  We present a practical apparatus for characterizing optical aberrations of
large collimation mirrors and lenses, and give a detailed analysis of
wavefront-detection errors. We utilize a scanning pentaprism technique for
precise measurements of local wavefront slopes, and reconstruct transmitted
wavefronts via a conventional least-squares method. Our proof-of-principle
experiment demonstrates transverse linear measurements of transmitted
wavefronts for a 20.3 cm lens developed for Canada's Quantum Encryption and
Science Satellite (QEYSSat) mission. Our demonstration shows the
wavefront-detection precision better than 0.01{\lambda} and the
divergence-angle resolution less than 20{\mu}rad over the range of 40 cm. We
model our optical setup using three-dimensional raytracing and find good
quantitative agreement between experimental results and theoretical predictions
which validates our methodology.
