Samsung NX100 ユーザーズマニュアル

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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 low 
shutter speed. However, in a dark place or at night, a low ISO sensitivity 
and a fast shutter speed will result in a blurry photo.
A photo taken with a tripod and high 
sensitivity
A blurred photo with a low ISO sensitivity