Canon 50D – Precision 9-Point AF System

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!

EOS 50D Auto Focus Sensors

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.

4 thoughts on “Canon 50D – Precision 9-Point AF System

  1. Hi Jeff. You say, “When using an f/2.8 or faster lens, the center point offers enhanced cross-type sensitivity”. What if I have a 50mm f/1.8 lens and have it stopped down to say f/6.3? Will it use the cross-type sensitivity? Perhaps I need to have a fast f/2.8 lens AND have it opened up to f/2.8 or faster? A subtle wording difference I know, but needs clarification for me, none the less.

    • Gavin,

      Thanks for reading. According to Canon, it won’t matter if you stop down your EF 50mm f/1.8 USM or not, the EOS 50D’s center AF point will use it’s diagonal cross-type sensors to assist in focusing. I have no idea exactly how this works but I have noticed a significant increase in AF speed and accuracy over my 40D.


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