Canon EOS 20D Instruction Manual page 141

3 Custom Function Settings N
C.Fn-01
You can change the function assigned to <0>. With C.Fn-01-1/2, you
can press <0>, then look at the LCD panel and set <5> directly.
0: Default (no function)
1: Change quality
Enables you to select the recording quality directly.
2: Change parameters
Enables you to select the processing parameter directly. "PA-P1,
P2" stand for Parameter 1 and 2, and "PA-1" to "PA-3" stand for
Set 1 to 3. "PA-B/W" is for monochrome.
3: Menu display
Gives the same function as the <M> button.
4: Image replay
Gives the same function as the <x> button.
C.Fn-02
0: Off
1: On
Reduces noise in exposures 1 sec. or longer. After the picture is
taken, the time required for noise-reduction processing will be the
same as the exposure time. During the noise reduction
processing, "buSY" will be displayed and shooting will not be
possible.
C.Fn-03
0: Auto
1: 1/250sec. (fixed)
Sets the flash sync speed to 1/250 sec. in the aperture-priority AE
(Av) mode. (Against dark backgrounds such as the night sky, the
subject's background will look dark.)
SET function when shooting
Long exposure noise reduction
Flash sync speed in Av mode
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