... By taking into account the area of the filament and the geometric conditions, acalculation by... more ... By taking into account the area of the filament and the geometric conditions, acalculation by the Van Citter-Zernike expression proved that this source was spatially incoherent. ... According to theorem of Van Citter-Zernike they will be : g/ = r Where F denotes Fourier transform, ...
SUMMARY : The process of comparing analogous images digi- tally obtained by means of a T.V. camer... more SUMMARY : The process of comparing analogous images digi- tally obtained by means of a T.V. camera is studied. This images suffer degradation owing to defocusing, variation in the degree of coherence or because of later application of digital smoothing filters. A numerical quality criterion based on the transfer function, the degree of coherence and a similarity coefficient is developped which put the images in the same order as established by several observers. The application of this criterion permits the automatic comparison and ordering of these images.
We present a new strategy to calculate an optimized refractive freeform surface for illumination ... more We present a new strategy to calculate an optimized refractive freeform surface for illumination purposes with a LED source. The goal of this paper is to present a new iterative flux based strategy to design plastic lens for LED lighting solutions. The new strategy considers the energy emission pattern of the LED and adjusts a plastic refractive surface to accomplish the target intensity distribution. This paper is divided in four parts, a brief introduction to LED systems and reviewing optical design strategies, the method of calculus is exposed in the second part, third part presents the results for a particular refractive optical design developed by new presented algorithm and finally, a set of conclusions about strategy is showed in fourth part.
A powerful technique is presented for processing complex fringe patterns with high noise levels a... more A powerful technique is presented for processing complex fringe patterns with high noise levels and arbitrary distributions of spatial frequencies, which can successfully extract the phase information. Artifacts that arise from phase extraction in local filtering approaches are avoided by using a simple design and implementation strategy for the adaptive filter, based on the theory of digital filter design used in electronics, and applied to pixel rows (or columns) in the fringe-pattern. The filter designed in this manner is then applied to phase extraction in an experimental fringe pattern measured in a digital Ronchi test setup using a Carré phase-shifting procedure. The filtering strategy has a very low computational cost and allows phase extraction in noisy ronchigrams regardless their spatial frequency distribution, provided the fringes are still visible.
A high-precision, low-cost tool for optimal alignment of a compensator group in anamorphic object... more A high-precision, low-cost tool for optimal alignment of a compensator group in anamorphic objectives is presented. The system provides highly accurate information by analyzing the axis and field PSFs in the focal plane of the optical system under test. The PSFs are provided by a bundle of 9 different pigtailed laser diodes placed in the object field, and they are recorded by a lensless 2/3" CCD camera. The comparison of the simulated and obtained PSFs allows determining the optical element introducing the differences so action may be taken precisely on that element. The system is especially useful in non-rotationally symmetrical systems, where errors in axis position result into asymmetries of the PSF images. The tool is used for precise alignment of the cylindrical lenses in the compensator group of an anamorphic objective prior to sealing. Results show the system is able to detect misalignments of 100μm and axis positioning errors of just 30arcsec using off-the-shelf components without the need of high-precision positioning equipment.
Third-order aberrations need the paraxial raytracing of a marginal as well as principal ray throu... more Third-order aberrations need the paraxial raytracing of a marginal as well as principal ray through the entire system to be determined. When the optical system has GRIN media, even the paraxial raytrace could be cumbersome. This work presents the use of the ABCD matrix for obtaining the raytracing of those rays and, thus, it could ease the calculation of the third-order aberration coefficients, i.e. contribution of GRIN to surface refraction and transfer, for each individual surface of GRIN optical elements. A procedure to be implemented in any modern commercial optical software has been presented and evaluated for simple systems.
The present works depicts a measurement technique intended to enhance the characterization proced... more The present works depicts a measurement technique intended to enhance the characterization procedures of the photometric emissions of automotive headlamps, with potential applications to any light source emission, either automotive or non-automotive. A CCD array with a precisely characterized optical system is used for sampling the luminance field of the headlamp just a few centimetres in front of it, by combining deflectometric techniques (yielding the direction of the light beams) and photometric techniques (yielding the energy travelling in each direction). The CCD array scans the measurement plane using a self-developed mechanical unit and electronics, and then image-processing techniques are used for obtaining the photometric behaviour of the headlamp in any given plane, in particular in the plane and positions required by current normative, but also on the road, on traffic signs, etc. An overview of the construction of the system, of the considered principle of measurement, and of the main calibrations performed on the unit is presented. First results concerning relative measurements are presented compared both to reference data from a photometric tunnel and from a plane placed 5m away from the source. Preliminary results for the absolute photometric calibration of the system are also presented for different illumination beams of different headlamps (driving and passing beam).
We present a simple method for increasing the number of data points obtained during performance o... more We present a simple method for increasing the number of data points obtained during performance of profilometric measurements with the Ronchi test. The method is based on multiple ronchigram acquisitions that are superimposed after a few very simple data-processing operations. The measurement method, experimental setup, and data processing are described in detail from the ronchigram to the measured profile, and experimental results for a concave surface of an spherical ophthalmic lens are provided. The radius of curvature values measured for that surface are compared with the ones obtained with a high-precision radioscope, showing very good agreement and demonstrating the capability of the technique to measure topographic profiles of reflective samples.
Recently, telescopes with segmented primary mirrors are becoming increasingly popular due to thei... more Recently, telescopes with segmented primary mirrors are becoming increasingly popular due to their ability of achieving large apertures without the inconveniences caused by the fabrication and handling of monolithic surfaces with 8m (or over) in diameter. The difference in position of each pair of adjacent segments along the local normal of their interface (called piston hereafter), however, needs to be precisely measured in order to provide a diffraction- limited image. If a system yielding the nanometric accuracy required in piston measurements worked in daylight hours, the resultant saving in observation time would be an important advance on a majority of the state-of-the-art piston measurement systems. An interferometric piston measurement instrument accomplishing such objectives has been designed starting from the usual Michelson configuration at the CD6 (Terrassa, Spain), and its final test has been carried out in the test workbench of the Instituto de Astrofisica de Canarias (IAC, Canary Islands, Spain). Its optical layout relies on projecting the reference arm of the interferometer onto one of the segments of the pair considered, along the direction of the local normal to the surface while the measurement arm is projected onto the interface which divides the pair of segments considered. The field of view and its illumination are calculated to be equivalent in both segments. The lateral shift of the fringes in both interferograms determines the piston error present. A combination of monochromatic and white light is used, in order to remove the (lambda) /2 phase ambiguities present in piston measurements without losing the required resolution in the measurement. In this paper, the optical design of this interferometric piston measurement instrument will be presented. The particular configuration used in the interferometer, the implementation of an imaging system allowing to see both the interface of the segments and the interference fringes, the effect of the extension of the source and the use of both monochromatic and whit light will be discussed. A detailed study of the wavefront errors embedded in the wavefront at different stages of the interferometer is performed. The analysis shows the validity of the design of the instrument, and some experimental results obtained at the test workbench are provided to demonstrate the ability of the instrument to perform nanometric piston measurements under daylight conditions.
Illumination engineering is a field that spans many topics and the number industries that activel... more Illumination engineering is a field that spans many topics and the number industries that actively work in the field is expanding. In this field the efficiency of the design is only a part of the design. Of nearly the same importance is the distribution of the light at the target. Many times the factors that are necessary to develop an illumination system will contradict one another, thus making the design of illumination systems complex and demanding. Optical modeling plays a basic role in obtaining new models. In general, the LED optical model obtains its parameters as a mathematical transformation or the average of a large set of measured experimental data. The main goal of this paper is to measure directly the parameters of the LED optical model. We use the typical LED spatial distribution model based on ray distribution. The basic parameters of this model are: the slope of the ray and the energy of each ray. The measurement system incorporates the slope measuring method used in deflectometry into an energy measurement technique. The method was tested using the measured data of two LEDs to analyze the illumination distribution provided at the image screen of standard Köhler illumination system.
In this work, an improvement of a previously-published human eye model with aging is presented. T... more In this work, an improvement of a previously-published human eye model with aging is presented. The previous eye model showed the overestimated performance of an averaged MTF at low spatial frequencies at all ages. Since that model had rotationally symmetrical corneal surfaces, these have been modeled to resemble an astigmatic element according to the recent experimental published data and have been included to produce a more accurate eye model. The gradient refractive index (GRIN) profile proposed for the crystalline lens has not been modified to test its robustness. Further, a tilt and decentration of the lens, and only a decentration for the iris, have been permitted in order to fit the average performance of the new eye model with aging. The results demonstrate that the GRIN profile for the crystalline lens fits the model well, since the decentration and/or tilt of the lens and the iris are sufficient free parameters to simulate the performance of the retinal image quality of an emmetropic human eye with aging, having an average astigmatic cornea.
We present an alternative formal calculation of the scaled Zernike coefficient expansion by means... more We present an alternative formal calculation of the scaled Zernike coefficient expansion by means of the inner product of the Zernike polynomials and the wavefront error corresponding to the scaled pupil. The relationship exhibited by the radial polynomials and Bessel functions leads to a general expression in terms of the Gauss hypergeometric function. Direct properties and index selection rules are established, and easy derivation of the non-normalized coefficients is also straightforward.
We present a system allowing the determination of the distribution of light at any given distance... more We present a system allowing the determination of the distribution of light at any given distance (e.g. 25m) from a light source, by measuring the intensity and direction of the illumination distribution at a closer distance (e.g. near 20 cm). The measurement principle is based on the acquisition of images taken by a CCD matrix-sensor through an optical system focused at infinity. A sequence of images is obtained by moving the camera at different positions in front of the source. The process involves the accumulation of shifted images and corrections for optics (geometrical distortion and vignetting) and electronic shutter (exposure time). We describe the developed experimental set-up and the calibration procedures needed to obtain absolute photometric values. We present results obtained for automotive headlamps: computed relative illumination distribution is very similar to that obtained using a reference given by a measurement tool using a lightmeter. Absolute calibration of the system is performed from the set of measured points
This paper proposes an instrument allowing the accurate characterization of the energetic distrib... more This paper proposes an instrument allowing the accurate characterization of the energetic distribution of a given source at a distant plane positioned at will. This is achieved by measuring the light pattern leaving the source by applying deflectometric techniques and photometric measurements, and then applying raytracing algorithms in order to propagate this distribution to a distant plane. The techniques allow a very compact setup, and a prototype of the optomechanical system has been implemented and tested. The system is intended to substitute the photometric tunnels now in use for testing, for instance, automotive reflectors.
... By taking into account the area of the filament and the geometric conditions, acalculation by... more ... By taking into account the area of the filament and the geometric conditions, acalculation by the Van Citter-Zernike expression proved that this source was spatially incoherent. ... According to theorem of Van Citter-Zernike they will be : g/ = r Where F denotes Fourier transform, ...
SUMMARY : The process of comparing analogous images digi- tally obtained by means of a T.V. camer... more SUMMARY : The process of comparing analogous images digi- tally obtained by means of a T.V. camera is studied. This images suffer degradation owing to defocusing, variation in the degree of coherence or because of later application of digital smoothing filters. A numerical quality criterion based on the transfer function, the degree of coherence and a similarity coefficient is developped which put the images in the same order as established by several observers. The application of this criterion permits the automatic comparison and ordering of these images.
We present a new strategy to calculate an optimized refractive freeform surface for illumination ... more We present a new strategy to calculate an optimized refractive freeform surface for illumination purposes with a LED source. The goal of this paper is to present a new iterative flux based strategy to design plastic lens for LED lighting solutions. The new strategy considers the energy emission pattern of the LED and adjusts a plastic refractive surface to accomplish the target intensity distribution. This paper is divided in four parts, a brief introduction to LED systems and reviewing optical design strategies, the method of calculus is exposed in the second part, third part presents the results for a particular refractive optical design developed by new presented algorithm and finally, a set of conclusions about strategy is showed in fourth part.
A powerful technique is presented for processing complex fringe patterns with high noise levels a... more A powerful technique is presented for processing complex fringe patterns with high noise levels and arbitrary distributions of spatial frequencies, which can successfully extract the phase information. Artifacts that arise from phase extraction in local filtering approaches are avoided by using a simple design and implementation strategy for the adaptive filter, based on the theory of digital filter design used in electronics, and applied to pixel rows (or columns) in the fringe-pattern. The filter designed in this manner is then applied to phase extraction in an experimental fringe pattern measured in a digital Ronchi test setup using a Carré phase-shifting procedure. The filtering strategy has a very low computational cost and allows phase extraction in noisy ronchigrams regardless their spatial frequency distribution, provided the fringes are still visible.
A high-precision, low-cost tool for optimal alignment of a compensator group in anamorphic object... more A high-precision, low-cost tool for optimal alignment of a compensator group in anamorphic objectives is presented. The system provides highly accurate information by analyzing the axis and field PSFs in the focal plane of the optical system under test. The PSFs are provided by a bundle of 9 different pigtailed laser diodes placed in the object field, and they are recorded by a lensless 2/3" CCD camera. The comparison of the simulated and obtained PSFs allows determining the optical element introducing the differences so action may be taken precisely on that element. The system is especially useful in non-rotationally symmetrical systems, where errors in axis position result into asymmetries of the PSF images. The tool is used for precise alignment of the cylindrical lenses in the compensator group of an anamorphic objective prior to sealing. Results show the system is able to detect misalignments of 100μm and axis positioning errors of just 30arcsec using off-the-shelf components without the need of high-precision positioning equipment.
Third-order aberrations need the paraxial raytracing of a marginal as well as principal ray throu... more Third-order aberrations need the paraxial raytracing of a marginal as well as principal ray through the entire system to be determined. When the optical system has GRIN media, even the paraxial raytrace could be cumbersome. This work presents the use of the ABCD matrix for obtaining the raytracing of those rays and, thus, it could ease the calculation of the third-order aberration coefficients, i.e. contribution of GRIN to surface refraction and transfer, for each individual surface of GRIN optical elements. A procedure to be implemented in any modern commercial optical software has been presented and evaluated for simple systems.
The present works depicts a measurement technique intended to enhance the characterization proced... more The present works depicts a measurement technique intended to enhance the characterization procedures of the photometric emissions of automotive headlamps, with potential applications to any light source emission, either automotive or non-automotive. A CCD array with a precisely characterized optical system is used for sampling the luminance field of the headlamp just a few centimetres in front of it, by combining deflectometric techniques (yielding the direction of the light beams) and photometric techniques (yielding the energy travelling in each direction). The CCD array scans the measurement plane using a self-developed mechanical unit and electronics, and then image-processing techniques are used for obtaining the photometric behaviour of the headlamp in any given plane, in particular in the plane and positions required by current normative, but also on the road, on traffic signs, etc. An overview of the construction of the system, of the considered principle of measurement, and of the main calibrations performed on the unit is presented. First results concerning relative measurements are presented compared both to reference data from a photometric tunnel and from a plane placed 5m away from the source. Preliminary results for the absolute photometric calibration of the system are also presented for different illumination beams of different headlamps (driving and passing beam).
We present a simple method for increasing the number of data points obtained during performance o... more We present a simple method for increasing the number of data points obtained during performance of profilometric measurements with the Ronchi test. The method is based on multiple ronchigram acquisitions that are superimposed after a few very simple data-processing operations. The measurement method, experimental setup, and data processing are described in detail from the ronchigram to the measured profile, and experimental results for a concave surface of an spherical ophthalmic lens are provided. The radius of curvature values measured for that surface are compared with the ones obtained with a high-precision radioscope, showing very good agreement and demonstrating the capability of the technique to measure topographic profiles of reflective samples.
Recently, telescopes with segmented primary mirrors are becoming increasingly popular due to thei... more Recently, telescopes with segmented primary mirrors are becoming increasingly popular due to their ability of achieving large apertures without the inconveniences caused by the fabrication and handling of monolithic surfaces with 8m (or over) in diameter. The difference in position of each pair of adjacent segments along the local normal of their interface (called piston hereafter), however, needs to be precisely measured in order to provide a diffraction- limited image. If a system yielding the nanometric accuracy required in piston measurements worked in daylight hours, the resultant saving in observation time would be an important advance on a majority of the state-of-the-art piston measurement systems. An interferometric piston measurement instrument accomplishing such objectives has been designed starting from the usual Michelson configuration at the CD6 (Terrassa, Spain), and its final test has been carried out in the test workbench of the Instituto de Astrofisica de Canarias (IAC, Canary Islands, Spain). Its optical layout relies on projecting the reference arm of the interferometer onto one of the segments of the pair considered, along the direction of the local normal to the surface while the measurement arm is projected onto the interface which divides the pair of segments considered. The field of view and its illumination are calculated to be equivalent in both segments. The lateral shift of the fringes in both interferograms determines the piston error present. A combination of monochromatic and white light is used, in order to remove the (lambda) /2 phase ambiguities present in piston measurements without losing the required resolution in the measurement. In this paper, the optical design of this interferometric piston measurement instrument will be presented. The particular configuration used in the interferometer, the implementation of an imaging system allowing to see both the interface of the segments and the interference fringes, the effect of the extension of the source and the use of both monochromatic and whit light will be discussed. A detailed study of the wavefront errors embedded in the wavefront at different stages of the interferometer is performed. The analysis shows the validity of the design of the instrument, and some experimental results obtained at the test workbench are provided to demonstrate the ability of the instrument to perform nanometric piston measurements under daylight conditions.
Illumination engineering is a field that spans many topics and the number industries that activel... more Illumination engineering is a field that spans many topics and the number industries that actively work in the field is expanding. In this field the efficiency of the design is only a part of the design. Of nearly the same importance is the distribution of the light at the target. Many times the factors that are necessary to develop an illumination system will contradict one another, thus making the design of illumination systems complex and demanding. Optical modeling plays a basic role in obtaining new models. In general, the LED optical model obtains its parameters as a mathematical transformation or the average of a large set of measured experimental data. The main goal of this paper is to measure directly the parameters of the LED optical model. We use the typical LED spatial distribution model based on ray distribution. The basic parameters of this model are: the slope of the ray and the energy of each ray. The measurement system incorporates the slope measuring method used in deflectometry into an energy measurement technique. The method was tested using the measured data of two LEDs to analyze the illumination distribution provided at the image screen of standard Köhler illumination system.
In this work, an improvement of a previously-published human eye model with aging is presented. T... more In this work, an improvement of a previously-published human eye model with aging is presented. The previous eye model showed the overestimated performance of an averaged MTF at low spatial frequencies at all ages. Since that model had rotationally symmetrical corneal surfaces, these have been modeled to resemble an astigmatic element according to the recent experimental published data and have been included to produce a more accurate eye model. The gradient refractive index (GRIN) profile proposed for the crystalline lens has not been modified to test its robustness. Further, a tilt and decentration of the lens, and only a decentration for the iris, have been permitted in order to fit the average performance of the new eye model with aging. The results demonstrate that the GRIN profile for the crystalline lens fits the model well, since the decentration and/or tilt of the lens and the iris are sufficient free parameters to simulate the performance of the retinal image quality of an emmetropic human eye with aging, having an average astigmatic cornea.
We present an alternative formal calculation of the scaled Zernike coefficient expansion by means... more We present an alternative formal calculation of the scaled Zernike coefficient expansion by means of the inner product of the Zernike polynomials and the wavefront error corresponding to the scaled pupil. The relationship exhibited by the radial polynomials and Bessel functions leads to a general expression in terms of the Gauss hypergeometric function. Direct properties and index selection rules are established, and easy derivation of the non-normalized coefficients is also straightforward.
We present a system allowing the determination of the distribution of light at any given distance... more We present a system allowing the determination of the distribution of light at any given distance (e.g. 25m) from a light source, by measuring the intensity and direction of the illumination distribution at a closer distance (e.g. near 20 cm). The measurement principle is based on the acquisition of images taken by a CCD matrix-sensor through an optical system focused at infinity. A sequence of images is obtained by moving the camera at different positions in front of the source. The process involves the accumulation of shifted images and corrections for optics (geometrical distortion and vignetting) and electronic shutter (exposure time). We describe the developed experimental set-up and the calibration procedures needed to obtain absolute photometric values. We present results obtained for automotive headlamps: computed relative illumination distribution is very similar to that obtained using a reference given by a measurement tool using a lightmeter. Absolute calibration of the system is performed from the set of measured points
This paper proposes an instrument allowing the accurate characterization of the energetic distrib... more This paper proposes an instrument allowing the accurate characterization of the energetic distribution of a given source at a distant plane positioned at will. This is achieved by measuring the light pattern leaving the source by applying deflectometric techniques and photometric measurements, and then applying raytracing algorithms in order to propagate this distribution to a distant plane. The techniques allow a very compact setup, and a prototype of the optomechanical system has been implemented and tested. The system is intended to substitute the photometric tunnels now in use for testing, for instance, automotive reflectors.
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