Patrick Moore s Practical Astronomy Series For further volumes: http://www.springer.com/series/3192
Amateur Telescope Making in the Internet Age Finding Parts, Getting Help, and More Robert L. Clark 123
Robert L. Clark Westminster, MD 21157, USA ISSN 1431-9756 ISBN 978-1-4419-6414-4 e-isbn 978-1-4419-6415-1 DOI 10.1007/978-1-4419-6415-1 Springer New York Dordrecht Heidelberg London Library of Congress Control Number: 2010935731 Springer Science+Business Media, LLC 2011 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)
Acknowledgments Many people should share in the credit or blame for this book, some for direct contributions and some for encouragement and support of the activities leading up to this book. Of the first group my wife, Nancy, tolerated lots of things not getting done as time went to the book. She copied files and pictures, providing needed technical support. Gerry Frishkorn from the Westminster Astronomical Society provided the neat photo of a spider from his famous binoculars. He also checked and detected errors in my math. Numerous folks from the same club provided leads for the supplier appendix. Cousins Ann Herbert and Faith Marchal provided help with the conversion material. Cousin Hughes Gemmill gave me some old Dallmeyer lenses with which I learned how to get them unglued and cleaned. In the second group are Duane Shie, who is inspiring as a dumpster diver; George Lockwood, who was always available for idea testing and ebay hints; Teresa Rosales; Blas Chavez; Roger Baker; and Mark Dennis, who helped with the lugging of telescopes and their parts. The folks at Springer publishing have been very tolerant of the questions of a beginning author and have provided important guidelines. v
Contents 1 Introduction... 1 Tools... 3 AbsolutelyNecessary... 3 VeryHelpfulorNecessaryforParticularTasks... 3 NicetoHave... 3 Ergonomics...... 5 What s Not Included in this Book..... 5 General Advice.... 6 SafetyTips... 6 2 To Buy or Build a Telescope... 9 3 Telescope Types and Designs... 19 Telescope Types.... 19 Reflector Telescopes..... 19 Refractor Telescopes...... 21 Telescope Design Considerations..... 22 A Real Simple Telescope.... 27 4 Build a Good Copyscope... 33 The Small Copyscope...... 33 OpticalParts... 33 Mechanical Parts... 34 The Medium Copyscope.... 35 OpticalParts... 35 Mechanical Parts... 35 The Large Copyscope...... 36 OpticalParts... 36 vii
viii Contents Mechanical Parts... 38 How to Make Your Copyscope...... 38 Focal Length.... 38 Alignment... 40 Mounting a Copyscope..... 42 5 The 80 mm Refractor... 45 Telescope Description and Capabilities... 45 Specifications and Components.... 46 6 Newtonian Telescopes... 57 Typical Newtonian Telescopes...... 57 TheObjectiveMirror... 59 MirrorMounting... 64 A Spider in Your Telescope... 65 MirrorCells... 68 Simple Collimation... 70 7 The F17 4-Inch Refractor... 73 The Rotating Star Diagonal... 74 The Back Two Bulkheads.... 75 The Diagonal Mirror...... 77 MountingtheRefractorUsingaCradle... 81 8 Focusers, Eyepieces, Barlows, and Finders... 83 Focusers... 83 Telescoping Tubes... 84 RackandPinionDesign... 85 HelicalDesign... 85 CrayfordDesign... 86 Eyepieces... 87 EyeRelief... 87 Exit Pupil... 88 Achromats... 89 Very Modern Wide Angle Eyepieces... 90 Compound Projection and Camera Lenses..... 91 BarlowLenses... 92 ImageInverter(ErectingLens)... 93 Finders... 93 Requirements for a Workable Finder Scope.... 94 Satisfying the Finder Requirements.... 95 Peep Sight Finder... 98 Laser Pointer as a Finder.... 99 9 Tubes... 101 Closed Tube Approaches.... 102 Wooden Tubes..... 103
Contents ix Getting Started.... 103 AssemblyoftheTube... 106 UsingGussets... 107 Wood Tubes Without Gussets... 110 Open Tubes...... 111 Truss Tubes...... 112 10 Building a 12.5-Inch Newtonian with Rotating Cage... 113 DimensionsoftheTube(Box)... 114 Diagonal... 119 Spider... 120 Upper Tube Rotation...... 121 Doughnuts to Preserve Alignment.... 121 Stabilizers... 123 Mounting... 124 11 Ergonomic Mounts... 127 Mounting Types.... 127 Supports... 128 Balance and Moment...... 129 Wedges... 132 An Ergonomic Altazimuth Mount.... 133 12 Evaluation, Quality Testing, and Optical Aberrations... 137 HowGoodDoesItNeedtoBe?... 137 CommonFaults... 138 Focal Length..... 139 Quality Testing.... 139 PossibleConstructionProblems... 140 Lenses... 140 Mirrors... 141 Mirror Reflective Coatings... 142 Optical Quality Terminology... 142 Wavelength-Based Measurements... 143 RaysandWaves... 143 Scratch and Dig Optical Surface Specifications...... 146 Scatter (Spot) Diagrams... 146 StrehlRatio... 146 Quality of Flat Mirrors... 148 TestingaFlat... 148 OpticalAberrations... 149 QuickandEasyTests... 152 13 Junk Collecting and Working with Modern Materials... 153 Junk Collection (Creative Cross Utilization).... 153 LensRestoration/UsedLenses... 155 LensCementing... 155
x Contents Getting a Lens Apart..... 156 Polishing and Coating Ideas... 157 NoDrag,NoProgress... 158 HowLongWillItTake?... 158 LapMaking... 160 WorkingwithPVCPipe... 161 PVC Eyepiece Canisters... 163 ForNCanisters... 163 OtherUsesforPVC... 163 AligningParts... 163 Telescope Mounts...... 165 LensCells... 165 RetainingRings... 165 Floor Underlay... 166 GluesandCements... 166 Appendix I Web Suppliers of Telescope Building Parts and Materials... 169 Alphabetical Listing of Suppliers..... 170 Products... 186 Supplier Codes by Product... 188 Appendix II Telescope-Building Books and Websites... 193 BookMust-Haves... 193 Magazines... 194 Websites... 194 Appendix III Polishing Log... 197 Appendix IV Units and Conversions... 199 General Conversions...... 199 WoodStockandHardwareConversions... 199 European Plywood Standards..... 199 Timber... 200 Hardware... 200 Index... 201
About the Author Although Clark was born in New Hampshire, he spent his early teen years in the New York City area. There he became acquainted with the Theodore Roosevelt Museum of Natural History and at the associated Hayden Planetarium, operated, at that time, by Newton and Margaret Mayhall. Their book Skyshooting provided his first introduction to the idea that someone with only moderate skills can build good scientific instruments. The three volumes of Amateur Telescope Making, edited by Albert G. Ingalls, completed the process of addiction. Clark received a B.S. degree in Mathematics from Stanford University. He then served in the US. Air Force at Strategic Air Command headquarters in Nebraska. After his discharge he did graduate work in Mathematics and Computer Science at the University of Maryland. After a few years spent in the Military Operations Research industry, he migrated to a university teaching position that lasted 33 years at the University of the District of Columbia. Throughout all this time he continued to be enamored by the process of building telescopes and actually built a few as time permitted. Since retirement he has allowed the addiction to occupy a large part of his enthusiasm, as is made evident by Fig. 2.3. Clark now resides in Westminster, Maryland, where he has built a hilltop observatory and is active with the Westminster Astronomical Society. xi