In-lens Drive Systems
When full-fledged autofocus technology first came out in 1985, most companies that made autofocus SLR cameras used an in-body range-finding/body drive system. This means that the AF drive motor is built into the camera body and a mechanical coupler controls the lens drive. Canon took a different approach. They thought that the key to future market success was to get rid of technologies that were holding them back and build a new system that would eventually be better than other systems in terms of performance and ability to immediately and accurately understand what the photographer wanted. This is where Canon's new, very accurate AF system got its start.
Canon got rid of the traditional in-body rangefinder/drive system in order to make the whole imaging system more efficient. Instead, they put separate motor drive systems inside each lens and chose the best motor design for each lens type, from fisheye to super telephoto. "An optimal actuator for the lens, is placed as close as possible to the drive unit, and all information transmission and controls should be electronic controlled." This is how the Canon AF drive system was designed. Canon was able to improve efficiency, lower energy transfer loss, and lower noise from the drive unit by putting the actuator next to it. Canon also made more actuators and designed units that can make the exact focus torque each lens needs. This way, even the biggest lens can focus quickly and smoothly. This system works better than a body drive system in super telephoto lenses where the drive unit is far from the camera body. This lets fast and accurate autofocus be built into super telephoto lenses. One of the best things about the professional L-series lenses is that the system can work well, last a long time, and perform well even in harsh conditions. This technology has been used in the EOS R system and RF Lenses, and new technologies are still being added to them to make them better.