Canon SPEEDLITE EL-1 Advanced User's Manual page 55

Note
If a correct exposure cannot be obtained when FE lock is performed, < > blinks in
the viewfinder. Move closer to the subject or open the aperture, and perform FE
lock again. You can also set a higher ISO speed and perform FE lock again when
using a digital camera.
If the target subject is too small in the viewfinder, FE lock may not be effective.
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