Areal texture and angle measurements of tilted surfaces using focus variation methods

Optical instruments for areal surface topography measurement have seen significant commercial development in the last five years, along with the ISO 25178 areal standard. Providing the user with confidence in new instruments depends on understanding instrument behavior and sources of error. Focus variation techniques rely on the inherent micro- or nano-scale roughness of a surface to allow acquisition of topography data. The work reported here has been examining the sensitivity of the focus variation technique to surface slope, using areal parameters to characterize surface roughness at extended slope values. The results illustrate links between instrument variables and slope characterization.