Canon T5i / 700D Experience
97
two properly exposed yet very different looking portraits of a subject. In one shot the
subject and the background behind them are all in focus and in another the subject is in
sharp focus but the background behind them is softly out of focus. These differences
are not dependent on chance or other circumstances, but can always be determined by
the photographer and controlled through the choice of shutter speed and/ or aperture
setting in conjunction with the ISO setting.
Aperture is the opening in the lens that controls the amount of light hitting the sensor.
You can control the size of this opening in Aperture Priority AE mode (Av), and in
Manual Exposure mode (M). A large opening lets in a lot of light and a small opening
lets in a little light.
Shutter Speed is the amount of time that the shutter, which is the curtain in front of the
sensor, is open. If it is open a long time, a lot of light hits the sensor and if it is open a
short time less light hits the sensor. You can control the shutter speed in Shutter Priority
AE mode (Tv), and in Manual Exposure mode (M).
ISO is the sensitivity of the sensor, its ability to grab the light that lands on it. A low ISO
is not very sensitive to light and does not grab much (relatively), and a high ISO is very
sensitive to light and grabs all it can.
Figure 93 - Shutter Speed setting, Aperture setting, and ISO setting all shown on the top
row of the Shooting Settings screen on the rear LCD Monitor. Because the camera is in
Aperture Priority (Av) Mode, the arrows around the Aperture setting indicate you can
turn the Main Dial to adjust this setting.
As you can see, they all relate to the light hitting the sensor. For a proper exposure, one
that isn’t too light or too dark, the right amount of light needs to hit the sensor and it
needs to be at the right sensitivity to accept that light. So all three work together to
control and accept the amount of light that hits the sensor (see Figure 93). In Auto+
Mode, the camera chooses what it thinks is the best combination of these three settings
and creates a proper exposure. So, for example, a small opening (aperture) will need
more time (shutter speed) to let in the necessary amount of light based on the current
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