Canon SPEEDLITE 540EZ Service Manual page 26

Part 2: Technical Information
1.3 Pre-flash Operation
The A-TTL mode pre-flash operation of previous EZ series flash units (flash head
in standard position: infrared pre-flash; bounce position: visible pre-flash from
flash head) was used for (1) setting the flash control aperture in P mode, and (2)
triggering the out-of-coupling-range warning when the shooting distance was
greater than the throw of the flash in all AE modes. However, due to system
rationalization, the "(2) triggering the out-of-coupling-range warning" function has
not been included in EOS models released since the beginning of 1990 (refer to
page 1-11). The EOS-1N, too, is designed accordingly. As a result, when the EOS-
1N is combined with the 430EZ in Tv-AE and Av-AE modes, pre-flash occurs but
serves absolutely no purpose.
To avoid this unnecessary waste of energy, the 540EZ is designed to switch to TTL
mode and prevent pre-flash when the flash head is not in the standard position or
pointed 7° downward in the close-shooting position. The flash coupling distance
range at this time can checked by reading the bar graph in the 540EZ's LCD panel
(note: the coupling distance range is not displayed when the flash head is ina
bounce position).
* This pre-flash prevention function is carried out by the 540EZ. Therefore, even
when the 540EZ is combined with EOS bodies other than the EOS-1N, pre-flash
is not performed in A-TTL mode when the flash head is moved to a bounce
position.
Pre-flash eee eee in Each Exposure Mode
Exposure Pre-flash | Pre-flash operation |
mode 540EZ 430EZ
= ae
ae ae
ae ae
no
1.4 Post-exposure Flash Exposure Confirmation
In conjunction with the change described above in item 3 (cancellation of pre-flash
in A-TTL program mode when flash head is not in standard position), the 540EZ
adds a flash exposure confirmation function using a lamp that lights after the
picture is taken to indicate that the flash exposure was correct. The lamp lights if
the 540EZ's flash emission duration falls within a specified length of time (the
determination is made by the 540EZ's control circuitry). If the flash emission is
not cut off by the camera within the specified time period, the lamp does not light,
indicating that exposure was insufficient.
Visible pre-
flash from flash
head in bounce
position
2-4