In this book and the animations apertures are represented by these realistic icons with a small aperture (left) and a large one (right).
In this book and the animations, shutter
speeds are represented by these symbolic icons with a fast shutter speed (left) and a slow one
(right). The cut out "pie slice" indicates how far an imaginary second hand would sweep.
Click to explore the relationship between the aperture and shutter speed.
When taking photos, one of the first decisions you make with many cameras is which exposure mode to use. As you've seen, your choice determines if you control the aperture or shutter speed. If your camera lets you select them, you can pair a fast shutter speed (to let in light for a short time) with a large aperture (to let in bright light) or a slow shutter speed (long time) with a small
aperture (dim light).
Speaking of exposure only, it doesn't make any difference which combination you use. But in other ways, it does make a difference, and it is just this difference that gives you some creative opportunities. Whether you know it or not, you're always balancing camera or subject movement against depth of field because a change in one causes a change in the other. Let's see why.
As you've seen, shutter speeds and apertures each have a standard series of settings called "stops".
- With shutter speeds, each stop is a second or more, or a fraction of second indicating how long the shutter is open.
- With apertures they are f/stops indicating the size of the opening through which light enters.
The stops are arranged so that a change of 1 stop lets in half or twice the light of the next setting. A shutter speed of 1/60 second lets in half the light that 1/30 second does, and twice the light of 1/125 second. An aperture of f/8 lets in half the light that f/5.6 does, and twice the light of f/11. If you make the shutter speed 1 stop slower (letting in 1 stop more light), and an aperture 1 full stop smaller (letting in 1 stop less light), the exposure doesn't change. (In all modes other than manual this happens automatically). However, you increase the depth of field slightly and also the possibility of blur from camera or subject movement.
- For fast-moving subjects you need a fast shutter speed (although the focal length of the lens you are using, the closeness of the subject, and the direction in which it's moving also affect how motion is portrayed). When photographing moving subjects shutter-priority mode is favored because it gives you direct control over the shutter speed.
- For maximum depth of field, with the entire scene sharp from near to far, you need a small aperture (although the focal length of the lens and the distance to the subject also affects depth of field). When photographing landscapes and portraits aperture-priority mode is favored because it gives you direct control over the aperture and depth of field.
Shutter Speed
30 seconds
4 seconds
2 seconds
1/2 second
1/4 second
1/30 second
Read Out
30”
4”
2"
2
4
30
On many cameras a quotation mark (") indicates full seconds and a fraction's denominator without a quotation mark indicates fractional
seconds. For example, 2" means 2 seconds and 2 means 1/2 second.
Exposure—Faucets & Buckets Analogy
One way to think of apertures and shutter speeds is to use the analogy of a faucet for the aperture and a timer for the shutter speed.
- When you open a faucet all the way, water gushes out so you fill a bucket in a very short time. This is the same as pairing a large aperture and fast shutter speed to let in bright light for a short time.
- When you open a faucet just a little, water trickles out and so it takes a much longer time to fill a bucket. This is the same as pairing a small aperture and slow shutter speed to let in dim light for a longer time.
No matter which combination you choose, the bucket is filled the same amount. Likewise, an image in a camera can be exposed the same amount by various aperture and shutter speed combinations while also controlling motion and depth of field.
1. We start with the aperture set to f/16 and the shutter speed to 1/30.
2. When you open the aperture one stop to f/11 the shutter speed has to decrease to 1/60 to keep the exposure the same. This change decreases depth of field slightly and freezes action better.
3. When you open the aperture another stop to f/8 the shutter speed has to decrease another stop to 1/125. This change decreases depth of field even more and freezes action even better.
Exposure —Seesaw Analogy
Another way to think of exposure is as a seesaw. As one child rises a given distance, the other falls by the same amount but their average distance from the ground is always the same. In photography, when you or the camera changes the aperture or shutter speed to let in more or less light, you or the camera must also change the other setting in the opposite direction to keep the exposure constant.
The illustrations below show how a change in the aperture setting must be matched by a change in the shutter speed and vice versa. As these offsetting changes are made, the exposure stays constant but depth of field changes slightly and subjects are more or less likely to be frozen.
1. Here the aperture is f/4 and the shutter speed is 1/125.
2. If you reduce the aperture one stop to
f/5.6 the shutter speed has to decrease one stop to 1/60 to keep the exposure the same.
Depth of field increases slightly and the possibility of subject or camera blur increases.
3. If you reduce the aperture one more stop to f/8 the shutter speed has to decrease one more stop to 1/30 to keep the exposure the same.
Depth of field increases even more as does the possibility of subject or camera blur.
