Canon EOS-3 Instructions Manual page 91

An EOS-dedicated EX-series or EZ-series Speedlite makes flash
photography with the EOS-3 as easy as any AE mode. With an EX-series
Speedlite, E-TTL autoflash photography as well as wireless E-TTL multi-
flash photography is possible.
Speedlite 550EX will be used to describe the flash photography features
provided with the EOS-3. For details on Speedlite 550EX, see the
Instructions that come with it.
Flash Photography
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