Year 10 Photography
Aperture and Shutter Speed Explained
Aperture and shutter speed are one of the most important concepts in photography and can
greatly affect the look of your photograph. Unfortunately almost all current compact digital
cameras have no specific settings to allow you to change the aperture and shutter speed directly.
This was not the case a few years ago with film cameras nor with more expensive digital compacts
and SLR cameras that are available today. These notes are written mostly for people with Digital
SLR (single lens reflex) or Compact cameras that have separate aperture and shutter speed
controls. BUT ALL cameras currently balance the amount of light being captured by adjusting
aperture of shutter speed.
Aperture
The aperture is the size of the lens opening. It controls the amount of light let in: a larger
aperture lets in more light, while a smaller aperture lets in less light.
An aperture is made out of aperture blades (usually five to nine) that form a rough circle to
control the size of the opening, and therefore the amount of light let in. The size of the opening is
usually referred to as the f stop and the number given is a ratio of the width of various openings.
Simply put, the smaller the f/number, the larger the opening. The following is a diagram of fstops. Each f-stop (or just a stop) lets in half the amount of light of the previous f-stop.
How can the size of this opening change what your picture looks like? Basically, a larger
aperture (lower f/number) will have your subject in focus, and everything in front of and behind it
blurry. A smaller aperture will have your subject in focus and everything in front of and behind it q
focused to an acceptable level. This is known as Depth of Field.
Large aperture (f/1.8). Short Depth of Field
Small aperture (f/16). Large Depth of Field
Summary: Large aperture, background out of focus; small aperture.
With a compact digital camera it is useful to know what the various automatic modes attempt to do
with the lenses aperture. E.g. Portrait Modes will use a large aperture to blur foreground and
background information. So if you want the background to be in focus as well as the person don’t
select portrait mode.
Shutter Speed
Shutter speed is a much simpler concept to understand. It's basically how long the sensor/film in
the camera is exposed to light. How long the shutter stays open depends on how much light there
is. For pictures with the same aperture setting, if the is shutter open too long, the picture will be
too bright, and if it's not open long enough, the scene will be too dark. Therefore, you control the
overall exposure (lightness and darkness) of the scene with both the aperture and shutter speed
control.
Modern compact cameras judge this for you and usually do a very good job. The shutter speed is
the other (usually larger) number that isn't the aperture value. Shutter Speeds are always
expressed as a fraction of a second and usually appear in the specifications for compact cameras
even if there are no controls to directly change the speed settings. As with the f stops used when
selecting an aperture each step up or down in shutter speed will also increase or decrease the
amount of light let in by one half.
What you can do with shutter speed is freeze motion with a fast shutter speed or capture
movement with a slow shutter speed. Flowing water looks silky smooth at speeds slower than 1/8th
of a second (with a tripod), while you can freeze water in time with fast shutter speeds. The same
thing goes for hip hop dancers.
The zoom setting on the camera can also greatly effect both how sharp the image is and how much
depth of field is available. In general when the lens is zoomed out you will need a faster shutter
speed as movement of the camera will become more apparent. Also when the lens is zoomed out
the depth of field will drop. Most modern cameras know the zoom setting you are using and will
automatically try to adjust the speed and aperture settings to give the best results. So if you are
taking a portrait and want the foreground and background nice and blurry, set the camera to
Portrait Mode and use zoom in. If you want a picture of someone with the background in focus as
well then use something like landscape mode and a wide angle setting on the zoom.
Summary: Fast shutter speed = freeze action. Slow shutter speed (w/ tripod if possible) = silky
flowing water, blurry backgrounds if panning.
How Aperture and Shutter Speed are Related
Aperture and shutter speed are bound together like an old married couple. For the same scene, if
you open the aperture, you increase the shutter speed, and if you close down the aperture, you
decrease the shutter speed. Think of a bucket of water with a hole in the bottom. If you have a
large hole in the bottom of the bucket (large aperture), water will drain out quickly (fast shutter
speed). Conversely, for the same amount of water, if you have a small hole in the bottom of the
bucket (small aperture), the water will drain out slowly (slow shutter speed).
Tripods and Flash Guns
When taking photos in poorly lit conditions or for close up (macro mode) work some form of
support for the camera to stop it moving is essential. Consider a tripod or similar device and use
the self timer function on the camera to eliminate possible shake as you press the shutter.
Built in Flash guns on all cameras are usually quite limited in how far they project sufficient light
so only use them for subjects that are within say 3 -5 metres of the camera. Flash guns can be
very useful to provide ‘fill in light’ particularly for subjects that are back lit or have disturbing
shadows. Check your camera settings and always experiment.