Optical Axis Alignment for Coaxial Cameras Using Infinity Mirror

Summary

Recent years have seen growing interest in sensing systems that combine multiple cameras with different characteristics, such as multispectral cameras, high-speed cameras, and event cameras. To observe a scene from the same viewpoint, the optical axes of these cameras must be aligned with high precision. However, conventional calibration methods based on planar patterns often suffer from increasing errors as the target moves away from the calibration plane, making accurate alignment over a wide depth range difficult. In particular, precise alignment across depth is required for variable-focus optical systems and high-speed imaging systems.

In this study, we propose an alignment method that visualizes optical-axis misalignment between coaxial cameras using an infinity mirror composed of mirrors and beam splitters (Fig. 1). By estimating a vanishing point (Fig. 2) from the reflected image sequence generated by the infinity mirror, optical-axis misalignment can be visualized over a wide depth range. The proposed method combines rotational adjustment based on the vanishing point with translational adjustment based on marker positions, enabling highly accurate optical-axis alignment between coaxial cameras (Fig. 3). High-speed spin measurement experiments of a table tennis ball using coaxially aligned high-speed cameras demonstrate that sufficient alignment accuracy can be maintained even for targets located farther away than the calibration device (Fig. 4). This research provides a fundamental technology for using multiple cameras with different characteristics or wavelength ranges from a common viewpoint and is expected to contribute to applications such as industrial inspection and robot vision.

Fig. 1 Proposed concept.	Fig. 2 Vanishing point geometry.
Fig. 3 Alignment results.	Fig. 4 Demonstration.

Reference

1. Tomohiro Sueishi and Masatoshi Ishikawa: Infinity-mirror-based Optical Axis Alignment for Coaxial Cameras Using Circularly Arranged Dot Markers, SICE Festival 2026 with Annual Conference (SICE FES 2026) (Yokohama, 2026.9.17)/Proceedings, pp.1202-1208