An adjustable optical system for determining aberration in a source beam by comparison of a test beam with a reference beam. The system includes a test source for producing a source beam having a spacial intensity distribution including an aberration component, a wavefront analyzer for processing a fringe signal associated with the aberration component, and an interferometer interposed between the test source and wavefront analyzer. The interferometer includes a beamsplitter for splitting the source beam into a test beam and a reference beam, a mirror disposed in the test beam path, and a micromirror disposed in the reference beam path. The micromirror reflects a central portion of the reference beam toward an imaging device and allows an outer portion of the reference beam to pass thereby. The interferometer is also provided with an alignment image assembly for collecting and detecting the outer portion of the reference beam so that the micromirror and test source may be independently adjusted relative to the central and outer portions of the reference beam.