Thus light emanating from the center will converge back upon itself. As one focus of the parabola lies at infinity, collimated light reflected from an aligned parabolic mirror converges to its finite focus. Optics where rays intersect or wavefronts converge. Paraxial Optics cardinal point of a paraxial system where the focal plane intersects the paraxial axis. Paraxial rays that are initially parallel to the axis intersect at a focal point.
Every paraxial system has two focal points.