Download pdf - Aperture & Shutter Speed.ppt

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• The focal length of the lens determines the angle of view

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43mm 43mm

28mm

43mm

28mm

135mm

Telephoto or Long Lenses

Bring things closer

A fast long lens. Note the large diameter front element designed for gathering lots of light.

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Wide angle or wide lenses

Enable you to get more into the picture

50mm lens 17mm lens

Features of wide angle lenses

•Gives a wide angle of view

•A tendency to distort near the edges

•Increases the apparent relative distance

between objects

•More

•susceptible to flair

•Small and light compared to long

lenses

•Increased depth of field

Wide angle

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Wide angle

Distortion

Lenses are described as fast or slow

A fast lens is one that allows lots of light to pass through it. It will be physically wider in diameter than a slow lens. Probably bigger, heavier and certainly more expensive than the slow lens.

However

It may not be as sharp when used wide open

As the boundaries of performance are pushed so the

price increases (usually exponentially)!

The aperture

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Aperture

The variable diameter diaphragm used to control the amount of light passing through the lens and on to the CCD or sensor

Termed f number

or

Stops

Each stop is or twice as much light

and is derived from a mathematical formula describing the amount of light passing through the lens for a given period of time

f stop values are represented in the following way

f 2 f 2.8 f 4 f 5.6 f 8 f 11 f 16 f 22 f32

Each one of these values is half or twice the amount of light

f 2 being the maximum and f 32 the minimum in this sequence

Typical standard values

How the aperture works

Aperture

Shutter Speed

Controls the length of time that the sensor is exposed to light

The shutter may be configured as a variable width blind

Travelling across the sensor face at a set speed. The width of the blind governing the relative amount of time the sensor is exposed to light. The wider the blind width the greater the amount of light reaching the sensor. These are called focal plane shutters.

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1/125th. sec

1/30th. sec

Conversely the blind may be of set width but the speed with which it travels across the sensor variable.

1/30th. sec

1/125th. sec

or

A simple shutter may consist of a sprung plate which passes across the lens

A more complex shutter might allow the speed of the passing plate to be varied.

More sophisticated shutters have variable speed diaphragms which open and close.

These are called leaf shutters

Copal Press camera shutter

The relationship between shutter & aperture

•Both control the amount of light reaching the sensor

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•The aperture effects the depth of field



•The aperture effects the depth of field

•That is the zone of focus

How much is in focus in front and behind the

object



•The shutter affects movement




•It can stop movement to keep objects sharp




•It can stop movement to keep objects sharp

•Or allow movement for effect

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f 4 f 5.6 f 8 f 11 f 16

1/250 1/125 1/60 1/30 1/15

Aperture to shutter speed

The exposure is expressed as a combination of the two.

i.e.f8 at 1/60