Camera Education Department (RSS) December, 1999 Physics.

Camera

Education Department (RSS)December, 1999

Physics

Body

Lens system

Lens

Focusing ring

ApertureShutter

Film

Structure

A camera is a light-tight box in which a convex lens forms ….

Film

A real & inverted image

Object

FocusingThe focusing ring is turned to move the lens forwards or backwards.

Focusing ring

(What is the range of the

object distance?)

Focusing ring moves out

Short objectdistance

Long image distance

Near Object

Focusing ring moves in

Long objectdistance

Short image distance

Far Object

Aperture( f-number)Aperture controls the amount of lightentering the camera.

Aperture

The size of aperture is controlled by the diaphragm.

f-number selector

The smaller the f-number, the larger the aperture.

f =11

f = 8

f = 5.6

f = 4 f = 2.8

Shutter speedWhen the button is pressed, the shutter opens and shuts quickly to allow a small amount of light into the camera.

Shutter speed selector125 stands for 1/125 s

Shutter button

What is the fastest shutter speed of this camera?

A fast moving object requires a shorter shutter speed otherwise it will appear blurred.

The night scene should be taken with a slow shutter speed.

If aperture is doubled in area, the shutter speed should be halved.

Lenses with different focal lengths (f)

Wide-angle lenses

f = 20 - 35 mm

Normal lenses f = 50 mm

Moderate Telephoto lenses

f = 85 - 150 mm

Telephoto lenses

f = 150 - 500 mm

Zoom lenses Adjustable f

( e.g. from 28 to 135 mm)

The longer the focal length, the greater the image.

F

F

Object

Object

image

image

300 mm

8°

105 mm

23° 45°

50 mm

75°

28 mm

Angle of view

Focal length

The longer the focal length, the narrower the angle of view.

Comparison between an eye and a camera

Eye Camera

film

pupil

　 invert & real image

The ciliary muscles adjust the shape of

the lens to focus

retina

aperture

real & inverted image

Adjust lens-to film distance to focus

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