A radiation conducting conduit functions as an off-axis filter and contrast enhancer for an imaging device. A core of transparent glass has an axis aligned with the line of sight of the device. Cladding is provided which has the same index of refraction and co-efficient of thermal expansion as the core glass, except that a small percentage of the cladding glass is made of thin fibers or leaves of absorbing glass aligned substantially radially to the axis of the conduit and distributed randomly in the volume of the cladding. The interface between the core glass and the cladding glass of the same composition does not involve reflection or refraction, and non-axial light passes through the interface and is trapped among the absorbing black fibers. There, it is reflected and diminuated until it is totally absorbed. The conduit may be formed by the steps of: forming a flat sheet of glass containing random parallel fibers or leaves or absorbing glass, cutting the sheet into beveled strips, assembling the strips into a cylindrical configuration with the absorbing elements extending radially of the axis, inserting a core of transparent glass, and fusing the assembly and core together.