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Popular Optics

Posted by Lee Spain   08/23/2006 09:11PM

Popular Optics

The purpose of this review is to introduce Astromart readers to a book that is overflowing with interesting do-it-yourself optics projects. First, I should note that I have no financial interest in the book or the publisher. Popular Optics is a 192-page paperback book originally published in 1974 by Edmund Scientific as part of their Popular Optics Library. It is a reprint of fifteen years worth of smaller booklets providing basic knowledge and project ideas for optics hobbyists.

The book itself is divided into 9 chapters:

1 - The Optical Bench
2 - Graphical Ray Tracing
3 - Basic Optical Math
4 - All about Magnifiers
5 - How to Condense and Project Light
6 - Optical Drawing Devices
7 - Telescopes You Can Build
8 - Homemade Telephoto Systems
9 - Fun with Optics

Each chapter is crammed with text surrounded by wide margins filled with math formulas, side bar project designs, quick treatments of special topics, and illustrations. The book presents a lot of practical project focused information and presents little information on the physics and theoretical background of the subject. It reads much like a vintage edition of Popular Mechanics. Amateur astronomers will be most interested in 11 telescope designs, four monocular ideas, two spotting scopes designs, and several telescope mounting ideas presented in the seventh chapter of the book. However, I'll summarize the contents of each chapter so that readers can see if the book contains other projects of personal interest.

The first chapter shows how to set up an optical bench, typical accessories that an amateur optician might have, the different kinds of lenses that exist, how to find the focal length of a lense, how to make a collimator, and testing methods. It's a lot of information to present in 30 pages. Unlike many books that advise readers what to buy, Popular Optics shows readers how to build the equipment required from basic parts.

The next 17 pages cover Graphical Ray Tracing. Basically, the book shows how light is passed through different kinds of lenses and how it is reflected by various mirrors. A hobbyist can use this information to figure out how various components of an optical assembly can work together to present light. With a mastery of ray tracing, optics hobbyists can tackle the design of a variety of optical devices.

Optical Math is presented in a short eight-page section. Much of the math is presented in tables with drawings and formulas. Typically, the math is focused on figuring out various focal lengths and exit pupils. Much of the math consists of very basic formulas that are not much more difficult than magnification = telescope focal length / eyepiece focal length. Two common problems addressed are how to determine the equivalent focal length of two lenses working together in a focal system and how to determine how an image will be positioned after light is passed through a lens or reflected off of a mirror.

The magnifier chapter opens with a dense table showing the power of magnifiers of a given focal length at 10, 20, and 30 inches from the eye. The chapter also shows the types of lenses that are used as magnifiers. Simple rules for determining the power of a magnifier are also presented. The fun for tinkerers begins with detailed instructions on how to make your own magnifier, an illuminated magnifier, how to convert a telescope to a magnifier and how to convert a telescope into a microscope by adding an additional objective lense. Low power Fresnel magnifiers, measuring magnifiers, binocular magnifiers, and reading glasses are also discussed.

The chapter on Condensing and Projecting Light discusses the types of projector bulbs available, provides a glossary of light terms, presents lamp math, and then presents topics like reflectors, condensers, spotlights and floods. The fun projects are projectors, rear projection screens, microscope projection, and light piping with fiber optics. While much of these functions are now handled with a projector and laptop computer, the fundamentals are still sound and I could see some of this information being useful for haunted driveway projects for Halloween or throwing an image of Santa Claus on the appropriate surface at Christmas.

The sixth chapter, which covers Optical Drawing Devices, seems quaint in this era of digital cameras. However, it does show how to make a drawing camera. Basically, this device takes in a scene and reflects it onto tracing paper for an artist. A drawing projector can also be made to magnify an existing drawing so that an artist can trace a larger image of it. The chapter also shows how to construct a project to throw an image on a wall for tracing. This concept is still used today by some interior decorators who want to throw a pattern on a wall for painting.

The seventh chapter presents 30 pages of interesting telescope, mount, eyepiece, and monocular designs. The telescope and monocular designs include:

4 1/4" reflector on pedestal mount
4 1/4" reflector in Square Plywood Tube
4 1/4" reflector on an equatorial mount
3" Skysweeper reflector with 16x eyepiece
3" erect image reflector Bazooka spotting scope
3" reflector for planetary and lunar viewing
6" reflector
1.6" refractor on equatorial mount
3" refractor
2" folded refractor
2" 33x erect-image prismatic refractor
1 1/4" 30x baby refractor
7x50 binocular to 13x60 monocular conversion
9x35 monocular

The mount designs include german equatorial mounts, turn-on-threads pipe mounts, tripods and pedestals. Topics such as pedestal bases, telescope cradles, telescope balancing are also addressed. Although this book was written prior to the Dobsonian revolution, most readers will find these scope designs inspirational. Modern readers will face the challenge of updating these designs to accomodate today's larger apertures, finding substitutions for old Edmunds part numbers, and using the appropriate mix of home-made and manufactured parts.

Chapter 8 presents homemade telephoto systems. Four systems are shown direct objectives, afocal, projection with a positive lense, and projective with a negative lense. I don't see how a modern autofocus camera can accomodate some of these add-ons, but they look like fun things to try with a cheap web cam or disposable film camera.

Finally, the last chapter presents a lot of miscellaneous fun topics like how to make microscopes, picture projectors, holograms, kaliedoscopes, light boxes, grating spectroscopes, and black lights. The chapter also covers how to take pictures through binoculars and how to take super close up pictures.

This book is not without shortcomings. The material is layed out in a haphazard, distracting, and overwhelming fashion. I found myself most interested in goofy little monocular project designs that are presented in margins or at the top or bottom of a page. This material also shows its age. I doubt that the offerings and part numbers will be the same in the modern Edmunds Scientific catalog. In addition, many people will pass on the smaller scopes. For example, a 1.6-inch refractor is smaller than most department store scopes. Often the book will present the same basic design in a complex format and a simpler format. Unfortunately, some of the complicated designs call for using tools that I don't have. However, the book more than makes up for this shortcoming with simpler projects.

After reading Popular Optics, I'm kicking myself for tossing junky old binoculars. I'm sure that I could have given them new life through some of these monocular project ideas. As a reference and a source of design inspiration, I'd rate this book as very useful. Overall, I'd highly recommend this book for any amateur astronomer with an interest in tinkering with optics.