In order to respond to the requirements from the semiconductor industry, a projection optics utilizing an ArF laser as the illumination source is being developed. The projection optics equipped on the FPA-6000AS4 has been designed with 0.85 NA and field size is 8 mm X 26 mm. The goal was to achieve an extremely small aberration level in order to satisfy the requirements for the 90nm node patterning device manufacturing. In addition, to achieve this performance, the lens-barrel structures have been redesigned from the conventional barrel type. Thus, it becomes possible to lower the aberrations generated in the lens manufacturing process to the minimum level. We developed the new lens-barrel structure to minimize the stress induced deformation placed on an optical element. This structure, which is called the SP-barrel structure, allows stable lens performance in spite of temperature change and the mechanical impact, compared with earlier structures. Moreover, it has been proven that this structure can reduce the deterioration of the lens performance due to manufacturing errors. This allows the lens performance to closely approach the intentions of the optical design. This report describes the performance enhancements for the FPA-6000AS4 projection optics. In particular, we discuss the lens barrel design, along with exposure test results and wavefront aberration measurement results.