Design of large field-of-view digital head-mounted night vision optical system based on low-light-level CMOS device

Digital night vision technology has developed rapidly with the development of semiconductor technology and optical manufacturing techniques. For the digital head-mounted night vision system, an optical system with large Field of View (FOV), low cost, and lightweight is of critical importance. In this paper, an optical system consisted of an objective and an eyepiece with unity magnification, large FOV and high resolution is designed for digital head-mounted night vision system based on Low-Light-Level (LLL) CMOS device. By combining the aspherical lens and spherical lens, aberrations of the objective and the eyepiece are effectively controlled, the number of optical lenses is reduced, the relative aperture and the FOV are improved. The F number and the focal length of the designed objective are 1.2 and 3.75 mm, respectively. The exit pupil diameter and the focal length of the designed eyepiece are 15 mm and 23 mm, respectively. The FOV of the designed optical system reaches to 70 degrees. The total optical length of the designed optical system is less than 95 mm. It is analyzed that the cutoff frequency of MTF curve corresponding to the optical axis for the designed objective reaches to 166 cycles per mm. The image distortion is less than 4% at the 30 degrees FOV for the designed objective and less than 4% at the half FOV for the designed eyepiece. Tolerances analysis indicates that the tolerance of the objective and eyepiece lens are reasonable.