A technique has been developed to enhance the resolution of an optical scanning microdensitometer. Phase shifting optics are used to obtain a signal with high resolution, but with a complex structure. This signal is subtracted from a reference signal to produce the equivalent of an isolated, very narrow, bright line. This line is then scanned across the specimen. Improvements in resolution of about a factor of 2, compared to a conventional optical system, have been observed at numerical apertures up to 0.55, without sacrificing either the working distance or the depth of focus. ©1997 American Institute of Physics.