Canon EOS REBEL T7i Instruction Manual page 134

Lenses and Usable AF Points
Group G
Autofocusing with 27 points is possible. (Not possible with all 45 AF
points.) Large Zone AF (manual selection of zone) cannot be selected
in AF area selection mode. During automatic AF point selection, the
outer frame marking the AF area (Area AF frame) will be different from
45-point Automatic selection AF.
Group H
Autofocusing is possible only with the center AF point.
If the maximum aperture is slower than f/5.6 (greater than f/5.6 but not

exceeding f/8), focus may not be achieved with AF when shooting low-
contrast or low-light subjects.
If the maximum aperture is slower than f/8 (greater than f/8), AF is not

possible during viewfinder shooting.
134
: Cross-type AF point. Subject
tracking performance is superior and
high-precision focusing is achieved.
: AF points sensitive to horizontal
lines.
: Disabled AF points (not displayed).
: Cross-type AF point. Subject
tracking performance is superior and
high-precision focusing is achieved.
: Disabled AF points (not displayed).