Named after a county in California, the Yolo was invented by Arthur S. Leonard of the University of California, Davis. It differs from a Schiefspiegler in that both mirrors are concave. The Yolo enjoys three advantages over the Schief with, (1) lower focal ratios possible, (2) lower image tilts, and (3) a more compact form. Its one major drawback probably accounts for so few Yolos built; it cannot correct for astigmatism without help. Three methods to do this have been successfully employed. Briefly, they are (1) the use of a warping harness, (2) polishing the correction into the secondary, and (3) adding a spectacle lens inside focus.

	From a design by José Sasian in "Telescope Making" #37, Albert Priselac built this 6" f/10.2 Yolo.
	Erwin Herrig of the former East Germany, without access to western literature, re-invented the Yolo.
	Close-up view of Erwin Herrig's harness for warping the Yolo secondary prior to final grinding and polishing. When the harness is released, the finished mirror assumes a toroidal figure.
	The covering has been removed from the telescope here to show internal details. An English translation of Erwin Herrig's method of figuring his toroidal secondaries is available. (To come soon!)

Curator: Hartmut Frommert [contact]
[Schiefspiegler Home] [SEDS]