Download - Auto Focus Camera
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Auto focus camera
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Canon EOS camera
Canon EOS 620 and 650 electro optical system
Control areas:1. Film speed and number of exposure uses DX code
2. Measurement of receiving light through lens3. Integration of operation with flash
4. Setting of aperture and shutter speed fully automatic
5. Other modes appropriate setting
6. Automatic film advance, depth of field and focal length of
the lens is controlled
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Aperture The aperture controls the amount of light that reaches
a digital camera sensor.
An aperture acts much like the pupil of an eye. It
opens wider as light decreases to let in more available
light.
It gets smaller when light increases to reduce theamount of light entering the eye.
The faster the shutter speed, the larger the opening of the
lens and visa versa.
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Microprocessor used in EOS
systemMICROPROCESSOR FUNCTION
Main Control of automatic exposure
and focus sequence of control
Lens Data communication: control of focusing drive
Flash Data communication flashing
element control
Data back Data communication storage
camera drive control
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Actuators in EOS system
Actuators Function
Motor I Film transport
Motor II
Shutter & mirror actionMotor III Focusing drive
Motor IV Lens aperture drive
Motor V Flash zoom drive
Shutter magnet Exposure time control
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Sensor in EOS systemParameter sensed CommentsFocus Distance measurement
Focal length Encoder sense change in focal
length of a zoom lens
Lens drive Photoelectric sensor generates
pulses as lens rotates and focus
changes
Lens mounting Leaf switch
DX code Pins detect pattern on the outsideof film cassette
Back open/close Leaf switch
Film transport Movement of film generates series
of pulses
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Power supplies
Power source Function
Lithium battery Main power supply for body and lens
Alkaline battery Power supply for flash
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Leaf switch
The leaf switches is a two-way
deflecting switch. It has a soft, red vinyl,
non-abrasive casing.
The switch is normally open and isactuated by deflecting the leaf as shown
above. It remains closed until the
deflection force is removed.
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Exposure
Exposure is the total amount of light allowed to fall on the photographic
medium (photographic film or image sensor) during the process of taking a
photograph
Longer shutter speeds result in increased exposure
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autofocus
Autofocus (AF) really could be called power-focus,as it often uses a computer to run a miniature motorthat focuses the lens for you.
Focusing is the moving of the lens in and out untilthe sharpest possible image of the subject isprojected onto the film.
Depending on the distance of the subject from thecamera, the lens has to be a certain distance fromthe film to form a clear image.
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In focus
Forward focus
Rearward focus
Film plane
Sensor output
Narrow than
when in
focus
Wider than
when in
focus
Reference image spacing for in focus image
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Depth of field setting
Depth of field set can be set by focusing
on nearby object and then distant object
required depth of field is preset
When shutter is pressed focus is
automatically adjusted to value between
two preset value and the aperture is
adjusted to give maximum depth of field
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Focusing Drive
Two forms of drive are used:
1.Arc form drive
2.Ultrasonic motor Works based on lens microprocessor
using information received from main
processor
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Arc Form Drive
Uses brushless hall motor as actuator
Basically permanent magnet stepper
motor which uses hall effect sensor todetect position of rotor
Gears helps in transmitting drive from
motor to focusing mechanism
Uses helicoid or cam to drive lens along
optical axis thus changes
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Ultrasonic motor The ultrasonic motor ( USM ) is a new type of
solid state motor, which is driven by theultrasonic vibration of a piezoelectric transducer.
The ultrasonic vibration is transformed into
output torque (in rotary USM) Current applied to individual elements
expand or contract according to polarity of thecurrent
Helical wave produced transmitted to helicoidsto move focusing element
Compact, silent , low speed ,high torque
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Ultrasonic motor
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