Many 3D systems work by presenting to the observer stereoscopic pairs of images that are combined to give the
impression of a 3D image. Discomfort experienced when viewing for extended periods may be due to several factors,
including the presence of optical crosstalk between the stereo image channels. In this paper we use two video cameras
and two LCD panels viewed via a Helmholtz arrangement of mirrors, to display a stereoscopic image inherently free of
crosstalk. Simple depth discrimination tasks are performed whilst viewing the 3D image and controlled amounts of
image crosstalk are introduced by electronically mixing the video signals. Error monitoring and skin conductance are
used as measures of workload as well as traditional subjective questionnaires. We report qualitative measurements of
user workload under a variety of viewing conditions. This pilot study revealed a decrease in task performance and
increased workload as crosstalk was increased. The observations will assist in the design of further trials planned to be
conducted in a medical environment.
Wavefront sensors, particularly those of the Hartmann-Shack type are now available in commercial form from several manufacturers. They have found increasing use in medical and industrial applications and, for consistent measurements over a range of instruments and measurement situations, traceability of measurement is essential.
We have investigated the use of simple artefacts such as an optical plate and a plano-convex lens, used with a point source, to generate prescribed values of optical aberration. Measured values obtained with Hartmann-Shack sensors are verified by comparison with calculated results and measurement by other means.
In 1940 Gabor described an optical system consisting of a pair of arrays of microlenses. The arrays were separated by the sum of their focal lengths and there was a small difference between the periods of the two arrays. The overall effect was to perform a function similar to that of a lens with dimensions much larger than the microlenses in the arrays. Images formed by this system exhibit unusual properties and appear not to obey the normal rules of optics, for example, the magnification is not necessarily equal to the ratio of image to object distances. Gabor assigned the term `superlens' to the system.
Diffracting optical components possess certain features that differ from reflecting or refracting optics. We discuss how these properties arise and illustrate how they may be used to advantage in metrology and sensing.
Arrays of small lenses have been used in many aspects of optical recording and the purpose of this paper is to describe some examples that have been realized using lenses made at the UK National Physical Laboratory. We have produced simple lenses ranging from 50 micrometers to 400 micrometers in diameter with aperture ratios of f/1 and larger and in arrays up to 120 mm X 120 mm. The lenses are formed in layers of photoresist, making use of surface tension forces to shape the refracting surface when the resist is heated to melting point. Applications range from 3D imaging to beam steering and matching of optical arrays.
The growing interest in microlenses and microlens arrays has created a need for measurement systems to characterize their performance, particularly important being the transmitted wavefront and focal length. A Mach Zehnder interferometer has been built into a microscope body to allow fast, convenient, and accurate measurement of these parameters.
A novel form of reflector, incorporating an array of microlenses, is described. Incident illumination is reflected through an angle of deviation that is nominally independent of the angle of incidence. The reflector performs a function that is similar to a retroreflector, but differs in that the angle of deviation is other than 180 degree(s). This dispenses with the need to use a beamsplitter to extract the reflected wavefront. The consequent reduction in light loss is of benefit to high speed and other forms of photography.
Microlenses have been with us for a long time as indeed the very word lens reminds us. Many early lenses,including those made by Hooke and Leeuwenhoek in the 17th century were small and resembled lentils. Many languages use the same word for both (French tilentillelt and German "Linse") and the connection is only obscure in English because we use the French word for the vegetable and the German for the optic.
Many of the applications for arrays of inicrolenses are also well established. Lippmann's work on integral photography at the turn of the century required lens arrays and stimulated an interest that is very much alive today. At one stage, lens arrays played an important part in high speed photography and various schemes have been put forward to take advantage of the compact imaging properties of
combinations of lens arrays. The fact that many of these ingenious schemes have not been developed to their full potential has to a large degree been due to the absence of lens arrays of a suitable quality and cost.
Blazed zone plates have been manufactured in germanium. A suitable surface relief pattern was first generated by recording in photoresist the circular fringes transmitted by a Fabry-Pérot interferometer. By scanning the fringe pattern and recording a series of exposures, we were able to generate a triangular groove profile. This was then transferred to the germanium substrate by ion-beam etching. By this means, diffraction efficiencies in excess of 80% have been achieved at 10μm for zone plates working in transmission and on axis.
The resolution in an image formed using a retroreflecting screen can be limited by the structure of the screen.
Improved image quality is possible by smearing the image at the screen with a diffraction grating.
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