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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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