Photography Basics - Exposure
In SLR (single lens reflex) camera photography:
☼ Exposure refers to the amount of light captured by a sensor in a
camera to produce a photograph
☼ There are four elements of exposure:
scene light, sensitivity, intensity and time
☼ They are dependant on each other to produce a successful
photograph.
1.
Scene light
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2.
The amount of light that is available at the scene to make a picture
Sensitivity
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Sensitivity refers to the amount of light that the camera’s image sensor requires
the ISO (International Organization for Standardization) setting determines how
sensitive the image sensor is to light.
The higher the ISO number, the more sensitive the sensor is to light and the less
light that’s needed to make a picture.
The lower the ISO setting, the finer the image grain
3200 ISO
100 ISO
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Digital photography usually has the following ISO sequence:
ISO 100, 125, 160, 200, 250, 320, 400, 800 and up.
Each ISO setting is twice as sensitive to light as the previous setting.
o Outdoors with sun use: 200 ISO
o Indoors use: 400 ISO
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3.
Intensity - The role of aperture
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The lens aperture is the size of the lens opening. It determines the intensity
(amount) of light that strikes the image sensor.
Lens aperture is an adjustable opening on the lens that allows more or less light to
reach the sensor.
Wide
aperture
narrow
aperture
▪
Aperture is shown as a set of “f-stops”
(focal stops) on the lens:
 The smaller the f-number the larger
the aperture opening which allows
more light to reach the film or image
sensor.
▪ When you increase or
decrease the f-stop by one
setting, it doubles or halves
the exposure.
For example, twice as
much light reaches the
image sensor at f/1.4
as at f/2.
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Aperture and Depth of Field
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Depth of field is the zone of sharp focus.
The further you are away from the subject the greater the depth of field will be.
Aperture is one factor that affects depth of field:
 small in focus zone because more light
is allowed through the lens
 corresponding aperture: f/1.4, f/2.8, f/4, f/5.6
 large or deep in focus zone because less light is
allowed through the lens

corresponding aperture: f/8, f/11, f/16, f/22
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Shallow Depth of Field
Deep Depth of Field
Description
Corresponding aperture
small in focus zone because f/1.4, f/2.8, f/4, f/5.6
more light is allowed through
the lens
Large or deep in focus zone f/8, f/11, f/16, f/22
because less light is allowed
through the lens
4. Time - The Role of Shutter Speed
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Shutter speed controls how long the lens “curtain” stays open to let light strike the
image sensor - it determines the length of time light enters the camera.
Shutter speeds are shown in fractions of a second.
Shutter speeds from slow to fast are:
Bulb (shutter stays open as long is shutter button is pressed),
1 second, ½, ¼, 1/8, 1/15, 1/30, 1/60, 1/125, 1/500, 1/1000 etc.
one fifteenth of a second
▪
When you increase or decrease a shutter speed by one setting, it doubles or
halves the exposure. For example, twice as much light reaches the image
sensor at 1/30 of a second as at 1/60 of a second.
▪
Shutter speed determines whether you can freeze a moving subject or allow it
to be blurred in a picture:
To capture motion
To freeze motion:
blur:
set shutter speed to 1/60
 try 1/30 second or
or faster
slower
 use a tripod
REMEMBER: scene light,
sensitivity,
intensity and time
are dependant on one another
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