aperture & shutter speed.ppt
DESCRIPTION
photo, imaging, camera, dpi, lccTRANSCRIPT
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• The focal length of the lens determines the angle of view
2
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.
3
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
4
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 relationship between shutter & aperture
•Both control the amount of light reaching the sensor
•The aperture effects the depth of field
The relationship between shutter & aperture
•Both 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 & aperture
•Both control the amount of light reaching the sensor
•The shutter affects movement
The relationship between shutter & aperture
•Both control the amount of light reaching the sensor
•The shutter affects movement
•It can stop movement to keep objects sharp
The relationship between shutter & aperture
•Both 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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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