Specifications

New AI Servo AF algorithm
As with the EOS-1D Mark III, AF processing, which includes focusing calculations as
well as lens driving
, is divided between a dedicated AF CPU and the camera CPU. It thus
uses a distributed processor configuration. To attain the maximum speed of approximately
10 fps in AI Servo AF, the AF CPU and camera CPU are both high-speed microcomputers
(48MHz 32-bit RISC for AF and 40MHz 32-bit RISC for camera).
The AF sensor’s basic configuration and focusing optics are similar to those of the
EOS-1D Mark III. However, there are now 39 cross-type AF points available for manual
AF point selection. (Note that these 39 points work as cross-type points only during
manual AF point selection. During automatic AF point selection, the same 19 AF points
as on the EOS-1D Mark III will work as
cross-type points.) Increasing the number
of cross-type AF points to 39 was made
possible by the high-speed, vertical line-
sensitive f/2.8 sensor components whose
reading position is switchable. The new
reading method improves both AF precision
and the subject tracking success rate. The
precision of the focusing optics has also
been enhanced with stricter AF adjustment
standards and improvements in the manu-
facturing process to improve the stability of
AF performance.
To go along with the hardware and manufacturing process improvements, Canon also
completely revamped the firmware used to calculate predictive focus. As a result, a
significantly improved AI Servo AF algorithm now called AI Servo II AF eliminates
focusing errors, maintains tracking and improves response. In the past, Canon AF system
development concentrated on achieving fast response. Highly responsive AF systems offer
accurate predictive AF (they focus quickly on subjects in the AF frame), but they have
difficulty stabilizing focus if the subject leaves the AF frame during AI Servo AF continuous
shooting. The 1D Mark III, highly responsive by design, consequently has a lower probability
of accurately focusing on fast-moving subjects that are hard to keep within the AF frame.
With the new 1D Mark IV AI Servo II AF algorithm, stability, reliability and AF precision
have all been improved without a sacrifice in responsiveness. Predictive AF is more intelligent
and avoids over-response, and difficult lighting — both low contrast and very bright
conditions — is handled better. Canon has conducted numerous field tests with professional
photographers both in the US and abroad and the resulting feedback has helped to make the
algorithm precisely suited to the shooting needs of pro users.
14
IV–1. NEW 45-POINT AUTOFOCUS SYSTEM
Reflective mirror
Cover glass
Infrared-blocking glass
AF sensor
Secondary image-
formation lens
Main mirror
Oblong,
secondary
mirror
AF Optics