Canon EOS-1 - Manual (Page 17)

High-precision focusing
Conventional At systems can
only detect vertical lines. A newly-
developed cross-type BASIS solves
this problem by also being able to
detect horizontal lines. Use of this
cross-line system greatly reduces the
number of difficult subjects for AF.
It also results in much more precise
focusing, particularly when using
lenses with maximum apertures of
f/2.8 or larger, and works extremely
well with difficult to focus wide-
angle lenses, improving speed and
accuracy.
Moving subject predictive control
The EOS-Ts AF system is better at
tracking moving subjects. When
using ultrasonic motor lenses or the
newly developed L series lenses, AF
tracking continues until just before
exposure begins. Depending on the
speed of the moving subject, the
camera automatically activates the
focus predict system.
Improved low-light performance
The AF system operates comfort­
ably at low-light levels down to EV-1
(With lenses having maximum aper­
tures of f/2.8 or larger and film
speed set at ISO 100). This means the
EOS-1 focuses quickly and precisely
in dark hallways, dimly lit rooms,
gardens at twilight — situations
where human vision is limited.
Having accurate AF operation avail­
able for these low-light situations
creates new possibilities for sophisti­
cated available-light photography.