exposure triangle sounds daunting but it really isn't, partly because
you can see the results of using it instantly with a digital camera
and because when you catch the photo that you want, you quickly
realise the power of the knowledge you have and how it fits into
every picture you take.
simply, it is the relationship between only 3 settings on your
camera. The aperture, shutter speed and ISO. These 3 are the
fundamental building blocks of every single image you will take and
each one affects the other directly. Used correctly, they will allow
you to control a scene and get that great photo almost every time.
Lets look at the 3 elements of the 'triangle' one by one.
shutter is extremely fine metal or fabric vanes that move out of the
way and allow light into the camera when you press the shutter button
and instantly close again. You can vary how fast they move and
therefore for how long light comes in. A typical digital camera will
have speeds from 1/8000th of a second, right up to 30 seconds and
these are measured in what we call 'stops'. A stop is simply a
notch,or a mark, it's a way of measuring the next step up or down and
each 'stop' is either double, or half, the speed.
explain that a bit better. The accepted standards for shutter speeds
s, 1/500 s, 1/250 s, 1/500 s, 1/250 s, 1/125 s, 1/60 s,1/30 s, 1/15
s, 1/8 s, 1/4 s. You can see that the numbers half each time. Each
one is called a stop so if you have 1/1000th of a second set on your
camera, and you change it to 1/500th of a second you've turned your
shutter speed down 1 stop. Using the stop as a measurement is useful
because everyone knows what it means, but also because the other two,
aperture and ISO are also measured in this way, and you'll see the
benefit of this later.
camera will probably have more speeds on than this as I said.So if
you're on 1/1000th of a second and you go up one stop you'll get
1/2000th, another stop is 1/4000th and yet another stop is 1/8000th
of a second. Each time you are halving the amount of time that the
shutter is open.
of a second is extremely fast, so you need a lot of light to ensure
that enough comes into the camera to make a picture in that short
space of time. 30 seconds is quite a long time so this is useful when
it's quite gloomy as it allows the small amount of light that is
there enough time to come into the camera. If your camera is set to
1/8000th of a second and you want to set it to 30 seconds, how many
stops difference is that?
1/4000, 1/2000, 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30,1/15, 1/8,
1/4, 1/2, 1sec, 2sec, 4sec, 8sec, 16sec, 30 seconds. So that's 18
steps to get down to 30 seconds, so that's 18 stops difference.
a bright sunny day you might use 1/1000th or 1/500th of a second
shutter speed, as there is so much light that you don't need the
shutter to be open for very long. If it's inside on a dull day
there's not much light so you might have to use 1/30th, or even as
low as 1/8th of a second. There's less light around, so you need the
shutter to be open longer to allow light in for a longer period.
Remember of course that the longer the shutter is open, the more risk
there is of blur from you moving!
of shutter speed:
say you wish to take photos of a surfer and you want to freeze the
action. They are moving fast so you need a fast speed of maybe
1/500th or even 1/1000th of a second. You may be covering a football
match so again you need a fast speed, this time 1/1000th or even
1/2000th of a second to freeze the motion of the players and the
you may want to take photos of a flag fluttering in the wind. You use
maybe 1/100th of a second so that there is some movement in the flag.
Perhaps you want to take a photo of a fast car but with background
blurred? So you 'follow' the car with your camera( called panning)
and use maybe 1/50th of a second. This keeps the car sharp as you are
moving the camera with it, but the background is blurred. You can see
then why you would need to chose a specific shutter speed rather than
just choosing any old speed.
the shutter determines how long light is allowed to come into the
camera for, and is measured in stops, each one being either half or
double the one before. A slow speed allows you to have movement in
the picture, a fast one freezes all movement.
next part of the exposure triangle is aperture. Where shutter speed
determines how 'long' light comes into the camera for, the aperture
determines how 'much' light comes in. It's called an aperture because
it is precisely that, an aperture, or hole. This aperture is in the
lens and is varied by thin metal vanes which open and close, making a
hole smaller or bigger. On some lenses if you take them off the
camera and look through them as you change the aperture you can see
the vanes moving. On most modern digital cameras you have to set an
aperture, then press the 'depth of field' button(if your camera has
one). Check your user manual to find out where this is. When you
press the depth of field, or DoF button you can see the vanes in the
is usually stated as an 'f stop' and like shutter speeds there is an
accepted standard, these are shown as f stops, f2, f2.8,f4, f5.6, f8,
f11, f16 and f22. There are often more numbers on some lenses but
don't worry about this for the time being. Again just like shutter
speeds, an f stop is either half, or double the one before.
let's say you have f2 set on your lens. The 'lower' the number, the
'larger' the aperture, therefore the 'more' light comes in. f2 is
said to be wide open as the aperture or the vanes that determine the
size of the hole is very large at f2 and so lets in lots of light.
Because it lets in lots of light the shutter speed can be set faster,
so lenses with f2 or even smaller, are said to be 'fast' lenses. Many
zoom lenses might only have the lowest number off 5.6, so they're
said to be slow lenses, because you need to set a slower shutter
speed to let more light in.
a bright sunny day you might use f11 because there is so much light
that you need to restrict how much comes in. If you're inside on a
dull day you need to let more light in, so you open the lens up to
maybe f4, or even f2.8 in order to let more light in.
let's say you have our child in a park and y want to take a photo.
You would like the child to be sharp, but everything else in the
background is distracting. So you set your aperture at a number such
as f2.8 if you have it, or f4. At these numbers the amount of
distance that is in focus will be limited, depending as well on what
lens you're using. This is the Depth of Field or DoF that we
mentioned earlier. At f2.8 if you are focussed on the child's face
there will be almost nothing behind or in front of the child that
will also be in focus. The further away things are the less focussed
they will be. You can use this creatively. On the other hand you may
wish to take a photo of a garden where you want the whole scene to be
sharp. So you choose an aperture such as f16. This time when you
focus on where the child might have been, things are in focus for
many metres in front of and behind where you focus.
the aperture determines how much light is allowed to come into the
camera and like shutter speed is measured in stops, each one being
either half or double the one before.
down means making that the aperture is small so that you have lots in
focus, which oddly means you choose a bigger number,like f16. Opening
the lens up means making that the aperture is very small so not much
is in focus, such as f2.8 or f2.
does aperture and shutter speed affect each other?
may have realised something here. By having a longer shutter speed
you allow the light a longer time to come into the camera, so that's
useful on dull days. However, on dull days you can also set an
aperture of f2, which allows much more light in. If you are using a
slow shutter speed, maybe then you don't need quite as much light
in,so you can turn the aperture to f5.6. That's great for those slow
lenses! However if you have a fast lens you can use f2, and because
there's more light coming in you can set a faster shutter speed,which
means less chance of camera shake right?
hear you say but how do I determine what shutter speed and what
aperture to use? Well there's two things here. Firstly most digital
cameras have an exposure scale in the viewfinder. It's a lot of
little upright lines going along the bottom of the viewfinder
usually, but they may be at the top or even at the side. There's one
taller line in the middle and a little marker which runs underneath
these lines. The centre line denotes the point at which correct
exposure is set when the marker is on it.
sure your camera is in manual mode. Set the aperture to f8,and set
the shutter speed to 1/60th. Where is the little marker in relation
to the centre line? If it is not on the centre line then you are not
correctly exposing the image. If the marker is below or to the left
of the marker, it's too dark and the photo will be underexposed. If
it's to the right or above the marker, it's too bright and the image
will be over exposed.
speed determines how long light can get into the camera,so if your
marker is to the left or below the centre line and the image is under
exposed, you need light coming in for a longer time,so you need to
set the shutter speed one stop higher, or 1/30th. Set the shutter to
1/30th which if you remember doubles he amount of light coming in and
see if the exposure indicator now says that it is correctly exposed.
is of course another way to do this. If your photo is going to be
under exposed remember that making your aperture wider can let more
light in. So if your shutter speed is so slow already that hand
holding it might result in a blurred photo, you can open the aperture
up instead. If it was f8 like we said try setting it to
f5.6. Remember, this is one stop higher, so is letting double the
amount of light in.
your exposure is now correct you've learned two things: one is that
you can choose to open or close the lens to let more or less light in
so that you can keep a faster shutter speed to prevent blur. The
other is that bother aperture and shutter speed work in 'stops' so
that 1 stop more doubles the light/speed, and 1 stop less halves the
light/speed. You don't need that meter in the camera. If you open the
lens by one stop to let twice as much light in, you need to shorten
the shutter speed by one stop to halve the length of time light comes
in. So effectively, the numbers change, and yet the exposure remains
correct! There are some good reasons why this is useful which we'll
read about later on.
is an acronym that comes from film but there has been a new ISO
standard set out for digital cameras and it is used to describe how
'sensitive' the camera is to light. The main part of the camera that
responds to light is the sensor and this sits behind the shutter
ready to record the light in a scene when the shutter opens. This is
exactly what used to happen with film cameras except the film would
be exposed to light by the shutter, not the sensor. ISO was expressed
as 'speed' because if you had 'fast' film, about 800 ISO, it was
sensitive to light so you could get a fast shutter speed. 100 ISO
film was slow, as it was less sensitive to light so you had to use
longer shutter speeds.
the shutter opens light falls onto the sensor, the data about how
much light there is and what colours there are is recorded by the
sensor, processed by a chip and sent to the memory card, saved in the
format of a picture file. The sensor isn't more or less sensitive to
light as film was, it simply amplifies all light that falls onto it.
During that amplification it introduces 'noise', which is a grainy
characteristic of the image. 100 ISO is taken to be the most
desirable 'speed' as it needs the least amount of amplification and
therefore brings the lowest levels of noise. If you double that to
200, the light falling on the sensor is amplified by double the
amount, it's 1 stop extra. If you then set the ISO to 400, the amount
of amplification the sensor applies to the available light is doubled
yet again, 2 stops extra and doubled a third time if you set it to
800, which as you might guess, is 3 stops over ISO 100. Some cameras
can go up to 25,600 and even beyond. Again you see how ISO uses the
stops system in the same way as aperture and shutter speed do. It's a
simple doubling or halving each time doubles or halves the light
means the camera can work in darker conditions because the low light
that is available can be amplified so much. However the downside is
that as the sensor amplifies the light more and more, the quality of
the image the light would have formed decreases. 'Noise',similar to
film grain, becomes extremely intrusive and there are other problems.
However despite these problems you can see how this might be useful.
take a quick example as we did in aperture.
say your camera meter has suggested that a correct exposure would be
f8 at 1/50th. You need to leave your aperture at f8 for the DoF but
as you're using 100mm lens you need to use 1/100th of a second
shutter speed. If you raise your shutter speed to let light in for
longer the image will be over exposed. You can't use f16 so, you
change your ISO from 100 to 200. The sensor will have to amplify the
light a little but only a little, but that raising of ISO 1 stop
means as the light is being amplified 1 stop, you can make the
shutter speed 1 stop faster, ie: 1/100th. Job done.
can see from this example how the relationship between aperture,
shutter speed and ISO is fundamental to all of your photography as it
is the basis for all of your creative control whether you use flash
units, daylight or studio lamps.
does all this fit together?
now we know all 3 elements of the exposure triangle work in stops and
that for all of them 1 stop up is double the value and 1 stop down is
half the value.
know that if you change one, the other two will also have to change.
Her are some examples:
have lots of light and are taking photos of birds on a bird table.
Lots of light means a low ISO, or low light amplification. So set ISO
to 100 and then say you want a fairly fast shutter speed to freeze
the birds. So choose 1/1000th of a second. Then adjust your aperture
until the meter says your shot is correctly exposed.
want to select one of the birds by focussing out everything else. So
leave your ISO at 100 and choose f2.8 for minimal DoF. Check the
camera's meter and adjust your shutter speed until you get correct
is a very simplified introduction. There are other things to take
you use a 50 mm lens, setting aperture of f2.8 might mean you get
everything from the front of the face to the back of the head in
focus. The depth of field is about 6 inches. If you use a 200mm
lens,the same aperture would mean you only get a depth of field of
about 2 inches so your focus is even more important. Depth of field
is affected by the focal length of a lens and by your distance from
a high shutter speed may let light in for a shorter period but it can
also mean that there is less detail recorded. Perhaps for a landscape
you could try a longer exposure, by stopping down the lens little?
may see much different numbers given for stops on your camera and in
other tutorials. This is because most now use half stop numbers, and
even 1/3 stop numbers. The principle of using stops is exactly the
actual practising of all of this is fun and within the normal sphere
of taking photos but the basic exposure triangle is the most
important primer you will need as it covers the fundamental elements
of taking photos.
hope you got something useful from this document.