  Wide-field survey instruments are used to efficiently observe large regions
of the sky. To achieve the necessary field of view, and to provide a higher
signal-to-noise ratio for faint sources, many modern instruments are
undersampled. However, precision photometry with undersampled imagers requires
a detailed understanding of the sensitivity variations on a scale much smaller
than a pixel. To address this, a near-infrared spot projection system has been
developed to precisely characterize near-infrared focal plane arrays and to
study the effect of sub-pixel non uniformity on precision photometry.
Measurements of large format near-infrared detectors demonstrate the power of
this system for understanding sub-pixel response.
