A measurement method of the focal distance of the virtual image in an augmented reality or virtual reality device

In most augmented reality (AR) or virtual reality (VR) devices, a virtual image is formed in front of the eye at a specific focal distance. Focal distance is the distance to the virtual image produced by the virtual image optics and is a display parameter of interest. In this study, a method to measure the focal distance is proposed. A positive lens was added adjacent to the AR device, and the image of the virtual image formed by this lens was photographed at the different distances with the translation of complementary metal–oxide–semiconductor (CMOS), which was used as two-dimensional spatial sensor arrays. Grating pattern with the various line thickness was used as input signal. Once the distance of the image of the virtual image formed by the addition of the positive lens was determined, the focal distance of the virtual image was found from the lens equation. The measurement accuracy of the proposed method with regard to the CMOS translation step was compared with the other conventional methods.