Canon EOS 55 Service Manual page 51

L-V-BASIS
Focusing Points
C-V-BASIS _
Fig. 2-6 Focusing Point Sensors
2) AF Sensor and Multi-BASIS
Part 2: Technical Information
R-V-BASIS
C-H-BASIS
The multi-BASIS uses a cross-type sensor like the EOS 500/Rebel X's multi-BASIS.
It
also uses the same control system to improve focusing performance for low-contrast
subjects. It enables focusing of very low contrast 90:80 subjects.
3) Faster Focusing Calculation and AF
1. Faster AF
With a clock speed of 16 MHz and a minimum access time of 0.0625 µs, the
super microcomputer enables high-speed calculations. The AF speed is conse-
quently faster than the EOS 5/A2E's.
2. Calculation process
In the One-Shot AF mode with automatic focusing point selection, the calculation
speed is the same as with the EOS 5 / A2E.
In the AI Servo AF mode with automatic focusing point selection and predictive
AF, the calculation speed is the same as with the EOS 5/ A2E. Since the center
focusing point is given priority, the subject must be placed at the center of the
viewfinder for autofocusing. The left and right focusing points are on standby all
the while. So if the subject moves to the left or right focusing point, the respec-
tive focusing point takes over for AI Servo AF. When Eye-Controlled Autofocus is
used, Servo AF applies.
With an EF 300mm
f
/2.8 lens attached, the predictive AF feature can track a
subject moving toward the camera at 40 km/h down to a distance of
12
meters.
In the AI Focus mode, either the One-Shot AF or AI Servo AF mode is used.
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