A diffuse reflectance apparatus comprising: a light source configured to produce a beam of light ; a diffuse reflectance mirror having a reflective surface and an aperture through which the beam of light passes to a target, wherein the diffuse reflectance mirror is positioned relative to the target such that a substantial portion of specular reflection from a surface of the target passes back through the aperture and the reflective surface collects a substantial portion of scattered light from the target and forms a second beam ; and a detector configured to produce a signal in response to the second beam ; characterized by : an optical assembly positioned to direct the second beam from the diffuse reflectance mirror to the detector , wherein the optical assembly comprises: a first flat mirror ; a second flat mirror ; and a concave ellipsoidal mirror , wherein the first flat mirror is positioned to reflect the second beam comprising the scattered light from the concave ellipsoid mirror to the second flat mirror , wherein the second flat mirror is positioned to reflect the second beam comprising the scattered light from the first flat mirror to the concave ellipsoidal mirror ; and wherein the concave ellipsoidal mirror is positioned to reflect the second beam comprising the scattered light from the second flat mirror to the detector . a light source configured to produce a beam of light ; a diffuse reflectance mirror having a reflective surface and an aperture through which the beam of light passes to a target, wherein the diffuse reflectance mirror is positioned relative to the target such that a substantial portion of specular reflection from a surface of the target passes back through the aperture and the reflective surface collects a substantial portion of scattered light from the target and forms a second beam ; and a detector configured to produce a signal in response to the second beam ; characterized by : an optical assembly positioned to direct the second beam from the diffuse reflectance mirror to the detector , wherein the optical assembly comprises: a first flat mirror ; a second flat mirror ; and a concave ellipsoidal mirror , wherein the first flat mirror is positioned to reflect the second beam comprising the scattered light from the concave ellipsoid mirror to the second flat mirror , wherein the second flat mirror is positioned to reflect the second beam comprising the scattered light from the first flat mirror to the concave ellipsoidal mirror ; and wherein the concave ellipsoidal mirror is positioned to reflect the second beam comprising the scattered light from the second flat mirror to the detector . a first flat mirror ; a second flat mirror ; and a concave ellipsoidal mirror , wherein the first flat mirror is positioned to reflect the second beam comprising the scattered light from the concave ellipsoid mirror to the second flat mirror , wherein the second flat mirror is positioned to reflect the second beam comprising the scattered light from the first flat mirror to the concave ellipsoidal mirror ; and wherein the concave ellipsoidal mirror is positioned to reflect the second beam comprising the scattered light from the second flat mirror to the detector . <EOS>