Canon AE-1 PROGRAM Instructions Manual page 35

The AE-l PROGRAM's viewfinder is especially
bright to facilitate viewing and focusing. It dis-
plays only the necessary information, using a
Light-Emitting Diode (LED) system of illumina -
tion . The degree of LED illumination changes in
four stages depending on the brightness of the
subject. When the subject is brighter, the LED
brightness is slightly higher; it is slightly lower
with a darker subject. Thus the LED maintains an
almost consistent degree of brightness to the
human eye.
35
Correct exposure is provided by the Central
Emphasis Averaging System , which reads the
entire viewing area with emphasis on the central
portion where the subject is most likely to be
placed . Since a new type of split-image range-
finder is used in the center of the viewfinder, the
brightness of the split-image rarely changes
even when using a lens whose maximum aper-
ture is f / 5.6 or smaller.