Abstract
Photogrammetry is a method for determining the 3 dimensional form of a structure through the recording and measurement of 2 dimensional photographs. An investigation into close-range applications of the technique, including the calibration of 3 coordinate measuring machines, have shown that there are several aspects of photogrammetry which may benefit from research. These relate to the performance of the recording camera, photographic emulsion and plate measuring microscope. A completely new camera lens, the Centrax, has been developed that overcomes some fundamental limitations associated with the optical properies of conventional lenses. The Centrax exhibits total freedom from distortion, enhanced depth-of-field and a high resolution. It has a designed specification that offers an order of magnitude improvement on the measurement accuracy of existing systems. Two examples of the Centrax, a liquid-filled and an all-glass version have been fabricated, assembled and installed into specially constructed camera bodies. The prototype has been rigorously tested to assess its perfection of construction and employed in a preliminary investigation involving a purpose-built 3 dimensional artefact. These trials have verified that the designed performance of the Centrax may already have been realised. As well as the development of the camera and its compatible colaborative targets, the associated plate measuring microscope has received attention. This research has lead to the modification of an existing precision microscope and the design of a compact measuring instrument based on moire interferometry. The principle of a spherically symmetric aperture in the Centrax has been extended to other lens designs and included in conventional camera lenses. In this way, classical photographic imaging is preserved together with the added advantages of increased depth-of-field and enhanced resolution for point source targets. A comparatitive measurement study between the Centrax system and the NPL precision 3 coordinate measuring machine, the Moore 5Z, has shown that for some applications, the Centrax may offer comparable accuracy with more simplicity of operation and a considerable saving in cost.