An illustrated chronological story about how Canon autofocus systems and viewfinders went from a single AF point (1987) to 191 AF points (2020).
This was the first AF system that offered AF points above and below the center AF point. The illustration shows the viewfinder coverage offered by an APS-C camera. The coverage is smaller on a 35mm film camera.
Each AF sensor is indicated with a small frame. The center is shaped as a uniform square whereas the remaining six AF sensors are rectangles, oriented depending on their sensitivity.
This was the first AF sensor that had a different chip package than the previous BASIS chips. For this new design, Canon embedded the active area inside a completely rectangular substrate and added transparent optical polymer on top. The active area accommodates eight detector pairs (black stripes in the illustration) as well as signal processing and amplifier circuitry surrounding the actual detectors.
All AF points are standard-precision sensors that are designed for use with lenses having a maximum aperture of f/5.6 or faster. The center point is a standard-precision cross-type (sensitive to both vertical and horizontal contrast lines). All other points are single line sensors. Their orientation is shown in the illustration. There are no f/2.8 high-precision sensors available. 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.