Nissin i40 Instruction Manual page 19

Flash Power Lock
When the back ground of the main subject is too bright, the camera's expo-
sure reading system adjusts the flash light intensity for such back ground
condition and it results in the main subject being underexposed. Or in case
the main subject is not placed in the center of the viewfinder, the flash picture
may result in the aimed targeted subject being under or over exposed.
You can lock the correct flash exposure for the targeted subject in such a
condition. This flash exposure pre-set remains locked in, even if you change
the aperture or zoom the lens in and out. This mode can only be set on the
camera.
FE lock
Focus the subject.
Aim the viewfinder center over the main subject and
press [ FEL ] button on some cameras.
Pre-flash is fired to pre-set the correct light amount
for the main subject.
Remarks: FEL only works on P, A, S & M mode.
(It depends on different type of camera, please check your camera instruction manual.)
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