An image-conducting optical fiber bundle extends along a central bundle axis between image input and image output ends. The bundle is twisted along a portion of its length such that an image inputted into the image input end is angularly displaced about the central bundle axis before being outputted through the image output end. Each constituent optical fiber includes a cladding with a cladding diameter corresponding with the fiber diameter of that fiber and a core with a core diameter. The ratio of the core diameter to the cladding diameter defines a core-to-clad diameter ratio relative to each fiber. In various embodiments, at least one of fiber diameter and core-to-clad diameter ratio varies as a function of a fiber's radial displacement from the central bundle axis.