Reference Guide

page J
dispersion, or UD glass. Less expensive than fluorite elements,
" UD glass elements are found in all L-Series telephoto lenses.
This includes the 4 fluorite lenses mentioned above plus the 80-
200mm f/2.8L and the 200mm f/l.8L.
FOCUS PREDICTION
Although conventional AF systems can perform well with most still
or slow moving subjects, they lose their effectiveness as the
speed of motion increases. In response to this, Canon has
developed a new technique called Focus Prediction, available in
the EOS 630 and the EOS-l.
Instead of taking a single AF reading of a moving subject, Focus
Prediction takes multiple readings at a fast rate. These readings
are passed through a special calculator which uses the 3 most
recent readings to determine subject speed and direction. Using
this data and allowing for the inevitable time lag caused by
moving the reflex mirror out of the light path before the shutter
can open, Focus Prediction drives the lens to focus at the point
where the subject will be during the actual exposure, ensuring
maximum sharpness.
Focus Prediction is effective in both Single Frame and Continuous
shooting. The maximum framing rate with Focus Prediction depends
on the equipment that is used, as shown in the following list:
EOS-l (Standard Body): 2.0 frames per second
EOS 630 .............. : 2.5 frames per second
EOS-l (w/Booster El).: 4.5 frames per second
INTELLIGENT PROGRAM AE
Program AE means fully automatic exposure. In other words, the
camera selects both shutter speed and aperture values according
to a mathematical program built into the camera's microprocessor.
Canon introduced Program AE in 1978 with the A-I. Though highly
advanced at the time, this initial implementation did not take
lens focal length into account. As a result, photos taken with
telephoto lenses could occasionally be blurred due to camera
shake caused by slow shutter speeds.
Intelligent Program AE solves this problem by automatically
reading the encoded focal length and maximum aperture information
from the lens and setting an appropriate shutter speed/aperture
combination. A special encoder for zoom lenses divides the focal
length range into 32 increments, providing unequaled precision.
Intelligent Program AE sets a minimum shutter speed value of
l/focal length at maximum aperture according to the light level,
thus taking full advantage of both focal length and maximum
aperture information. Even variable aperture zoom lenses are
taken into account, with the EOS setting a constant aperture
value throughout the zoom range whenever possible .
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