A specular variable angle absolute reflectometer , comprising: a light source ; a detector ; a sample mount configured to position an optically reflective sample at a plane containing a rotation axis such that the sample is rotatable by a first angle about the rotation axis ; a mirror system in a light path of the light source , the mirror system configured to reflect a light beam from the light source towards the sample ; a roof mirror disposed in the light path after the sample , the roof mirror configured to reflect the light beam reflected by the sample back towards the sample and wherein the roof mirror comprises a "V" shaped wedge with an inner angle of the "V" shaped wedge facing the sample ; a mechanism connected to the roof mirror , the mechanism being configured to rotate the roof mirror by a second angle about the rotation axis , the second angle being about twice the first angle; wherein the detector is arranged in the light path after the roof mirror and is configured to receive light that has been reflected from the roof mirror , thence back to the sample , thence back to the mirror system , and thence to the detector ; wherein the specular variable angle absolute reflectometer further comprises: a light trap associated with the mirror system ; and a movement system connected to the mirror system and configured to move the mirror system such that the light trap intercepts the light from the light source with a forward movement of the mirror system and a direct path from the light source to the detector when the mirror system is retracted from intercepting the light from the light source . a light source ; a detector ; a sample mount configured to position an optically reflective sample at a plane containing a rotation axis such that the sample is rotatable by a first angle about the rotation axis ; a mirror system in a light path of the light source , the mirror system configured to reflect a light beam from the light source towards the sample ; a roof mirror disposed in the light path after the sample , the roof mirror configured to reflect the light beam reflected by the sample back towards the sample and wherein the roof mirror comprises a "V" shaped wedge with an inner angle of the "V" shaped wedge facing the sample ; a mechanism connected to the roof mirror , the mechanism being configured to rotate the roof mirror by a second angle about the rotation axis , the second angle being about twice the first angle; wherein the detector is arranged in the light path after the roof mirror and is configured to receive light that has been reflected from the roof mirror , thence back to the sample , thence back to the mirror system , and thence to the detector ; wherein the specular variable angle absolute reflectometer further comprises: a light trap associated with the mirror system ; and a movement system connected to the mirror system and configured to move the mirror system such that the light trap intercepts the light from the light source with a forward movement of the mirror system and a direct path from the light source to the detector when the mirror system is retracted from intercepting the light from the light source . a light trap associated with the mirror system ; and a movement system connected to the mirror system and configured to move the mirror system such that the light trap intercepts the light from the light source with a forward movement of the mirror system and a direct path from the light source to the detector when the mirror system is retracted from intercepting the light from the light source . <EOS>