Canon EOS 20D Service Manual page 82

Technical Information
2) AF sensor
A newly-developed CMOS sensor serves as the AF sensor. It has a total of 8.84
megapixels. The 0.2x image magnification is the same as the EOS 10D's. The
sensor pitch has been changed from 18 µm to 16 µm. The focus detection
performance is on par or better than the EOS 10D's. The sensor features COB
(Chip on Board), and the approx. 7.0 × 9.6 mm package size is smaller than the
EOS 10D's approx. 8.3 × 9.8 mm.
Fig. 014 AF sensor
6.0
Fig. 016 Focusing area
(1) Configuration of AF optics
As shown in Fig. 33, the AF optics
have the image reproduced on the AF
sensor. First, 22 light flux rays for 11
points (7 vertical, 4 horizontal) pass
through the camera lens and are
sampled independently. Then the image
first forms in midair (focus plane) and
the secondary image-formation lens
reproduces the image on the AF sensor
for each focusing area. The light flux for
focusing is set to f/2.8 for the two light
flux at the center horizontal, while it is
f/5.6 for the other 20 light flux (same as
with previous EOS cameras).
3.6
f/5.6-compatible horizontal
sensor at center
f/2.8-compatible horizontal
sensor at center
Fig. 015 AF sensor layout
Table 005 AF sensor configuration
f/2.8 horizontal
f/5.6 horizontal
Center
f/5.6 vertical
(2-line zigzag pattern)
Top/Bottom f/5.6 horizontal
Diagonal f/5.6 vertical
Left/Right f/5.6 vertical
Secondary image-
formation lens
Fig. 017 AF optics
10
f/5.6-compatible vertical sensor at center
(2-line focusing/Zigzag pattern)
Pixel Size Effective Pixels
38 × 2
42 × 2
16 µm
36 × 4
×
140 µm
34 × 4
38 × 8
35 × 4
AF sensor
Field lens
Primary image formation plane