Abstract:
A one-time-use camera with a built-in flash, an external flash unit therefor and system in which the camera and external flash unit have mating mounting structures enabling the external flash unit to be mounted on the camera in manner that blocks direct flash emission from camera flash unit onto a subject being photographed and the flash emission device of the external flash unit is positioned farther away from the camera taking lens than the built-in flash thereby substantially eliminating red-eye effect on the subject being photographed. The external flash unit includes a flash re-directing channel which directs built-in flash emission generally upwards to provide indirect illumination of the photographed subject. A camera ready light enable/disable circuit in the external flash unit is connected to the camera ready light to disable normal operation of the ready light until the external flash unit is fully charged thereby enabling the camera user to rely solely on the camera ready light as an indicator of when the camera and external flash units are ready for taking the next picture. The external flash unit is also provided with a user-operated start switch that simultaneously starts flash charger operation in both the camera and external flash unit.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     Reference is made to co-pending U.S. application Ser. No. 09/535,870 entitled ONE-TIME-USE CAMERA WITH EXTERNAL FLASH UNIT, Douglas W. Constable, filed concurrently herewith. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the field of photography, and in particular to attachable flash apparatus useful with one-time-use cameras. 
     BACKGROUND OF THE INVENTION 
     One-time-use cameras are rapidly gaining in popularity due to in large part to their convenience and low cost relative to user-reloadable cameras. Many of such cameras include a built-in flash device to enable indoor picture taking. For cost reasons, such flash devices are typically fixed in place and, because of the small size of the cameras, are necessarily located close to the optical axis of the taking lens. As a result, the phenomenon known as “red-eye” becomes a problem. Red-eye occurs when flash light is reflected by a subject&#39;s retina through the taking lens onto the exposed image frame. Numerous techniques are known for reducing the red-eye effect. One of such techniques involves the use of a pop-up flash device that moves the flash emitter away from the optical axis of the taking lens. Such a built-in, pop-up arrangement, while effective, is costly to implement and would not be suitable for one-time-use cameras where cost must be kept at a minimum. 
     U.S. Pat. No. 5,384,611 discloses a user-reloadable camera with a retractable built-in flash and provision for attachment of an external flash. When the external flash is mounted on the camera, the retractable flash which is close to the optical axis of the taking lens is retracted into the camera and does not fire. Thus, the external flash unit and built-in flash unit do not fire simultaneously. Since the spaced, externally mounted flash is the sole source of flash emission, the red-eye effect is effectively eliminated. However, the disclosed arrangement involves the use of a retractable built-in flash with provision on the flash to electrically disable the built-in flash. Such an arrangement is costly to implement and would not be suitable for low cost one-time-use cameras. 
     There is therefore a need for a one-time-use camera system with an externally mountable flash unit that moves the point of direct subject flash emission away from the optical axis of the camera taking lens so as to eliminate or substantially reduce the red-eye effect without significantly adding to the cost of the camera itself. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, therefore, there is provided a one-time-use camera and detachable flash system which comprises a one-time-use camera having a taking lens, a fixed, built-in flash unit with a flash emission device and a first mounting structure accessible on an outer surface of the camera; and an external flash unit having a second flash emission device and a second mounting structure thereon configured to mate with the first mounting structure on the camera permitting the external flash unit to be detachably mounted on the camera with the second flash emission device spaced farther away from said taking lens than said first flash emission device, the external flash unit having a portion thereof which, when mounted on the camera, physically blocks direct illumination by flash light actually emitted from the camera built-in flash unit of a subject being photographed; whereby red eye effect on photographed subjects is substantially eliminated. 
     These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a one-time-use camera adapted for mounting of an external flash unit in accordance with a first embodiment of the present invention; 
     FIG. 2 is a rear isometric exploded view of a camera system according to the first embodiment of the invention; 
     FIG. 3 is a front elevation view of the camera system of FIG. 2 with an external flash unit mounted on the camera; 
     FIG. 4 is a bottom plan view of the camera system of FIG. 2 with the external flash unit shown in section; 
     FIG. 5 a  is a side elevation view of the camera system of FIG. 2 with the external flash unit shown in section; 
     FIG. 5 b  is a cutaway detail of a portion of the FIG. 5 camera system showing details of mounting and electrical connection arrangements therefor; 
     FIG. 6 is a partially schematic, block diagram of electronic circuits useful in the camera system of FIG. 2; 
     FIG. 7 is an isometric view of a one-time-use camera illustrating a second embodiment of the invention; 
     FIG. 8 is a rear isometric exploded view of the camera system according to the second embodiment of the invention; 
     FIG. 9 a  is a side elevation view of the camera system of FIG. 8 with the external flash unit shown in section; 
     FIGS. 9 b  and  9   c  are cutaway views of portions of the camera system of FIG. 9 a  showing details of the mounting and electrical connection arrangements therefor; 
     FIG. 10 is an isometric view of a one-time-use camera illustrating a third embodiment of the invention; 
     FIG. 11 is a rear isometric exploded view of the camera system according to the third embodiment of the invention; 
     FIG. 12 a  is a side elevation view of the camera system of FIG. 11 with the external flash unit shown in section; and 
     FIG. 12 b  is a cutaway view of a portion of the camera system of FIG. 12 a  showing details of the mounting and electrical connection arrangements therefor. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring jointly to FIGS. 1-3, a one-time-use and detachable flash system is shown which comprises a one-time-use camera  10  and an external flash unit  20 . The camera comprises a housing  11 , a taking lens  12 , a shutter release button  13 , a viewfinder  14  and a film advance wheel  15 . A label sheet  15   a  is typically placed around the front and back the camera to provide printed material such as operating instructions and a company logo. The label sheet also serves to hide any holes in the camera housing which might be used for circuit testing purposes and the like during manufacturing of the camera. The illustrated camera is provided with a built-in flash unit which includes a flash emission device  16 , a flash charger start button  17  and a flash charge ready light  18 . The trend in the design of a one-time-use camera is to make the camera as small as possible for the convenience of the user. It is also important to keep the manufacturing cost as low as possible. As the size of the camera is reduced, the built-in flash emission device  16  becomes closer to the optical axis of the taking lens which increases the red-eye effect, particularly when taking indoor pictures of human and animal subjects. The need to keep manufacturing costs as low as possible dictates against the use of pop-up flash devices which are commonly used in more costly user-reloadable cameras to temporarily move the flash emission device away from the optical axis of the taking lens for picture taking operations. 
     In accordance with the system of the invention, an external flash unit  20  is provided to serve as the primary flash unit for the system with a flash emission device spaced sufficiently away from the taking lens optical axis to substantially eliminate the subject red-eye effect. To this end, camera  10  includes a mounting structure comprising, in the embodiment of FIGS. 1-3, a pair of elongated slots  19   a  and  19   b  formed in the upper and lower surfaces of the camera housing  11  and extending parallel to the long dimension of the camera. The external flash unit  20  comprises an elongated housing  21  having, at the upper end, a flash emission device  22 . An open mounting chamber  24  in the lower portion of the housing  21  has a complementary pair of elongated ridges  26   a  and  26   b  (FIG. 5 a ) on the upper and lower surfaces, respectively, of the chamber. With the external flash unit positioned at the end of the camera, the ridges  26   a  and  26   b  align with and extend in the direction of the slots  19   a  and  19   b  and permit the external flash unit to be mounted into position on the camera as shown in FIG. 3 by sliding the ridges into the slots. As seen in FIGS. 2 and 4, the chamber surface  28  facing the front of the camera is provided with a spherical recess  30  that allows charger start button  17  to project slightly, in its normal manner, beyond the surface of camera housing  11  after the flash unit is mounted on the camera. A radiused portion  32  of the surface  28  comprises a detent which acts to depress the button  17  as the flash unit slides into its mounted position thereby to automatically start the flash charging circuit in the camera into its charging operation. A user operated plunger button  38  extends through the front surface of the flash unit  20  and includes a pin  39  that extends through the center of the spherical recess  30 . An enlarged shaft portion  39   a  (FIG. 5 a ) engages a flexible electrical contact of switch  40  which is connected to a flash charging circuit on circuit board  41  mounted inside the external flash unit housing. With this arrangement, in accordance with an aspect of the invention, both the camera and external flash unit charging circuits may be restarted simultaneously be depressing button  38 . The slots  19   a ,  19   b  and ridges  26   a ,  26   b  are provided, respectively, with mating electrical terminals  42   a ,  42   b  and  44   a ,  44   b  to enable electrical communication between the camera and external flash unit. 
     Referring to FIGS. 5 a  and  5   b , external flash unit  20  is a self-contained unit having the necessary flash charging circuit, flash capacitor  48 , flash emission device (flash tube)  22  and associated reflector  49  mounted within the unit housing and one or more power supply batteries  49   a . A camera flash light redirecting channel  50  is structured in the external flash unit to direct flash light from the built-in flash emission device generally upward to provide a source of indirect illumination of a subject being photographed. This flash light redirecting channel  50  includes a transparent window panel  51  on the surface  28  which is located so as to align with the camera&#39;s built-in flash emission device  22  when the external flash unit is mounted on the camera. The channel further includes an angled mirror  52  and a transparent light exit window panel  54 . A photosensor  56  is located in the light redirecting channel  50  to detect flash emission from the built-in camera flash to provide a trigger signal to initiate flash operation in the external flash unit. It will be appreciated that with the external flash unit mounted on the camera, direct flash illumination onto the subject is blocked by housing  21  of the external flash unit thereby preventing any red-eye effect which might normally occur from the built-in flash illumination. However, the built-in flash is nonetheless advantageously employed to provide “bounce” flash or indirect illumination on the subject. 
     FIG. 6 shows circuits, partially in schematic and partially in block form, which may be used in the camera flash unit and the external flash unit. The camera flash unit comprises a charging circuit  60 , a charge pulse rectifying diode D 3 , a main flash capacitor C 2 , a trigger circuit  70  and flash emission device  16 . Trigger circuit  70  is activated by a trigger switch  68  when the camera lens shutter is opened to initiate flash emission from flash emission device  16 , the flash emission being sustained by discharge of flash capacitor C 2  through the device  16 . Charging circuit  60  is more fully described in U.S. Pat. No. 5,781,804, the disclosure of which is incorporated herein by reference. Briefly, portion  62  is an oscillator circuit to generate pulses in transformer primary winding P which are stepped up in secondary winding S. The stepped up negative-going pulses are rectified by diode D 3  to charge flash capacitor C 2  to a full charge voltage of −300 volts, with −280 volts typically being sufficient to sustain flash emission from flash emission device  16 . In the charging circuit  60 , portion  63  is an optional bias supply circuit driven during charging operation by a few tertiary winding turns T inductively coupled to secondary winding S to provide a suitable DC bias current to the base of oscillator transistor Q 1  to improve the operating efficiency of the oscillating circuit  62 . Portion  64  is a timing circuit operative after the flash capacitor reaches full charge to sustain oscillation for a few minutes to insure retention of full charge on the flash capacitor thus giving the camera user time to compose and take the picture. Of particular interest to the present invention is portion  66  which comprises a charge ready indicating circuit including a light emitting diode LED (ready light  18 ) and resistor R 5  connected in series from an intermediate tap on the secondary winding S to ground. During the charging of flash capacitor C 2 , negative pulses are generated across the indicator circuit  66  which gradually increase in voltage as the flash capacitor is charged. The position of the tap on secondary winding S is chosen such that negative pulses will begin to forward bias and illuminate the LED ready light  18  when sufficient negative charge is achieved on flash capacitor C 2  to sustain flash emission from device  16 . Unlike other ready light indicators which are directly connected to the flash capacitor, the LED in circuit  66  is operated at a low 1.5 volt level. The terminals of the LED ready light  18  are connected to the terminal connections  42   a  and  42   b  for reasons explained later. 
     In the external flash unit, the flash circuit includes a battery voltage supply  49   a , flash charging circuit  72 , trigger circuit  75 , rectifier diode D 4 , main flash capacitor  48  and flash emission device  22 . Photosensor  56  is connected through an amplifier  76  to trigger circuit  75  to initiate flash emission from device  22  in response to detection of flash emission from camera flash emission device  16 . Charger circuit  72  is automatically restarted in known manner after each flash emission by a pulse feedback from trigger circuit  75 . As previously described, a charger start switch  40  operates to manually start charging operation in circuit  72  and is mechanical by interconnected plunger  39  to camera charge start button  17  to simultaneously start charger circuit  60  when button  38  on the external flash unit is depressed. 
     Since the external flash unit has a charger circuit and main flash capacitor that are separate from the camera, it is necessary to provide an indication of when the flash capacitor in the external flash unit is ready to enable flash emission. Conventionally, this would be done with a separate ready light indicator in the external flash unit responsive to the charge level of the external unit&#39;s flash capacitor. However, in accordance with another aspect of the invention, provision is made for communication between the external flash unit and the camera flash unit to utilize the camera LED ready light  18  as the sole indicator of when the system is ready for taking a flash picture. To this end, the external flash unit circuit includes a camera ready light override circuit  80  connectable to the camera ready light  18  to disable normal operation of the camera ready light  18  unless and until the charge level of the external unit&#39;s flash capacitor  48  is sufficiently charged to a desired voltage lever, e.g. −280 volts sufficient to sustain flash emission by the external unit&#39;s flash emission device  22 . In the illustrated embodiment, the override circuit  80  includes a comparator  81  with its positive input side connected to intermediate terminal  77  of a resistor voltage divider R 6 , R 7  which is connected between the negative charge terminal of flash capacitor  48  and ground. The negative input side of comparator  81  is connected to a reference potential at terminal  78  established by zener diode Z 1  connected from ground through resistor R 8  to the +3 volt battery source. The values of resistors R 6  and R 7  are chosen such that, when flash capacitor  48  is sufficiently charged, the voltage on terminal  77  is the same as the reference voltage on terminal  78 . The output of comparator  81  is coupled to a normally-closed solenoid actuated switch  82 , the switch contacts of which are connected to contact terminals  44   a  and  44   b.    
     In operation, with the external flash unit  20  mounted on the camera  10 , and assuming the external unit flash capacitor is uncharged or at a low negative charge voltage, the camera ready light  18  is shorted out by the normally closed solenoid switch contacts in solenoid switch  82 . When the flash charger circuit is started, either manually by depressing button  38  to close contacts  40 , or automatically by feedback from trigger circuit  75  after taking a picture, flash capacitor  48  begins charging negatively. When the capacitor  48  negative charge voltage begins to exceed the −280 volt level sufficient to sustain discharge through flash emission device  22 , the voltage at terminal  77  falls below the reference voltage on terminal  78 . This causes the output of comparator  81  to change state and initiate current through the winding of solenoid switch  82 . The resultant opening of the switch  82  contacts removes the short across camera LED ready light  18 . At this point, the camera ready light  18  is enabled to operate as described above depending on the charge condition of the camera flash capacitor C 2 . On the other hand, if the camera flash capacitor C 2  reaches the charge ready level before the external flash capacitor  48 , the short across the camera LED ready light  18  prevents the light from being activated until the external flash capacitor reaches its charge ready level and solenoid switch  82  releases the short from across the camera LED ready light  18 . This offers the convenience to the camera user of needing to check with only a single ready light existing on the camera to ensure that both flash units will fire when the picture is taken. 
     FIGS. 7,  8  and  9   a - 9   c  illustrate an alternative embodiment of the camera and external flash unit system of the invention in which features of this system that are the same as those of the system of FIGS. 1-3 carry the same reference numerals. In this embodiment, a one-time-use camera  100  is provided with recesses  102   a  and  102   b  on upper and lower surfaces of the camera body  101 . The external flash unit  120  includes a chamber  124  formed in the lower portion of the external unit housing  121 . The chamber  124  includes a detent  105  on the upper surface of the chamber and a pair of separated detents  106   a  and  106   b  on the lower surface of the chamber. The detents and recesses are in mating alignment allowing the external flash unit to be snapped in place on the camera from the front as shown in FIG. 8. A pair of contacts  108   a  and  108   b , leading from the solenoid switch  82  (FIG. 6) in the external flash unit, project between the detents  106   a  and  106   b . FIG. 9 b  shows the connection between contact  108   b  and a terminal  104   b  in the lower recess  102   b  which leads to the camera ready light  18  as shown in FIG.  6 . Another terminal (not shown) connects with contact  108   a  in similar fashion and also leads to camera ready light  18 . 
     FIGS. 10,  11  and  12   a - 12   b  illustrate a further alternative embodiment of the camera and external flash unit system of the invention in which features of this system that are the same as those of the system of FIGS. 1-3 carry the same reference numerals. In this embodiment, the exposed electrical terminals on the camera  100 ′ leading to the camera ready light  18  of the previous embodiments are eliminated. In their place, a pair of LED access holes  132   a  and  132   b  are formed in the front of the camera housing  101 ′ to provide access to terminals on the internal printed circuit board connecting to the camera LED ready light  18  (FIG.  6 ). The external flash unit  130  is provided with contact pins  136   a  and  136   b , colloquially referred to herein as “pogo pins”. These pogo pins extend outwardly through holes  133   a  and  133   b  formed in the surface  138  of chamber  134 . They are mounted on the internal printed circuit board  41  of the external flash unit  130  and are electrically connected to the solenoid switch as shown in FIG.  6 . Preferably, the pogo pins are slidably journalled in cylinders  140   a  and  140   b  and are spring loaded by means of springs  142   a  and  142   b . A continuous detent  106 ′ is provided in the lower surface of chamber  134  for engagement with recess  102   b  in the bottom of camera housing  101 ′. In operation, when the external flash unit  130  is clipped onto the front of camera  100 ′, with detents  105  and  106 ′ lodged in recesses  102   a  and  102   b , the pogo pins pierce the outer label  15   a  and are pressed against the LED terminal contacts on the circuit board  139  inside the camera. The spring loading of the pogo pins provides some spacing tolerance between the external flash unit and the camera and assures good electrical connection with the camera circuit board terminal contacts. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
       10  camera 
       11  camera housing 
       12  taking lens 
       13  shutter release button 
       14  viewfinder 
       15  film advance wheel 
       15   a  camera label 
       16  flash emission device 
       17  flash charger start button 
       18  flash charge ready light 
       20  external flash unit 
       21  external flash unit housing 
       22  external flash emission device 
       24  mounting chamber 
       26   a, b  elongated ridges 
       28  chamber surface 
       30  spherical recess 
       32  radiused portion 
       38  plunger button 
       39  plunger pin 
       39   a  enlarged shaft portion 
       40  external charger start switch 
       41  circuit board-external flash unit 
       42   a, b  electrical terminals-camera 
       44   a, b  electrical terminals-external flash unit 
       48  flash capacitor-external flash unit 
       49  flash reflector 
       49   a  power supply batteries 
       50  flash redirecting channel 
       51  window 
       52  angled mirror 
       54  exit window panel 
       56  photosensor 
       60  camera charging circuit 
       63  bias supply circuit 
       64  charge timer circuit 
       66  charge ready indicator circuit 
       72  external flash charging circuit 
       75  trigger circuit 
       76  amplifier 
       77  intermediate terminal 
       78  reference terminal 
       80  ready light override circuit 
       81  comparator 
       82  solenoid actuated switch 
       100  camera 
       102   a, b  recesses 
       105  detent 
       106   a, b  detents 
       108   a, b  contacts 
       121  housing 
       124  chamber 
       132   a, b  LED access hole 
       133   a, b  holes in external flash unit surface  138   
       134  chamber 
       136   a, b  contact pins (“pogo pins”) 
       138  external flash unit surface 
       139  camera printed circuit board 
       140   a, b  cylinder 
       142   a, b  springs 
     C 2  flash capacitor-camera 
     D 3  charge pulse rectifying diode 
     D 4  rectifier diode-external flash unit 
     Q 1  oscillator transistor 
     R 6 ,  7  voltage divider circuit