Telecentric lenses with focus tunable lenses

24. October 2016

In many industrial inspection applications, different object heights have to be measured. Therefore, object sided telecentric lenses are recommended to use the entire depth of field with a constant magnification.

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.

Distinguished with the quality seal "TOP INNOVATION 2017" from inVision magazine.