An optical system comprising: a light source; a light delivery system comprising a reflector of a first numerical aperture having a first optical axis, the reflector being configured for directing light emitted from the light source to a sample material positioned along the first optical axis; a light collection system comprising a light collection optical element of a second numerical aperture having a second optical axis, the light collection optical element being configured for collecting light diffusely reflected or emitted from a surface of the illuminated sample material and for transferring the collected light to an analysis device; and a light displacement optical device positioned between the light source and the sample material comprising a light displacement optical element configured for transferring at least a portion of the light diffusely reflected or emitted from the surface of the sample material to the light collection optical element; wherein the light displacement optical device comprises a shielding element surrounding, at least partially, the light displacement optical element, the shielding element comprising at least a first opening, through which opening light diffusely reflected or emitted from the surface of the sample material enters the light displacement optical element, and at least a second opening, through which second opening the diffusely reflected or emitted light entered through the first opening exits the light displacement optical element and is transferred to the light collection optical element, characterized in that the light displacement optical element is a prism having a rhomboid shape. a light source; a light delivery system comprising a reflector of a first numerical aperture having a first optical axis, the reflector being configured for directing light emitted from the light source to a sample material positioned along the first optical axis; a light collection system comprising a light collection optical element of a second numerical aperture having a second optical axis, the light collection optical element being configured for collecting light diffusely reflected or emitted from a surface of the illuminated sample material and for transferring the collected light to an analysis device; and a light displacement optical device positioned between the light source and the sample material comprising a light displacement optical element configured for transferring at least a portion of the light diffusely reflected or emitted from the surface of the sample material to the light collection optical element; wherein the light displacement optical device comprises a shielding element surrounding, at least partially, the light displacement optical element, the shielding element comprising at least a first opening, through which opening light diffusely reflected or emitted from the surface of the sample material enters the light displacement optical element, and at least a second opening, through which second opening the diffusely reflected or emitted light entered through the first opening exits the light displacement optical element and is transferred to the light collection optical element, characterized in that the light displacement optical element is a prism having a rhomboid shape.