Abstract
An off-axis system refers to an optical system in which the optical axis and the normal vector at the vertex of each surface do not match. An off-axis optical system can be applied in order to construct a thin and light optical system. In particular, the optical system used for a see-through head-mounted display (HMD) must be designed asymmetrically, with respect to the optical axis. Because the vision of a human is different for each individual, HMD requires focus adjustment. The effective focal length (EFL) of the optical system must be calculated to obtain the focus adjustment. However, the off-axis optical system cannot be calculated by conventional methods. In this study, the EFL was calculated by rotating the coordinates of the rays near the optical axis by the angle of reflection or refraction at the intersection of each surface, with the rays coinciding with the optical axis. The magnitude of movement of the micro-display for focus adjustment was obtained from the calculated EFL, for a see-through type HMD.
Highlights
An imaging system can be categorized into an asymmetric optical system and a rotationally symmetric optical system, with respect to the optical axis [1,2]
The rotationally symmetric optical system has been applied to many products and the lenses used in the symmetric optical system are rotationally symmetric, so it has the advantage of easy lens fabrication and assembly [3,4,5]
The see-through type head-mounted display (HMD) is designed as an off-axis system as it is an augmented reality product that allows simultaneous observation of external scenes and virtual objects
Summary
An imaging system can be categorized into an asymmetric optical system and a rotationally symmetric optical system, with respect to the optical axis [1,2]. Owing to recent developments in optical component processing technology, asymmetric component processing is possible. This optical system is used in head-mounted displays (HMDs). In this optical system, the axial ray passing through the center of the stop is not a straight line, and there is asymmetry about this ray [9]. The axial ray passing through the center of the stop is not a straight line, and there is asymmetry about this ray [9] This is called an off-axis optical system. It describes an optical system in which the axial ray coinciding with the optical axis do not coincide with a normal vector at the vertex of the surface [10]
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