Exposure amount control device

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.

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.

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.

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.