The AF system on the EOS 5D Mark II
includes 9 visible AF points and six
invisible assist points,for a total 15
points concentrated toward the center.
The outer points on the extreme left and
right are actually located at the same
positions as the corresponding points in
the EOS-1Ds Mark III,giving the
camera a wide field for detecting moving
subjects crossing the scene or improved
ability to focus on off-center subjects.
While only 9 AF points are visible
through the viewfinder,all can be revealed
using ZoomBrowser or ImageBrowser software.Among the six Assist AF
points,the top and bottom points at the center are ver tical-line sensitive
with lenses featuring f/2.8 or brighter maximum apertures, while all other
points are sensitive at f/5.6 or brighter.Focusing is started using the f/5.6,
horizontal line-sensitive central sensors with individual pixels arranged in
a zigzag pattern for improved extreme defocus detection. When focusing is
nearly achieved (and when using an f/2.8 or brighter lens) focusing is handed
off to the f/2.8 sensitive vertical line sensors.
The purpose of the supplemental points is to enhance the camera’s subject tracking
performance by filling in the gaps between the highly sensitive central AF point and the
8 adjacent linear sensors.
As on the EOS 50D,the EOS 5D Mark II’s AF system is sensitive to light levels as low as
EV -0.5,and capable of locking on to a moving subject and tracking it across the diamond-
shaped AF area.Improved precision over previous AF systems stems from each camera’s
ability to adjust for different light sources while calculating focusing distance. Here’s how it
works:during P hase Detection AF,the AF engine rapidly measures the density of horizontal
and vertical details in a scene and the camera processor uses this data to determine where
the sharpest edges and details are located. When found,the AF is loc ked on target.But
under fluorescent lighting and some other artificial lighting sources,a rapid, imperceptible
flickering of the light occurs along with sudden color temperature shifts.These tend to
throw off the density measurements and therefore the accuracy of the AF calculations.In both
the EOS 50D and EOS 5D Mark II,the ty pe of lighting is taken into effect,and readings
are averaged and processed with the help of the super-fast DIGIC 4 Image Processor.
The result is improved AF accuracy and speed when shooting under lighting conditions that
could fool the AF systems found on earlier Canon and competitive models alike.
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IV. PERFORMANCE AND RELIABILITY
AF Sensor
f/2.8 / f/5.6-sensitive sensors
f/5.6 sensors
f/5.6-sensitive
major defocus
detection sensors
Intermediate
AF points
: Sensitive to f/5.6
Assist AF points
: Sensitive to f/2.8
Assist AF points
AF points and invisible AF pointsAF sensor configuration
EOS5D Mark II AF Systems