Canon EOS DIGITAL REBEL XTI Service Manual page 79

４）AI SERVO AF
⑴Predictive AF
With an EF300mm f/2.8L IS USM lens, the camera can focus-track a moving subject
approaching at 50 kph up to about 10 meters/32.8 feet away.
The predictive AF calculation is the same as with the EOS KISS DIGITAL N.
⑵Still subjects
As with the EOS 30D, the lens drive keeps still when focusing a still subject with AI
SERVO AF. If the subject begins to move, the camera can begin to focus-track the subject
immediately since the focus detection is conducted continuously.
⑶ Pressing the shutter button suddenly
As with the EOS 30D, if you press the shutter button completely in one quick stroke (no
halfway pressing), the lens will focus, if possible, before the picture is taken. If focusing is
not possible, the picture will be taken anyway to give priority to taking the picture.
５）Automatic AF point selection
With the same algorithm used by the EOS 30D, a high probability of selecting the desired
AF point automatically is attained.
６）Manual AF point selection
The selection procedure is the same as with the EOS KISS
DIGITAL N. With the EOS D REBEL XTI / EOS 400D D, you
can select the AF point on the LCD monitor's large display
(Fig. 015).
７）AF-assist beam
As with the EOS KISS DIGITAL
N, the AF-assist beam is a series of
stroboscopic flashes. The working
range is approx. 4 meters/13.1
feet at the center and approx. 3.5
meters/11.5 feet at the other 8 AF
points.
Table 004 AF-assist beam with External Speedlites
Automatic
Speedlite
Selection
Center
580EX ○ ○
550EX ○ ○
430EX ○ ○
420EX ○ ○
380EX ○* ○
220EX ○* ○
ST-E2 ○ ○
* Focus can be achieved only with the center AF point.
10
Technical Information
Fig. 015 AF point selection
screen
Manual Selection
Top/ Left/ Mid-left/
Bottom Right Mid-right
○ ○ ○
× ○ ○
○ ○ ○
○ ○ ○
× × ×
× × ×
× ○ ○