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Spie Press Book

Survey Telescope Optics
Author(s): Valery Yu. Terebizh
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Book Description

Survey investigations, with the end goal of monitoring the entire celestial sphere, have become a priority in astronomy. This book is the first monograph devoted to wide-field telescopes, intended to bridge the gap between astronomers and professional opticians. It emphasizes the deep connection between classical and new telescopes, as well as the continuity of ideas underlying the development of telescope construction. The contents are presented in the simplest form to promote a clear understanding of new designs; descriptions of optical systems are accompanied by extensive graphic information provided by Zemax. Both exact modern optimization and the theory of aberrations are used in explanations, with the former given priority.

Book Details

Date Published: 5 November 2019
Pages: 162
ISBN: 9781510631281
Volume: PM311

Table of Contents
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1 Introduction
1.1 Preliminary Definitions
     1.1.1 Types of telescopes
     1.1.2 Image quality
     1.1.3 Efficiency of a survey
     1.1.4 Limiting stellar magnitude and survey speed
1.2 Cursory Review of Modern Wide-Field Telescopes
     1.2.1 Large wide-field telescopes
     1.2.2 Survey telescopes of moderate size
1.3 Some Attendant Issues of Optics
     1.3.1 Aperture stop and pupils
     1.3.2 Curvature of the focal surface
     1.3.3 'Ideal' wide-field telescope and Schmidt camera
     1.3.4 Remarks on color correction in catadioptric systems
     1.3.5 Basic types of optical surfaces
1.4 Matching of Optics and Detector with Atmospheric Image Quality
     1.4.1 Detectors of light
     1.4.2 Sampling factor

2 Reflective Telescopes
2.1 Single Paraboloid
2.2 Two-Mirror Systems
     2.2.1 Basic relations
     2.2.2 Classical telescopes: Mersenne, Gregory, and Cassegrain
     2.2.3 Approximate aplanatic telescopes: Schwarzschild, Ritchey-Chrétien, and Gregory-Maksutov; Hubble Space Telescope
     2.2.4 General Schwarzschild aplanats
     2.2.5 Mirror Schmidt; LAMOST system
2.3 Selected Three-Mirror Telescopes
     2.3.1 Paul system
     2.3.2 Korsch anastigmats; the SNAP design

3 Catadioptric Systems with a Lens Corrector in a Converging Beam
3.1 Lens Corrector at a Prime Telescope Focus
     3.1.1 Wynne designs for Ritchey-Chrétien and classical primaries
     3.1.2 All-spherical three-degree corrector of single glass
     3.1.3 Dark Energy Camera; the DESI project
     3.1.4 Subaru Hyper Suprime Camera
3.2 Lens Corrector in a Secondary Telescope Focus
     3.2.1 Quasi-Ritchey-Chrétien system; VST telescope
     3.2.2 Corrected Cassegrain system; Pan-STARRS telescope
     3.2.3 Corrected Cassegrain design with a 2.5-m aperture and 3° field
     3.2.4 Corrected Gregory telescope
     3.2.5 Folded Gregory-Maksutov telescope with a lens corrector
3.3 Three-Mirror Paul Telescope with a Lens Corrector
     3.3.1 LSST project

4 Catadioptric Systems with a Full-Aperture Lens Corrector
4.1 Singlet Full-Aperture Corrector
     4.1.1 Classical Schmidt camera
     4.1.2 Modifications of Schmidt camera
     4.1.3 Maksutov telescope
4.2 Doublet Full-Aperture Corrector
     4.2.1 Richter-Slevogt system
     4.2.2 Symmetrical corrector
     4.2.3 Hamiltonian telescopes
     4.2.4 The V2 design
4.3 Triplet Full-Aperture Corrector
     4.3.1 Schmidt-Houghton systems
     4.3.2 Baker-Nunn and Super-Schmidt cameras
     4.3.3 Meniscus Schmidt design of Hawkins and Linfoot; VAU telescope
     4.3.4 Family of Sonnefeld cameras; the V3 system
4.4 All-Spherical System with an Extremely Large Field
     4.4.1 Statement of the problem
     4.4.2 Examples of designs with an ultra-wide field of view


A. Limiting Stellar Magnitude and Sky Survey Rate
B. Schwarzschild Aplanats
C. The Complexity of Optical Surfaces
D. Base Prime-Focus Lens Corrector with a 2.5° Field
E. List of Referenced VT Designs
F. New Algorithm for Calculating Anastigmatic Three-Mirror Telescopes


Since the first telescopic surveys of the sky by Charles Messier and William Herschel in the late 18th century, investigations of this kind delivered astronomers an immense amount of information. In recent decades, the need for deep optical surveys has become especially urgent. In particular, cosmologists hope that new surveys will help them to discover so-called dark matter, to clarify the model of the universe, to explore the effects of gravitational lensing in clusters of galaxies, and to understand deeper the nature of sources of gravitational waves and powerful x-ray bursts. Wide-field telescopes are also needed to search for the planets around stars, to detect asteroids that pass dangerously close to the Earth, and to monitor the system of satellites around the Earth. Perhaps the most ambitious goal of modern observational astronomy is the acquisition of data concerning the current positions and magnitudes of all celestial objects brighter than approximately 24th magnitude in the visible waveband with the time scale of the order of one day.

A recent description of the purposes and results of sky surveys across the spectrum is provided by S. Djorgovski et al. (2012), who state that, "Surveys are now the largest data generators in astronomy, propelled by the advances in information and computation technology, and have transformed the ways in which astronomy is done. This trend is bound to continue, especially with the new generation of synoptic sky surveys that cover wide areas of the sky repeatedly, and open a new time domain of discovery."

The subject of this book is the optical systems of telescopes that make it possible to implement a wide field of view in the visual waveband. As one can see, the key concept of 'size of the field of view' is vague without indicating the appropriate image quality of a point light source. Previously, with regard to wide-field telescopes, such requirements were rather mild - it was enough to provide images of stars with a diameter of about a dozen arc seconds in the integral waveband; since the beginning of this century, the requirements were toughened by an order of magnitude and approached the atmospheric resolution limit. This was abetted by the need to match optics with detectors of light whose characteristics differ significantly from those of the photographic emulsion.

Over the past decades, the nature of design in optics has changed markedly due primarily to the increased power of computers and the sophistication of optical calculation programs. While analytical analysis relies mainly on a theory of third-order aberrations, a numerical approach takes full account of aberrations of complex systems. Charles Wynne, an outstanding creator of optical systems, wrote in 1968: "It was stated above that for Ritchey-Chrétien mirror systems the Seidel aberrations give for most purposes an adequate description of performance. For prime focus correctors consisting of systems of lenses, this is no longer the case."

In this regard, it might seem that the analytical approach has already lost its significance, but it still lies at the root of the search for basic systems. Formally, the design of an optical system reduces to the search for a conditional minimum image quality function in the space of system parameters, the number of which is sometimes several dozen. The term 'conditional' is used because it is necessary to specify in detail the entire set of constraints and the desired performance. The case is radically complicated by the fact, discovered in the middle of the last century, that the quality function has a huge number of local minima in a multidimensional 'optical' space, but we are interested, as a rule, in an unique global minimum corresponding to the objectively best system. This mathematical problem does not yet have an exact solution, so the direct design of even a simple system can take an extremely long time with the most powerful computers. For this reason, the search for a best solution is largely based on the understanding of the desired optical system, which the approximate theory of aberrations gives.

Taken together, modern tools allowed the designs to reach a field of view measuring tens of degrees with image quality close to diffraction-limited one.

The purpose of this book is to give a concise and simple, as far as possible, description of the ideas underlying basic wide-field astronomical systems. It is hoped that such an approach will be useful not only for professional optical designers but also for astronomers who are interested in creating survey systems. In the modern literature, it is not often possible to find a complete description of the new optical system, so many of the issues discussed are illustrated by our own designs.

It is a pleasure to thank my colleagues who have helped me for years, in particular, Mark Ackermann (University of New Mexico), Vadim Biryukov (Crimean Astro-physical Observatory), Yuri Petrunin (Telescope Engineering Company), Vladimir Skiruta (Crimean Astrophysical Observatory), and John Tonry (Institute for Astronomy, University of Hawaii).

Valery Terebizh
September 2019

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