The algorithm for automatic AF point selection in the EOS 40D is the same as the EOS
30D's. However, because all the AF points are now cross-type sensors, subject detection
is improved, making the AI SERVO AF subject-tracking performance better. Also, in the
One-Shot AF mode, the probability of capturing the subject as intended is increased.
The EOS 40D can use its built-in flash
as an AF Assist beam, by emitting a
series of flashes in low light. The
effective range is approximately
13.1 ft./ 4m at the center AF point
and approximately 11.5 ft./ 3.5m at
the eight off-center AF points.
Alternatively, certain accessory
Canon Speedlites, listed in the accompanying table, can emit an AF-assist beam that is
more discreet and covers a greater distance range.
As with the EOS 30D, one can use the Multi-controller or Main/Quick Control dial (C.Fn
III-3-1/2) to select the AF point while looking at the superimposed AF point in the
viewfinder or the LCD panel's AF point selection display. Also as with the EOS 30D, the
AF mode (One-Shot AF, AI Focus AF, AI SERVO AF) is selectable even in the Creative Zone
modes. The provision of an <AF-ON> button is a feature from the EOS-1D Mark III.
Alternately, one can press the shutter button half way to activate the AF.
The EOS 40D has the highest continuous shooting speed in its class † , approximately
Drive
6.5 fps in both One-Shot AF and AI SERVO AF modes. Despite increased resolution and
its concomitant increase in file size, this exceptional speed and a stable viewfinder
image are attained by combining several technologies. The powerful new DIGIC III
processor and 4-channel sensor readout have been mentioned here already. The buffer
memory of the EOS 40D is DDR SDRAM (double data rate, synchronous dynamic random
access memory) for high-speed reading and writing, whereas the EOS 30D used the
slower SDRAM.
† As of August 2007.
Of considerable importance, the EOS
40D uses a 2-motor system, one
dedicated to driving the mirror, and
one dedicated to cocking the shutter
speedily. Also, a stopper is incorpo-
rated to prevent the rebounding or
bouncing of the main mirror and
secondary mirror. This results in shorter
viewfinder blackout and a more stable
viewfinder image during continuous shooting.
III. PERFORMANCE
AF-assist Beam with External Speedlites
Automatic
Speedlite
Selection
Center
580EX II
Yes
Yes
580EX
Yes
Yes
550EX, ST-E2
Yes
Yes
430EX, 420EX
Yes
Yes
380EX, 220EX
Yes*
Yes
*Focus can be achieved only with the center AFpoint.
Two-Motor System
Manual Selection
Top/
left/
Mid-left/
Bottom
Bottom
Mid-right
Yes
Yes
Yes
Yes
Yes
Yes
N/A
Yes
Yes
Yes
Yes
Yes
N/A
N/A
N/A
12
Halaman Cetak