3D sensors based on pattern projection are a popular measuring instrument for the three-dimensional acquisition of people, e.g., for identification purposes or for human-machine interaction. State-of-the-art sensors typically project the pattern(s) at a wavelength of 850 or 940 nm. Although illumination at these wavelengths is barely perceptible or completely imperceptible to the human eye, almost 80 or 50% of the incident radiation reaches the retina. In order to make the 3D measurement of faces not only free of disturbance, but also to make it considerably easier to fall below the limits for retinal exposure, the short-wave infrared (SWIR) is well suited. For instance, at a wavelength of 1450 nm, only a negligible portion of the incident radiation hits the lens of the eye, let alone the retina. Since the terrestrial solar spectrum has a minimum in this wavelength range, the susceptibility to natural ambient light is also reduced. Therefore, we have developed an SWIR 3D scanner, which we present and characterize in this article.
In general, spherochromatism is denoted as the color variation of spherical aberration in refracting optical systems. If primary axial and lateral color is corrected, in most of the cases spherochromatism is the dominating chromatic aberration. However, in literature only some selected design examples and certain special cases were discussed, but a general analytical 3rd-order description based on the chromatic variation of Seidel’s surface contribution for spherical aberration, has not been considered yet. Since furthermore, those selected design examples indicates that spherochromatism is expected to show induced aberration parts, caused by the primary color aberrations of the system, this paper introduces a new description of the 3rd-order surface contribution for spherochromatism and gives a discussion on its dependencies on intrinsic and induced aberration parts.
In this paper, we are reporting a systematic investigation of striae tolerance in various optical systems. A surface-based phase plate model and a volume striae model are given to simulate the striae strength that introduces optical path difference. The striae could be modeled at an arbitrary location in the element and with both rectangular and cosine shape. Concerning the striae functionality, various criteria were investigated and combined for system analysis, which particularly demonstrate the impact of striae on resolution, distortion and chromatic aberration. Three characteristic optical system types, aperture-dominant, field-dominant and front aperture systems, are investigated in system tolerancing. Both the analysis of striae at different position and in different systems were implemented. According to the study, the impact of striae is related with the marginal ray, chief ray and material properties. Consequently, based on the quantitative analysis, recommendations for the right choice of glass striae grades could be given in optical system tolerancing, which is beneficial to both the optical designer and glass vendors.
The correction of modern microscopic lenses is rarely described in literature. Here an outline of the basic methods of correction is given and a systematic approach to design various types of lenses is proposed.