AR/VR front-stop lenses

Imaging LMK with special adapted lenses offers an effective and efficient alternative for the metrological characterization of near-eye display systems (NED).

The user of a NED system perceives the whole image field only if his eyes are within the so-called Eye-box of the NED system. For each eye, the Eye-box corresponds to a 3-dimensional space around the respective exit pupil (XP) of the optical system.
Often the diameter of the NED-XP is larger than in conventional optical instruments (e.g., microscopes) and the distance to the last optical surface (Eye-relief) is relatively small.

For a correct photometric or colorimetric perception-accurate measurement, the entrance pupil (EP) of the measuring system must be located in the XP of the NED system, analogous to the human eye. On the other hand, it must be ensured that the EP of the measuring system is smaller than the XP of the NED system in order to achieve a complete filling of the aperture of the measuring system. Thus, valid measurement data can be guaranteed.
If the LMK aims to capture the complete NED field of view, the LMK-EP has to be placed in the NED-XP within the Eye-box. For this purpose, an optical system is necessary whose aperture-stop (respectively the EP) is in front of the optical surfaces.

Beside the existing conoscopic lens that offers a virtual EP (appr. 2mm diameter) in front of the lens and a measuring field of 120° a special front-stop lens was built.
This front-stop lens works with a real intermediate image plane and can be equipped with several focal lengths of 8mm; 12mm and 16mm. Thus it offers a measuring field of 30°- 60°. The diameter of the EP can be changed from 2 - 7mm.

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