Gerardo Trujillo-Schiaffino

Robust wave-front estimation from multiple directional derivatives

A quadratic cost functional for computing an estimate of a wave front from multiple directional derivatives is presented. This functional is robust to noise and is specially suited for moiré deflectometry, Ronchi testing, and lateral shearing interferometry.

Wave-front retrieval from Hartmann test data

In the classical Hartmann test the wave front is obtained by integration of the transverse aberrations, joining the sampled points by small straight segments, in the so-called Newton integration. This integration is performed along straight lines joining the holes on the Hartmann screen. We propose a modification of this procedure, considering the cells of four holes of the Hartmann screen to fit a small second-power wave front recovering each square. This procedure has some important advantages, as described here.

Simple Hartmann test data interpretation for ophthalmic lenses

This article describes a simple Hartmann test data interpretation that can be used to evaluate the performance of ophthalmic lenses. Considering each spot of the Hartmann pattern such as a single test ray, using simple ray tracing analysis, it is possible to calculate the power values from the lens under test at the point corresponding with each spot. The values obtained by this procedure are used to plot the power distribution map of the entire lens. We present the results obtained applying this method with single vision, bifocal, and progressive lenses.

Measurement of spectacle lenses: A review

Spectacle lenses are the most commonly used solution for refractive errors of the eye, such as myopia, hyperopia, presbyopia and astigmatism. To correct a refractive error, the spectacle lens needs to have the correct lens power and an appropriate distribution of power along the surface of the lens, to measure these characteristics several methods have been developed, this paper presents a review of some of these methods and their optical principles.

Three‐dimensional Profilometry of Solid Objects in Rotation

In this paper we present the development of a laboratory prototype to obtain the digitalization and three‐dimensional reconstruction of a solid object applying the laser line projection technique. The object under test is placed on a motorized rotary stage, a diode laser system projects a line on the object, the deformed line pattern is acquired by a CCD camera. The information for its reconstruction is extracted of the bi‐dimensional images of the deformation that the laser line suffers according to the three‐dimensional topography of the object. The present prototype digitizes an object in approximately 20 seconds without affecting it the ambient illumination.

Refractive correction measurement in an ophthalmic lens

An ophthalmic lens is designed so that its refractive power is constant when the observer looks through the center of the lens, as well as when the observation is made through the edge of the lens. This state of correction of an ophthalmic lens can be confirmed by direct measurements of the dioptric refractive power by means of a typical lens meter, if some special precautions are taken. Here we describe a method to perform these measurements.

Sphere power measuring in ophthalmic lenses by infinite fringe moiré deflectometry

We present a method to measure spherical power in ophthalmic lenses based on the measurement of moiré patterns, using the technique called infinite fringe moiré deflectometry. We develop a theoretical model using a geometrical analysis that was validated by a computer simulation using the LabVIEW software; also we build an experimental setup in which we get experimental data. As results, we obtain a measurement of the spherical power of a set of ophthalmic test lenses in the range of ± 0.50 to ± 3.00 diopters. This power is obtained by measuring the separation between each fringe of moiré pattern, from the obtained data we analyze the theoretical model and we make the necessary corrections, using polynomial regression by the method of least squares, to comply with standard ISO8598. At the same time, some components of the experimental setup were being improved to facilitate its implementation and obtain better experimental data.

Power measuring in ophthalmic lenses using lateral amplification

Nowadays refractive errors in the human eye affect approximately 10% of world’s population, decreasing vision acuity and life quality. However a simple common solution is the use of an adequate ophthalmic lens. Due to the importance of ophthalmic lenses, the best measurement equipment is required for testing, these days experimental and commercial apparatus are available but with the possibility of improvement. We present a method to measure spherical and cylindrical power in ophthalmic lenses. The system uses an equation obtained from lateral amplification concept and Gauss formula to make calculations. Also an experimental setup is presented for the measurement of ophthalmic lens from -20 diopters to 20 diopters in the case of spherical lenses, and from -6 diopters to 6 diopters in the case of cylindrical lenses. The setup contains a reference object, the lens to be tested and a digital camera connected to a computer with software designed in LabVIEW for the data processing. Satisfactory preliminary results were obtained according to ISO 8598.

Surfaces Relief Profilometry of Solid Objects by Sweeping of a Laser Line

This paper describes the development of a laser system for the digitalization and three‐dimensional reconstruction of solid objects. The first step consists of applying on the object a linear sweeping of a thin laser line using a laser diode with 635 nm and 5 mW, a motorized stage for linear displacement of 138 mm, and a controller with RS232 interface. The next step consists of capturing and transmitting the image of the deformed line on the object to a computer. For this step was used a monochrome camera CCD, and an image acquisition board. The last step consists of the three‐dimensional reconstruction of the solid object. All the corresponding algorithms were implemented using the programming language LabVIEW.