We propose in this work a model for describing visual acuity (V) as a function of defocus and pupil diameter. Although the model is mainly based on geometrical optics, it also incorporates nongeometrical effects phenomenologically. Compared to similar visual acuity models, the proposed one considers the effect of astigmatism and the variability of best corrected V among individuals; it also takes into account the accommodation and the “tolerance to defocus,” the latter through a phenomenological parameter. We have fitted the model to the V data provided in the works of Holladay et al. and Peters, showing the ability of this model to accurately describe the variation of V against blur and pupil diameter. We have also performed a comparison between the proposed model and others previously published in the literature. The model is mainly intended for use in the design of ophthalmic compensations, but it can also be useful in other fields such as visual ergonomics, design of visual tests, and optical instrumentation.
With the advent of techniques devised for the mass production of optical components made with surfaces of arbitrary form (also known as free form surfaces) in the last years, a parallel development of measuring systems adapted for these new kind of surfaces constitutes a real necessity for the industry. Profilometry is one of the preferred methods for the assessment of the quality of a surface, and is widely employed in the optical fabrication industry for the quality control of its products. In this work, we present the design, development and assembly of a new profilometer with five axis of movement, specifically suited to the measurement of medium size (up to 150 mm of diameter) "free-form" optical surfaces with sub-micrometer accuracy and low measuring times. The apparatus is formed by three X, Y, Z linear motorized positioners plus and additional angular and a tilt positioner employed to locate accurately the surface to be measured and the probe which can be a mechanical or an optical one, being optical one a confocal sensor based on chromatic aberration. Both optical and mechanical probes guarantee an accuracy lower than the micrometer in the determination of the surface height, thus ensuring an accuracy in the surface curvatures of the order of 0.01 D or better. An original calibration procedure based on the measurement of a precision sphere has been developed in order to correct the perpendicularity error between the axes of the linear positioners. To reduce the measuring time of the profilometer, a custom electronics, based on an Arduino™ controller, have been designed and produced in order to synchronize the five motorized positioners and the optical and mechanical probes so that a medium size surface (around 10 cm of diameter) with a dynamic range in curvatures of around 10 D, can be measured in less than 300 seconds (using three axes) keeping the resolution in height and curvature in the figures mentioned above.
Fresnel lenses and other faceted or micro-optic devices are increasingly used in multiple applications like solar light
concentrators and illumination devices, just to name some representative. However, it seems to be a certain lack of
adequate techniques for the assessment of the performance of final fabricated devices. As applications are more exigent
this characterization is a must. We provide a technique to characterize the performance of Fresnel lenses, as light
collection devices. The basis for the method is a configuration where a camera images the Fresnel lens aperture. The
entrance pupil of the camera is situated at the focal spot or the conjugate of a simulated solar source. In this manner,
detailed maps of the performance of different Fresnel lenses are obtained for different acceptance angles.
Fresnel lenses and other faceted or micro-optic devices are increasingly used in multiple applications like solar light
concentrators and illumination devices. As applications are more exigent this characterization is of increasing
importance. We present a technique to characterize the surface topography of optical surfaces. It is especially well
adapted to Fresnel lenses where abrupt surface slopes are usually difficult to handle in conventional techniques. The
method is based on a new photometric strategy able to codify the height information in terms of optical absorption in a
liquid. A detailed topographic map is simple to acquire by capturing images of the surface. Some experimental results
are presented. A single pixel height resolution of ~0.1 μm is achieved for a height range of ~50 μm. A surface slope
analysis is also made achieving a resolution of ~±0.15°.
We present a variable spectral and angular light source generator. The design and presented results are focused on solar
radiation simulation, reproducing the spectral and angular distribution observed from the sun. This system is particularly
interesting in the area of solar concentration. It permits to measure and test multi-junction photovoltaic cells alone or
together with concentrating optics. We present some system setups and its performance in reproducing solar radiation
around the visible band.
XtremeFringe is a new library for fringe pattern processing which incorporates modern methods for automatic
analysis including fringe pattern demodulation, fringe pattern filtering and phase unwrapping methods. XtremeFringe
is written in C# and is usable as an assembly from any .NET language (C#, C++ .NET, J#) and additionally as a
Matlab toolbox, which ensures an easy adaptation in custom applications, providing the user with a versatile and
powerful tool for fringe pattern analysis in a flexible way. The functions of XtremeFringe are suitable to be employed
in metrological applications such interferometry, photoelasticity, Moire techniques, holography, etc. supplying the user
with up-to-date fringe analysis tools.
In this work, we demonstrate the capabilities of the XtremeFringe library, processing different examples showing the
ability of the library to analyze complex fringe patterns in a fast, reliable and automatic way.
Phase detection is an important issue when dealing with optical metrology techniques for which the magnitude to be
measured is encoded through the phase of a given fringe pattern. Asynchronous phase detection techniques are
employed when the rate of phase change (frequency) it is not known. These techniques always present a variable
frequency response, in other words, their ability to recover properly the phase depends strongly on the local frequency.
In many experiments, it is possible to have a rough knowledge about the range of frequencies involved. Therefore, it
constitutes a great advantage to have a procedure to design an asynchronous demodulation method which is suited to a
particular frequency response for a given experiment. In this way, we get a better behaviour against noise which leads to
more accurate and reliable phase extraction.
In this work we present a technique to design asynchronous demodulation algorithms with a desired frequency response
using a Fourier-based technique. The method allows the design of algorithms with a limited algebraic error in the
recovered phase which have better properties than standard asynchronous phase detection techniques as it is shown in
numeric and real experiments.
We present a high-speed 3-D spatiotemporal shape measurement technique by means of structured light. Current methods use a constant number of images that do not take into account the available temporal continuity of the measured object. That is, they focus on acquiring and processing as quickly as possible a fixed number of images to solve for the correspondence problem and later obtain the 3-D shape by triangulation. The number of images used imposes the use of some spatial support. The major contribution of our research is a new spatiotemporal scheme that, depending on the object's movement, adaptively uses the maximum number of projected images consistent with the local temporal continuity, therefore solving the correspondence problem with the minimum possible spatial support for each position. This is achieved by the use of a hybrid color pattern composed of an analog sinusoidal periodic code in the red channel and a digital binary spatial code in the blue channel that is cyclically displaced. No subpixel calculation is used and it is possible to implement error correction strategies that make the method fast and reliable, enabling dynamic online 3-D measurement of objects in movement.
In this work, we present a method for the asynchronous direct demodulation of spatiotemporal fringe patterns by the estimation of the quadrature sign (sign of the fringe pattern quadrature signal) from one of the irradiance gradient components. The technique is based in the normalization of one plane of a spatio-temporal fringe pattern, an arcos demodulation and a final sign correction by means of the estimated quadrature sign. We present two experimental applications of the direct demodulation method presented. The first application is the measurement of surface topography by RGB Shadow-Moire. The second application is isochromatics retardation measurement by load stepping photoelasticity. In both cases good results are obtained confirming the suitability of the presented technique.
In fringe pattern processing, quadrature operators are useful to obtain the corresponding modulating phase. In the case that a carrier exists (spatial or temporal), there are good methods for phase demodulation as Fourier analysis and asynchronous methods, for example. However, if there is no carrier or is too low, robust demodulation from a single image is a difficult task.
In this work we present some recent advances in the processing of single fringe patterns with closed fringes based in a isotropic n-dimensional quadrature transform. In particular we address several problems related with the application of this quadrature operator. One of these problems is the Fringe direction, its role in the demodulation process is discussed and a practical method for its computation is presented. Fringe pattern normalization is also an important subject in the demodulation process from a singe image, taking this into account we present a technique for isotropic fringe pattern normalization based in the n-dimensional quadrature transform. All these techniques together configure a robust method for automatic demodulation of single fringe patterns. The performance and limitations of the method are discussed and illustrated by experimental results.
We have developed a prototype for in-line detection of surface defects in metallic wires, specially for scratches. A simple geometrical relationship between surface topography and conical reflection, permits to correlate the defects with intensity patterns in a simple way. The presented apparatus consists basically in a grating-divided laser beam incident on angular equidistant points. A CCD and an associated optics capture the information of the whole wire perimeter at once. Analytic rudiments are provided in agreement with the experimental results.
We have computed the prismatic effects presented by several kinds of ophthalmic lenses: spherical, aspherical and spherotorical ones by means of the generalized expression of the Prentice's law. This expression use the local dioptric power matrix formalism (developed by us in previous works) in order to compute the prismatic deviation of the light rays along the surface of an ophthalmic lens made by arbitrary refracting surfaces with an acceptable degree of accuracy. This formalism allows the computation of prismatic powers without employing numerical ray tracing. We have compare the calculated prismatic effects with those obtained by means of numerical ray tracing finding a good agreement between them.
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