Canon EOS-1 - Manual (Page 6)

I. CAMERA FEATURES AND OPERATION 6
I. CAMERA FEATURES
AND OPERATION
EOS-1 class digital SLRs use an improved version of the 45-point Area AF CMOS sensor
unit that was originally introduced in 1998 with the EOS-3. The pixel density and layout
of sensor elements together with the patented design of the camera’s sub-mirror and
separator lenses gave rise to the name “Area AF” and resulted in a coverage area of 8 x
15mm with 45 selectable focusing points. (Previous EOS AF designs had 5 points or
fewer, all in a single line.) When the camera is oriented horizontally, all 45 points are
sensitive to horizontal or diagonal subject contrast with lenses featuring maximum
apertures as small as f/5.6. Six of the central-area focusing points become high-
precision cross-type sensors when the lens has a maximum aperture of f/2.8 or larger.
The central focusing point is high-precision cross-type with f/4 or faster lenses, and can
maintain single-line autofocus with maximum apertures as small as f/8. These factors
can come into play when choosing lenses and extenders for maximum AF performance.
The focusing area is 8 x 15mm regardless of the camera’s imaging format.
Consequently, AF coverage is proportionately larger with the EOS-1D and EOS-1D Mark II
with their 19.1 x 28.7mm imaging format than it is with the EOS-1Ds Mark II, EOS-1Ds,
EOS-1v or EOS-3 which feature 24 x 36mm coverage.
EOS 1Ds Mark II EOS 1D Mark II
Black: Horizontal line detection
sensors operational with
f/5.6 or faster lens.
Red: Vertical line detection sensors
operational with f/2.8 or
faster lens.
AF Frame
45-point Area AF Sensor