Canon EOS 30D - Manual (Page 170)

3 Custom Function SettingsN
170
C.Fn-06 Exposure level increments
0: 1/3-stop
1: 1/2-stop
Sets 1/2-stop increments for the shutter speed, aperture, exposure
compensation, AEB, etc.
C.Fn-07 Flash firing
You can enable the built-in flash, external Speedlite, and non-Canon
flash connected to the PC terminal to fire.
0: Fires
1: Does not fire
This will disable the flash, but the AF-assist beam will still be
emitted. Note that whether or not the AF-assist beam is emitted is
dependent on the C.Fn-05 setting.
C.Fn-08 ISO expansion
0: Off
1: On
For the ISO speed, “H” (equivalent to ISO 3200) will be selectable.
The exposure level will be displayed in the viewfinder and on the LCD
panel as shown below.