Abstract: An apparatus for projecting a laser beam at an angle to an axis and sweeping the laser beam around the axis around a conical surface having a selected slope is described. The apparatus may be used to aid in the alignment of structures having conical surfaces. The apparatus projects a laser beam along an axis onto a rotating deflection assembly. The deflection assembly contains two mirrors which are optically equivalent to the reflective faces of a pentaprism. Consequently, the angle of the deflected beam is relatively insensitive to vibrations of the deflection assembly. The angle of the deflected beam may be varied by tilting the two mirrors. The alignment of the mirrors is maintained as the mirrors are tilted by a linkage which includes a roller mounted to one of the mirrors which rides on a cam surface coupled to the other mirror. The adjustable mirror-alignment linkage may be used in other optical equipment.