Customer Reviews

Telescope Optics : Complete Manual for Amateur Astronomers

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There was a time once when amateur astronomers had exposure to only a few different kinds of telescopes--mostly simple achromatic refractors, which comprise just two lenses cemented together (plus an eyepiece), and Newtonian reflectors, which include a mirror plus the eyepiece. Many, possibly most, of these amateurs also made their own optics, and as a result, they knew most of what there was to know about these designs.

Nowadays, it's quite different. Not only are there vastly more types of telescopes, but most amateurs now buy telescopes; telescope building is a diminishing part of amateur astronomy, and people make their own telescopes out of desire, not necessity. It's harder than ever now for amateurs to really know about optical designs in breadth and depth.

Into this breach step Rutten and van Venrooij, two Dutch astronomers who wanted to know more about optics but found that resources were generally unavailable to amateurs. So, they wrote their own. Telescope Optics is a compendium of optical information, geared to the intermediate to advanced amateur. Like Gaul, it can be divided into three parts: Chapters 1 through 4 discuss optical principles; Chapters 5 through 16 apply those principles to various telescope and accessory designs; and Chapters 17 through 22 cover evaluation and design.

The manner of the text is generally scholarly but informal. Although optical principles are explained from the fundamentals, the authors still assume a certain level of comfort with high school mathematics and analytical exposition. In particular, it helps if the reader can easily digest information in two-dimensional graphs. This can make the book somewhat imposing for those readers who really just want to know, at a high level, what makes their own telescope tick.

For those readers capable of making their way through the analysis, however, the authors clearly and comprehensively explain the workings of several telescope and camera designs, and discuss in brief the quirks of at least half a dozen more. The compromises of each design are detailed to the level of so-called "third-order aberrations"; these include coma, astigmatism, field curvature, spherical aberration, and distortion.

The authors also make available their own design software. Being 15 years down the line, the software is somewhat out of date, and it does not come free with the book; it must be purchased separately. The book does explain how to use the software, though.

Overall, the book should find its way onto the shelf of anyone who wants to learn, seriously, about their optics. For those who simply want a taste of how optics work, or who need a gentle introduction to the field, it probably ought to wait until later.

Telescope Optics is a comprehensive, educational and practical manual for beginners and advanced amateur opticians and astronomers. It is probably one of the best overall sources of information on basic optics, optical instruments and their prformance. The book comes with a DOS-based computer program that allows users to design their own systems and evaluate theoretical or existing optical configurations. Telescope Optics fills the gap between simple amateur telescope and optics manuals and professional literature. The book is due for a second edition, as well as an upgraded optical design and analysis program suitable for Windows-driven computer environment. Although Telescope Optics came with some errata sheets, the book has notable omissions and errors, summarized below. - Page 5, line 19. No mention is made of either F. B. Wright (1935) or Y. Väisälä (1936), whose modifications to the original Schmidt camera design resulted in more compact, flat-field instruments suitable for visual as well as photographic work. - Page 88, line 5. Credit is given to K. Slevogt (October, 1942) for developing a modification to the famous Baker camera. His work was preceeded, however, by C. R. Burch (April, 1942) in Monthly Notices of the Royal Astronomical Society (Vol. 102, No. 3, "Design of Approximately Flat-fielded System, with Two Spherical Mirrors and One Plate"). - Page 127, line3. The book incorrectly relates R. J. Lurie's work with that of J. L. Houghton. Houghton (U.S. Patent No 2,350,112, May 30, 1944) proposed a two-element all-spherical corrector used in conjunction with a spherical mirror for a Newtonian-like configuration. The system is aplanatic (free of coma and spherical aberration). Lurie (Journal of the Optical Society of America, March 1975, p. 261) proposes two-element all-spherical correctors in conjunction with aspheric (conic-section) mirrors resulting in a fully systems that are fully anastigmatic - free of coma, spherical aberration and astigmatism. The two systems are not interchangable and only bear superficial resemblence. The value of Lurie's configurations is in superior optical performance, which in all aspects except distortion rival that of a true Schmidt camera, and in the applicability of converting smaller Newtonian configurations into first-class astrographs. - Page 145, Section 14.4, the book omits to mention that Ross-type correctors can be used in conjunction with hyperboloidal primary mirrors, resulting in anastigmatic flat-field astrographs (offered by Takahashi of Japan). Since full-aperture correctors are not practical for large Newtonian-like configurations, vast number of amateurs with telescopes larger than 10-inches in diameter could convert their instruments to high quality astrocameras. Suitable correctors, other than the Ross, have also been investigated and implemented on existing observatory Newtonian systems. Availability of their design and analysis would be of paramount importance to serious amateur observers and astrophotographers. Mladen K. Vranjican

I totally disagree with Mladen K. Vranjican's review "- Page 127, line3. The book incorrectly relates R. J. Lurie's work with that of J. L. Houghton."
I don't have a copy of Lurie's paper (Journal of the Optical Society of America, March 1975, p. 261), but I have an article named "Gleanings for ATM's--Making an Aplanatic 4-inch Telescope" on Sky & Telescope Nov. 1979 issue. It mentioned Lurie's great thought in his paper:
"In Example IV [of U.S. Patent No.2350,112, May 30, 1944] J.L.Houghton presents a design for an aplanatic system that consists of a two-element afocal corrector at the optical focus of a spherical mirror. The corrector...is shown made of glasses that have different refractive indices. However, such a corrector can be designed using the same glass type for both elements. This aplanat has interesting properties. Like the Wright telescope...its tube length is equal to its focal length. However, its astigmatism is only half that of the Wright telescope, and its surfaces are all spherical. The image surface of best focus has the same curvature as the mirror."

So, Mr. Lurie not only invented the aspheric (conic-section) mirror type as Mladen K. Vranjican said in the review, but also footnoted the telescope with all spherical and same glass, just what we called 'Lurie-Houghton' now a days. Mr. Lurie ofcouse should own the honor for the name together with Houghton. What Houghton invented is using different glass and it is the source of Lurie-Houghton telescope.