This paper described an off-axis head-mounted display system. It is composed of a 7-piece coaxial relay lens group and a freeform surface combiner. This configuration has a simple structure and a wide field of view (FOV). In this design, a freeform surface is chosen as the combiner, to simplify the structure and attain good image quality. We generated this freeform surface by considering both coordinates and normals of discrete data points. Moreover, we realize a coaxial structure in the relay lens group, which is compact and benefits from a loose tolerance requirement. The HMD system we finally realized has a 40°× 30° FOV and 15-mm exit pupil diameter.
A new method improving the design of panoramic lens with a long focal length based on ogive and aspheric surface is proposed. In this design, we use a special conjugation between "annular entrance pupil" and aperture stop to correct the chromatic transverse aberrations. Moreover, we use a new imaging relationship to increase the Effective Focal Length (EFL) of the panoramic lens and the CCD utilization. We realize a panoramic lens with a 360° × (45°~85°)field of view (FOV) and a 10.375mm EFL, which is 1.54 times than the conventional imaging relationship.
A new method to design a low distortion, even relative illumination, optical see-through head-mounted display (HMD) with a freeform reflective mirror (FFRM) based on the two similar ellipsoids structure is proposed. The HMD we have realized has a simple structure which consists of two similar ellipsoid surfaces, an FFRM, a 7-piece co-axis relay lens, and an OLED. This structure can be applied to offset distortion, reach even relative illumination, and correct the off-axis aberrations. The HMD we finally have realized has a near 3% low distortion, a higher than 80% relative illumination, and a 40°×30° field of view (FOV).
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