Stopping down a system. You are designing a system to focus a laser beam that will work only on axis, that is with a single spot. Analysis of your first design reveals that the transverse ray aberration at the paraxial image plane is a factor of x larger than the diffraction limited spot size. By what factor must you reduce radius of the laser beam to reduce the ray aberration to be equal to the diffraction limited spot size if you are also allowed to defocus the system?
