Fig. 19. (Top) Schematic diagram of a night-vision pocketscope. The pocketscope contains a light-emitting diode to provide supplementary illumination within 3 meters and is powered by two AA batteries. It weighs 13.8 oz. and is 4.5 in. long by 2 in. wide by 2.25 in. high. (Bottom) Single-stage image intensifier tube, 3 cm in length, contained in the night vision pocketscope. (From Berson EL, Rabin AR, Mehaffey L. Advances in night vision technology: A pocketscope for patients with retinitis pigmentosa. Arch Ophthalmol 1973;90:427.)