In memory of Arthur S. Leonard, who died in October 2001.

I only know a little about Mr. Leonard. He was a professor of mechanical engineering at the University of California, Davis who lived in the San Fransisco - Sacramento area of Calilfornia. He was a member of the Sacramento Valley Astronomical Society. Mr. Leonard designed two original types of telescopes, the Yolo and Solano. Both are named after Mr. Leonard's favorite counties in California.

The Yolo telescope is a two mirror off-axis design. Mr. Leonard appears to have invented it in the early 1960's. The Yolo has some elements in common with the schiefspiegler designs of Anton Kutter. There are two main innovations. The secondary mirror is concave, where the secondary of a schiefspiegler is convex, and the secondary is warped to counter astigmatism while schiefspieglers typically use a lens. A schiefspiegler can be thought of as an off-axis Cassegrain, but a Yolo can not be compared to an off-axis Gregorian because the secondary intercepts the light path before the primary focus.

Mr. Leonard was not the first to suggest mechanically warping the secondary to counteract astigmatism. Anton Kutter tried it in a schiefspiegler about ten years earlier, but settled on the lens method for most of his designs. Mr. Leonard elaborated the warping method, both in theory and in practice, more thoroughly than did Kutter.

Sometime after 1965, Mr. Leonard published a booklet detailing the design of Yolo telescopes. That booklet is the subject of this web site. The booklet was distributed by the Optica b/c company of Oakland, California. (No longer in business.) When I bought my copy in the 1970's, the price was $1.10.

It is apparent that the booklet did not achieve wide sales. Also, the information it contains has not, to my knowledge, been published elsewhere. I have chosen to prepare this web version of the booklet based on the following considerations:

I hope that by publishing this web version of The Yolo Reflector I will encourage amateur makers to build Yolo telescopes and/or invent more telescope designs. Computer capabilities now available enable more detailed design analysis than was available when Mr. Leonard wrote. I would be especially interested to see a more rigorous analysis of the surface shape resulting from the warping Mr. Leonard describes. A program which could easily predict the parameters necessary for successful warping would be a significant advance. I am certain the knowledge to produce such a program exists. Unfortunately, I do not posess it.

Mr. Leonard died at nearly the same time I began to think of preparing this web site. I never had any contact with him, and now regret that I did not begin the project earlier.

I have not built a Yolo telescope, so I can not give any practical advice.

The text of the original booklet was prepared with a typewriter (except for the references on page 28). I have attempted to design the HTML of this web site so that the text will appear much as it does in the original. Different browser programs interpret HTML differently, so the effect may not always be achieved. In particular, the width of pages depends on the available width and resolution of each computer's display. Page width, and therefore line length will adjust depending on the characteristics of individual computers. Figures 3b and 3a were printed as halftone images on the inside front and inside back covers respectively. I have included them in the order in which one encounters them while paging through the booklet.

The original text is double-spaced. Double spacing looked like too much to me on a computer screen, so I have set the spacing at 140%. The spacing is set with an HTML <STYLE>. If your browser does not support styles, it will probably display the text single spaced. Otherwise, it should look much the same.

Internet Explorer and Netscape Navigator seem to have slightly different default settings for text size. In Internet Explorer, you will probably get more nearly the size I intended if you select the menu item,: View, Text Size, Smaller. I designed the pages for an 800 x 600 screen. If you have a screen with more pixels, you may want to select a larger text size. To select a larger text size in Netscape Navigator, you have to work one frame at a time. Mouse click in the frame you want to change, then press <Ctrl> [  to increase or <Ctrl> ]  to decrease. (Where <Ctrl> means the Control key on your keyboard. Press and hold <Ctrl> while you press the [ or ] key.)

I formatted the equations in the equation editor of WordPerfect 7. Their appearance is close, but not identical to the appearance in the booklet. In particular, equations in the booklet are not in Italic. I could not find a way to disable Italic in WordPerfect's equation editor. The symbol for the Greek letter phi in the orginal looked like a circle with a vertical line through it. I prefer that symbol myself, but the only fonts in WordPerfect's equation editor that produced phi that way did not produce good results for other letters. In the equations of the web version, phi therefore looks like lowercase greek letter phi

Because the equations are .gif files and not HTML text, they do not change size if you change the text size in your browser. If you have difficulty reading the equations, please e-mail me. I can produce larger versions of them.

The equation summary, which appears in this web site after the back cover, was not present in the original booklet. I included it as a convenience.

In most cases, capital letters, indicating algebraic variables, that appear in the body of the text were set off by double spaces. Occasionally, the typist seems to have forgotten this detail. I have tried to reproduce the spacing as it actually appears in the booklet. I also found one obvious omission of a word, but I did not correct it. It doesn't seriously impact understanding. At one point, a phrase is repeated erroneously. I did omit the repetition, because it is in a complex sentence that is hard enough to understand without the error.

The booklet was printed on white paper except for the cover. The cover was printed on off-white, heavy paper containing some grey fibers. My copy has yellowed some over the years. I have specified white background for the text pages of the web version. The background of this page, and the other panels of the web site are a somewhat darker version of the color the cover of my copy of The Yolo Reflector has become. The scanned versions of the covers and figures presented as part of this web site have been converted to grey scale. They do not show the true color of the paper, but, in compensation for that inauthenticity, the files are smaller and download faster than true color versions would.

I can be reached by e-mail at I would be especially interested in hearing about any Yolo or Solano telescopes, existing or under construction, any more documentation of these designs, computer programs to aid design, especially the warping problem, and any background about Mr. Leonard.

All portions of this web site which are not derived directly from The Yolo Reflector are copyrighted by Mark D. Holm © 2001.

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