The advantages are obvious: The integration of coaxial illumination into the lens requires less space and saves costs for an additional illumination.
Furthermore, the design of the telecentric illumination enables a collimated illumination, which simplifies specific applications, e.g. the detection of surface defects.
Due to different measurement surfaces the lens design is very demanding with regard to stray light and back reflections.
As only polarized beam splitters eliminate back reflections completely, special attention has to be paid to the beam splitting. However, polarized beam splitters cause a loss of light intensity and illumination homogeneity.
They enable sufficient illumination quality for small object fields up to 50 mm. For larger object fields, deficits become visible especially at high reflecting mesurement surfaces.
With a modular lens setup Sill Optics offers the opportunity to adapt the standard series (polarized coaxial coupling) in accordance with the requirements of the measurement configuration:
First of all, the beam splitter can be replaced by a non-polarized version and furthermore the illumination homogeneity can be improved by a retardation plate.
A smart mechanical solution avoids the necessity of an expensive external retardation plate in the according diameters for large object fields (>60 mm).