Canon 40D - EOS 40D DSLR, Service Manual

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Technical Information
6
1.4 AF System
１）Newly-developed AF sensor
With all cross-type sensors, improved AF detection precision,
and extreme-defocus compatibility, the newly-developed AF
sensor (Fig. 009) has much higher performance than the EOS
30D's AF sensor (Table 004). With the EOS 40D, the minute
shifting the point of focus due to the difference in the spectral
characteristics of the light source is corrected automatically and
more stable autofocusing is enabled. This feature is especially
effective for artificial light sources. The positioning of the AF
points (Fig. 010) is almost the same as with the EOS 30D's AF
sensor.
Table 004 Specifications Comparison of AF Sensors
EOS 40D EOS 30D
Cross-type sensors 9 (All cross-type) 1 (Center)
High-precision f/2.8
compatibility Cross-type sensor
at center
Vertical-line
sensitive at center
Extreme-defocus
compatibility
Yes ―
EV range [EV] -0.5 - 18
Sensor pitch [ m] 14.4 16
⑴All cross-type AF points
All the AF points have a cross-type line sensor for f/5.6. Both vertical- and horizontal-
line sensitive focus detection works with any AF point for stable focusing.
⑵Improved AF detection precision (Fig. 011)
・ Cross-type focusing at f/2.8
Previously, the sensor for f/2.8 was only vertical-
line sensitive. But now, for the first time, it is both
vertical- and horizontal-line sensitive. The focusing
is thereby more sensitive. Also, with the sensor
pitch made smaller from 16 m to 14.4 m, the
detection performance is higher.
＊ Excluding the EF50mm f/2.5 MACRO and EF28-80mm f/2.8-4L
USM lenses.
・ Two-line focusing with horizontal-line sensitive sensors
The upper center, center, and bottom three
horizontal-line sensitive sensors are in a two-line,
zigzag configuration. With this double focusing system,
inconsistent focusing detection is reduced.
⑶Extreme defocus compatibility
By using the entire two-line focusing sensors described above, a subject in extreme
defocus can be detected and AF control is quick and easy. (Fig. 011)
Fig. 009 AF sensor
Fig. 010 AF point position and spacing
Two-line sensors
in zigzag pattern
Cross-type sensor at f/2.8
Focusing sensors
for extreme defocus
Fig. 011 Sensor configuration