A lens assembly including a first lens, a second lens, a third lens, a fourth lens, and a fifth lens, arranged from the magnification side to the reduction side, is provided. The fourth lens and the fifth lens are combined into a cemented lens having an aspherical surface. The lens assembly includes 5 to 6 lenses with a refractive power. The first lens is a glass lens, and the others are aspherical lenses. R1 is the radius of curvature of the lens surface of the first lens facing the magnification side, R2 is the radius of curvature of the lens surface of the first lens facing the reduction side, T is the thickness, on the optical axis of the lens assembly, of the first lens, wherein the refractive index of the first lens>1.55, the Abbe number of the first lens>55, and R1-R2-T