By using a translating phase mask, a Fourier-transforming lens and a spatial filter, we can process laser light reflected from a surface in such a way as to avoid the diffraction effects common in conventional imaging. This optical technique is thus inherently capable of measuring minute surface features such as the width of deposited or inscribed lines with better than Rayleigh resolution and should therefore be applicable for metrology of sub-micron features. The novelty of the technique is to transfer linewidth information into the zero-order spatial frequency component of the light reflected from the surface. We present analyses and computer simulations to detail the effects of such features of the system as the sharpness of a step edge in a phase-shifting mask, the magnitude of the phase shift introduced by the mask, the variation in reflectivity and height of various regions of the surface structure, and the effect of instrumental noise on the determination of linewidth. Experimental measurements were performed on specimens with large feature dimensions to verify the inherent capability of the technique. The results agree well with theoretical predictions. It is hard to validate this technique at smaller dimensions because of the necessity for precise lateral translation of the mask with respect to the surface and the sensitivity of the system to the mask-to-surface distance. We discuss modifications in the next-generation experimental set-up that will address both these issues. Current results indicate that this technique will be viable well into the submicron range.