Patrick Moore s Practical Astronomy Series

Transcription

1 Patrick Moore s Practical Astronomy Series

2 Other titles in this series Telescopes and Techniques (2nd Edn.) Chris Kitchin The Art and Science of CCD Astronomy David Ratledge (Ed.) The Observer s Year Patrick Moore Seeing Stars Chris Kitchin and Robert W. Forrest Photo-guide to the Constellations Chris Kitchin The Sun in Eclipse Michael Maunder and Patrick Moore Software and Data for Practical Astronomers David Ratledge Amateur Telescope Making Stephen F. Tonkin (Ed.) Observing Meteors, Comets, Supernovae and other Transient Phenomena Neil Bone Astronomical Equipment for Amateurs Martin Mobberley Transit: When Planets Cross the Sun Michael Maunder and Patrick Moore Practical Astrophotography Jeffrey R. Charles Observing the Moon Peter T. Wlasuk Deep-Sky Observing Steven R. Coe AstroFAQs Stephen Tonkin The Deep-Sky Observer s Year Grant Privett and Paul Parsons Field Guide to the Deep Sky Objects Mike Inglis Choosing and Using a Schmidt-Cassegrain Telescope Rod Mollise Astronomy with Small Telescopes Stephen F. Tonkin (Ed.) Solar Observing Techniques Chris Kitchin Observing the Planets Peter T. Wlasuk Light Pollution Bob Mizon Using the Meade ETX Mike Weasner Practical Amateur Spectroscopy Stephen F. Tonkin (Ed.) More Small Astronomical Observatories Patrick Moore (Ed.) Observer s Guide to Stellar Evolution Mike Inglis How to Observe the Sun Safely Lee Macdonald The Practical Astronomer s Deep-Sky Companion Jess K. Gilmour Observing Comets Nick James and Gerald North Observing Variable Stars Gerry A. Good Visual Astronomy in the Suburbs Antony Cooke Astronomy of the Milky Way: The Observer s Guide to the Northern and Southern Milky Way (2 volumes) Mike Inglis The NexStar User s Guide Michael W. Swanson Observing Binary and Double Stars Bob Argyle (Ed.) Navigating the Night Sky Guilherme de Almeida The New Amateur Astronomer Martin Mobberley

3 Care of Astronomical Telescopes and Accessories A Manual for the Astronomical Observer and Amateur Telescope Maker M. Barlow Pepin With 82 Figures

4 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 ISBN X 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 ) Includes bibliographical references and index. ISBN X (pbk. : alk. paper) 1. Telescopes Amateur s manuals. I. Title. II. Series. QB88.P dc 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 reproduced, 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 ISBN X Springer-Verlag London Berlin Heidelberg Springer Science+Business Media springeronline.com 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 therefore free for general use. The publisher makes no representation, express or implied, with regard to the accuracy of the information 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 personal 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/ Printed on acid-free paper SPIN

5 To my Sun and Stars: Mary, Danielle and Jeannette

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7 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 valuable 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

8 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 equipment 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 fastchanging 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 appreciation 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

9 x Preface and Acknowledgments theirs: to impart some basics of contemporary instrument acquisition and maintenance 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, kudos to all the fine people on the business side whose hearts are in the right place, especially Al Nagler who gave open permission 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 fascinating 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.

10 Contents Section I: Optical Equipment 1 Treasure in the Cellar Buying It Right: Consumer Strategies New Instruments Tool or Toy? Basic Optical Definitions Light Gathering and Performance Aperture and Focal Length Focal Ratio The Eyepiece and Magnification Field Figure, Focal Length and Performance Fast and Slow Telescopes Practical Limits of Magnification Aperture and the 50 Rule Exit Pupil and the 5 Rule Visual Limiting Magnitude Apparent Brightness of Extended Objects The Airy Disc Resolution and Dawes Criterion Wavefront Error and the Rayleigh Limit System Components Optical Tube Assemblies in General Mount, Tripod and Pier (Plinth) A Beginner s Telescope A Note on Historical Cost Relationships Types of Telescopes Refracting Telescopes Reflecting and Compound Telescopes Siderostats and Fixed-Eyepiece Telescopes Point-of-Purchase Checks Checkpoint List Shipping and Warranties Shipping Costs and Modes xi

11 xii Contents Return Policies Warranties Used Equipment They Don t Make Them Like They Used To Sources Condition Checks and Evaluation Refracting Telescopes-Optical Tubes Collimation and Adjustment-General Information Lens Alignment Problems Reflecting Instruments-Optical Tubes Catadioptric and Compound Optical Tubes Optical Accessories Eyepieces and Barlow Lenses Choosing Standard Oculars That Fit Your Needs The Barlow Lens Star Diagonals and Prisms Finders Visual Filters Color Band-Pass Filters Nebular and Other Dichroic Filters Solar Filters for White Light Specialized Visual Accessories Telecompressors Binocular Viewers Eyepiece Micrometers and Analog Measurement Ocular Turrets Section II: Care and Maintenance 6 Lens Optics Introduction: Glass as a Lens Material Environmental Factors Intrusion of Water and Water Vapor Airborne Abrasives Fungus Attack Human Factors Lens Optics-Light Cleaning Dealing with Moisture and Dust Particles Light Cleaning Sunlight Prophylaxis Flooding by Water Lens Optics Advanced Cleaning Cell and Objective Lens Mechanics Cleaning a Disassembled Objective

12 Contents xiii 7 Figured Mirrors and Flats Environmental Factors Dealing with Moisture and Dust Particles Figured and Flat Mirrors Advanced Cleaning A Standard Wet Method Strippable Optical Coatings Optical Tube Features Focusers Tension Adjustment Lubrication Interior Finish of the Tailpiece Friction Focusers Drawtubes Handling and Disassembling Small Objectives Cemented Objectives Small Air-Spaced Objectives Dew Control and Dewcaps Mounts and Tripods General Care of Equatorial Mounts Lubrication Play in Equatorial Shafts Loose Tension Adjustment Latitude Adjustment Drive Motors Clutch Adjustment Setting Circles Right Ascension Reconditioning Equatorial Mount Bearings General Procedure Aspects of Care of Dobsonians Platform Maintenance and Adjustment Altitude Bearings Routine Maintenance Wooden Tripods General Care Tips on Protection, Touchup and Refurbishing Collimation and Adjustment Techniques Refracting Telescopes Routine Collimation Check The Candle Test Newtonians The Laser-Diode Collimator Mechanical Adjustments Spider Hub and Focuser Visual Collimation

13 xiv Contents General Daytime Tests Collimation by Star Image Star Testing in General Collimation Using a Star Image General Procedure for Primary Mirrors, Objectives and Secondaries Miscellaneous Adjustments A Note on Tilted Component Telescopes Diagnosing Diagonal Alignment Aligning Optical Tubes in the Tube Cradle or Mount Block Protection, Refinishing and Surface Treatments Care of Metal Bare Metal Protection Permanent Clear Coatings Exterior Metal Finishes General Touch-Up Refilling Engraved Index Marks and Lettering Wood and Wood Finishes Historic Wooden Tubes Exterior Wooden Finishes Surface Preparation Renewing a Non-reflective Finish; Tubes and Accessories Antireflective Coatings in General Cleaning Refinishing Storage Shipping Boxes and Storage Containers Wooden Containers Silica Gel and Humidity Equipment Projects and Tips Antihumidity Focuser Plugs Ventilating a Newtonian Tube Baffling A Refractor Tube Focusing Tube Problems Working Method Making Finder and Eyepiece Cross-Hair Reticles General Disassembly-Finders and Eyepieces Adding Eyepiece Cross-Hairs Threads Made from Liquid Cement Styrene Threads for Low-Magnification Uses Thin Threads for Interchangeable Eyepieces Making and Mounting Cement Threads Separating and Recementing Small Achromats Separating a Small Cemented Achromat Recementing a Small Achromat

14 Contents xv Appendix A: Tools and Materials Hand and Power Tools Hand Tools Optical Hand Tools Power Tools Wood and Metal Finishing Products Wood Sealers and Stains Coatings Wood Waxes, Oils and Touchup Coating Tools and Materials Brushes and Applicators Wood and Metal Abrasives Useful Solvents and Coating Removers Paint Stripping Compounds Mirror and Lens Cleaning Products Advanced Mirror Cleaning Materials Lists Appendix B: Practical Information and Formulas Measuring the Apparent Field of an Eyepiece Light Gathering Power Coma-Free Field of a Newtonian Reflector in Millimeters List of Hints for Protecting Equipment The Wratten Series Filters A Partial Listing Scales of Seeing Relative Brightness Appendix C: Short-Lists; Equipment Suppliers Astronomical Equipment and Specialties Equipment and Tools Appendix D: Popular Astronomical Journals Bibliography Index

15 Section I Optical Equipment