The Auto Focus system on the new EOS 50D is very similar to the system used on the EOS 40D but with several key improvements including faster AF speed, improved AF precision, and AF Microadjustment for individual lenses.
The EOS 50D’s AF system consists of 9 cross-type AF points arranged in a diamond pattern, with all AF points being sensitive to both horizontal and vertical details when using f/5.6 or faster lenses. This sensitivity helps achieve faster, more precise focusing with hard-to-focus subjects, and enables high-speed (6.3 fps) continuous shooting in AI SERVO mode while tracking a moving subject. For a bird photographer like me, this is HUGE!
When using an f/2.8 or faster lens, the center point offers enhanced cross-type sensitivity and faster detection of subjects that may be extremely unfocused. This is done by adding diagonal sensors and a 2-line, zigzag configuration to the existing f/5.6 sensor already positioned in the center of the diamond.
I’m very pleased with the improved accuracy and performance of the EOS 50D’s AF system and while not as sophisticated as the Nikon 51-point system, it does function very well for wildlife photography.