Wavefront measuring systems and methods are disclosed which may be employed, for example, in detecting phase aberrations in a spectacle lens and in an eye. Various embodiments include disposing a modulation pattern in the path of a return beam from the spectacle lens or the eye, and imaging a diffraction pattern at a self-imaging plane relative to the modulation pattern with a detector. The diffraction pattern is analyzed and the results are used to produce a representation of the wavefront phase characteristics that describe aberrations in the lens or eye being measured. Illumination and processing techniques for improving the measurement results are disclosed. Various embodiments comprise systems adaptable to both measure aberrations in lenses in spectacles as well as in a patient's eyes.