A collimator was required to qualify the Advanced Land Imager (ALI) instrument of the EO-1 new millennium satellite for focus, MTF measurements, and distortion. It was used during assembly of the instrument and during thermal cycling while the instrument was in a vacuum tank. It had to be diffraction-limited over a 3 $MUL 3 degree field of view and over a waveband of 400 to 2500 nm, have no obstruction, and have a virtual exit pupil that could be imaged onto the entrance pupil of the telescope. To satisfy these requirements the collimator, external to the vacuum tank, was built comprising a spherical mirror with exit pupil at its center of curvature, a full-aperture beamsplitter in collimated space, and a single lens to flatten the field. The optical layout and method of verifying collimation will be presented as well as optical performance, of interest since no corrector plate could be used as in the usual Schmidt camera configuration.
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