Canon 540EZ - Manual (Page 14)

6. Recycle Time
Short recycle times are invaluable in fast-changing situations where quick
shooting is necessary. For this purpose, the 540EZ provides a quick firing
mode in addition to its normal, full-power firing mode. In quick firing
mode, the flash can be fired before it is fully charged to provide fast recy­
cle times. You can tell whether the flash is operating in normal firing
mode or quick firing mode by the color of the ready lamp, as described
below.
• For details on recycle times and guide numbers in normal and quick firing modes,
refer to page n in the Specifications section.
• Normal firing
Normal, full-charge firing is possible when the ready lamp lights red.
• Quick firing
When the A-TTL mode is set and the camera is set to single-frame
shooting, the pilot lamp turns green and quick firing is enabled.
What is a guide number?
The guide number of a flash unit is a numerical indicator of its light output capaci­
ty. The appropriate shooting distance or lens aperture required for proper flash
exposure can be calculated from the guide number using the following formulas:
Guide number -r- shooting distance (m) = proper aperture value
Max, shooting distance = guide number largest lens aperture
• The film speed is usually assumed to be ISO 100 when stating guide numbers.
At different film speeds, the guide number increases or decreases accordingly.