Re: New study: FPL-53 is unstable

Ed Neuzil said:

04/01/2009 FOR IMMEDIATE RELEASE:

A long-term study to be published in the SPIE (Society of
Photo-Optical Instrumentation Engineers) journal Optical
Engineering has found that the fluoro-crown glass FPL-53,
widely used in telescope lenses, suffers from long-term
degradation. While it is well known that standard crowns
and flints, such as BK-7 and F2, have a stability now
measured in centuries, FPL-53 is a fairly recent glass
formulation and up to now there had been very little
data on its long term stability. The study finds that
the glass begins to devitrify after 20 years, and will
eventually become cloudy and opaque. Numerous microscopic
stress fractures also form in the glass. Full details
can be found in the May issue of Optical Engineering.