The focal length of the lens determines the angle of view

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28mm

43mm

43mm

Telephoto or Long LensesBring things closer28mm

43mm

135mm

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

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Wide angle or wide lensesEnable you to get more into the picture

50mm lens

17mm lens

Features of wide angle lensesGives 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

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.

Distortion

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 Termed

for

number

StopsEach stop is or

twice

as much light

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

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 wayTypical standard values

How the aperture works

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 Aperture

The shutter may be configured as a variable width blind

Shutter SpeedControls the length of time that the sensor is exposed to light 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 Conversely the blind may be of set width but the speed with which it travels across the sensor variable. 1/30th. sec 1/30th. sec or

1/125th. sec

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

More sophisticated shutters have variable speed diaphragms which open and close. These are called leaf shutters

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

Copal Press camera shutter

The relationship between shutter & apertureBoth control the amount of light reaching the sensor

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The relationship between shutter & apertureBoth control the amount of light reaching the sensor The aperture effects the depth of field

The relationship between shutter & apertureBoth control the amount of light reaching the sensor 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 relationship between shutter & apertureBoth control the amount of light reaching the sensor The shutter affects movement

The relationship between shutter & apertureBoth control the amount of light reaching the sensor The shutter affects movement It can stop movement to keep objects sharp

The relationship between shutter & apertureBoth control the amount of light reaching the sensor The shutter affects movement It can stop movement to keep objects sharp Or allow movement for effect

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Aperture to shutter speed

f4 1/250

f 5.6 1/125

f8 1/60

f 11 1/30

f 16 1/15

The exposure is expressed as a combination of the two. i.e.f8 at 1/60

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