Automatic flash control system for cameras

Claim 2

In a camera having an objective, flash means having a preparatory flash operation prior to a main flash operation for providing a given amount of preparatory flash illumination during said preparatory flash operation, internal photosensitive means situated within the camera for receiving light which has travelled through the objective during the preparatory flash operation and for determining when a predeterMined amount of light is internally received, external photosensitive means situated with respect to said flash means for receiving light during said preparatory flash operation, and preparatory electrical circuit means electrically connected with said external means and said internal means for integrating the amount of light received by said external means during said preparatory flash operation, said internal means terminating the integration of said preparatory electrical circuit means without terminating the preparatory flash illumination from said flash means when said predetermined amount of light is received by said internal means, the integrated value achieved at the termination of integration being retained for subsequent use during the main flash illumination.

Claim 3

The combination of claim 1 and wherein said flash means provides a main flash illumination during said main flash operation, said external means receiving light during said main flash operation, the combination further comprising, flash terminating means electrically connected with said flash means for automatically terminating the main flash operation thereof, and main electrical circuit means electrically connected with said external means and said flash terminating means for integrating the amount of light received by said external means during the main flash operation and controlling said flash terminating means when said last integrated value has a predetermined proportionate relationship to the retained integrated value.

Claim 4

The combination of claim 2 and wherein said main electrical circuit means includes integration circuit means for integrating an electrical quantity from said external photosensitive means and computation means electrically connected between said integration circuit means and said preparatory electrical circuit means for comparing the integrated electrical quantity with the retained integrated value.

Claim 5

The combination of claim 3 and wherein said integration circuit means includes a first capacitor means and wherein said preparatory electrical circuit means includes second capacitor means for retaining the integrated value, and wherein the predetermined proportionate relationship is represented by the ratio of the first capacitor to the second capacitor.

Claim 6

The combination of claim 1 and wherein said internal photosensitive means receives light for converting the received light into a corresponding electrical quantity, integration circuit means for integrating said electrical quantity and control circuit means responsive to the integrated electrical quantity for producing an output signal when the integrated electrical quantity reaches a predetermined value.

Claim 7

The combination of claim 1 and wherein said external photosensitive means receives light for converting the received light into a corresponding electrical quantity and wherein said preparatory electrical circuit means includes integration circuit means for integrating the electrical quantity from said external photosensitive means and memorizing means for retaining the integrated electrical quantity.

Claim 8

The combination of claim 1 and wherein said internal means includes a light activated silicon controlled rectifier, a first preparatory integration capacitor electrically connected to a gate of said light activated silicon controlled rectifier and causing said light activated silicon controlled rectifier to conduct when a predetermined amount of integration voltage is reached, and first transistor means electrically connected to said light activated silicon controlled rectifier to conduct when said light activated silicon controlled rectifier conducts.

Claim 9

In a camera having an objective, flash means having a preparatory flash operation prior to a main flash operation for providing a preparatory flash illumination during said preparatory flash operation, internal photosensitive means situated within the camera for receiving light which has travelled through the objective during the preparatory flash operation and for determining when a predetermined amount of light is internally received, external photosensitive means situated with respect to said flash means for receiving light during said preparatory flash operation, and preparatory electrical circuit means electrically connected with said external means and said internal means for integrating the amount of light received by said external means during said preparatory flash operation and for terminating the integration when said predetermined amount of light is received by said internal means, the integrated value achieved at the termination of integration being retained for subsequent use during the main flash illumination, and wherein said internal means includes a light activated silicon controlled rectifier, a first preparatory integration capacitor electrically connected to a gate of said light activated silicon controlled rectifier and causing said light activated silicon controlled rectifier to conduct when a predetermined amount of integration voltage is reached, and first switching circuit means electrically connected to said light activated silicon controlled rectifier to conduct when said light activated silicon controlled rectifier conducts, and wherein said external means includes an external photosensitive diode located in parallel with said first switching circuit means, and wherein said preparatory electrical circuit means comprises the combination of second switching circuit means electrically connected to said diode to conduct when said diode conducts, and second preparatory integration capacitor means electrically connected to said second switching circuit means for providing an integration voltage corresponding to the light received by said diode, whereby when said first switching circuit means conducts, said second preparatory integration capacitor means terminates integration.

Claim 10

In a camera having an objective, flash means having a preparatory flash operation prior to a main flash operation for providing a preparatory flash illumination during said preparatory flash operation, internal photosensitive means situated within the camera for receiving light which has travelled through the objective during the preparatory flash operation and for determining when a predetermined amount of light is internally received, external photosensitive means situated with respect to said flash means for receiving light during said preparatory flash operation, and preparatory electrical circuit means electrically connected with said external means and said internal means for integrating the amount of light received by said external means during said preparatory flash operation and for terminating the integration when said predetermined amount of light is received by said internal means, the integrated value achieved at the termination of integration being retained for subsequent use during the main flash illumination, and wherein said internal means includes a light activated silicon controlled rectifier, a first preparatory integration capacitor electrically connected to a gate of said light activated silicon controlled rectifier and causing said light activated silicon controlled rectifier to conduct when a predetermined amount of integration voltage is reached, and first switching circuit means electrically connected to said light activated silicon controlled rectifier to conduct when said light activated silicon controlled rectifier conducts, and wherein said external means includes an external photosensitive diode located in parallel with said first switching circuit means, and wherein said preparatory electrical circuit means comprises the combination of second switching circuit means electrically connected to said diode to conduct when said diode conducts, and second preparatory integration capacitor means electrically connected to said second switching circuit means for providing an integration voltage corresponding to the light received by said diode, whereby when said first switching circuit means conducts, said second preparatory integration capacitor means terminates integration.

Claim 11

The combination of claim 8 and further comprising main electrical circuit means electrically connected with said external means and including third integration capacitor means, differential amplifier means, the voltage across said second preparatory integration capacitor means and the voltage across said third integration capacitor means being compared by said differential amplifier means, and flash terminating means electrically connected with the output of said differential amplifier means and providing in response to a comparison an output which terminates the flash means during the main flash operation.

Claim 12

In a camera, flash means for providing prior to film exposure a given total amount of preparatory flash illumination and for then providing main flash illumination during film exposure, photosensitive means for responding to said preparatory flash illumination and preparatory electrical circuit means electrically connected with said photosensitive means for achieving therefrom an electrical quantity corresponding to less than the total amount of preparatory flash illumination actually provided by said flash means for subsequently determining the duration of the main flash illumination required for proper exposure, flash terminating means electrically connected with said flash means for terminating the operation thereof during main flash illumination, and main electrical circuit means electrically connected between said preparatory electrical circuit means and said flash terminating means for automatically actuating the latter to terminate the operation of said flash means during main flash illumination in accordance with said electrical quantity.

Claim 13

In a camera, flash means for providing prior to film exposure a given total amount of preparatory flash illumination and for then providing main flash illumination during film exposure, photosensitive means for responding to said preparatory flash illumination and preparatory electrical circuit means electrically connected with said photosensitive means for achieving therefrom an electrical quantity corresponding to less than the total amount of preparatory flash illumination actually provided by said flash means for subsequently determining the duration of the main flash illumination required for proper exposure, flash terminating means electrically connected with said flash means for terminating the operation thereof during main flash illumination, and main electrical circuit means electrically connected between said preparatory electrical circuit means and said flash terminating means for automatically actuating the latter to terminate the operation of said flash means during main flash illumination in accordance with said electrical quantity.

Claim 14

The combination of claim 10 and wherein said flash terminating means is electrically connected only between said main electrical circuit means and said flash means for operating only during main flash illumination.

Claim 15

The combination of claim 10 and wherein said photosensitive means includes an external photosensitive unit used during both preparatory and main flash illumination and internal photosensitive unit situated in the camera and operating only dUring preparatory flash illumination.