Canon EOS 20D Service Manual page 65

General Information
[AF]
12. With the EF 70-200mm f/2.8L USM
attached with an Extender, use the
center AF point to focus.
13. If you use the AI SERVO AF mode
with flash, the AF-assist beam will
not be emitted by the camera or
external Speedlite.
[Flash]
14. Regardless of the C.Fn-09 setting,
the FEB sequence will follow the
Speedlite's setting.
15. With EOS-dedicated Speedlites other
than the EX-series, autoflash is not
possible.
16. When using the Landscape or Sports
mode, do not use an EOS-dedicated,
external Speedlite.
17. When using the built-in flash,
detach any lens hood from the lens.
18. Do not connect a 250V or higher
high-voltage flash unit to the PC
terminal.
19. Do not connect a high-voltage flash
unit to the hot shoe.
Although focusing is possible with all 9 AF
points, the focusing precision can be
guaranteed only with the center AF point.
Since AF-assist beam does not match
predictive AF very well.
ONE-SHOT AF is recommended for flash
photography.
The C.Fn-09 setting applies only to AEB and
WB-BKT. (During flash exposure
compensation, the external Speedlite's
setting overrides the camera's setting. To
avoid confusion, this rule has also been
applied to FEB.)
The camera does not have a flash exposure
sensor compatible with A-TTL/TTL. (The
flash will not fire in the A-TTL/TTL
autoflash mode. Use the manual flash mode
instead. EOS-dedicated Speedlites not
having a manual flash mode and wired,
multi-Speedlite accessories cannot be used.
The flash would fire at all times and the
photo might not come out as you desire.
This is to prevent flash coverage cut-off.
A voltage of 250V or higher will damage the
PC terminal's internal circuitry.
It may not fire.
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