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 increased, resulting in a 19-point AF system. This AF system soon earned a reputation of Canon's fastest and most reliable autofocus system available at that time.
Each AF sensor is indicated with two frames. AF points are divided into five zones, indicated by black frames. Viewfinder coverage is fairly large.
Pairs of detector lines on this sensor chip are laid out in a similar way to the 9-point AF system with the center dual cross-type sensor. However, this chip has an increased number of detectors in the center area. Further improvements have been made to the chip electronics (amplifiers, readout, etc.)
All AF points are standard-precision cross-type sensors designed for lenses having a maximum aperture of f/5.6 or faster. The center AF point turns into a high-precision dual cross-type sensor when an f/2.8 or faster lens is attached to the camera. Autofocus is not possible during viewfinder shooting with lenses having maximum apertures slower than f/5.6.
The system has an AF working range of EV -0.5 - 18 at ISO 100.