Exposure amount control device

• US 4,375,321 A
• Filed: 02/04/1981
• Issued: 03/01/1983
• Est. Priority Date: 02/08/1980
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Suzuki, Ryoichi, Tokuda, Ryuji, Hirohata, Michio
• Primary Examiner(s): Perkey, William B.
• Application Number:
  US06/231,044
• Time in Patent Office: 755 Days
• Field of Search: 354/49-51, 354/59, 354/234, 354/235, 354/238, 354/42, 354/26-30, 354/246, 354/247, 354/230, 354/60 L, 354/24
• US Class Current: 396/229
• CPC Class Codes: G03B 7/083 for control of exposure time
• CPC Class Codes: G03B 7/093 for control of exposure time

Abstract

An exposure control device for use with a set of shutter blades which form a principal opening through which an exposure is made, includes a member which forms an auxiliary opening of a predetermined aperture before the shutter release starts. Upon release of the shutter, the auxiliary opening closes and thereafter opens fully in accordance with opening movement of the shutter blades so that the amount of light incident through the auxiliary opening is measured to control the exposure time through the principal opening. A time constant circuit which determines the time the shutter blades form the principal opening is arranged to start operation by detecting the variation of incident light measured through the auxiliary opening when the auxiliary opening has the predetermined aperture before shutter release, and when the auxiliary opening is brought into the closed state immediately after shutter release.

Claims

1. An exposure control device arranged so that an amount of light incident through an auxiliary opening is measured to control exposure through a principal opening formed by a set of movable shutter blades, the auxiliary opening having a predetermined aperture before a shutter release and being arranged to open in corresponding relation with the opening movement of the shutter blades and after the auxiliary opening has fully closed, comprising:

light measuring means for measuring the incident light through the auxiliary opening;

a time determining circuit responsive to an amount of light measured by the light measuring means for determining an exposure time and for producing as its output a closing signal to start a closing movement of the shutter blades;

timer means for starting an action when the opening movement of the shutter blades is started by the shutter release and for producing as its output a count start signal when a length of time necessary for the auxiliary opening to become fully closed from a pre-open state has ended; and

switching means for starting operation of the time determining circuit in response to the count start signal.

3. An exposure control device arranged so that an amount of light incident through an auxiliary opening is measured to control exposure through a principal opening formed by a set of movable shutter blades, the auxiliary opening having a predetermined aperture before a shutter release and being arranged to open in corresponding relation with the opening movement of the shutter blades and after the auxiliary opening has fully closed, comprising:

light measuring means for measuring the incident light through the auxiliary opening;

detecting means for detecting the open or the closed state of the auxiliary opening in response to the amount of light measured by the light measuring means;

a time determining circuit responsive to the amount of light measured by the light measuring means for determining an exposure time and for producing as its output a closing signal to start a closing movement of the shutter blades;

signal producing means for producing a count start signal when the detecting means detects the closed state of the auxiliary opening after the shutter release and for stopping the production of the count start signal when said closing signal is produced; and

switching means for starting an operation of the time determining circuit in response to the count start signal.

2. An exposure control device in accordance with claim 3, wherein the timer means stops production of the count start signal when the closing signal is produced.

4. An exposure control device arranged so that the amount of light incident through an auxiliary opening is measured to control exposure through a principal opening formed by a set of movable shutter blades, the auxiliary opening having a predetermined aperture before a shutter release and being arranged to open in corresponding relation with the opening movement of the shutter blades and after the auxiliary opening has fully closed, comprising:

light measuring means for measuring the incident light through the auxiliary opening and producing an output;

expanding means for expanding the output of the light measuring means;

detecting means for detecting the open and the closed state of the auxiliary opening in response to the output of the expanding means;

a time determining circuit responsive to the amount of light measured by the light measuring means to determine an exposure time;

signal producing means for producing a count start signal when the detecting means detects the closed state of the auxiliary opening after the shutter release;

switching means for starting operation of the time determining circuit in response to the count start signal;

said signal producing means including first signal forming means for providing a first operation signal in response to the shutter release;

second signal forming means for providing a second operation signal when the detecting means detects the closed state of the auxiliary opening;

gate means connected to the first and the second signal forming means for producing the count start signal in response to the first and the second operation signals;

a driving circuit for driving the shutter blades in response to the shutter release, and means for disabling the driving circuit in response to the output of the time determining circuit;

the first and the second signal forming means include flip-flops arranged to be reset when the driving circuit is disabled.

5. An exposure control device arranged so that the amount of light incident through an auxiliary opening is measured to control exposure through a principal opening formed by a set of movable shutter blades, the auxiliary opening having a predetermined aperture before a shutter release and being arranged to open in corresponding relation with the opening movement of the shutter blades and after the auxiliary opening has fully closed, comprising:

light measuring means for measuring the incident light through the auxiliary opening;

detecting means for detecting the open and the closed state of the auxiliary opening in response to the amount of light measured by the light measuring means;

a time determining circuit responsive to the amount of light measured by the light measuring means to determine an exposure time;

signal producing means for producing a first count start signal when the detecting means detects the closed state of the auxiliary opening after the shutter release;

timer means arranged to be triggered in response to the shutter release for producing a second count start signal after the lapse of a predetermined time from a movement when an opening movement of the shutter blades has been started; and

switching means for starting the operation of the time determining circuit in response to one of the first and second count start signals.

6. An exposure control device in accordance with claim 5, further comprising:

a driving circuit for driving the shutter blades in response to the shutter release, and means for disabling the driving circuit in response to the time determining circuit.

7. An exposure control device arranged so that the amount of light incident through an auxiliary opening is measured to control exposure through a principal opening formed by a set of movable shutter blades, the auxiliary opening having a predetermined aperture before a shutter release and being arranged to open in corresponding relation with the opening movement of the shutter blades and after the auxiliary opening has fully closed, comprising:

light measuring means for measuring the incident light through the auxiliary opening and logarithmically compressing a value of light measured and producing the same as an output;

expanding means for logarithmically expanding the output of the light measuring means and generating an expanding current corresponding to the output of the light measuring means;

load means to which said expanding current is supplied, said load means varying a terminal voltage in correspondence with a variation of the expanding current;

detecting means for detecting the open and the closed state of the auxiliary opening in response to the terminal voltage;

a time determining circuit responsive to the amount of light measured by the light measuring means to determine an exposure time;

signal producing means for producing a count start signal when the detecting means detects the closed state of the auxiliary opening after the shutter release; and

switching means for starting operation of the time determining circuit in response to the count start signal.

8. An exposure control device in accordance with claim 7, wherein said load means includes a resistor.

9. An exposure control device in accordance with claim 8, wherein the signal producing means includes:

first signal forming means for providing a first operation signal in response to the shutter release;

second signal forming means for providing a second operation signal when the detecting means detects the closed state of the auxiliary opening; and

gate means connected to the first and the second signal forming means for producing the count start signal in response to the first and the second operation signals.

10. An exposure control device in accordance with claim 9, further comprising:

a driving circuit for driving the shutter blades in response to the shutter release, and means for disabling the driving circuit in response to the output of the time determining circuit.

11. An exposure control device in accordance with claim 10, wherein the first and the second signal forming means include flip-flops arranged to be reset when the driving circuit is disabled.