Understanding Foucault David A Harbour 9781623740030 Books
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David A. Harbour presents a brilliant narrative for the Amateur Telescope Maker (ATM), on exactly how the "Foucault Test" is interpreted. Through a series of "foundation lessons" Mr. Harbour ensures the ATM understands what the Foucault Test is revealing, and what to do about it as he figures the telescope mirror to achieve the perfect paraboloid. Imagine if the makers of the Hubble Space Telescope had used this book as a guide to test the HST's primary before launch! The savings would have been in the millions! Well, that may be a stretch, but for the ATM, who has taken on the delightful but challenging task of making his own telescope mirror, how nice it would be to have a guide to ensure success!. Success is at hand. Dave Harbour presents a thorough and informative instruction on just how to be sure the mirror is perfect! This book is for the ATM bookshelf to accompany the classics of Porter, Texereau and others.
Understanding Foucault David A Harbour 9781623740030 Books
I had encountered some of this work previously on the Internet. But having it in a convenient, bound booklet is all the better. And while there are some sections on figuring and correcting a mirror, the primary focus of the book is to acquaint aspiring telescope makers to the whys and wherefores of the parabolic mirror and the Foucault (knife-edge) test used to assess the mirror's optical quality. It is in this role that the book succeeds spectacularly.I can remember, as a fourteen year old, being terribly confused about why parabolas had a deeper center than spheres. Harbour starts with the sphere, explains why it doesn't produce good images of distant objects (moon, planets, stars) due to spherical aberration (S.A.), then proceeds to show a step by step cure for S.A. resulting the the parabolic curve. And while the few dollars spent on the book may seem too much for just this one topic, it may be cheap to buy clarity rather than suffer with doubts, misperceptions, and clouded understandings of this issue.
Yet in addition, the author goes on to explore the genius of the Foucault knife-edge test, which enables amateurs of modest means to produce telescope mirrors of surpassing precision and accuracy. Judging the shadows of a mirror in fabrication, can be a most confusing task. Harbour's illustrations provide the clues necessary to fully understand what the shadows mean, and don't mean.
While the experienced telescope maker has likely absorbed the information contained in this book, there are some shop hints and personal experiences which they may find useful as well. I was particularly impressed by the author's evolution - transition from zone masks to the curved pointers of the modified Everest scale. And the section on using graduated pattern pitch laps for parabolizing may be worth considering on future projects. All in all, not a bad buy for ten dollars or less.
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Understanding Foucault David A Harbour 9781623740030 Books Reviews
One of the hardest things to understand in amateur telescope making is how the Foucault test works. Measuring the curve of a mirror to a quarter wave length of light is necessary to produce a working mirror (remember Hubble?). While there are many ways to do this, most involve equipment that costs thousands of dollars (lasers, balance tables, huge lab spaces, etc). The Foucault test needs just a pinpoint light source (can use a super bright LED and a pin hole or slit) and a knife edge. Some sort of micrometer is required to measure the movement of the knife edge, but you can make this with graph paper and a ruler. This book gives you a total understanding of the shadows produced by the test. Once you know this you will feel at ease with the simple math to measure the performance of a home ground mirror. There are other books that show you how to grind your own telescope mirror and assemble it into a working telescope. This book shows you how to test how good your mirror is.
I've known David Harbour for many years. His deep understanding of optical shop methods and testing has been evidenced by the incredible telescopes that he has made. David has clearly walked the walk.
This work is destined to go down in history alongside the works of Draper, Ellison, Porter and Ingalls.
This book goes into the intricacies of setting up the test and understanding and interpreting the results. The reader will be left with a fine understanding of optical testing without being intimidated by complex mathematical formula.
I highly recommend this book!
Francis J. O'Reilly
Ground my first set of optics back in 1980...now over a dozen and a half optics later I still found this book useful. I am not one to give glowing reviews about everything but rather honest appraisal based upon my experiences. So what is great about this book? Except for 1 item, SIMPLICITY. It gives clear, concise SIMPLE explanations and details about how to use the foucault test. Other sources (especially online forums) consist of the writers either trying to show you how mathematically smart they are or how nothing less than 100% PERFECT optics are acceptable (which is even more of a hindrance to a good set of optics). Get real. This book is more down to earth. You want a telescope and want the thrill of making it yourself? Great. Guess what? You dont need to be a perfectionist nor a mathematician to do the figuring, and Harbour makes that clear. This book is NOT the only book you will need. It covers only figuring and testing. You still need the basic books, this is a supplement to those books. Set up, grinding, polishing, lap making, etc while sometimes mentioned is left to the other books. Again this book is for the testing and figuring aspect only. Softbound, 114 pages, well written. My only fault with it is Harbours explanation of indexing the mirror. Very confusing. Indexing is important to make sure you give each section of the mirror equal treatment, but his method, while perfectly acceptable, is a mess to read. Once you understand what he is doing though it becomes clearer and you can use his method or your own (I simply mark the back with a sharpies and makes sure the mirror is rotated regulary, and that I stop rotation just before I get to the start mark). In any case his parabolization methods and his methods of fixing defects are really good. I recommend this book.
I had encountered some of this work previously on the Internet. But having it in a convenient, bound booklet is all the better. And while there are some sections on figuring and correcting a mirror, the primary focus of the book is to acquaint aspiring telescope makers to the whys and wherefores of the parabolic mirror and the Foucault (knife-edge) test used to assess the mirror's optical quality. It is in this role that the book succeeds spectacularly.
I can remember, as a fourteen year old, being terribly confused about why parabolas had a deeper center than spheres. Harbour starts with the sphere, explains why it doesn't produce good images of distant objects (moon, planets, stars) due to spherical aberration (S.A.), then proceeds to show a step by step cure for S.A. resulting the the parabolic curve. And while the few dollars spent on the book may seem too much for just this one topic, it may be cheap to buy clarity rather than suffer with doubts, misperceptions, and clouded understandings of this issue.
Yet in addition, the author goes on to explore the genius of the Foucault knife-edge test, which enables amateurs of modest means to produce telescope mirrors of surpassing precision and accuracy. Judging the shadows of a mirror in fabrication, can be a most confusing task. Harbour's illustrations provide the clues necessary to fully understand what the shadows mean, and don't mean.
While the experienced telescope maker has likely absorbed the information contained in this book, there are some shop hints and personal experiences which they may find useful as well. I was particularly impressed by the author's evolution - transition from zone masks to the curved pointers of the modified Everest scale. And the section on using graduated pattern pitch laps for parabolizing may be worth considering on future projects. All in all, not a bad buy for ten dollars or less.
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