DOCSLIB.ORG

Space Surveillance Telescope: Focus and Alignment of a Three Mirror Telescope

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Space Surveillance Telescope: focus and alignment of a three mirror telescope The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Woods, Deborah Freedman. “Space Surveillance Telescope: focus and alignment of a three mirror telescope.” Optical Engineering 52, no. 5 (May 1, 2013): 053604. As Published http://dx.doi.org/10.1117/1.oe.52.5.053604 Publisher SPIE Version Final published version Citable link http://hdl.handle.net/1721.1/80363 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. Space Surveillance Telescope: focus and alignment of a three mirror telescope Deborah Freedman Woods Ronak Y. Shah Julie A. Johnson Alexander Szabo Eric C. Pearce Richard L. Lambour Walter J. Faccenda Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 08/07/2013 Terms of Use: http://spiedl.org/terms Optical Engineering 52(5), 053604 (May 2013) Space Surveillance Telescope: focus and alignment of a three mirror telescope Deborah Freedman Woods Abstract. The Space Surveillance Telescope (SST) is a three-mirror Ronak Y. Shah Mersenne-Schmidt telescope with a 3.5 m primary mirror. It is designed MIT Lincoln Laboratory to rapidly scan for space objects, particularly along the geosynchronous 244 Wood Street belt, approximately 36,000 km above the Earth. The SST has an unusually Lexington, Massachusetts 02420 short focal ratio of F/1.0 and employs a camera composed of curved E-mail: [email protected] charge-coupled devices to match the telescope’s inherent field curvature. The field-of-view of the system is 6 square degrees. While the unique sys- Julie A. Johnson tem design is advantageous for space surveillance capabilities, it presents Alexander Szabo a challenge to alignment due to an inherently small depth of focus and the MIT Lincoln Laboratory additional degrees of freedom introduced with a powered tertiary mirror. Stallion Range Center The alignment procedure developed for the SST at zenith pointing is dis- Building 34560 cussed, as well as the maintenance of focus and alignment of the system Socorro, New Mexico 87801 across a range of elevation and temperature conditions. Quantitative per- formance metrics demonstrate the success of the system alignment during the telescope’s first year of operation. © The Authors. Published by SPIE under a Eric C. Pearce Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in Richard L. Lambour whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10 Walter J. Faccenda .1117/1.OE.52.5.053604] MIT Lincoln Laboratory 244 Wood Street Subject terms: telescopes; alignment; wavefront sensors; astronomy. Lexington, Massachusetts 02420 Paper 130113 received Jan. 22, 2013; revised manuscript received Apr. 12, 2013; accepted for publication Apr. 12, 2013; published online May 7, 2013. 1 Introduction instrumentation. Instead, we align SST’s optics using only The Space Surveillance Telescope (SST), sponsored by the intra- and extra-focal images of stars. Defense Advanced Research Projects Agency (DARPA) is a The alignment process for two mirror telescopes is well documented and demonstrated in operation.1–5 The tech- 3.5 m diameter Mersenne-Schmidt telescope with a curved 1 focal surface. The camera mosaic of 12 charge-coupled devi- nique described by McLeod for the case of a Ritchie- ces (CCDs) employs curved substrates built to the shape of the Cretian telescope is to first remove coma by a translation or telescope’s focal surface tiled across a 6 square degree field- tilt of the secondary mirror about its vertex. The coma pro- of-view (FOV). The telescope has an extremely short focal duced by miscollimation does not vary across the FOV and ratio, F/1.0, whose compact layout ensures a highly agile so identifying and correcting for coma observed on-axis is sufficient for coma correction for the full field. However, the pointing system. Figure 1 shows a model of the optical sys- astigmatism produced by miscollimation varies as a function tem. Table 1 lists the system parameters, including details of of field position. Alignment of the two mirror telescope is the CCD mosaic. The combination of wide FOV and pointing accomplished by observing the effects of astigmatism at performance enables SST to rapidly scan the entire sky. Its multiple off-axis field positions and applying translation and location on an 8000-foot peak in the White Sands Missile tilt to the secondary mirror to remove the astigmatism due to Range (WSMR) south of Socorro, New Mexico, USA, pro- miscollimation. Astigmatism that is intrinsic to the optical vides a dry environment with excellent seeing conditions. ’ prescription will present a recognizable signature that can The SST s mission is to perform space surveillance and be separated from the astigmatism due to miscollimation.1 space situational awareness. That is, the telescope provides Theoretical expectations for alignment of three mirror the position with respect to the stars and the brightness of telescopes have been described in recent literature. satellites and space debris, particularly at the geosynchro- Thompson et al.6 discuss the optical aberrations generated nous region located at approximately 36,000 km from the by misalignment of a three mirror anastigmatic (TMA) tele- ’ Earth s surface. MIT Lincoln Laboratory developed the pro- scope, such as for the future James Webb Space Telescope. gram and L-3 Brashear built the telescope optics and mount. The misalignment-induced aberrations that will most signifi- The telescope achieved first light in February 2011 and is cantly affect the image quality are coma and astigmatism. currently transitioning from a commissioning to an opera- Thompson et al. note that while coma can be effectively tional phase. canceled by a combination of mirror tilt and decenter, the While the unique design of the SST is advantageous for resulting mirror positions will not generally remove astig- space surveillance, it creates a challenge to alignment as a matism due to misalignment. The astigmatism must be mea- result of the inherently small depth of focus and the addi- sured at multiple field positions to be fully characterized. In tional degrees of freedom introduced with a powered tertiary addition, they describe a field-asymmetric aberration that is mirror. Furthermore, the installation of the large CCD array intrinsic to the TMA optical design. Characterization of this at the prime focus of the telescope does not allow us to field-asymmetric aberration aids alignment. Plans for align- use a dedicated wavefront sensor or other special focusing ment of the three-mirror Large Synoptic Survey Telescope Optical Engineering 053604-1 May 2013/Vol. 52(5) Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 08/07/2013 Terms of Use: http://spiedl.org/terms Woods et al.: Space Surveillance Telescope: focus and alignment of a three mirror telescope employed at the SST to align the telescope at zenith pointing are similar in spirit to the techniques described for two and three mirror telescopes. We obtain a quantitative measure of the magnitude and direction of optical aberrations manifest in the system wavefront using defocused image techniques. The algorithms of the DONUT program, which we adapt for use with the SST, generate a measurement of optical aberra- tions from a single defocused star.9 Comparison of the DONUT measured aberrations with the sensitivity analysis generated by a Zemax model of the as-built optical system leads to predictions for the required adjustments to mirror alignment. We accomplish the focus and alignment of the SST using a five-step iterative process to find the optimal Fig. 1 Optical layout of the SST. Light enters the system from the left mirror positions at a given temperature for the zenith point- in this image. ing case. After achieving optimal focus and alignment at zenith pointing, we then develop an elevation dependent focus Table 1 Space Surveillance Telescope system parameters, includ- and alignment model to correct for gravity sag. The eleva- ing the optical system and the camera. tion dependent corrections are applied real-time to maintain focus and alignment across all elevation angles. We likewise develop a model to describe the temperature dependent focus Telescope corrections. Real-time adjustments to focus as a function of mount structure temperature ensure that the system remains Diameter (actual) 3.50 m in focus as the temperature environment varies over the Diameter (effective) 2.90 m course of the night. In this paper we describe the method that we developed Effective focal length 3.49 m for the focus and alignment of the SST and present quan- titative measures of the alignment performance. Section 2 Nominal field-of-view 3 × 2 deg contains an introduction to the measurement and representa- tion of wavefront aberrations; Sec. 3 describes the Zemax Camera sensitivity analysis; Sec. 4 provides details on the focus and alignment method to achieve best focus at zenith point- Sensors (thinned, backside illuminated) 2 K × 4 K CCD ing, including adjustments for different elevation angles in Sec. 4.1 and for temperature in Sec. 4.2. Section 5 provides Pixel size 15 μm 0.89 arcsec performance results and Sec. 6 discusses applicability to other systems. We conclude in Sec. 7. Mosaic 6 × 2 chips 2 Measurement and Representation of Effective size 12288 × 8192 pixels Wavefront Aberrations The telescope mirror alignment is accomplished through the Readout time 0.65 to 1.30 s measurement of optical aberrations present in the system. The shape of the wavefront produced by an optical system, Exposure time 0.025 to 10 s Wðρ; θÞ, carries with it information on the optical aberrations Filter Open (0.4 to 1.0 μm) of the system that generated it.
Recommended publications
  • Chapter 3 (Aberrations)

    Chapter 3 (Aberrations)

    Chapter 3 Aberrations 3.1 Introduction In Chap. 2 we discussed the image-forming characteristics of optical systems, but we limited our consideration to an infinitesimal thread- like region about the optical axis called the paraxial region. In this chapter we will consider, in general terms, the behavior of lenses with finite apertures and fields of view. It has been pointed out that well- corrected optical systems behave nearly according to the rules of paraxial imagery given in Chap. 2. This is another way of stating that a lens without aberrations forms an image of the size and in the loca- tion given by the equations for the paraxial or first-order region. We shall measure the aberrations by the amount by which rays miss the paraxial image point. It can be seen that aberrations may be determined by calculating the location of the paraxial image of an object point and then tracing a large number of rays (by the exact trigonometrical ray-tracing equa- tions of Chap. 10) to determine the amounts by which the rays depart from the paraxial image point. Stated this baldly, the mathematical determination of the aberrations of a lens which covered any reason- able field at a real aperture would seem a formidable task, involving an almost infinite amount of labor. However, by classifying the various types of image faults and by understanding the behavior of each type, the work of determining the aberrations of a lens system can be sim- plified greatly, since only a few rays need be traced to evaluate each aberration; thus the problem assumes more manageable proportions.
  • Higher-Order Aberrations

    Higher-Order Aberrations

    Higher-order aberrations Lens Design OPTI 517 Prof. Jose Sasian Higher order Aberrations • Aberration function • Six-order terms (fifth-order transverse) • Wavefront shapes and field dependence • Coefficients • Pupil matching • References. Prof. Jose Sasian References • 1) J. Sasian, “Theory of sixth-order wave aberrations,” Applied Optics, June 2010. • 2) O. N. Stavroudis, “Modular Optical Design” • 3) Buchdahl, “Optical Aberration Coefficients” • 4) M. Herzberger, “Modern Geometrical Optics” Prof. Jose Sasian “Back of the envelope” Prof. Jose Sasian Coordinate system and reference sphere y' E ' yI H Exit pupil plane Image plane Prof. Jose Sasian Aberration function Prof. Jose Sasian Prof. Jose Sasian Aberration orders Roland Shack’s aberration diagram Prof. Jose Sasian Terminology •W240 Oblique spherical aberration •W331 Cubic coma •W422 Quartic astigmatism •W420 Six order field curvature •W511 Six order distortion •W600 Six order piston •W060 Six order spherical aberration •W151 •W242 •W333 Prof. Jose Sasian Some earlier terminology • Oblique spherical aberration • Elliptical coma • Line coma • Secondary spherical aberration • Secondary coma • Lateral coma • Lateral image curvature/astigmatism •Trefoil Prof. Jose Sasian Wavefront deformation shapes Prof. Jose Sasian Spherical aberration: W060 Prof. Jose Sasian W151 & W333 Prof. Jose Sasian W242 Prof. Jose Sasian Higher-order aberration coefficients • Harder to derive/calculate than fourth- order • Intrinsic coefficients • Extrinsic coefficients • Depend highly on coordinate system Prof. Jose Sasian Intrinsic spherical aberration 1 2 u W040 A y 8 n 2 1 y 1 u' u y 8 y W060I W040 2 A 2 u W040 W040 2 r 2 n' n r y 2 1 y 1 u' u y 8 y W060I W040 2 A 2 u' W040 W040 2 r 2 n' n r y 3 5 7 y Y y c3 y c5 y c7 y ..
  • Strehl Ratio for Primary Aberrations: Some Analytical Results for Circular and Annular Pupils

    Strehl Ratio for Primary Aberrations: Some Analytical Results for Circular and Annular Pupils

    1258 J. Opt. Soc. Am./Vol. 72, No. 9/September 1982 Virendra N. Mahajan Strehl ratio for primary aberrations: some analytical results for circular and annular pupils Virendra N. Mahajan The Charles Stark Draper Laboratory, Inc., Cambridge, Massachusetts 02139 Received February 9,1982 Imaging systems with circular and annular pupils aberrated by primary aberrations are considered. Both classical and balanced (Zernike) aberrations are discussed. Closed-form solutions are derived for the Strehl ratio, except in the case of coma, for which the integral form is used. Numerical results are obtained and compared with Mar6- chal's formula for small aberrations. It is shown that, as long as the Strehl ratio is greater than 0.6, the Markchal formula gives its value with an error of less than 10%. A discussion of the Rayleigh quarter-wave rule is given, and it is shown that it provides only a qualitative measure of aberration tolerance. Nonoptimally balanced aberrations are also considered, and it is shown that, unless the Strehl ratio is quite high, an optimally balanced aberration does not necessarily give a maximum Strehl ratio. 1. INTRODUCTION is shown that, unless the Strehl ratio is quite high, an opti- In a recent paper,1 we discussed the problem of balancing a mally balanced aberration(in the sense of minimum variance) does not classical aberration in imaging systems having annular pupils give the maximum possible Strehl ratio. As an ex- ample, spherical with one or more aberrations of lower order to minimize its aberration is discussed in detail. A certain variance. By using the Gram-Schmidt orthogonalization amount of spherical aberration is balanced with an appro- process, polynomials that are orthogonal over an annulus were priate amount of defocus to minimize its variance across the pupil.
  • Doctor of Philosophy

    Doctor of Philosophy

    RICE UNIVERSITY 3D sensing by optics and algorithm co-design By Yicheng Wu A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE Doctor of Philosophy APPROVED, THESIS COMMITTEE Ashok Veeraraghavan (Apr 28, 2021 11:10 CDT) Richard Baraniuk (Apr 22, 2021 16:14 ADT) Ashok Veeraraghavan Richard Baraniuk Professor of Electrical and Computer Victor E. Cameron Professor of Electrical and Computer Engineering Engineering Jacob Robinson (Apr 22, 2021 13:54 CDT) Jacob Robinson Associate Professor of Electrical and Computer Engineering and Bioengineering Anshumali Shrivastava Assistant Professor of Computer Science HOUSTON, TEXAS April 2021 ABSTRACT 3D sensing by optics and algorithm co-design by Yicheng Wu 3D sensing provides the full spatial context of the world, which is important for applications such as augmented reality, virtual reality, and autonomous driving. Unfortunately, conventional cameras only capture a 2D projection of a 3D scene, while depth information is lost. In my research, I propose 3D sensors by jointly designing optics and algorithms. The key idea is to optically encode depth on the sensor measurement, and digitally decode depth using computational solvers. This allows us to recover depth accurately and robustly. In the first part of my thesis, I explore depth estimation using wavefront sensing, which is useful for scientific systems. Depth is encoded in the phase of a wavefront. I build a novel wavefront imaging sensor with high resolution (a.k.a. WISH), using a programmable spatial light modulator (SLM) and a phase retrieval algorithm. WISH offers fine phase estimation with significantly better spatial resolution as compared to currently available wavefront sensors.
  • Wavefront Control Simulations for the Giant Magellan Telescope: Field-Dependent Segment Piston Control

    Wavefront Control Simulations for the Giant Magellan Telescope: Field-Dependent Segment Piston Control

    Wavefront control simulations for the Giant Magellan Telescope: Field-dependent segment piston control Fernando Quir´os-Pachecoa, Rodolphe Conana, Brian McLeodb, Benjamin Irarrazavala, and Antonin Boucheza aGMTO Organization, 465 North Halstead St, Suite 250, Pasadena, CA 91107, USA bSmithsonian Astrophysical Observatory, 60 Garden St, MS 20, Cambridge, MA 02138, USA ABSTRACT We present in this paper preliminary simulation results aimed at validating the GMT piston control strategy. We will in particular consider an observing mode in which an Adaptive Optics (AO) system is providing fast on-axis WF correction with the Adaptive Secondary Mirror (ASM), while the phasing system using multiple Segment Piston Sensors (SPS) makes sure that the seven GMT segments remain phased. Simulations have been performed with the Dynamic Optical Simulation (DOS) tool developed at the GMT Project Office, which integrates the optical and mechanical models of GMT. DOS fast ray-tracing capabilities allows us to properly simulate the effect of field-dependent aberrations, and in particular, the so-called Field Dependent Segment Piston (FDSP) mode arising when a segment tilt on M1 is compensated on-axis by a segment tilt on M2. We will show that when using an asterism of SPS, our scheme can properly control both segment piston and the FDSP mode. Keywords: Giant Magellan Telescope, phasing, wavefront control, numerical simulations 1. INTRODUCTION The Giant Magellan Telescope (GMT)1 is a 25.4m diameter aplanatic Gregorian telescope that will be located at the Las Campanas Observatory (LCO), in Chile. The GMT is a segmented telescope, with a primary mirror (M1) composed of seven circular 8.4m segments.
  • Aperture-Based Correction of Aberration Obtained from Optical Fourier Coding and Blur Estimation

    Aperture-Based Correction of Aberration Obtained from Optical Fourier Coding and Blur Estimation

    Research Article Vol. 6, No. 5 / May 2019 / Optica 647 Computational aberration compensation by coded- aperture-based correction of aberration obtained from optical Fourier coding and blur estimation 1, 2 2 3 1 JAEBUM CHUNG, *GLORIA W. MARTINEZ, KAREN C. LENCIONI, SRINIVAS R. SADDA, AND CHANGHUEI YANG 1Department of Electrical Engineering, California Institute of Technology, Pasadena, California 91125, USA 2Office of Laboratory Animal Resources, California Institute of Technology, Pasadena, California 91125, USA 3Doheny Eye Institute, University of California-Los Angeles, Los Angeles, California 90033, USA *Corresponding author: [email protected] Received 29 January 2019; revised 8 April 2019; accepted 12 April 2019 (Doc. ID 359017); published 10 May 2019 We report a novel generalized optical measurement system and computational approach to determine and correct aberrations in optical systems. The system consists of a computational imaging method capable of reconstructing an optical system’s pupil function by adapting overlapped Fourier coding to an incoherent imaging modality. It re- covers the high-resolution image latent in an aberrated image via deconvolution. The deconvolution is made robust to noise by using coded apertures to capture images. We term this method coded-aperture-based correction of aberration obtained from overlapped Fourier coding and blur estimation (CACAO-FB). It is well-suited for various imaging scenarios where aberration is present and where providing a spatially coherent illumination is very challenging or impossible. We report the demonstration of CACAO-FB with a variety of samples including an in vivo imaging experi- ment on the eye of a rhesus macaque to correct for its inherent aberration in the rendered retinal images.
  • Physics of Digital Photography Index

    Physics of Digital Photography Index

    1 Physics of digital photography Author: Andy Rowlands ISBN: 978-0-7503-1242-4 (ebook) ISBN: 978-0-7503-1243-1 (hardback) Index (Compiled on 5th September 2018) Abbe cut-off frequency 3-31, 5-31 Abbe's sine condition 1-58 aberration function see \wavefront error function" aberration transfer function 5-32 aberrations 1-3, 1-8, 3-31, 5-25, 5-32 absolute colourimetry 4-13 ac value 3-13 achromatic (colour) see \greyscale" acutance 5-38 adapted homogeneity-directed see \demosaicing methods" adapted white 4-33 additive colour space 4-22 Adobe® colour matrix 4-42, 4-43 Adobe® digital negative 4-40, 4-42 Adobe® forward matrix 4-41, 4-42, 4-47, 4-49 Adobe® Photoshop® 4-60, 4-61, 5-45 Adobe® RGB colour space 4-27, 4-60, 4-61 adopted white 4-33, 4-34 Airy disk 3-15, 3-27, 5-33, 5-46, 5-49 aliasing 3-43, 3-44, 3-47, 5-42, 5-45 amplitude OTF see \amplitude transfer function" amplitude PSF 3-26 amplitude transfer function 3-26 analog gain 2-24 analog-to-digital converter 2-2, 2-5, 3-61, 5-56 analog-to-digital unit see \digital number" angular field of view 1-21, 1-23, 1-24 anti-aliasing filter 5-45, also see \optical low-pass filter” aperture-diffraction PSF 3-27, 5-33 aperture-diffraction MTF 3-29, 5-31, 5-33, 5-35 aperture function 3-23, 3-26 aperture priority mode 2-32, 5-71 2 aperture stop 1-22 aperture value 1-56 aplanatic lens 1-57 apodisation filter 5-34 arpetal ratio 1-50 astigmatism 5-26 auto-correlation 3-30 auto-ISO mode 2-34 average photometry 2-17, 2-18 backside-illuminated device 3-57, 5-58 band-limited function 3-45, 5-44 banding see \posterisation"
  • Representation of Wavefront Aberrations

    Representation of Wavefront Aberrations

    Slide 1 4th Wavefront Congress - San Francisco - February 2003 Representation of Wavefront Aberrations Larry N. Thibos School of Optometry, Indiana University, Bloomington, IN 47405 [email protected] http://research.opt.indiana.edu/Library/wavefronts/index.htm The goal of this tutorial is to provide a brief introduction to how the optical imperfections of a human eye are represented by wavefront aberration maps and how these maps may be interpreted in a clinical context. Slide 2 Lecture outline • What is an aberration map? – Ray errors – Optical path length errors – Wavefront errors • How are aberration maps displayed? – Ray deviations – Optical path differences – Wavefront shape • How are aberrations classified? – Zernike expansion • How is the magnitude of an aberration specified? – Wavefront variance – Equivalent defocus – Retinal image quality • How are the derivatives of the aberration map interpreted? My lecture is organized around the following 5 questions. •First, What is an aberration map? Because the aberration map is such a fundamental description of the eye’ optical properties, I’m going to describe it from three different, but complementary, viewpoints: first as misdirected rays of light, second as unequal optical distances between object and image, and third as misshapen optical wavefronts. •Second, how are aberration maps displayed? The answer to that question depends on whether the aberrations are described in terms of rays or wavefronts. •Third, how are aberrations classified? Several methods are available for classifying aberrations. I will describe for you the most popular method, called Zernike analysis. lFourth, how is the magnitude of an aberration specified? I will describe three simple measures of the aberration map that are useful for quantifying the magnitude of optical error in a person’s eye.
  • Zernike Piston Statistics in Turbulent Multi-Aperture Optical Systems

    Zernike Piston Statistics in Turbulent Multi-Aperture Optical Systems

    Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 3-2020 Zernike Piston Statistics in Turbulent Multi-Aperture Optical Systems Joshua J. Garretson Follow this and additional works at: https://scholar.afit.edu/etd Part of the Optics Commons Recommended Citation Garretson, Joshua J., "Zernike Piston Statistics in Turbulent Multi-Aperture Optical Systems" (2020). Theses and Dissertations. 3161. https://scholar.afit.edu/etd/3161 This Thesis is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. ZERNIKE PISTON STATISTICS IN TURBULENT MULTI-APERTURE OPTICAL SYSTEMS THESIS Joshua J. Garretson, Capt, USAF AFIT-ENG-MS-20-M-023 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio DISTRIBUTION STATEMENT A APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. The views expressed in this document are those of the author and do not reflect the official policy or position of the United States Air Force, the United States Department of Defense or the United States Government. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. AFIT-ENG-MS-20-M-023 ZERNIKE PISTON STATISTICS IN TURBULENT MULTI-APERTURE OPTICAL SYSTEMS THESIS Presented to the Faculty Department of Electrical and Computer Engineering Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command in Partial Fulfillment of the Requirements for the Degree of Master of Science in Electrical Engineering Joshua J.
  • Wavefront Aberrations

    Wavefront Aberrations

    11 Wavefront Aberrations Mirko Resan, Miroslav Vukosavljević and Milorad Milivojević Eye Clinic, Military Medical Academy, Belgrade, Serbia 1. Introduction The eye is an optical system having several optical elements that focus light rays representing images onto the retina. Imperfections in the components and materials in the eye may cause light rays to deviate from the desired path. These deviations, referred to as optical or wavefront aberrations, result in blurred images and decreased visual performance (1). Wavefront aberrations are optical imperfections of the eye that prevent light from focusing perfectly on the retina, resulting in defects in the visual image. There are two kinds of aberrations: 1. Lower order aberrations (0, 1st and 2nd order) 2. Higher order aberrations (3rd, 4th, … order) Lower order aberrations are another way to describe refractive errors: myopia, hyperopia and astigmatism, correctible with glasses, contact lenses or refractive surgery. Lower order aberrations is a term used in wavefront technology to describe second-order Zernike polynomials. Second-order Zernike terms represent the conventional aberrations defocus (myopia, hyperopia and astigmatism). Lower order aberrations make up about 85 per cent of all aberrations in the eye. Higher order aberrations are optical imperfections which cannot be corrected by any reliable means of present technology. All eyes have at least some degree of higher order aberrations. These aberrations are now more recognized because technology has been developed to diagnose them properly. Wavefront aberrometer is actually used to diagnose and measure higher order aberrations. Higher order aberrations is a term used to describe Zernike aberrations above second-order. Third-order Zernike terms are coma and trefoil.
  • Tese De Doutorado Nº 200 a Perifocal Intraocular Lens

    Tese De Doutorado Nº 200 a Perifocal Intraocular Lens

    TESE DE DOUTORADO Nº 200 A PERIFOCAL INTRAOCULAR LENS WITH EXTENDED DEPTH OF FOCUS Felipe Tayer Amaral DATA DA DEFESA: 25/05/2015 Universidade Federal de Minas Gerais Escola de Engenharia Programa de Pós-Graduação em Engenharia Elétrica A PERIFOCAL INTRAOCULAR LENS WITH EXTENDED DEPTH OF FOCUS Felipe Tayer Amaral Tese de Doutorado submetida à Banca Examinadora designada pelo Colegiado do Programa de Pós- Graduação em Engenharia Elétrica da Escola de Engenharia da Universidade Federal de Minas Gerais, como requisito para obtenção do Título de Doutor em Engenharia Elétrica. Orientador: Prof. Davies William de Lima Monteiro Belo Horizonte – MG Maio de 2015 To my parents, for always believing in me, for dedicating themselves to me with so much love and for encouraging me to dream big to make a difference. "Aos meus pais, por sempre acreditarem em mim, por se dedicarem a mim com tanto amor e por me encorajarem a sonhar grande para fazer a diferença." ACKNOWLEDGEMENTS I would like to acknowledge all my friends and family for the fondness and incentive whenever I needed. I thank all those who contributed directly and indirectly to this work. I thank my parents Suzana and Carlos for being by my side in the darkest hours comforting me, advising me and giving me all the support and unconditional love to move on. I thank you for everything you taught me to be a better person: you are winners and my life example! I thank Fernanda for being so lovely and for listening to my ideas and for encouraging me all the time.
  • Digital Light Field Photography

    Digital Light Field Photography

    DIGITAL LIGHT FIELD PHOTOGRAPHY a dissertation submitted to the department of computer science and the committee on graduate studies of stanford university in partial fulfillment of the requirements for the degree of doctor of philosophy Ren Ng July © Copyright by Ren Ng All Rights Reserved ii IcertifythatIhavereadthisdissertationandthat,inmyopinion,itisfully adequateinscopeandqualityasadissertationforthedegreeofDoctorof Philosophy. Patrick Hanrahan Principal Adviser IcertifythatIhavereadthisdissertationandthat,inmyopinion,itisfully adequateinscopeandqualityasadissertationforthedegreeofDoctorof Philosophy. Marc Levoy IcertifythatIhavereadthisdissertationandthat,inmyopinion,itisfully adequateinscopeandqualityasadissertationforthedegreeofDoctorof Philosophy. Mark Horowitz Approved for the University Committee on Graduate Studies. iii iv Acknowledgments I feel tremendously lucky to have had the opportunity to work with Pat Hanrahan, Marc Levoy and Mark Horowitz on the ideas in this dissertation, and I would like to thank them for their support. Pat instilled in me a love for simulating the flow of light, agreed to take me on as a graduate student, and encouraged me to immerse myself in something I had a passion for.Icouldnothaveaskedforafinermentor.MarcLevoyistheonewhooriginallydrewme to computer graphics, has worked side by side with me at the optical bench, and is vigorously carrying these ideas to new frontiers in light field microscopy. Mark Horowitz inspired me to assemble my camera by sharing his love for dismantling old things and building new ones. I have never met a professor more generous with his time and experience. I am grateful to Brian Wandell and Dwight Nishimura for serving on my orals commit- tee. Dwight has been an unfailing source of encouragement during my time at Stanford. I would like to acknowledge the fine work of the other individuals who have contributed to this camera research. Mathieu Brédif worked closely with me in developing the simulation system, and he implemented the original lens correction software.