by James Daley
Hardbound, 6 by 9 inches, 200 pages
Perfecting the refracting telescope has frustrated lens designers and glass makers since the invention of the telescope. This is because when using standard crown and flint glasses, residual longitudinal color (its dominant defect) cannot be reduced to an optically harmless value. Even today, the most expensive special glass apochromats show some noticeable color, especially at the limits of the visual spectrum.
However, for over 106 years a refractor design has been available that is totally free of harmful color defects. Employing but one glass type, this design, called a Schupmann medial after its inventor Ludwig Schupmann, achieves amazing performance. It is this neglected telescope, along with its close relative the brachymedial, that this book describes in detail, along with an historical account, a discussion of the Schupmann’s role in modern amateur research, system principles and practical applications. Also included are design prescriptions and construction information giving the advanced telescope maker a new world to explore. Here for the first time is a comprehensive discussion of the design and fabrication of these high resolution instruments. Many successful medials are shown in a photo gallery, giving the builder a wealth of further ideas.