Learning about Exposure – The Exposure Triangle
The three elements are:
– the measure of a digital camera sensor’s sensitivity to light
– the size of the opening in the lens when a picture is taken
- ShutterSpeed – the amount of time that the shutter is open
It is at the intersection of these three elements that an
image’s exposure is worked out.
Most importantly – a change in one of the elements will impact
the others. This means that you can never really isolate just one of
the elements alone but always need to have the others in the back of
Many people describe the relationship between ISO, Aperture and
Shutter Speed using different metaphors to
help us get our heads around it.
Let me share three.
A quick word of warning first though – like most metaphors – these are
far from perfect and are just for illustrative purposes:
Imagine your camera is like a window with shutters that open and
Aperture is the size of the window. If it’s bigger more light gets
through and the room is brighter.
Shutter Speed is the amount of time that the shutters of the window
The longer you leave them open the more that comes in.
Now imagine that you’re inside the room and are wearing sunglasses
(hopefully this isn’t too much of a stretch).
Your eyes become desensitized to the light that comes in (it’s like alow ISO).
There are a number of ways of increasing the amount of light in the
room (or at least how much it seems that there is.
You could increase the time that the shutters are open (decrease
you could increase the size of the window (increase aperture) or you
could take off your sunglasses (make the ISO larger).
Ok – it’s not the perfect illustration – but you get the idea.
Another way that a friend recently shared with me is to think about
digital camera exposure as being like getting a sun tan.
Now getting a suntan is something I always wanted growing up – but
unfortunately being very fair skinned it was something that I never
All I did was get burnt when I went out into the sun. In a sense your
skin type is like an ISO rating.
Some people are more sensitive to the sun than others.
Shutter speed in this metaphor is like the length of time you spend
out in the sun.
The longer you spend in the sun the increased chances of you getting a
tan (of course spending too long in the sun can mean being over
Aperture is like sunscreen which you apply to your skin. Sunscreen
blocks the sun at different rates depending upon it’s strength.
Apply a high strength sunscreen and you decrease the amount of sunlight
that gets through –
and as a result even a person with highly sensitive skin can spend more
time in the sun (ie decrease the Aperture and you can slow down shutter
speed and/or decrease ISO).
As I’ve said – neither metaphor is perfect but both illustrate the
interconnectedness of shutter speed, aperture and ISO on your digital
Update: A third metaphor that I’ve heard used is the
Garden Hose (the width of the hose is aperture, the length that the
hose is left on is shutter speed and the pressure of the water (the
speed it gets through) is ISO.
Bringing It All Together
Mastering the art of exposure is something that takes a lot of
practice. In many ways it’s a juggling act and even the most
experienced photographers experiment and tweak their settings as they
Keep in mind that changing each element not only impacts the exposure
of the image but each one also has an impact upon other aspects of it
(ie changing aperture changes depth of field,
changing ISO changes the graininess of a shot and changing shutter
speed impacts how motion is captured).
The great thing about digital cameras is that they are the ideal
testing bed for learning about exposure.
You can take as many shots as you like at no cost and they not only
allow you to shoot in Auto mode and Manual mode –
but also generally have semi-automatic modes like aperture priority and
shutter priority modes which allow you to make decisions
about one or two elements of the triangle and let the camera handle the
A lot more can be said about each of the three elements in the
exposure triangle. Check out other relevant posts on the topic at:
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