Canon EOS 30D Instruction Manual

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The ISO speed is a numeric indication of the sensitivity to light. A higher 
ISO speed number indicates a higher sensitivity to light. Therefore, a 
high ISO speed is suited for low light and moving subjects. However, 
the image may look more coarse with noise, etc. On the other hand, a 
low ISO speed is not suited for low light or action shots, but the image 
will look cleaner. 
The camera can be set between ISO 100 and 1600 in 1/3-stop 
increments.
The ISO speed is set automatically within ISO 100-400.
ISO 100-1600 can be set in 1/3-stop increments. With C.Fn-08 [ISO 
expansion
] set to [1: On] (p.170), “H” (ISO 3200) can also be set.
1
Press the <R> button. 
(9)
X
The current ISO speed will be 
displayed on the LCD panel.
 
In a Basic Zone mode, “Auto” will be 
displayed on the LCD panel.
2
Setting the ISO Speed.
 
While looking at the LCD panel or 
viewfinder, turn the <5> dial.
g
 Setting the ISO SpeedN
ISO Speed in the Basic Zone Modes
ISO Speed in the Creative Zone Modes
 
At higher ISO speeds and higher ambient temperatures, the image will 
have more noise.
 
High temperatures, high ISO speeds, or long exposures may cause 
irregular colors in the image.