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1.
J Opt Soc Am A Opt Image Sci Vis ; 37(8): 1381-1389, 2020 Aug 01.
Artículo en Inglés | MEDLINE | ID: mdl-32749272

RESUMEN

Placido disk methods for corneal topography use a target with concentric rings in order to obtain measurements of the corneal surface, codifying the topography from the deformations of the rings' image. Knowing exactly how the corneal surface departs from a rotational symmetric shape is difficult by using Placido rings. This is due to the fact that any ray deviations in the angular direction (sagittal transverse aberrations) are not easily detected and measured. This is the so-called skew ray error. For that reason, this technique has been considered as limited, especially when one tries to measure corneal aberrations with large rotational symmetry errors. However, we considered that the Placido disk topography has the potential to obtain a full description of the corneal surface as long as the skew ray error is fixed. Here, we present a solution based in the assumption that a corneal topography calculated with the presence of the skew ray error has hidden information that can be extracted by applying some basis of the classical Hartmann test. To achieve that solution, we improve some aspects of the Hartmann test to be later applied in the processing of Placido disk images. Our solution gives us the ability to solve the skew ray error in a simple and direct method, with an effectiveness that is probed by the computing of some simulated representative surfaces without rotational symmetry and the performance of our algorithm.

2.
Appl Opt ; 56(7): 1898-1907, 2017 Mar 01.
Artículo en Inglés | MEDLINE | ID: mdl-28248387

RESUMEN

Instead of measuring the wavefront deformations, Hartmann and Shack-Hartmann tests, we measure the wavefront slopes, which are equivalent to the ray transverse aberrations. Numerous different integration methods have been described in the literature to obtain the wavefront deformations from these measurements. Basically, they can be classified in two different categories, i.e., modal and zonal. In this paper, we describe a proposed new zonal procedure. This method finds a different analytical expression for each square cell formed by four sampling points in the pupil of the system. In this manner, a full single analytical expression for the wavefront is not obtained. The advantage is that small localized errors that cannot be adjusted by a single polynomial function can be represented with this method. A second advantage is that the analytical function for each cell is obtained in an exact manner, without the errors in a trapezoidal integration.

3.
Appl Opt ; 56(4): 1215-1224, 2017 Feb 01.
Artículo en Inglés | MEDLINE | ID: mdl-28158136

RESUMEN

In a previous work, we introduced the concept of transversal aberrations {U,V} calculated at arbitrary Hartmann-plane distances z=r [Appl. Opt.55, 2160 (2016)APOPAI1559-128X10.1364/AO.55.002160]. These transversal aberrations can be used to estimate the wave aberration function W, as well as the classical transversal aberrations {X,Y} calculated at a theoretical plane z=f, where f is the radius of a reference semisphere. However, when the ray identification is difficult to achieve at z=f, the use of {U,V} can be of great help. In the context of a least-squares fitting of the Hartmann data, the use of {U,V} is proposed by analyzing some simple examples for the case of a W with aberration terms up to the third order. These examples also consider the hypothesis f≫W, as presented in the majority of the optical applications.

4.
Appl Opt ; 55(9): 2160-8, 2016 03 20.
Artículo en Inglés | MEDLINE | ID: mdl-27140548

RESUMEN

In the Hartmann test, a wave aberration function W is estimated from the information of the spot diagram drawn in an observation plane. The distance from a reference plane to the observation plane, the Hartmann-plane distance, is typically chosen as z=f, where f is the radius of a reference sphere. The function W and the transversal aberrations {X,Y} calculated at the plane z=f are related by two well-known linear differential equations. Here, we propose two nonlinear differential equations to denote a more general relation between W and the transversal aberrations {U,V} calculated at any arbitrary Hartmann-plane distance z=r. We also show how to directly estimate the wavefront surface w from the information of {U,V}. The use of arbitrary r values could improve the reliability of the measurements of W, or w, when finding difficulties in adequate ray identification at z=f.

5.
Appl Opt ; 54(28): E113-22, 2015 Oct 01.
Artículo en Inglés | MEDLINE | ID: mdl-26479640

RESUMEN

A least-squares procedure to find the tilts, curvature, astigmatism, coma, and triangular astigmatism by means of measurements of the transverse aberrations using a Hartmann or Shack-Hartmann test is described. The sampling points are distributed in a ring centered on the pupil of the optical system. The properties and characteristics of rings with three, four, five, six, or more sampling points are analyzed with more detail and better mathematical analysis than in previous publications.

6.
J Opt Soc Am A Opt Image Sci Vis ; 32(1): 35-45, 2015 Jan 01.
Artículo en Inglés | MEDLINE | ID: mdl-26366488

RESUMEN

In optical design, many error functions can be used to generate an optical system with desired characteristics. These error functions are optimized by iterative algorithms. However, these error functions should be theoretically and mathematically differentiable to be optimized. In this paper, the differentiability of an error function is partially justified. The error function herein is called the projection functional. This proposed projection functional can be used to estimate the coefficients of an arbitrary lens with conic surfaces by means of the spot distributions on two planes produced by a fixed Hartmann plate. The differentiability of the projection functional is required to guarantee the existence of its Jacobian matrix, which is a suitable condition to minimize this functional by iterative methods. Numerical examples of the functional minimization are given.

8.
Appl Opt ; 54(9): 2296-301, 2015 Mar 20.
Artículo en Inglés | MEDLINE | ID: mdl-25968514

RESUMEN

In this paper we will review some of the many different practical arrangements that have been obtained to measure the transversal aberrations of optical systems based on the odd and vulnerable Hartmann test. There are many optical testing configurations that apparently are not related to the original Hartmann test. However, they are really the same thing and can be considered just a variation of the same basic arrangement, as will be described here.

9.
Appl Opt ; 53(31): 7422-34, 2014 Nov 01.
Artículo en Inglés | MEDLINE | ID: mdl-25402908

RESUMEN

Instead of measuring the wavefront deformations, Hartmann and Shack-Hartmann tests measure wavefront slopes, which are equivalent to ray transverse aberrations. Numerous integration methods have been described in the literature to obtain the wavefront deformations from these measurements. Basically, they can be classified in two different categories, i.e., modal and zonal. Frequently, a least squares fit of the transverse aberrations in the x direction and a least squares fit of the transverse aberrations in the y direction is performed to obtain the wavefront. In this work, we briefly describe a modal method to integrate Hartmann and Shack-Hartmann patterns by means of a single least squares fit of the transverse aberrations simultaneously instead of the traditional x-y separate method. The proposed method uses monomial calculation instead of using Zernike polynomials, to simplify numerical calculations. Later, a method is proposed to convert from monomials to Zernike polynomials. An important obtained result is that if polar coordinates are used, angular transverse aberrations are not actually needed to obtain all wavefront coefficients.

10.
Appl Opt ; 53(16): 3438-47, 2014 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-24922418

RESUMEN

Principal meridians of the corneal vertex of the human ocular system are not always orthogonal. To study these irregular surfaces at the vertex, which have principal meridians with an angle different from 90°, we attempt to define so-called parastigmatic surfaces; these surfaces allow us to correct several classes of irregular astigmatism, with nonorthogonal principal meridians, using a simple refractive surface. We will create a canonical surface to describe the surfaces of the human cornea with a short and simple formula, using two additional parameters to the current prescription: the angle between principal meridians and parharmonic variation of curvatures between them.


Asunto(s)
Aumento de la Imagen/instrumentación , Interpretación de Imagen Asistida por Computador/instrumentación , Dispositivos Ópticos , Refractometría/instrumentación , Resonancia por Plasmón de Superficie/instrumentación , Diseño de Equipo , Análisis de Falla de Equipo
11.
J Opt Soc Am A Opt Image Sci Vis ; 31(4): 846-51, 2014 Apr 01.
Artículo en Inglés | MEDLINE | ID: mdl-24695148

RESUMEN

Instead of measuring the wavefront deformations directly, Hartmann and Shack-Hartmann tests measure the wavefront slopes, which are equivalent to the ray transverse aberrations. Numerous different integration methods have been described in the literature to obtain the wavefront deformations from these measurements. Basically, they can be classified in two different categories, i.e., modal and zonal. In this work we describe a modal method to integrate Hartmann and Shack-Hartmann patterns using orthogonal wavefront slope aberration polynomials, instead of the commonly used Zernike polynomials for the wavefront deformations.

12.
J Opt Soc Am A Opt Image Sci Vis ; 30(8): 1670-9, 2013 Aug 01.
Artículo en Inglés | MEDLINE | ID: mdl-24323228

RESUMEN

The Fourier analysis of two-stage phase-shifting (TSPS) algorithms is growing in interest as a research topic, specifically, the algorithm's insensitivity properties to various error sources. The main motivation of this paper is to propose TSPS algorithms that perform well in the face of detuning and harmonics for each of the two sets of interferograms with different or equal reference frequencies. TSPS algorithms based on the development of generalized equations consider both the frequency sampling functions that represent them and nonconstant phase shifts.

13.
J Opt Soc Am A Opt Image Sci Vis ; 29(4): 431-41, 2012 Apr 01.
Artículo en Inglés | MEDLINE | ID: mdl-22472818

RESUMEN

From generalized phase-shifting equations, we propose a simple linear system analysis for algorithms with equally and nonequally spaced phase shifts. The presence of a finite number of harmonic components in the fringes of the intensity patterns is taken into account to obtain algorithms insensitive to these harmonics. The insensitivity to detuning for the fundamental frequency is also considered as part of the description of this study. Linear systems are employed to recover the desired insensitivity properties that can compensate linear phase shift errors. The analysis of the wrapped phase equation is carried out in the Fourier frequency domain.

14.
Appl Opt ; 51(9): 1257-65, 2012 Mar 20.
Artículo en Inglés | MEDLINE | ID: mdl-22441470

RESUMEN

A simple phase estimation employing cubic and average interpolations to solve the oversampling problem in smooth modulated phase images is described. In the context of a general phase-shifting process, without phase-unwrapping, the modulated phase images are employed to recover wavefront shapes with high fringe density. The problem of the phase reconstruction by line integration of its gradient requires a form appropriate to the calculation of partial derivatives, especially when the phase to recover has higher-order aberration values. This is achieved by oversampling the modulated phase images, and many interpolations can be implemented. Here an oversampling procedure based on the analysis of a quadratic cost functional for phase recovery, in a particular case, is proposed.

15.
Appl Opt ; 50(21): 4083-90, 2011 Jul 20.
Artículo en Inglés | MEDLINE | ID: mdl-21772395

RESUMEN

In this manuscript, some interesting properties for generalized or nonuniform phase-shifting algorithms are shown in the Fourier frequency space. A procedure to find algorithms with equal amplitudes for their sampling function transforms is described. We also consider in this procedure the finding of algorithms that are orthogonal for all possible values in the frequency space. This last kind of algorithms should closely satisfy the first order detuning insensitive condition. The procedure consists of the minimization of functionals associated with the desired insensitivity conditions.

16.
Appl Opt ; 49(32): 6224-31, 2010 Nov 10.
Artículo en Inglés | MEDLINE | ID: mdl-21068852

RESUMEN

In this work, we have developed a different algorithm than the classical one on phase-shifting interferometry. These algorithms typically use constant or homogeneous phase displacements and they can be quite accurate and insensitive to detuning, taking appropriate weight factors in the formula to recover the wrapped phase. However, these algorithms have not been considered with variable or inhomogeneous displacements. We have generalized these formulas and obtained some expressions for an implementation with variable displacements and ways to get partially insensitive algorithms with respect to these arbitrary error shifts.

17.
Appl Opt ; 49(12): 2302-8, 2010 Apr 20.
Artículo en Inglés | MEDLINE | ID: mdl-20411009

RESUMEN

A wavefront aberration can be retrieved from a defocused image or a Hartmanngram by several different methods using diffraction theory and Fourier transforms. In this manuscript, we describe an alternate method for wavefront aberration determination from a defocused image or a Hartmanngram using a geometric l approximation. The main assumption is that the image is defocused, with the observation plane outside the caustic limits. The result will be applied to the retrieval of a wavefront with primary aberrations from a Hartmanngram or defocused image without the need for any transversal aberration integration.

18.
Appl Opt ; 44(20): 4228-38, 2005 Jul 10.
Artículo en Inglés | MEDLINE | ID: mdl-16045209

RESUMEN

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.

19.
Appl Opt ; 43(21): 4123-6, 2004 Jul 20.
Artículo en Inglés | MEDLINE | ID: mdl-15291053

RESUMEN

Keystone distortion that occurs in overhead projectors when the projecting lens head is tilted upward to a high screen is commonly observed. Here we suggest a modification of the typical overhead projector to eliminate this distortion of the image.

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