The push to achieve higher density devices continues to place tremendous demands on optical lithography. Several techniques have been used to achieve 0.35 micrometers feature sizes. This paper presents data on the practical application of numerical aperture (NA) and partial (sigma) for 0.35 micrometers imaging. A number of conventional photoresist systems are characterized at various NA/(sigma) . Important differences in the response of photoresists have been observed. These are quantified with respect to various types of structures. Of particular interest are the affects on dense lines and contact structures. The affect of bias also is quantified by using a special reticle where pitch is held constant and the chrome linewidth is varied to determine optimal process latitude. After examining the imaging performance of a few high-contrast photoresists, the use of normalized image log-slope (NILS) is applied for two stepper conditions. Finally, response curves are generated to show optimal exposure conditions for resolution and depth of focus versus NA/(sigma) performance for a number of different NILS photoresists.