A method for measuring virtual image distance in head-mounted display using the variable focus optics

Head-mounted displays (HMDs) require precise measurement of virtual image distance for user comfort, but this is challenging due to dynamic variations. This paper addresses the difficulty by proposing a prototype using a variable-focus liquid lens and a calculation model for virtual image distance. We developed an experimental platform to validate the method and introduced an optimization algorithm to find the optimal focal length for maximum sharpness. Results showed a distance error of about 5 cm, confirming that our method accurately measures virtual image distance in HMDs, with potential applications in virtual and augmented reality.