Canon SPEEDLITE EL-1 Advanced User's Manual page 76

Metered Manual Flash Exposure
When using an EOS-1D series camera, the flash exposure level can be manually set before
shooting. This is effective when you are close to the subject. Use a 18% gray reflector
(commercially available) and shoot as follows.
1.
Configure the camera and Speedlite settings.
2.
Focus on the subject.
3.
Set up an 18% gray reflector.
4.
Press the <
Set the shooting mode of the camera to <
Set the Speedlite's flash mode to <
Focus on the subject manually.
Place the gray reflector at the subject's position.
Aim the camera so that the entire spot metering circle within the
viewfinder center is over the gray reflector.
>, <
The Speedlite will fire a preflash and the required flash output for the
correct flash exposure is retained in memory.
On the right side of the viewfinder, the exposure level indicator will
show the flash exposure level against the standard exposure.
>.
>, or < > button (
76
> or < >.
).