Roughness, texture or optical finish is a defect that originates from the element's manufacturing. Texture is a periodical phenomenon with a high spatial frequency (or in other words, in small dimensions), which affects the entire surface and causes the scattering of incident light. A higher value of roughness means a rougher surface. The texture is especially important in cases where the polishing is carried out using new processing methods such as diamond turning, which leaves a residual periodical signature on the surface, affecting the quality of the obtained image or the level of scattering from the surface. The amount of scattered light is proportional to the square of the RMS of the roughness.