Novel optical system of helmet display unit

The invention discloses a new optical system for helmet display; it relates a light, compact and well optical aberration correction adjustable focus optical system, it can be used as visual optical system for perspective helmet display apparatus. The visual optical system comprises a group of eyepiece lens and a built-up prism construction. The eyepiece lens comprises at least a penetrance element. The built-up prism construction comprises at least a concave reflector, at least a half reflecting and half translucenting optical surface, light reflects at least two times between the optical surfaces, the refractivity of the polarizability full filled in the space between the optical surfaces. The visual optical system uses mini LCD as image plane display equipment, it can fuse the image sent from the image source in internal channel by the visual optical system with the image outside, making the said image form at infinite distance in the direction of observation, and it can focus to a point limited distance from the observer.