Practical Astronomy Springer-Verlag London Ltd.
Other titles in this series The Observational Amateur Astronomer Patrick Moore (Ed.) The Modern Amateur Astronomer Patrick Moore (Ed.) Telescopes and Techniques Chris Kitchin Small Astronomical Observatories Patrick Moore (Ed.) 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
Martin Mobberley Springer
Martin Mobberley, BSc British Library Cataloguing in Publication Data Mobberley, Martin Paul Astronomical equipment for amateurs. - (Practical astronomy) 1.Astronomical instruments 2.Astronomy - Amateurs' manuals I.Title 522.2 ISBN 978-1-85233-019-4 ISBN 978-1-4471-0583-1 (ebook) DOI 10.1007/978-1-4471-0583-1 Library of Congress Cataloging-in-Publication Data Mobberley, Martin, 1958- Astronomical equipment for amateurs / Martin Mobberley. p. cm. - (Practical astronomy) 1. Astronomical instruments-handbooks, manuals, etc. 2. Astronomical instruments-amateurs' manuals. 1. Title. II. Series. QB86.M62 1998 98-7025 522'.2-dc21 CIP 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. Springer-Verlag London 1999 Originally published by Springer-Verlag London Berlin Heide1berg in 1999 3rd printing 1999 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. Typeset by EXPO Holdings, Malaysia Printed at the Cromwell Press, Trowbridge, Wiltshire 58/3830-5432 Printed on acid-free paper SPIN 10754570
Preface When Springer invited me to write a book about Astronomical Equipment, my biggest dilemma was what to put in and what to leave out, especially with the rapid recent growth in CCD technology and the associated PC-based technologies. There are over 200 astronomical suppliers out there that I know about and an equal number of astronomical and photographic gadgets and accessories, and I knew it would be impossible to cover everything in detail. My eventual solution to this dilemma was simple. I asked myself: if I were starting again, from scratch, and was about to buy my first decent telescope, what advice would I have wanted, and which pitfalls would I wish to avoid? The glossy advertisements in astronomy magazines do not tell the amateur what it is really like to own and use astronomical equipment. I hope this book does. If I can save a few amateurs from making expensive mistakes by NOT buying the wrong equipment then the book will have been worthwhile. Astronomy can be a relaxing, visual pastime with a pair of binoculars and a deck-chair. Or it can be a battle against the elements, to clinch that perfect photo of a comet at its peak. I do far more of the latter type of observing, so this book is biased in that direction! I very much hope you find something in the book to interest you. March 1998 Martin Mobberley
Acknowledgements I am indebted to a number of people for their advice, help and the supply of photographs for this book. Firstly, I must thank my parents for their support; in particular, my father's help with the figures has been considerable. I am extremely grateful to Hazel McGee for meticulously reading through the first draft of the book. I am also indebted to the following amateur astronomers who have kindly donated figures for the book: Mike Collins; Neil Bone; Steve Evans; Henry Soper; Nick James; Mark Armstrong; Henry Hatfield; Maurice Gavin; Gerald North; Andrew Elliott; Glyn Marsh; Denis Buczynski; Terry Platt and Eric Strach. My thanks must also go to John Watson of Springer, who originally suggested I could write such a book, much to my surprise! March 1998 Martin Mobberley
Contents 1 Fundamentals for Beginners.............. 1 Using Low Magnification............... 1 Using High Magnification.............. 4 Formulae... 4 Jargon............................. 4 Eyepiece Sizes... 6 2 Refractors and Reflectors... 7 Achromatic Refractors................. 7 Apochromatic Refractors... 9 Semi-Apochromatic Refractors... 11 Refractors or Reflectors?... 12 Newtonian Reflectors.................. 14 Long-Focus Newtonians... 20 Collimation... 22 Dobsonians... 25 Buying a Telescope.................... 27 Beginners'Telescopes... 27 Buyer Beware!... 28 High-Quality Refractors... 31 Apochromats for the Connoisseur....... 33 Other Telescope Considerations... 35 3 Catadioptrics, Cassegrains and Schmidt-Cassegrains.................... 37 Cassegrains... 37 Schmidt-Cassegrains.................. 38 Electronic Drive Control............. 41 Periodic Error Correction............ 44 Autoguiders... 45 Summary... 46 Maksutovs... 47 Schiefspieglers........................ 50 4 Binoculars................ 53 Stands for Binoculars.................. 56 Image-Stabilised Binoculars... 57
x Contents 5 Eyepieces... 61 Magnification... 61 Lowest Practical Magnification... 62 Highest Practical Magnification....... 62 Practical Considerations... 63 Comet Seeking.................. 64...... Focusing-Tube Diameter.............. 65. Real Field Limitations... 66 Popular Commercial Eyepieces... 67 High-Definition Eyepieces........... 70... Barlow Lenses... 72 Eyepiece Projection... 73 Illuminated-Reticle Eyepieces... 74 Commercial Guiding Eyepieces... 76 6 Telescope Mountings................ 79.... The Equatorial Mounting... 79 Commercial Telescope Mounting Systems... 80 Fork Mountings... 81 German Equatorial Mountings... 84 The Split-Ring Equatorial.......... 85.. Commercial Drive Systems.......... 86... Home-Made Drives and Unusual Mountings... 89 Electronic Drive Design............. 89... Unusual Mountings... 91 Poncet Platforms..................... 94 Alt-azimuth Field De-Rotators.......... 95 7 Accessories..... 97 Finders.... 97 Unity-Power Finders............. 98... Low-Power Finders... 99 Guide Telescopes... 100 Off-Axis Guiders.................. 101... Horses for Courses................ 101... Photographic Equipment - Film versus CCD... 102 Un driven Astrophotography... 103 Simple Tracking... 106 Dew... 108 Film, Meteor-Photography Equipment and Wide-Field Camera Equipment... 110 Satellite Trails... 113 Medium-Format Cameras... 114 Fish-Eye Lenses................... 114.... Developing and Printing.............. 115
Contents xi Developing Tanks................. 116.... Developing Colour Film... 118 Black-and-White Printing... 119 Cold Cameras and Film Hypersensitising................ 121...... Camera Interfaces.................. 125... Focusers... 126 Commercial Schmidt -Cassegrain Focusing...................... 130....... Manual Guiding and Off-Axis Guiders... 130 Guiding for Comet Photography... 133 A Comet Marathon... 137 Coma Correctors................. 137.... A Final Word on Focusers... 139 Filters... 140 Planetary Filters... 140 Venus... 141 Mars........................ 141...... Jupiter and Saturn....... 142 The Moon... 142 Deep Sky Filters........... 142 Comet Filters................... 145..... Photographic Filters................ 145... Photometric Filters for CCDs... 146 Schmidt Cameras and Astrographs...... 149 8 Electronic Imaging and the Electronics Revolution....... 153 CCDs... 153 The Basics... 153 Camera Design... 155 CCDs Compared with Film.......... 158 Disadvantages of CCDs........... 161.. Image Scale and Pixel Size... 162 Buying a CCD Camera... 167 Starlight Xpress................... 167... Colour Imaging..... 170 SBIG and Meade... 172 Auto-Slewing with a Schmidt-Cassegrain and a CCD Camera................. 173... SBIG Autoguiding..... 174 Other Manufacturers... 176 Using a CCD Camera... 177 Understanding and Processing the Digital Image................... 179..... A Dark Frame... 182 Background Brightness... 183 Flat-Field....... 184
xii Contents Diffraction Focusers................ 187... Useful Processing Routines.......... 187... Unsharp Masking........... 187 Deconvolution................... 190..... Median Filters....... 190 Non-Linear Contrast-Stretch... 190 Image Formats... 191 Astrometry...................... 193..... Photometry......... 196 9 Image Processing, Planetarium and Telescope Control Software............ 199.. QMips 1.81 by Christian Buil... 200 MIRA AL by Axiom..... 201 Hidden Image by Sehgal... 202 CCD Astrometry................. 202.... Paintshop Pro... 202 Adobe Photoshop... 203 Printers and Scanners....... 204 Scanning Photographs............. 205 Planetarium Software............... 205... Redshift 2................... 206...... The Sky....... 207 Real Sky..................... 207..... Guide... 207 Megastar................ 208 Starry Night Deluxe... 208 NGCView 5.02................. 209.... Universe Explorer... 209 V oyager II... 209 Comet Explorer... 209 The Astronomer Software... 210 Planetarium Telescope Control... 210 10 Video Astronomy... 215 Image Intensifiers....... 218 11 Observatories..................... 223..... The Simplest Solution......... 224 Simple Observatories............... 225... If It Can Go Wrong.............. 229...... Observatory Domes.................. 232 12 Equipment for Observing the Sun..... 239 Eyepiece Projection... 240 Direct Solar Observation............ 240.. Observing in White Light... 241 Solar Filters: Inconel... 241 Solar Filters: Mylar............. 241
Contents xiii Seeing... 242 Hydrogen-Alpha Equipment... 243 Viewing Eclipses.................... 247.. 13 Star Atlases and Deep Sky Atlases.......... 253 Appendix 1 Dealers, Bibliography and URLs... 257 Equipment Suppliers.................. 257..... Quality Binocular Mounting Suppliers... 258 Societies Worth Joining... 258 Internet URLs............................. 259 Books... 260 Appendix 2 Photographic and Visual Magnitude Limits.............. 263.. Index 265