Electronic trim control for dual-photodetector exposure control system

• US 4,717,935 A
• Filed: 08/09/1985
• Issued: 01/05/1988
• Est. Priority Date: 08/09/1985
• Status: Expired due to Term

• Current Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Original Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Inventors: Anacreon, Robert V.
• Primary Examiner(s): Adams, Russell E.
• Application Number:
  US06/764,205
• Time in Patent Office: 879 Days
• Field of Search: 354/417, 354/420, 354/422, 354/433, 354/434, 354/436, 354/437, 354/483, 354/79
• US Class Current: 396/161
• CPC Class Codes: G03B 7/095 for control of aperture
• CPC Class Codes: G03B 7/16 in accordance with both the intensity of the flash source and the distance of the flash source from the object, e.g. in accordance with the "guide number" of the flash bulb and the focusing of the camera

Abstract

A photographic camera of the type having a quench-type strobe, a scanning blade shutter and an exposure control system having separate ambient and artificial light sensing devices for establishing distinct signals representative of the amount of ambient and artificial light illuminating a particular scene, is provided with a unitary, manually operable electronic trim control for simultaneously varying both of these signals, to a limited degree, to compensate for variations in ambient scene lighting conditions and/or slight variations in the sensitometric characteristics of a photographic film. The electronic trim control system includes a common voltage source capable of providing a plurality of different magnitude trim voltages for regulating both ambient and artificial scene light levels. The electronic trim control couples a manually selected common trim voltage corresponding to desired ambient and artificial scene light levels to shutter and strobe control circuitry for ambient and strobe light control purposes.

Claims

1. An exposure control system for a camera having means for defining a film plane and an optical path for directing light from a scene onto photosensitive film located in the film plane, said exposure control system comprising:

a blade mechanism;

means for mounting said blade mechanism for displacement from an initial closed arrangement wherein said blade mechanism precludes scene light from being transmitted from the optical path to the film plane to an open arrangement wherein said blade mechanism defines a maximum size aperture to allow the passage of scene light to the film plane and then to a final closed arrangement wherein said blade mechanism again precludes scene light from being transmitted to the film plane;

drive means responsive to the actuation thereof for effecting the displacement of said blade mechanism from its initial closed arrangement to its said open arrangement and then to its final closed arrangement to define an exposure interval during which scene light is incident upon the film plane;

means for detecting and integrating substantially only the ambient scene light during the photographic exposure interval wherein said integrated ambient scene light is converted to a digital pulse count;

a flash discharge tube;

means for storing energy;

means for triggering said flash discharge tube at a select instant during said exposure interval so as to discharge the energy stored in said energy storage means through said flash discharge tube to provide an artificial flash of illumination;

means for detecting and integrating substantially only the artificial scene light during the photographic exposure interval wherein said integrated artificial scene light is converted to an analog voltage value; and

control means responsive to said digital pulse count reaching a select value for actuating said drive means to effect the displacement of said blade mechanism from its said open arrangement to its said final closed arrangement and to said analog voltage value reaching a select level for terminating the flash of artificial illumination, said control means further comprising manually actuable unitary trim control means for simultaneously increasing or decreasing said select value of said digital pulse count at which said drive means is actuated to effect the displacement of said blade mechanism from its said open arrangement to its said final closed arrangement and said select level at which said flash of artificial illumination is terminated.

2. An exposure control system for a camera having means for defining a film plane and an optical path for directing light from a scene onto photosensitive film located in the film plane, said exposure control system comprising:

blade means for selectively unblocking and blocking the optical path to define an exposure interval;

a quench strobe;

photodetector means for determining whether a high or low ambient scene light condition exists prior to the commencement of an exposure interval and for detecting and integrating scene light in correspondence with the amount of scene light incident upon the film during the exposure interval;

analog and digital control means responsive to said photodetector means determination of the ambient scene light condition for defining a first exposure control mode for use in high ambient scene light conditions wherein the optical path blocking movement of said blade means is commenced responsive to the integration of scene light reaching a first predetermined value, or for a defining a second exposure control mode for use in low ambient scene light conditions wherein said strobe is fired and then quenched prior to the commencement of the optical path blocking movement of said blade means responsive to the integration of scene light reaching a second predetermined value; and

manually actuable unitary trim control means for simultaneously electrically increasing or for simultaneously electrically decreasing said first and second predetermined values of integration.

3. The exposure control system of claim 2 wherein in said first exposure control mode said strobe is additionally fired and then quenched prior to the commencement of the optical path blocking movement of said blade means responsive to the integration of scene light reaching a third predetermined value, and said trim control means additionally includes means for electrically increasing or for electrically decreasing said third predetermined value of integration in simultaneous correspondence with the increasing or decreasing of said first and second predetermined values of integration.

4. The exposure control system of claim 2 wherein in said second exposure control mode said strobe is fired in response to the integration of scene light reaching a third predetermined value and then quenched in response to the integration of scene light reaching a fourth predetermined value and said trim control means additionally includes means for electrically increasing or for electrically decreasing said third and fourth values of integration in simultaneous correspondence with the increasing or decreasing of said first and second predetermined values of integration.

5. An electronic trim control for regulating film exposure in photographic apparatus of the type having means for defining a film plane and an optical path for transmitting light from a scene along the optical path to expose photosensitive film located in the film plane together with a system for controlling the firing of an electronic flash of the quench type, said apparatus comprising:

means for controlling the amount of scene light incident on the film plane, said scene light controlling means including a blade assembly movable along a predetermined path to define a range of apertures through which scene light must pass in reaching the film plane;

actuatable drive means for displacing said blade assembly between scene light blocking and unblocking positions to define an exposure interval;

first and second means for detecting and integrating scene light in correspondence with the scene light admitted to the film plane by said blade assembly during an exposure interval;

digital control means responsive to said first scene light detecting and integrating means for actuating said drive means to displace said blade assembly from its said unblocking position to its said blocking position so as to terminate said exposure interval and/or for firing said electronic flash;

analog control means reponsive to said second scene light detecting and integrating means to a selected light level for quenching the artificial light from said electronic flash; and

manually actuatable means for simultaneously changing the light level at which the blade assembly drive means is actuated to its said blocking position and/or said electronic flash is fired, and the light level at which the artificial light from said electronic flash is quenched.

6. The apparatus of claim 5 further comprising:

ranging means for determining subject distance and for providing an electrical range signal indicative of subject distance; and

means responsive to said electrical range signal for establishing an aperture size from said range of aperture sizes, for the purpose of firing the electronic flash, whereby said established aperture size corresponds to the distance that a particular scene being photographed is positioned from the camera.

7. The apparatus of claim 6 wherein said means for simultaneously changing said light levels includes a common voltage source that provides a plurality of different magnitude voltages and means for manually selecting a particular common voltage and said given levels are dependent upon the magnitude of a selected one of said different magnitude voltages.

8. The apparatus of claim 7 wherein said means for manually selecting a particular common voltage includes a manually actuatable electrical switch having a plurality of discrete switch positions and switch decoding means for generating an electrical signal representative of the particular switch position selected.

9. The apparatus of claim 8 wherein said means for changing the light level at which the blade assembly drive means is actuated to its said blocking position includes a digital comparator for establishing signals representative of scene light levels sensed by said first scene light detecting and integrating means and a digital multiplexer responsive to the electrical signals generated by said decoding means and to the signals established by said digital comparator for generating an electrical signal for initiating the actuation of said blade assembly to its said blocking position.

10. The apparatus of claim 8 wherein said means for changing the light level at which said electronic flash is quenched includes an analog multiplexer, responsive to the electrical signals generated by said switch position decoding means, for generating an electrical signal representative of a selected switch position and an analog comparator responsive to electrical signals representative of scene light levels established by said second scene light detecting and integrating means and to the electrical signals generated by said analog multiplexer for generating an electrical signal for quenching said electronic flash.

11. The apparatus of claim 5 wherein each of said first and second means for detecting and integrating scene light includes a photodiode.