Reflectographic method for inspection of the internal surface of smooth cylinders

A simple technique is described for the inspection of the interior of smooth or polished cylinders. The technique may be described purely in terms of geometric optics and either a laser or a white-light source can be used. The point source of light is arranged to be coaxial with the cylinder and at a short distance from one end of it. The light emerging from the source is reflected by the walls of the cylinder in a controlled fashion, and is collected on a photographic film or viewing screen on the far side of the cylinder from the source. Minor deviations from parallelism of the cylinder walls are thereby greatly magnified and may easily be measured using the formulae given in the text.

This method can be used by unskilled soldiers to take reflectographs of gun barrels for inspection, and for following the working life of a particular barrel. The technique can be further refined by replacing the screen by a cylindrical one.