For a measurement system with backlight illumination, a telecentric lens with tunable working distance has no benefit as the whole object depth has to be imaged with a certain resolution at one single shot. A bright or dark field illumination in a defined angle of incidence (e.g. ring light) is limited, since the best homogeneity will be realized only for one working distance and not for all focusing planes. The appropriate solution would be a special illumination setup for different focal positions or a coaxial bright field illumination.
Since more than 10 years, Sill Optics offers telecentric lenses with coaxial collimated illumination successfully. Their main applications are high precision measurement tasks of surfaces. Last year, we presented a modular system for lenses with field of view larger than Ø60mm, whereby the beam splitter can be changed by the customer himself and a retardation plate can be inserted into the lens easily. For magnifying lenses, the retardation plate is available as an add-on at the front lens. Thus, the customer has the possibility to fit the lens to different illumination conditions.
For many of our telecentric lenses with focus tunable liquid lens, a coaxial coupling through the lens is combinable. Thus, you can prevent shading at the detection plane and a very good edge detection is possible because of the
collimated illumination beam path. The illumination beam path is not affected while tuning the liquid lens.