Specifications

III. NEW AND IMPROVED DESIGN FEATURES 10
A
ll-New Autofocus System
im
age processing, which can be turned on or off by the user, takes the same amount of
time a
s the exposure. Even though the EOS 20D with its noise reduction feature turned
off
produces less noise during long exposures than the EOS 10D, the activation of dark
fr
ame subtraction produces maximum image quality during long exposures with the 20D.
C
ompared with the Canon EOS 10D, the 20D features
greater AF detection precision, improved focusing per-
formance in low light and an improved focusing point lay-
out. The 20D has a totally new 9-point, CMOS, AF sensor.
This new design, seen for the first time in the 20D, pro-
vides full cross-type performance with maximum aper-
tures as small as f/5.6, yet it achieves up to 3 times the
standard focusing precision when used with EF Lenses featuring maximum apertures
larger than or equal to f/2.8. This is made possible by a new AF sensor design that fea-
tures two sets of vertical line-sensitive linear pixel arrays for the central cross-type
focusing point. When an f/2.8 or faster lens is used, the camera automatically switches
to a wider baselength measurement system to maximize autofocusing precision.
The new central cross-type sensor also has a dual line vertical component with twice as
many pixels for horizontal line detection as the 10D, resulting in more consistent focus
detection. Similarly, the off-center focusing points feature a baselength that is 30%
longer than the type used in the 10D, resulting in greater focusing precision for those
points as well when compared to previous EOS models. This is the first time that an
f/2.8 compatible sensor has been used on a camera other than the EOS-1 and EOS-3
series of cameras.
The other eight AF points are single-axis sensors that are sensitive to maximum apertures
as small as f/5.6. Four of those points are near a golden section point, in keeping with
classical theories of harmony, proportion and balance in composition. Use of these four
points should help to make well-balanced, and perhaps lovely, images.
Th
anks to the new sensor, focusing sensitivity in low light has been improved by 1 stop
compared with the EOS 10D. The brightness range for focusing is now EV –0.5 to 18.
The new AF unit is configured to minimize ghosting. Unwanted light is blocked by
narrowing the field of view and the separator uses a low-reflectance material. Additionally,
the AF optics and framework have a low-line expansion coefficient and a low moisture
absorption coefficient that make them highly resistant to temperature and humidity
changes, thus maintaining maximum performance under all shooting conditions.
The EOS 20D has three autofocus modes in addition to manual focus: One Shot AF
(AF operation stops and locks when focus is achieved), AI Servo AF (tracks subject
movement and focuses continuously until the start of the exposure), and AI Focus AF
(automatic switching between One Shot and Predictive AI Servo). In the Basic Zone