Canon SPEEDLITE 540EZ Service Manual page 33

Part 2: Technical Information
2.2 540EZ Compatibility With Pre-EOS Cameras
In a word, TTL automatic flash operation is possible with the T90, but with other
cameras the flash must be used manually using guide number calculations.
Supplementary explanations are provided below.
(1) With AE SLRs equipped with a CCC contact on the accessory shoe, the
synchronous shutter speed is automatically set upon completion of flash
charging.
(2) With the T90, which is equipped with TTL automatic flash control circuitry,
both A-TTL and TTL automatic flash exposure are possible.
However, since data communications between the camera and flash differ from
the EOS system, operation is restricted as follows:
¢ Auto zoom, f/No display and coupling range display are not provided on the
540EZ.
e Flash exposure compensation from the flash unit side can be set on the
540EZ, but it does not function.
e Second-curtain synchronization can be set but does not function.
(3) When attached to the T80 and previous cameras which are not equipped with
a TTL automatic flash control function, the 540EZ fires at full power because
the camera does not send a stop signal to the flash unit.
— Manually set the aperture according to the value calculated from the "Guide
number + Shooting distance" formula.
In manual firing mode, the 540EZ operates at the output level indicated in the
display (1/1~1/128).
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