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Message: <blockquote data-quote="Binastro" data-source="post: 3476734" data-attributes="member: 111403">Early Canon 300mm f/2.8 lenses had the crystal element fail badly, but they got better.The instruments have to carefully designed also as I think moisture can damage the crystal.I suppose there are crystal elements in high end astro scopes.If I look at such instruments I carefully examine them.I am not sure that I would buy such second hand optics.Even high end exotic glass is very delicate. Top end lenses lenses containing such elements have to be multi coated as soon as the element is made as they begin to tarnish straight away.Yet there are lenses with simple glass which look good after 150 years.</blockquote>