Compact design of projection lens for 3D profilometry based on interferometric fringes

As for the new type of 3D fringe-based profilometry we proposed, a compact projection lens is designed to meet the requirements of interferometric fringes magnification. Fringe projection profilometry requires that the projection lens has super short focus length and wide field of view (FOV) as well as large projection area as possible. In this case, the measurement system is able to capture a frame of fringe map with enough information of object and achieve a high accuracy. Thus the projection lens was designed with focus length of 9.45 mm, F-number of 2.8 and FOV of 72.45°. The total track of lens was 76.355 mm, less than 80 mm. The projection resolutions were 800 × 600 pixels. The lens design showed that the modulation transfer function (MTF) is higher than 80% at 32 lp/mm for all field angles. The maximum distortion was about −3.0% at field angle of 72.45°. According to the size requirement of measured object, the projection area was 40″ at the distance of 1 m. Therefore, the compact lens design with super short focus length and wide FOV as well as large projection area is absolutely adaptable for the 3D fringe-based profilometry which is shown in this paper. Meanwhile, the proposed lens design could also be used for the mini LCoS (Liquid Crystal on Silicon) projector.