Canon EOS-1D X Mark III Advanced User's Manual page 197

Note
Metered manual flash exposure
This feature enables you to set the flash exposure level manually for close-up shots.
Using a Speedlite with manual flash mode and a standard 18% gray card, follow
these steps.
1. Configure the camera and Speedlite settings.
• On the camera, set the shooting mode to <
• On the Speedlite, set the firing mode to Manual flash.
2. Focus on the subject.
3. Set up the standard 18% gray card.
• Place the card at the position of the subject.
• Place the card so that it fills the entire spot metering circle in the
viewfinder or on the screen.
4. Press the <
5. Set the flash exposure level.
• Adjust the Speedlite's manual flash level and the camera's aperture value
to align the flash exposure level with the standard exposure index.
6. Take the picture.
• Remove the card and shoot.
> button ( ).
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