Collimating a Newtonian Scientifically: Incorporating the Cave and Laser Telescope Collimators

By Peter R. Clark-Fras

In 2003 my partner Kathleen, proposed a bungalow with a great view of the night sky. December 2005 and one year into telescopes, the optics of the length halved again 8” Cape-Newise got me tasting my own medicine unwittingly and gladly. The confident advertising style mirrored mine for Bailey designed hi-fi speakers, making 100 in the 70’s, exporting 30 to Germany.
My approach has been that of being Isaac Newton through the ages, and after each advancement writing down the achievements at the eyepiece. The 3rd edition of March 2014 was still only 16 pages, 6 of which were the instructions and still are. 50 pages of interest were enabled by 2 months in a recliner chair waiting for surgery. Edition numbers change only with improvements to method. They settled down in October 2014 and the 4th edition printings began in March 2015 and have been selling an average of 6 a day at events since 2012. Intuitive adjustments, too easily fallen into, are prevented by following the instructions chapter in this book. The first 2 sentences of stage [1] and all of stage [4] work equally well for Cassegrain type in-line optics. Mirror cleaning, vetted by a mirror manufacturer, has always been included.

• Language: English
• Publisher: AuthorHouse UK
• Release date: Oct 26, 2020
• ISBN: 9781665580823

Peter R. Clark-Fras

At age 15 in 1953 at the Boulevard Nautical School, Hull, Yorkshire, it was noted that I had risen from 13th to 3rd in General Science and remember the extra effort made at home. The view of the night sky from our back garden led to the Boy Scouts’ Astronomy badge. My mother bought me a Norton’s Star Atlas, but I had no reason to check out the telescope section until 2014. Astronomy started with Dad’s 2” night glasses on variable stars until a pulsating cargo liner on my first voyage ended astronomy for 50 years and I became a Master Mariner. The Decca Navigator wasn’t performing well off the Bombay transmitter. The Radio Officer hid behind, ‘Nothing to do with Marconi.’ As the tanker’s Navigating Officer down came chartroom deck head panels until finding a break in the aerial cable, then 12 years later between ships stumbled into solving TV and radio reception problems, including installing EQ mounted satellite TV dishes, self-employed.

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© 2020 Peter R. Clark - FRAS. All rights reserved.

No part of this book may be reproduced, stored in a retrieval system, or

transmitted by any means without the written permission of the author.

Published by AuthorHouse  10/26/2020

ISBN: 978-1-6655-8083-0 (sc)

ISBN: 978-1-6655-8082-3 (e)

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CONTENTS

Author’s Note

Preface

Chapter 1     Key Moments And Bold Initiatives

Chapter 2     Scaling Up

Chapter 3     Preface To The Correct, Easier Way To Collimate A Newtonian

Chapter 4     Preparation Of The Telescope

Chapter 5     Once More!

Chapter 6     The Development Story To Completion Night, 1 October 2014

Chapter 7     Narrative Version

Chapter 8     The Easier And Definitive Way To Collimate A Newtonian

Chapter 9     Don’t Bottle Out!

Chapter 10   Making The Cave Collimator

Chapter 11   Suggestions For Matching And Upgrading Eyepieces

Chapter 12   The New Approach Consolidated

Chapter 13   It Just Takes Somebody New

Acknowledgements

Appendix A    Two Medium-Field Eyepieces

Appendix B    A Handy Catadioptric Newtonian

Appendix C    Celestial Truant Catching

Appendix D    Intuitive Collimation De-Bunked

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AUTHOR’S NOTE

The first edition was published as a booklet in 2012. The problems it cured highlighted others for which solutions had to be found. I have taken the opportunities to do this and also to add pages of interest before and after the actual instructions in Chapter 4 that comprise only six pages, including drawings. It is a highly appropriate edition, made so by improved optics creating the possibility of a wider range of targets within one telescope, given the excellent collimation these instructions achieve easily as you progress beyond completion of the adjustments in the first two sentences of stage 1.

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PREFACE

Collimation is a relatively new word for the action of aligning mirrors so that light is reflected to where it is wanted. Reflection can be of the sun’s rays off a signalling mirror onto a receiving station or potential rescuer, or more to the point, it can occur when light off a dish-shaped telescope’s primary mirror is directed towards a second, flat mirror set at 45° to produce a 90° reflection towards a more convenient position for the eye.

The price of a mirror is cheaper than that for an equivalent lens, and the telescope length is reduced to half that of refractors. This century has seen the better optics now available encourage experiments in a further halving of the length of the Newtonian with a variety of lenses affecting price and performance.

The basic Newtonian easily gives the greatest light capture for your money and so should be the most popular, up to a limit of 10″ f/4 for a handy size. Until its secondary mirror became a slice of glass tube bonded to a rod of smaller diameter, as shown in the lower drawing on the inside front cover, the mirrors could rotate sufficiently to need attention by the user.

Another thorn is in trying to collimate the Newtonian secondary mirror or flat mirror in the same way as you do for the in-line Schmidt–Cassegrain, by adjusting any of the usual three adjuster bolts as necessary. Help is at hand, but there is a hindrance. The help is the rotation needed to direct the cone of light towards the eye, which reduces the number of adjusters to one plus a central bolt. Unfortunately, this is countered by few being able to resist the instructions of esteemed mentors to adjust any bolt by trial and error. The lucky and persistent with this common sense can, by compensation for mistakes made unwittingly, achieve collimation with slower telescopes, which is that second- to third-magnitude stars, when magnified, look the same shape as they do when observed by the naked eye. They’ll be brighter, of course, but common sense instead of science and engineering applied when there’s a fast primary mirror is like flat or earth centralism. It never quite gets the secondary collimated, just passing acceptability maybe, through twisted light paths that come good for a certain temperature or by way of dogged determination.

Chapter 4 is the actual instruction manual. Absolute beginners will first want to apply their telescope’s setting up and handling instructions, helped in the final stages by page 26, then use their telescope until seeing something that looks as if it needs fixing. Stages 1–7 scale up gradually from the slowest to the fastest optics for correcting the secondary mirror. In stages 5–7, effects of adjustment will be seen in real time on a star without the retightening delays of the first stages. And we shall see the support for the new approach that really makes things a lot easier as the adjustments become finer. Reliability of the secondary mirror goes from one or two nights to a continuous process. For the primary mirror, adjustment once at the beginning and then once in the middle of a season, at most, is recommended. The classic small Newtonian of f/4.5 or slower can now be all ready for use after completing stage 3 on a well-lit bench, not being waved bye-bye to as the defocussed star is screwed beyond the field of view without any reduction in visible distortion because not all the good materials and knowledge the twentieth century had to offer have been used, including the Frisbee!

Towards the end of 2015, I was getting fed up with forecasts of cloudlessness being repeatedly inadequate for calling members of my astronomy society for a dark site for observing the night sky. By phoning the Meteorological Office, I discovered that although I’d clicked on the information pertinent to my locality at www.metoffice.gov.uk, I was not then going on to the specialised forecasts. These fine-tune the symbols so they show any fine high clouds that put us astronomers off generally, but through a telescope these clouds can actually help with viewing interests such as Venus and bright double stars. Another internet tool you should find well worth opening is the jet stream forecast. From it, one gets a better idea in advance of what magnification is likely to be usable.

Page 27, on the cleaning of mirrors and lenses, is manufacturer and optician supported. I refer to it every occasional time when one or more of them is about to be cleaned. The chapter headed ‘Once More!’ has its own side elevation drawing that is intended as a window on both standard and more esoteric secondary mirror alignment. I have yet to see a problem that only lateral movement of the secondary mirror will solve.

There is no need to make a big thing of understanding the instructions first. Just use them. Understanding will follow.

CHAPTER 1

KEY MOMENTS AND BOLD INITIATIVES

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