Reflecting Telescope Optics II: Manufacture, Testing, Alignment, Modern Techniques

565 Pages·1999·19.65 MB·English

by  Raymond N. Wilson (auth.)

~I ASTRONOMY AND
11
~I ASTROPHYSICS LIBRARY
LIBRARY
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ForlegendseefrontmatterpageIV
R. N. Wilson
Reflecting
Telescope Optics 11
Manufacture, Testing, Alignment,
Modern Techniques
With 240 Figures and 39 Tables
i
Springer
Raymond N. Wilson
Waaler Str. 29
85296 Rohrbach/llm
GERMANY
Cover picture:
The two 10 m Keck telescopes at the observatory on Mauna Kea, Hawaii. On the left Keck II, on the right Keck I. At
the time of completion of the text of this book (December 1997), these were not only the largest unit telescopes in
the world, but also the only very large telescopes using new technology which were aIready in operation. (Photograph
courtesy of the W.M. Keck Observatory, through J. Nelson and A. Perala. The high-resolution copy used was kindly
provided by Richard J. Wainscoat, who holds the copyright).
Legend to frontispiece:
The ESO VLT: Unit Telescope No. 2 (Kueyen), photographed in March 2000 by Hans-Hermann Heyer, ESO.
Photo upperleft: A 3-colour composite photo ofthe Crab Nebula (Messier 1) laken with the VLT Unit Telescope No. 2
and the FORS-2 instrument on 10 November, 1999. Distance about 6000 light-years. Exposures 1-5 min with seeing
(FWHM) 0.65-0.80 arcsec.
Photo upper right: A 3-colour composite photo of the Spiral Galaxy NGC 2997 taken with the VLT Unit Telescope
No. 1 (Antu) and the FORS-l instrument on 5 March, 1999. Distance about 55 million light-years. Exposures 3-5
min. With a best star image quality of 0.25 arcsec (FWHM) in the near-infrared band (the other bands gave 0.35 and
0.34 arcsec FWHM), this is probably still the highest-resolution photo ever laken with a large ground-based telescope.
Formatting of the photos by Ed Janssen, ESO. All photos and information courtesy of ESO.
Library of Congress Cataioging-in-Publication Data applied for.
Die Deutsche Bibliothek - Cip Einheitsaufnahme
Wilson, Raymond N.: Reftecting telescope optics 1 R.N. Wilson. - Berlin; Heidelberg; New York; Barcelona; Hong
Kong; London; Milan; Paris; Singapore; Tokyo: Springer (Astronomy and astrophysics library)
2. Manufacture, testing, alignment, modern techniques: with 39 tables. - 1999 ISBN 3-540-60356-5
Corrected Second Printing 2001
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ISBN 978-3-642-08223-8 ISBN 978-3-662-08488-5 (eBook)
DOI 10.1007/978-3-662-08488-5
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© Springer-Verlag Berlin Heidelberg 1999
Originally published by Springer-Verlag Berlin Heidelberg New York in 1999.
Softcover reprint ofthe hardcover Ist edition 1999
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To
Gerhard Schwesinger
born 1913 in Krappitz, Upper Silesia,
who developed the first complete Fourier theory
for the support of primary mirrors of telescopes
and thereby also stimulated my thinking on
active optics, culminating in the ESO NTT
To
The NTT Team
at ESO, Garehing, who developed the telescope;
to all the consultants and industrial groups
who contributed to its manufacture; and to
the team at ESO, La Silla, who have ensured
correct maintenance and operation
General Preface (Preface to Volume I)
The development of telescope optics is a fascinating story. U ntil this cen
tury, the optical theory of reflecting telescopes was essentially limited to the
Cartesian treatment ofaxial imagery. In 1905, Karl Schwarzschild initiated
a revolution by applying third order (Seidel) theory to the field imagery of
2-mirror telescopes. Since then, the whole gamut of possible telescope systems
has been invented, analysed and, in many cases, tried out in practice.
Over all its history, the optical development of the telescope has also de
pended on technical inventions, above all in mirror materials, glasses, support
systems and means of achieving high reflectivity. Over the last 30 years, de
velopments have been particularly spectacular, above all in manufacture and
test techniques and generally in enhancing the image quality available.
When I started this work in 1988 there was little literature in book form
available on telescope optics. Two of the best were in German: "Die Fern
rohre und Entfernungsmesser" by König-Köhler (1959) and the monograph
on "Teleskope" by K. Bahner in "Handbuch der Physik", Vol. XXIX, which
appeared in 1967. A major part of this latter work was devoted to a con
densed, but excellent exposition of the theory of telescope optics. Inevitably,
more modern technical developments which have since assumed great im
portance could not be included; furthermore, the fact that it was written in
German has reduced its impact and dissemination to a limited section of the
interested community.
In 1987, "Astronomical Optics" by D. J. Schroeder appeared. Harland
Epps kindly drew my attention to this excellent book in 1988 and I reflected
then whether scope for a furt her work on the subject still existed. I finally
concluded that it did: Schroeder's book covers a much wider field, since
"astronomicai" optics includes the broad subject of astronomical instruments,
whereas my intention was (and remains) only the comprehensive coverage of
the optics of the reflecting telescope, in the broadest interpretation of that
term. Furthermore, Schroeder's work emerged more from the university orbit
and includes much basic optical theory addressed to graduate students who
need, and can profit from, the whole physics background.
The aim of the present book is different from Schroeder's. It is addressed
primarily to specialists in the field, both in the astronomical community itself
and in the industries concerned, although I hope it may also be useful to stu
dents. Consequently, subjects such as practical alignment and test techniques,
VIII General Preface (Preface to Volume I)
aS wen as maintenance aspects, occupy a significant part. Nevertheless, there
are inevitably major overlap areas with both Bahner's and Schroeder's books
which the informed reader will recognise. This overlap, involving repetitions
in a somewhat different context, is unavoidable for a complete presentation.
Bahner's book included sections on achromatic objectives for refracting
telescopes, astrographic objectives and oculars. No such material is included
in this book. The refractor as such and the optical design of oculars are
only of historical interest in large telescope optics and are only mentioned
in this context. Of course, refracting elements still play an important role
in wide-field telescopes, field correctors and focal reducers, and these are
dealt with in Chapters 3 and 4. In general, mirrors supply the optical power
while refracting elements have only the sub ordinate but important role of
improving the imagery.
I favour the morphological approach with a strong emphasis on the his
torical background of the subject. In this sense, Chapter 5 is to be seen as
essential background for understanding the current situation in telescope op
tics. For the background of the general theory of optical aberrations and
diffraction, the reader is referred to specialist books in the field of optics.
Only the essential consequences of Gaussian optics, third order theory and
diffraction theory are given: the emphasis is on a complete treatment of the
application to reflecting telescope optics.
At the suggestion of the publisher, the work has been split into two vol
umes. The first volume deals with the historical development (but there is
no claim to completeness as a history of telescope optics - that would be a
separate work) and the theory of reflecting telescope optics, including that
of the refracting corrector elements. The second volume deals with technical
aspects and modern developments in general. Although there is considerable
cross-referencing between the volumes, the split is a logical one, since each
volume has its own entity.
Every attempt has been made to give complete references to the interna
tionalliterature. It is hoped that the work will be useful, apart from its own
content, as a "source book" of the subject.
While I was writing the book, three further works on the subject were pub
lished: "Telescope Optics" by Rutten and van Venrooij (1988), "Astrooptik"
by Laux (1993) and "Reflective Optics" by Korsch (1991). The first two are
primarily destined for amateurs, but have equally great value for profession
als. As with the works of Bahner and Schroeder, there is considerable overlap
with my material and I have referred to them liberally in my text. I only
became aware of Korsch's work when my own text was finished, but again
there is inevitably considerable overlap of treatment. However, not only the
content and aim of these five works, an admirable, are very different, but also
their styles. In this sense, I feel confirmed in my own enterprise.
Chapter 3 of Vol. I, dealing with the aberration theory of reflecting tele
scopes, is the longest and certainly one of the most important in the whole
work. It is in this area that there is the greatest overlap with the above
General Preface (Preface to Volume I) IX
books. However, an illustration of the major, and legitimate, differences in
presentation is the data given on the optical quality of systems discussed.
Spot-diagrams are the commonest way of representing the quality according
to geometrical optics. Rutten-van Venrooij and Laux give virtuaIly complete
spot-diagram analyses of the systems they discuss, a very valuable feature.
To keep Vol. I within reasonable bounds, I have preferred to limit myself to
chosen examples, intended to illustrate with spot-diagrams the key points of
the development. Some of these are taken from the literaturej but most of
those in Chapter 3 (and a few in Chapter 4) have been optimized by Bernard
Delabre of ESO from starting systems I set up from the basic theory, or with
minor modifications emerging from the calculations. I am deeply grateful for
this major contribution to the work.
I owe a great debt of gratitude to many specialist members of the as
tronomical community and associated industrial concerns, particularly Carl
Zeiss (Oberkochen) and REOSC (Paris), who have generously supplied in
formation. This debt extends, too, to many ESO coIleagues. Above aIl, I am
grateful to the ESO management for supporting the project and for extensive
help in establishing the final text. In the detailed work, I wish to thank specif
ically, as weIl as Bernard Delabre mentioned above, Marion Beelen, Samantha
Milligan, Baxter Aitken (who has not only played a major role in the text
processing but also kindly read through the entire work), Ed Janssen (who
drew and formatted the figures) and Hans-Hermann Heyer for much hard
work and enthusiastic support. My gratitude is also due to Richard West for
general encouragement and support. Finally, I thank the publisher, Springer
Verlag, for exceIlent cooperation, and, last but by no means least, my wife
Anne, for much help with the text and, above aIl, for patience throughout
the whole task.
D-85296 Rohrbach Ray N. Wilson
January 1996
Preface to Volume 11
The aim and style of Vol. II follows exactly the intentions expressed in the
preface to Vol. I, above. The general approach is, therefore, again historical
and morphological, although the subjects of Vol. II are, in general, more re
cent than much of the theory of Vol.1. Most of the developments described
are a product of the last 50 years - many of them, indeed, of the last 20
years. Nevertheless, the history of the developments discussed often goes
back a long way: in Chap.4 there is a reference to W. Herschel in 1800, in
Chap.3 to S. D. Poisson in 1829. It is my hope that the two volumes together
include the most complete bibliography of reflecting telescope optics that
exists. Chapter 1 of Vol. II, dealing with manufacture and test technology,
has 166 numbered references; Chap.3, dealing with modern technical solu
tions for reflecting telescopes in general and the longest in the book, has 260
numbered references. So Vol. II will hopefuBy also serve as a source book.
One important consequence of the fact that the bulk of the material of
Vol. II is, in its nature, modern or ultra-modern, is that the exposition given
is bound to date fairly rapidly in those areas where development is most
intensive. Such a key area is, of course, adaptive optics, the correction of
atmospheric seeing dealt with in Chap. 5. Depending on the material involved,
the cut-off date for new developments in this book lies between about 1993
and February 1998 at the latest. So developments after 1993 are only partially
covered and effectively not at all after 1997.
Since no developments occurring in 1998 could be included in the text, it
follows that there is no reference to the remarkable "First Light" results of
the ESO VLT UT1, the first telescope with an 8 m monolithic primary to be
completed. The image quality (raw) published at "First Light" was remark
able enough, with best star images having a FWHM equal to 0.43 arcsec or
even 0.38 arcsec. However, on 6 June 1998 this was bettered by star images
of the globular cluster M55 with a FWHM of 0.27 arcsec! Such remarkable
results, expected to be achieved only about 3 years later, are a complete vin
dication both of the thin-meniscus active technology of the telescope and of
the excellent site of Paranal in Chile. It is clear that the age of very large
telescopes based on new technology, initiated with dramatic success by the
two Keck 10 m telescopes completed in 1992 and 1996 respectively, will in
the next few years be represented by about a dozen or more superb individ
ual instruments using different technologies and aB with apertures between
XII Preface to Volume 11
61/2 m and 10 m, some of which are intended for linked operation in the inter
ferometric mode. A marvellous astronomical prospect for the new millenium
indeed! It is my hope that I have done justice in this book to all these projects
and the remarkable technologies driving them.
It was my intention to inelude specific chapters on solar telescopes, X-ray
telescopes using near-grazing incidence, and interferometry with telescopes.
Subsequently, I abandoned coverage of these fields for the following reasons.
Solar telescopes have very different requirements from those of normal astro
nomical telescopes, and refracting telescopes, which are not treated in this
work, still playa significant role. Similarly, X-ray telescopes have very special
technical requirements, though the elose link to the Mersenne telescope was
indicated in Vol.1. Furthermore, these systems have been admirably dealt
with by Korsch in his "Reflective Optics" (Academic Press, 1991). The inter
ferometric requirements for telescopes have been treated briefly in Chap.5;
but I coneluded that a treatment in depth of interferometry with telescopes
would require a whole book in its own right, even if my own expertise in this
field were adequate, which is not the case.
I owe a vast debt of gratitude to a wide cirele of friends and colleagues
in the astronomical community and the "big optics" community associated
with it. Specific acknowledgments are given at the beginning of Chap. 1 in
the areas of manufacture and testing of optical surfaces. The other chapters,
above all Chap. 3, are so wide-ranging that it would be impossible to express
adequate acknowledgment in this preface to the many sources of generous
help and advice. I hope, therefore, it will suffice here if I thank globally
all those who have helped with information or figure material. I believe the
credits in the text, references and, above all, the figures are the best way to
express my deep gratitude.
Specifically, I wish here to thank the management of ESO for their con
tinued encouragement and support of the whole project, above all for the
major work of the preparation of the figures. This was organised through the
kind help of Richard West and executed, as for Vol. I, by Ed Janssen. He
has again done a wonderful job in a key area and I express here my grateful
thanks to hirn. My thanks are also due to Hännes Heyer for his assistance
on the photographic side. On the technical side, many colleagues have given
valuable information, particularly Philippe Dierickx, Lothar Noethe, Martin
Cullum, Paul Giordano, Bernard Delabre and Francis Franza. The original
text processing was done by Marion Beelen, Samantha Milligan and Baxter
Aitken, to whom I express my gratitude for an enormous task. Ingrid Weber
has given valuable secretarial help in many ways. Finally, the ESO library
has been a central factor in the fundamentally important area of literature:
my grateful thanks are due to Uta Grothkopf and Angelika Treumann for
their efficient and friendly service.
As with Vol. I, the collaboration with Springer-Verlag has been excellent
in all respects. I express here my grateful thanks to Prof. W. Beiglböck and his
staff for the help and understanding they have constantly given me; also for