Image processing Telecentric lenses with focus tunable lenses
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 furthermore, defocusing is necessary to maintain the required resolution. The new 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.