Canon SPEEDLITE 540EZ Service Manual page 27

Part 2: Technical Information
1.5 Manual Flash Operation
1) Guide number selection and exposure setting
When the 540EZ is set to the M (manual) mode, TTL automatic flash operation is
canceled and the flash fires manually. The guide number (output level) in manual
mode peaks at full power (1/1), and can be reduced in eight steps to 1/2, 1/4,
1/8, 1/16, 1/32, 1/64 and 1/128 power. When combined with the manual zoom
function (including combined use with the wide panel), a total of 64 different guide
numbers are available.
The output level can be selected by pressing the "+" and "-" up/down buttons in M
mode.
Exposure settings are made by manually selecting the output level and manually
setting the lens' aperture. However, when the camera's shutter button is pressed
halfway (SW-1 ON), the bar indicator in the 540EZ's LCD panel displays the
distance necessary to achieve correct exposure (the flash unit's internal
microcomputer automatically calculates the distance for proper exposure by
dividing the selected guide number by the set aperture value), allowing the user to
carry out the following operations to verify the proper exposure settings:
(1) Autofocus the subject in one-shot AF mode.
(2) With the camera in AF lock mode, check the shooting distance in the lens'
distance scale window.
(3) With the camera in AF lock mode, check the shooting distance in the flash
unit's LCD panel.
(4) With the camera in AF lock mode, change the aperture or the manual output
level until the bar segment closest to the distance value checked in step (2) is
displayed in the flash unit's LCD panel.
However, to make sure that accurate exposure is achieved, we recommend using a
commercially-available flash meter to determine the optimum aperture value.
2) Manual continuous firing capacity
With the output level set to 1/4~1/128, the 540EZ's continuous shooting capacity
when used at high continuous shooting speeds is as shown in the following table:
Laminate Pack
* The maximum number of continuous firings is limited to 40 times to prevent the
flash head from overheating. After such use, the photographer should let the
flash head cool naturally (at room temperature) for at least 10 minutes before
reuse.
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