Canon EOS 1D Mark III User Guide - Page 17

Sensor vertical-line sensitive at f/2.8 Sensor horizontal-line sensitive at f/5.6 Previous 45-point sensor EOS-1D Mark III Sensor horizontal-line sensitive at f/5.6 Sensor vertical-line sensitive at f/2.8 The 19 cross-type AF points take advantage of the following technologies: • With finer processing steps, the peripheral circuit could be made smaller and the f/2.8 AF sensor area could be expanded • The secondary image-forming lens (see diagram) is glass mold. By incorporating a newly-developed aspherical surface on the lens, the focusing area of the f/2.8 light flux could be expanded Prime lens Focusing plane (Image plane) Subject CMOS area sensor Secondary image-forming lens As with the EOS-1D Mark II N, the center AF point is a cross-type sensor. It is vertical-line sensitive with maximum apertures as small as f/4, and horizontal-line sensitive with maximum apertures as small as f/8. If the maximum aperture of the attached lens or lens/extender combination is f/4 or faster, high-precision, cross-type focusing is possible. If the maximum aperture of the attached lens or lens/extender combination is f/8 or faster, horizontal-line sensitive AF is possible. Compared with the other 18 cross-type AF points, the center AF point's focusing line width is larger while the fill factor for each pixel is larger (f/2.8 field of view). Also, the number of focusing lines increases along with : Cross-type AF points : Assist points (Not user-selectable) : f/2.8 sensors (Center AF point is f/4) : f/5.6 sensors the brightness (f/5.6 field of view) to attain higher pre-cision. Gross defocus is also detected. The camera 3.00 2.25 can also detect a grossly defocused subject 1.8 times better than with the EOS-1D Mark II N. 4.00 2.00 6.6 4.5 7.50 V. INCOMPARABLE EOS AUTOFOCUS, NOW EVEN BETTER 17