Complex sentence: It was the first camera in Canon's new EOS series, designed from scratch for autofocus and featuring the new EF lens mount, which used only electrical signals to communicate between the camera and the lens.
Split into simpler sentences: It was the first camera in Canon's new EOS series, which was designed from scratch to support autofocus lenses. The EOS system featured the new EF lens mount, which used electrical signals to communicate between the camera and the lens.