Transmittance of projection lenses used in DUV exposure tools changes depending on the exposure light path. We studied the impact of this phenomenon (Across Pupil Transmittance Variation, APTV) on fine device pattern imaging. Zernike polynomials, which are commonly used for analysis of wavefront aberration, were applied for inspecting the influence of APTV. We investigated influences of each Zernike component on fine pattern imaging, and clarified that a significant component of APTV can be extracted by Zernike polynomial series expansion. Even components of APTV cause CD variation depending on the pattern pitch, that is, change of optical proximity effect (OPE), while odd components of APTV have little influence. In this paper, we present a method of decomposing APTV in Zernike coefficients together with the results of Zernike sensitivity analysis of the influence on OPE change. APTV was found to differ from tool to tool, and varies across the exposure field. Impact of tool dependence, across-field variation, and vertical-horizontal deviation of APTV are discussed.