Functional surfaces of optical lens are commonly achieved by a multi-stage diamond turning. This high precision process acts in a wide range of wavelength and allows producing 3-dimensional free form optical surfaces with excellent surface finish that meets application requirements. However, the relationships between process variables and surface characteristics are not yet predictable. In this paper, the concept of the multiscale process signature (MPS) is applied to track the effect of diamond turning process variables (cutting velocity, feed rate, cutting depth, tool roughness,...) on the surface topography from micro-roughness to waviness. The MPS is developed based on continuous wavelet transform and it depicts the essential changes of the surface state produced on the original surface after diamond turning. Using this concept, the effects of different working variables are isolated and theirs active wavelength bands were identified.