Practical Astronomy. Springer-Verlag London Ltd.

Transcription

1 Practical Astronomy Springer-Verlag London Ltd.

2 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

3 Martin Mobberley Springer

4 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 ISBN ISBN (ebook) DOI / Library of Congress Cataloging-in-Publication Data Mobberley, Martin, 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.M '.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 rd 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/ Printed on acid-free paper SPIN

5 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

6 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

7 Contents 1 Fundamentals for Beginners Using Low Magnification Using High Magnification Formulae... 4 Jargon Eyepiece Sizes Refractors and Reflectors... 7 Achromatic Refractors Apochromatic Refractors... 9 Semi-Apochromatic Refractors Refractors or Reflectors? Newtonian Reflectors Long-Focus Newtonians Collimation Dobsonians Buying a Telescope Beginners'Telescopes Buyer Beware! High-Quality Refractors Apochromats for the Connoisseur Other Telescope Considerations Catadioptrics, Cassegrains and Schmidt-Cassegrains Cassegrains Schmidt-Cassegrains Electronic Drive Control Periodic Error Correction Autoguiders Summary Maksutovs Schiefspieglers Binoculars Stands for Binoculars Image-Stabilised Binoculars... 57

8 x Contents 5 Eyepieces Magnification Lowest Practical Magnification Highest Practical Magnification Practical Considerations Comet Seeking Focusing-Tube Diameter Real Field Limitations Popular Commercial Eyepieces High-Definition Eyepieces Barlow Lenses Eyepiece Projection Illuminated-Reticle Eyepieces Commercial Guiding Eyepieces Telescope Mountings The Equatorial Mounting Commercial Telescope Mounting Systems Fork Mountings German Equatorial Mountings The Split-Ring Equatorial Commercial Drive Systems Home-Made Drives and Unusual Mountings Electronic Drive Design Unusual Mountings Poncet Platforms Alt-azimuth Field De-Rotators Accessories Finders Unity-Power Finders Low-Power Finders Guide Telescopes Off-Axis Guiders Horses for Courses Photographic Equipment - Film versus CCD Un driven Astrophotography Simple Tracking Dew Film, Meteor-Photography Equipment and Wide-Field Camera Equipment Satellite Trails Medium-Format Cameras Fish-Eye Lenses Developing and Printing

9 Contents xi Developing Tanks Developing Colour Film Black-and-White Printing Cold Cameras and Film Hypersensitising Camera Interfaces Focusers Commercial Schmidt -Cassegrain Focusing Manual Guiding and Off-Axis Guiders Guiding for Comet Photography A Comet Marathon Coma Correctors A Final Word on Focusers Filters Planetary Filters Venus Mars Jupiter and Saturn The Moon Deep Sky Filters Comet Filters Photographic Filters Photometric Filters for CCDs Schmidt Cameras and Astrographs Electronic Imaging and the Electronics Revolution CCDs The Basics Camera Design CCDs Compared with Film Disadvantages of CCDs Image Scale and Pixel Size Buying a CCD Camera Starlight Xpress Colour Imaging SBIG and Meade Auto-Slewing with a Schmidt-Cassegrain and a CCD Camera SBIG Autoguiding Other Manufacturers Using a CCD Camera Understanding and Processing the Digital Image A Dark Frame Background Brightness Flat-Field

10 xii Contents Diffraction Focusers Useful Processing Routines Unsharp Masking Deconvolution Median Filters Non-Linear Contrast-Stretch Image Formats Astrometry Photometry Image Processing, Planetarium and Telescope Control Software QMips 1.81 by Christian Buil MIRA AL by Axiom Hidden Image by Sehgal CCD Astrometry Paintshop Pro Adobe Photoshop Printers and Scanners Scanning Photographs Planetarium Software Redshift The Sky Real Sky Guide Megastar Starry Night Deluxe NGCView Universe Explorer V oyager II Comet Explorer The Astronomer Software Planetarium Telescope Control Video Astronomy Image Intensifiers Observatories The Simplest Solution Simple Observatories If It Can Go Wrong Observatory Domes Equipment for Observing the Sun Eyepiece Projection Direct Solar Observation Observing in White Light Solar Filters: Inconel Solar Filters: Mylar

11 Contents xiii Seeing Hydrogen-Alpha Equipment Viewing Eclipses Star Atlases and Deep Sky Atlases Appendix 1 Dealers, Bibliography and URLs Equipment Suppliers Quality Binocular Mounting Suppliers Societies Worth Joining Internet URLs Books Appendix 2 Photographic and Visual Magnitude Limits Index 265