Abstract: The present invention relates to a device for scanning the surface of a generally cylindrical object carrying a raised pattern, such as a finger, which device comprises:a. a transparent optical body having a substantially arcuate configuration about a first axis and having an axial cross-section which is convergent for at least part of its radial dimension, and a channel parallel to and substantially co-axial with that axis, which channel presents a face substantially parallel to the said axis, upon which the object whose surface is to be observed can be placed;b. a source of incident light adapted to be directed onto a light entry face of the convergent cross-section of the body, the configuration of the body being such that the incident light is adapted to strike the under-side of the said base face at substantially the angle of total internal reflection and to be reflected through the same another face of the convergent cross-section of the body;c.