 and 8 are selectively energized by a change-over 
switch 10 which is connected through a power source switch 9 to a power 
supply 11, as illustrated in FIG. 3. Change-over switch 10, along with 
another change-over switch 12, is interconnected to A-M switching member 
3, so that when A-M switching member 3 is set in the "M" mode, change-over 
switches 10 and 12 will both be connected to terminal P. In this mode, 
light emitting diodes 7 and 8 will not be illuminated since the connection 
to the power supply 11 will be interrupted. Accordingly, no indicia on the 
aperture setting dial 5 will be illuminated. A gate 13a of a thyrister 13 
is shortcircuited to a lower potential line 14, so that a trigger circuit 
15 including thyrister 13 will reman inoperative. Consequently, a flash 
operation without automatic flash control will be effected. In other 
words, capacitor 17 which has been previously charged to a predetermined 
level through a DC-DC converter circuit 16 from power source 11 will 
discharge through flash tube 20 in association with operation of trigger 
circuit 19 which is caused by a synchronizing switch 18 which has been 
brought to a closed position. The flash device will therefore emit a 
quantity of light determined by its predetermined guide number. 
When A-M switching member 3 is set at the "A.sub.1 ", position change-over 
switches 10 and 12 will both be connected to the terminals Q. Accordingly, 
only light emitting diode 7 will be energized so that an aperture setting 
(f5.6 as illustrated in the drawing) which is positioned above diode 7 
will be illuminated. The illuminated aperture setting should then be set 
on the lens system of the camera. Simultaneously, the maximum permissable 
distance between the camera and the photographic object will be indicated 
as the one on the distance setting dial 4 that is aligned with the 
illuminated aperture setting on dial 5. Accordingly, in FIG. 2b the 
maximum permissable distance setting for aperture setting 5.6 will be 3 
meters. Gate 13a of thyrister 13 is connected to capacitor 21 so that the 
automatic controlling operation in accordance with the aperture setting on 
the camera lens system will be effected. 
When light is emitted from the flash tube 20 a certain portion of the 
emitted light will be reflected by the photographic object and will act on 
a light receiving element 22. Charge will then begin to build up across 
capacitor 21 with a current proportional to the intensity of the light 
received by element 22. When the potential across the capacitor reaches a 
predetermined level determined by the resistance of potentiometer 25 
thyrister 13 will begin to conduct. Trigger circuit 15, including 
thyrister 13 will then begin to operate so that a bypass discharge tube 23 
will be allowed to discharge. Flashing of tube 20 will therefore cease 
resulting in the automatic control of the flash device. Since the 
intensity of light which is received by light receiving element 22 is 
inversely proportional to the square of the distance between the camera 
and the object being photographed, the closer the object is to the camera 
the sooner the flash tube 20 will stop firing. 
When A-M switch member 3 is set to the "A2" position change-over switches 
10 and 12 will both be connected to terminals R. In this mode current will 
be supplied to the other light emitting diode 8, and an aperture setting 
positioned above this diode (f11 as illustrated in FIG. 2b) will be 
illuminated. The indicia which is on the distance setting dial 4 and which 
is aligned with the illuminated setting on dial 5 will indicate the 
maximum permissable distance between the camera and the object. In the 
case where light emitting diode 8 is energized and, as illustrated in FIG. 
2b aperture setting 11 is illuminated, the maximum permissable distance is 
indicated as 2 meters. Gate 13a of thyrister 13 in this case is connected 
to capacitor 24 and the automatic control for ceasing operation of flash 
tube 20 will be initiated in the same manner as described above. 
It should be understood by those skilled in the art that light emitting 
diodes could be replaced by other illuminating means for purposes of 
indicating the aperture setting on dial 5. Similarly, the aperture setting 
indicator may be arranged radially outward of dial 5 rather than beneath 
the dial. Other alternatives could be to indicate the desired aperture 
setting through the use of different colored illuminating means. 
In the embodiment described above the particular setting for the aperture 
opening is clearly indicated and cannot be mistakenly confused with other 
aperture settings. This is accomplished through the use of the 
illuminating means, i.e. the light emitting diodes. The aperture setting 
to be chosen is easily seen in areas where there is little ambient light 
and is therefore of unique advantage. The present invention is therefore 
well suited for situations in which only a single diaphram value is to be 
indicated. 
While the present invention has been described and illustrated with respect 
to a certain preferred embodiment, it will be apparent to those skilled in 
the art, after understanding the purposes of the invention, that various 
changes and modifications may be made without departing from the spirit 
and scope of the invention, and it is therefore intended to cover such 
changes and modifications in the appended claims.