A method and an apparatus of a powder bed fusion additive manufacturing system that enables a quick change in the optical beam delivery size and intensity across locations of a print surface for different powdered materials while ensuring high availability of the system. A dynamic optical assembly containing a set of lens assemblies of different magnification ratios and a mechanical assembly may change the magnification ratios as needed. The dynamic optical assembly may include a transitional and rotational position control of the optics to minimize variations of the optical beam sizes across the print surface.