Canon EOS 20D Instruction Manual page 76

Tv
Shutter-Priority AE
In this mode, you set the shutter speed and the camera automatically
sets the aperture value to suit the brightness of the subject. This is
called Shutter-Priority AE. A fast shutter speed can freeze the motion of
a fast-moving subject and a slow shutter speed can blur the subject to
give the impression of motion.
* <Tv> stands for Time value.
Fast shutter speed Slow shu_erspeed
_'_I Set the Mode Dial to
<Tv>.
"2_,,j_ S et the desired shutter speed.
_ While looking at the LCD panel, turn
the <_> dial.
_ It can be set in 1/3-stop increments.
_J_!Focus the subject.
Press the shutter button halfway.
_ The aperture value is set automatically.
_S_ Check the viewfinder display and shoot.
_ As long as the aperture value is not
blinking, the exposure will be correct.
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