A spatial frequency optical measurement instrument (100) is provided according to the invention. The instrument (100) includes a spatial frequency mask (120) positioned in a light path and configured to encode light with spatial frequency information, a light receiver (140) positioned to receive the light encoded with the spatial frequency information, wherein the light encoded with the spatial frequency information has been interacted with a sample material, and a processing system (180) coupled to the light receiver (140) and configured to determine a change in the spatial frequency information due to the interaction of the light with the sample material.