Care of astronomical telescopes and accessories : a manual for the astronomical observer and amateur telescope maker

255 Pages·2005·3.18 MB·English

by  M Barlow Pepin

Patrick Moore’s Practical Astronomy Series
Other titles in this series
Telescopes and Techniques (2nd Edn.) Astronomy with Small Telescopes
Chris Kitchin Stephen F. Tonkin (Ed.)
The Art and Science of CCD Astronomy Solar Observing Techniques
David Ratledge (Ed.) Chris Kitchin
The Observer’s Year Observing the Planets
Patrick Moore Peter T. Wlasuk
Seeing Stars Light Pollution
Chris Kitchin and Robert W. Forrest Bob Mizon
Photo-guide to the Constellations Using the Meade ETX
Chris Kitchin Mike Weasner
The Sun in Eclipse Practical Amateur Spectroscopy
Michael Maunder and Patrick Moore Stephen F. Tonkin (Ed.)
Software and Data for Practical Astronomers More Small Astronomical Observatories
David Ratledge Patrick Moore (Ed.)
Amateur Telescope Making Observer’s Guide to Stellar Evolution
Stephen F. Tonkin (Ed.) Mike Inglis
Observing Meteors, Comets, Supernovae and How to Observe the Sun Safely
other Transient Phenomena Lee Macdonald
Neil Bone The Practical Astronomer’s Deep-Sky
Astronomical Equipment for Amateurs Companion
Martin Mobberley Jess K. Gilmour
Transit: When Planets Cross the Sun Observing Comets
Michael Maunder and Patrick Moore Nick James and Gerald North
Practical Astrophotography Observing Variable Stars
Jeffrey R. Charles Gerry A. Good
Observing the Moon Visual Astronomy in the Suburbs
Peter T. Wlasuk Antony Cooke
Deep-Sky Observing Astronomy of the Milky Way: The Observer’s
Steven R. Coe Guide to the Northern and Southern Milky Way
AstroFAQs (2 volumes)
Stephen Tonkin Mike Inglis
The Deep-Sky Observer’s Year The NexStar User’s Guide
Grant Privett and Paul Parsons Michael W. Swanson
Field Guide to the Deep Sky Objects Observing Binary and Double Stars
Mike Inglis Bob Argyle (Ed.)
Choosing and Using a Schmidt-Cassegrain Navigating the Night Sky
Telescope Guilherme de Almeida
Rod Mollise The New Amateur Astronomer
Martin Mobberley
Care of
Astronomical
Telescopes and
Accessories
A Manual for the Astronomical Observer
and Amateur Telescope Maker
M. Barlow Pepin
With 82 Figures
All illustrations in this book are by the author, unless otherwise noted.
British Library Cataloguing in Publication Data
Pepin, M. Barlow
Care of astronomical telescopes and accessories : a manual
for the astronomical observer and amateur telescope maker.
(Patrick Moore’s practical astronomy series)
1. Telescopes–Maintenance and repair
I. Title
522.2′0288
ISBN 185233715X
Library of Congress Cataloging-in-Publication Data
Pepin, M. Barlow.
Care of astronomical telescopes and accessories : a manual
for the astronomical observer and amateur telescope
maker / M. Barlow Pepin.
p. cm. — (Patrick Moore’s practical astronomy series,
ISSN 1617-7185)
Includes bibliographical references and index.
ISBN 1-85233-715-X (pbk. : alk. paper)
1. Telescopes–Amateur’s manuals. I. Title. II. Series.
QB88.P46 2004
522.2–dc22 2004049148
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as
permitted under the Copyright, Designs and Patents Act 1988, this publication may only be repro-
duced, stored or transmitted, in any form or by any means, with the prior permission in writing of the
publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued
by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be
sent to the publishers.
Patrick Moore’s Practical Astronomy Series ISSN 1617-7185
ISBN 1-85233-715-X Springer-Verlag London Berlin Heidelberg
Springer Science+Business Media
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© Springer-Verlag London Limited 2005
Printed in the United States of America
The use of registered names, trademarks, etc. in this publication does not imply, even in the absence
of a specific statement, that such names are exempt from the relevant laws and regulations and there-
fore free for general use.
The publisher makes no representation, express or implied, with regard to the accuracy of the infor-
mation contained in this book and cannot accept any legal responsibility or liability for any errors or
omissions that may be made. Observing the Sun, along with a few other aspects of astronomy, can be
dangerous. Neither the publisher nor the author accepts any legal responsibility or liability for per-
sonal loss or injury caused, or alleged to have been caused, by any information or recommendation
contained in this book.
Typeset by EXPO Holdings, Malaysia
58/3830-543210 Printed on acid-free paper SPIN 10901120
To my Sun and Stars: Mary, Danielle and Jeannette

Foreword
Many new books about astronomical telescopes are published each year, but this
one, by M. Barlow Pepin, is unlike any other – at least as far as I know.
The emphasis has shifted lately. Amateur telescope making is less popular than
it used to be because professionally made telescopes are much cheaper than they
were only a year or two ago. But there is no point in having a good telescope
unless it is well cared for, and many observers pay too little attention to this. It is
not only a question of common sense; expert guidance is also needed, and in this
book M. Barlow Pepin gives it. He goes into detail with regard to all aspects of
telescope care and maintenance, and even experienced observers will learn a
great deal from it.
Astronomy is one of the very few sciences in which amateurs can make valu-
able contributions, but good, well-maintained equipment is essential. If you want
to get the best out of your telescopes and other astronomical instruments, then
this is the book for you.
Sir Patrick Moore CBE, FRS
vii
Preface and
Acknowledgments
This book fills a gap left by earlier works of general practical advice, most of
which are either out of date or long out of print. It is both a contribution and a
tribute to its predecessors’ tradition of handing down craft knowledge. Although
the volume distills years of practical experience working with astronomical
equipment and accessories, it doesn’t pretend to be complete in every detail. It
would have been illogical to try to set down everything about maintaining equip-
ment for every branch of the pursuit. Such a work would fill an already groaning
bookshelf. Furthermore, I don’t cover things I have no personal experience with –
that’s what compendium works are for, and there are some good ones around
that cover most aspects of amateur astronomy. Several are included in the
Bibliography. Finally, experts continuously cover new developments in fast-
changing fields like electronic imaging, optical fabrication methods, narrowband
imaging and robotic systems. This work concentrates on the practical acquisition
and maintenance of the optics and mechanics that support such endeavors.
Despite the fabulous armchair journeys we can now make on the Internet,
using optics under the sky is still what makes the pursuit of amateur astronomy
enjoyable. Even the best astronomical equipment requires both care and appreci-
ation to yield good results. Acquiring and caring for it takes patience and a few
special skills. There is still time, place and a need for hands-on work.
Years ago I carried a pencil sketch and part of a homemade mount into a
machine shop and asked if they could make a simple modification. The foreman
in blackened coveralls took a look and said, “Sure, come back tomorrow, it
should cost you about twenty.” The last time I tried this, a fellow in a golfing shirt
looked up from his computer and said, “Sure, send me a CAD file for our CNC
guys, and we’ll work up a quote for next week. How many units do you need?”
Just the software would have cost more than a new mount!
The artisans aren’t gone, but they are increasingly hard to find. When you do,
they are busier than the devil. Thus, all the more need for a work that covers a
little history, with some basic fixes and workarounds for the practical amateur.
That’s what Section II does. A few processes I have personally worked out and
tested are outlined in Chapter 13.
My hat is off as I write this, aware of the many individuals and groups whose
collective knowledge is far greater than my own. It was fascinating to review the
works of earlier authors around the world, many of whom lived at a time when a
telescope was a rare commodity, and most equipment cobbled together in the
garages and basements of dedicated enthusiasts. The mission here is the same as
ix
x Preface and Acknowledgments
theirs: to impart some basics of contemporary instrument acquisition and main-
tenance to new astronomers, and to provide a useful lookup resource for the old
hands. There is always room for improvement. In fact, I fully expect to hear about
matters that weren’t addressed.
I wish to express sincere appreciation to my present editor John Watson. I am
especially gratified for the opportunity here to acknowledge mentors such as
series editor Sir Patrick Moore, the late solar observer Donald Trombino, FRAS
and editors in the past, including Richard Berry who accepted my first efforts at
publication, William J. Cook, Martin Neumann and Simon Mitton. For hints and
help over the years I am indebted to Alan MacRobert, Roger Sinnott, supportive
members of management and staff at Sky Publishing, and to the Astronomical
League, the British Astronomical Society, the Royal Astronomical Society of
Canada and the Vereinigung der Sternfreunde (VdS) of Germany. A wide range
of amateur and professional optical historians, from Peter Abrahams to Drs.
Albert van Helden and Wayne Orchiston, pointed the way to valuable references
on historical techniques. Additionally, kudosto all the fine people on the business
side whose hearts are in the right place, especially Al Nagler who gave open per-
mission to use equipment of his design to illustrate a few basic instruments and
accessories for the book. Thanks also to New Focus, Inc. of San Jose, California,
and Aerotech, Inc. of Pittsburgh, Pennsylvania, for the loan of bench components
for generating laser visualizations of light through the telescope, published before
only as line drawings.
Sincere regards to a host of observing companions too numerous to mention,
and the many unseen folks, friendly voices in the dark from around the world.
Here, too, is a nod to all amateurs’ patient spouses and offspring who have lain
awake at night wondering “what could possibly be so interesting out there?”
Finally, this volume is dedicated to fellow ATMs and Telescope Nuts, those
people who insist on continuing to make contraptions out of odd glass and spare
parts that rival or exceed the performance of the best manufactured equipment.
The special community of amateur astronomers has endured for centuries. Our
activities will doubtless continue long into the future as one of the most fascinat-
ing pursuits in this or any other universe. If this volume eases the path for a few,
or just helps to pass time on a cloudy night, it will have repaid the effort.
M. Barlow Pepin
Duncanville, Texas
July, 2004
The author. Photo: L. Lattin.
Contents
Section I: Optical Equipment
1 Treasure in the Cellar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Buying It Right: Consumer Strategies . . . . . . . . . . . . . . . . . . . . . 7
3 New Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Tool or Toy? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Basic Optical Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Light Gathering and Performance . . . . . . . . . . . . . . . . . . . . . 11
Aperture and Focal Length . . . . . . . . . . . . . . . . . . . . . . . . . 13
Focal Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
The Eyepiece and Magnification . . . . . . . . . . . . . . . . . . . . . . 14
Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure, Focal Length and Performance. . . . . . . . . . . . . . . . . . . 18
Fast and Slow Telescopes . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Practical Limits of Magnification. . . . . . . . . . . . . . . . . . . . . . 19
Aperture and the 50×Rule . . . . . . . . . . . . . . . . . . . . . . . . . 20
Exit Pupil and the 5×Rule. . . . . . . . . . . . . . . . . . . . . . . . . . 21
Visual Limiting Magnitude . . . . . . . . . . . . . . . . . . . . . . . . . 22
Apparent Brightness of Extended Objects. . . . . . . . . . . . . . . . . 23
The Airy Disc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Resolution and Dawes’ Criterion. . . . . . . . . . . . . . . . . . . . . . 24
Wavefront Error and the Rayleigh Limit. . . . . . . . . . . . . . . . . . 26
System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Optical Tube Assemblies in General . . . . . . . . . . . . . . . . . . . . 29
Mount, Tripod and Pier (Plinth) . . . . . . . . . . . . . . . . . . . . . . 31
A Beginner’s Telescope . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
A Note on Historical Cost Relationships. . . . . . . . . . . . . . . . . . 33
Types of Telescopes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Refracting Telescopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Reflecting and Compound Telescopes. . . . . . . . . . . . . . . . . . . 41
Siderostats and Fixed-Eyepiece Telescopes . . . . . . . . . . . . . . . . 50
Point-of-Purchase Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Checkpoint List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Shipping and Warranties. . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Shipping Costs and Modes . . . . . . . . . . . . . . . . . . . . . . . . . 57
xi