Grin optical system

An optical system includes graded refractive index ("GRIN") optical elements. An objective optical element and an ocular optical element, each including at least one GRIN element, are located in an optical path which is substantially voidless. The optical system is not susceptible to fogging due to the absence of voids in the optical path. An image intensifier may be positioned in the optical path between the objective and ocular optical elements. The image intensifier responds primarily to invisible light and creates an amplified level of light substantially at a predetermined visible wavelength. A beam splitter may be used to split the light from the objective optical element into ranges of visible and invisible wavelengths. The range of visible light is directed through a first light channel to a beam combiner. The range of invisible light is directed through a second light channel to the image intensifier. The invisible light is changed to visible light substantially at the predetermined wavelength by the image intensifier. The beam combiner combines the visible light from the first and second light channels to achieve viewing in both high level and low level light conditions.