An illustrated chronological story about how Canon autofocus systems and viewfinders went from a single AF point (1987) to 191 AF points (2020).
The number of AF points was drastically increased, resulting in a 191-point AF system. This AF system delivers the fastest and most precise focusing that has ever been achieved by the phase detection approach. In addition, it provides a new level of AF tracking supported by deep learning, including head detection, face detection, and people prioritization. On most other Canon DSLR cameras, autofocus data is processed by the camera's CPU called DIGIC which is responsible for all data processing. By contrast, the enormous amounts of autofocus data produced by this 191-point AF system is analyzed by a dedicated Canon DIGIC 8 chip which is used as a powerful co-processor to the even more powerful DIGIC X central processing unit.
The dotted position indicators are arranged in three zones. During focusing, each active AF point turns into a small pixelated square. Viewfinder coverage is roughly the same as on the predecessor (2nd generation 61-point AF system).
This sensor chip is a complete innovation for a phase detection system. Instead of small pairs of linear detector strips, this new AF sensor uses arrays of tiny square pixels (pixel-dot-matrix). These light receptive surfaces are arranged in three zones. Detector pixels are 28 times denser than in the previous 61-point AF sensor of the EOS 1D X II. The total number of pixels used is roughly 100 times higher than in the previous system. This results in a significant boost in autofocus precision.
The maximum number of available AF points is 191. Depending on the lens attached to the camera, the number of usable AF points, AF point patterns or the types of AF sensors may vary.
If a lens with a maximum aperture of f/2.8 or faster is attached to the camera, 155 AF points are standard-precision cross-type detectors, and 36 AF points in the outer zones are standard-precision vertical detectors. Out of the 155 cross-type sensors, the center AF point is also a high-precision dual cross-type detector.
When a lens having a maximum aperture of f/4 is used, the 155 AF points remain standard-precision cross-type detectors and the 36 AF points remain standard-precision vertical detectors. However, the center high-precision dual cross-type detector turns into a regular standard-precision cross-type detector.
When a lens having a maximum aperture of f/5.6 is used, all 65 AF points in the center zone remain standard-precision cross-type detectors but all 90 cross-type AF points from the two outer zones turn into standard-precision vertical detectors, resulting in 126 vertical sensors in the outer zones.
The autofocus capabilities with effective apertures of f/8 is similar to the latest 61-point AF system. With lens and extender combinations having an effective maximum aperture as small as f/8, the same 65 AF points in the center zone remain standard-precision cross-type detectors and 126 AF points from the two outer zones remain standard-precision vertical detectors (as if an f/5.6 lens was used). Autofocus is not possible during viewfinder shooting with effective maximum apertures slower than f/8.
The system has an AF working range of EV -4 - 21 (with the center AF point supporting f/2.8) at ISO 100.