This root beer colored ceramic glass compound is Astrositall. Astrositall has a
virtually zero (0 +/- 0.06ppm) coefficient of thermal expansion over the
temperature range the telescope will experience during observing. This feature
provides stable focal length and figure. In this photo most of its figure is
ground in and the sag is quite visible by comparison to the metal straight edge.
The mirror is 10 inches in diamter and
1.4 inches thick at the edges. It has a spherical figure as required by the
Lurie-Houghton design with a
radius of curvature close to 89.4 inches.
This photo was taken by Mike Spooner of Page, Arizona. Mike is an amateur
telescope maker that made the primary mirror and corrector lenses for me.
Astrositall Mirror Blank
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Updated: 19 August 2000