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18
Concepts in Photography
ISO sensitivity
The exposure of an image is determined by the sensitivity of the camera.
This sensitivity is based on international film standards, known as ISO
standards. On digital cameras, this sensitivity rating is used to represent
the sensitivity of the digital mechanism that captures the image.
ISO sensitivity doubles as the number doubles. For example, an
ISO 200 setting is capable of capturing images at twice the speed of an
ISO 100 setting. However, higher ISO settings can result in “noise”—small
specks, spots, and other phenomena in a photo that give the shot a noisy
or dirty appearance. As a general rule, it is best to use a low ISO setting
to prevent noise in your photos, unless you are shooting in darkened
environments or at night.
Changes in the quality and brightness according to ISO sensitivity
Because a low ISO sensitivity means the camera will be less sensitive to
light, you need more light to have an optimal exposure. When using a low
ISO sensitivity, open the aperture more or reduce the shutter speed to
allow more light to enter the camera. For example, on a sunny day when
light is abundant, a low ISO sensitivity does not require a slow shutter
speed. However, in a dark place or at night, a low ISO sensitivity will
result in a blurry photo. Therefore, it is recommended to increase the ISO
sensitivity by a moderate amount.
A photo captured with a tripod and
high ISO sensitivity
A blurred photo with a low ISO sensitivity