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
![](/library/attachments/ServiceWareImages/LDImages/SolutionAnswer/550EX%20Speedlite/ratio%202%20slave.jpg)
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
![](/library/attachments/ServiceWareImages/LDImages/ratio%20on.jpg) |
On the sender unit, press the <SEL/SET> button and select <RATIO>
- Pressing the <SEL/SET> button changes the selection in the following loop:
![](/library/attachments/ServiceWareImages/LDImages/SolutionAnswer/550EX%20Speedlite/ratio%203%20slave%202.jpg)
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Press the <-> button to select <RATIO> on A:B
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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.
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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.
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- 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
![](/library/attachments/ServiceWareImages/LDImages/SolutionAnswer/550EX%20Speedlite/ratio%20scale.jpg)
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