US 4,394,079 A · Photographic flash device operatively responsive to the luminance of an object to be photographed to prevent overexposure

Abstract

A photographic flash control device for enabling the firing of a flash light when the luminance level of an object to be photographed is less than a predetermined level and for inhibiting the firing of the flash light when the luminance of an object to be photographed is brighter than a predetermined level. A DC-DC converter generates an oscillating signal for charging a main discharge capacitor. A photoconductive device inhibits the generation of the oscillating DC signal when the luminance level of the object to be photographed exceeds a predetermined level. If the main discharge capacitor is charged to a predetermined firing level, firing of the flash light by a triggering circuit will be inhibited if a sudden change in illumination causes the luminance of the object to be photographed to exceed the level where a flash light is necessary.

Claims12

Dependent claims

A photographic flash device operatively responsive to the luminance of an object to be photographed comprising:

a DC power source including:
a DC-DC converter;
means connected to the primary winding of said DC-DC converter for repetitively switching said converter ON and OFF to generate an oscillating DC signal, said switching means including a transistor having a collector connected to the primary winding of said DC-DC converter, a base, and an emitter;
a main discharge capacitor coupled to said DC-DC converter for charging thereby;
a flash light discharge tube coupled to said main discharge capacitor;
means for triggering said flash light discharge tube in response to the charging of said main discharge capacitor to a predetermined level;
and
means for detecting the luminance of the object to be photographed and for terminating the charging of said main discharge capacitor if said detected luminance is greater than a preselected value, said detecting means being connected between said base and said emitter of said transistor.

5 more elements

A photographic flash device operatively responsive to the luminance of an object to be photographed and for use with a camera including means for positioning a flash light device into a retracted, nonoperative position and into an extended, operative position, the photographic flash device comprising:

a DC power source;
charge storage means coupled to said DC power source for charging thereby;
means for triggering said flash light device when the charge level of said charge storage means exceeds a predetermined charge level;
means for detecting the luminance level of an object to be photographed and for inhibiting the charging of said charge storage means when the detected luminance level is greater than a predetermined luminance level;
and
means for driving the positioning means to control the positioning of said flash light device in said operative position responsive to the detection of the luminance of the object to be photographed being less than said predetermined level and in said nonoperative position responsive to the detection of the luminance of the object to be photographed being greater than said predetermined level.

3 more elements

Dependencies are inferred from the claim text.

Photographic flash device operatively responsive to the luminance of an object to be photographed to prevent overexposure

Life of this patent

Photographic flash device operatively responsive to the luminance of an object to be photographed to prevent overexposure

Life of this patent

Abstract

Claims12