550EX Speedlite : How to set up wireless E-TTL Autoflash with Flash Ratio ON.
Article ID: ART123995 | Date published: 05/12/2015 | Date last updated: 11/29/2017


How to set up wireless E-TTL Autoflash with Flash Raio ON.


As shown in the figure below, the wireless E-TTL autoflash system described as an example consists of a sender unit set to sender flash OFF and two receiver units.
  • The receiver ID of the receiver unit on the camera's left is A
  • The receiver ID of the receiver unit on the camera's right is B
  • sender flash OFF is set for the sender unit
  • The camera (attached with the sender unit) and two receiver units properly positioned for the subject


Setting the Flash Ratio for Two receiver Units: A and B

With receiver unit A being the main flash and receiver B being the fill flash the flash ration (A:B) between these two receiver units can be set from 8:1 to 1:1 or from 1:1 to 1:8. (Thirteen 1/2 stop increments.) In terms of stops, the flash ratio can be adjusted from 3:1 to 1:1 or from 1:1 to 1:3. The E-TTL autoflash system then controls the total flash amount according to the flash ratio to obtain a correct exposure

On the sender unit, press the <SEL/SET> button and select <RATIO>
  • Pressing the <SEL/SET> button changes the selection in the following loop:

Press the <-> button to select <RATIO> on A:B
  • <RATIO> A:B will blinkPress the <SEL/SET> button again
  • Ratio A:B and - (flash ratio bar) will blink
  • In the left figure, the flash ratio bar indicates a flash ratio of 1:1

Press the <+> or <-> button to set the A:B flash ratio

  • Press the <+> button to move the flash ratio bar to the left or press the <-> button to move it to the right on the flash ratio scale.
Press the <SEL/SET> button to register the flash ratio
  • The flash ratio bar stops blinking and remains displayed
  • To indicate that a flash ratio has been set <RATIO A:B will remain displayed on the sender unit's LD panel.
  • During the setting procedure A:B and - blink for 8 sec. and then remain displayed. To make them blink again (so you can alter the flash ratio, press the <SEL/SET> button again
  • The flash ratios corresponding to the positions on the flash ratio scale are shown below

After you set the flash ratio and the flash ratio bar is displayed, you can still change the A:B flash ratio with the <+> and <-> buttons