A spectroscopy system separates the diffuse reflectance component of a reflectance spectrum from the specular reflectance component using a remote field stop filter. The surface of the sample is placed at a focal plane of an optical system. The optical system forms an image on the surface of the sample...http://www.google.com.au/patents/US4859064?utm_source=gb-gplus-sharePatent US4859064 - Diffuse reflectance spectroscopy system and method
