Automatic exposure time control for cameras

Claim 2

In a camera, an objective, external photosensitive means for receiving light which is external to said objective, electrical means electrically connected with said external photosensitive means for automatically determining exposure time at least partly according to the light received by said external photosensitive means, actuation of said electrical means by said external photosensitive means alone having inherent inaccuracies due to the difference between light received by said external photosensitive means and light which has passed through said objective as well as the difference, if any, between the image angle of said external photosensitive means and the image angle of said objective, and internal photosensitive means for receiving the light which has passed through the objective internally thereof, said internal photosensitive means being electrically connected with said electrical means for providing a compensating signal which compensates at least partly for said inaccuracies inherent in actuation of said electrical means by said external photosensitive means alone.

Claim 3

The combination of claim 1 and wherein said electrical means includes a capacitor electrically connected between said external and internal photosensitive means for introducing into said electrical means the difference between the light received by said external photosensitive means and the light received by said internal sensitive means.

Claim 4

The combination of claim 2 and wherein said electrical means includes a capacitor switch electrically connected with said capacitor and a control switch electrically connected with said external photosensitive means, said capacitor switch and Control switch normally being connected in series between said external and internal photosensitive means for normally maintaining said capacitor in a position for receiving a signal corresponding to the difference between the light received by said external and internal photosensitive means, and shutter-actuating means and a camera shutter to be actuated thereby, said shutter-actuating means coacting with said capacitor and control switches for first actuating said capacitor switch to disconnect said capacitor from said external and internal photosensitive means and connect it, to the remainder of said electrical means and for then actuating said control switch to connect said external photosensitive means to the remainder of said electrical means, said shutter-actuating means actuating said camera shutter simultaneously with actuation of said control switch.

Claim 5

The combination of claim 3 and wherein said electrical means includes a timing capacitor connected with said external photosensitive means when said control switch is actuated by said shutter-actuating means simultaneously with the camera shutter, current-control transistor means connected electrically with said first-mentioned capacitor when said capacitor switch is actuated by said shutter-actuating means, trigger transistor means connected electrically with said timing capacitor and current-control transistor means for providing a trigger signal according to the timing capacitor as influenced by said external photosensitive means, and said current-control transistor means, as influenced by the differential stored in said first-mentioned capacitor, electromagnetic means for maintaining the shutter open as long as said electromagnetic means is energized, and switching transistor means connected with said electromagnetic means for maintaining the latter energized as long as said switching transistor means remains conductive, said switching transistor means being operatively connected to said trigger-transistor means to be rendered non-conductive in response to a trigger signal from said trigger-transistor means, so that when said switching transistor means becomes non-conductive said electromagnetic means becomes unenergized and the shutter closes to terminate the exposure.

Claim 6

The combination of claim 4 and wherein a potentiometer is situated in said electrical means between said current-control transistor means and said trigger-transistor means for introducing into the electrical means an exposure-determining factor different from exposure time.

Claim 7

The combination of claim 4 and wherein said trigger-transistor means is electrically connected directly with said external photosensitive means in parallel with said timing capacitor by said control switch when the latter is actuated by said shutter-actuating means.

Claim 8

The combination of claim 4 and wherein said current-control transistor means is electrically connected directly with said external photosensitive means by said control switch when the latter is actuated by said shutter-actuating means.

Claim 9

The combination of claim 4 and wherein an adjustable diaphragm is situated in the path of light received by said external photosensitive means for influencing the amount of light received thereby, and meter means electrically connected between said current-control transistor means and said adjustable diaphragm for automatically adjusting the latter according to a signal received from said current-control transistor means as influenced by said first-mentioned capacitor, to influence the amount of light received by said external photosensitive means in accordance with a compensating signal determined by the light received by said internal photosensitive means.

Claim 10

The combination of claim 1 and wherein an adjustable means coacts with said external photosensitive means for influencing the light received thereby according to an exposure-determining factor different from exposure time, and a variable resistor means forming part of said electrical means and conNected with said adjustable means to be adjusted simultaneously therewith for eliminating from said electrical means a false influence which otherwise would be introduced by actuation of said adjustable means.

Claim 11

The combination of claim 9 and wherein said adjustable means is a diaphragm, and a second diaphragm coacting with the objective for determining the exposure aperture, said second diaphragm being electrically connected with the diaphragm which forms an adjustable means to bring about simultaneous adjustment of both diaphragms, and said electrical means including a second variable resistor means electrically connected with said second diaphragm to be actuated simultaneously therewith for eliminating a false influence which otherwise might be introduced by actuation of said second diaphragm.

Claim 12

The combination of claim 9 and wherein a diaphragm coacts with said objective for setting the exposure aperture, said electrical means including a pair of variable resistors both actuated simultaneously with said diaphragm for adjusting the electrical means according to the setting of said diaphragm, and a third variable resistor actuated by said adjustable means which coacts with said external photosensitive means.