To increase the useable depth futhermore, defocusing is necessary to maintain the required resolution. In cooperation with the company Optotune Switzerland, Sill Optics designed telecentric lenses including a focus tunable lens that can adapt the focus to change working distance.
Initially, the electrically tunable liquid lens EL-16-40-TC with a refractive power of -3.0 to +3.5 diopters was combined with an already existing 2-times magnifying telecentric lens. Within milliseconds, different heights or working distances can be measured reliable and reproducible. Due to the power adjustment, it’s possible to reach a maximum working distance change of about 13 mm. The magnification varies thereby by approximately+/- 3% along the working distances. The working distance as well as the magnification show a linear dependence to the optical power of the lens. Thus, the influence to the measurement results can be eliminated by calibrating the measurement system.
Additional, distortion error less than 1% and a telecentric error less than 0.1% were achieved. The evaluation of the first prototypes show a very good image quality even in the field edges. Because all design parameters were confirmed by measurements, new application fields open up for telecentric lenses.