This paper describes the application of multiple beam shearing interferomet
ry to beam collimation in the presence of lens aberrations. To realize mult
iple beam shearing interferometry, a shear plate is used, wedged slightly i
n thickness at an angle of 2.7 ", with coatings of 90% reflectance. The bea
m collimation in the presence of aberrations is analyzed in terms of the ef
fects apparent at the paraxial focus, circle of least confusion and margina
l focus. It is shown to be possible to collimate a beam very accurately by
moving a lens under test around the position of circle of least confusion w
hile observing the fringe line. (C) 2001 Elsevier Science B.V. All rights r
eserved.