# Spinel lenses (if only)



## anthonyd (Apr 30, 2015)

Spinel is a mineral (magnesium aluminate) that creates optically clear objects and is so much tougher, stronger, harder than glass that doesn't get scratched in a sand storm and won't break as easily as glass. Ok, ok it's very hard (and expensive) to polish, so if not lenses, maybe we can dream of some clear filters made of it in the future. Read more at the NRL page:

http://www.nrl.navy.mil/media/news-releases/2015/transparent-armor-from-nrl-spinel-could-also-ruggedize-your-smart-phone


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## neuroanatomist (Apr 30, 2015)

Sounds a lot like the sapphire (synthetic aluminum oxide crystal) lens on my iPhone. There's a filter company ( in Korea?) that is launching UV and CPL filters made from it, too.


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## anthonyd (Apr 30, 2015)

neuroanatomist said:


> Sounds a lot like the sapphire (synthetic aluminum oxide crystal) lens on my iPhone. There's a filter company ( in Korea?) that is launching UV and CPL filters made from it, too.



This is true, but sapphire is significantly harder (Mohs rating of 9 vs 7.5 to 8 for Spinel), so it's unlikely they will ever grind it down into an aspherical lens shape (flat screens covers and filters are much easier to make). Also, Spinel is slightly more transmissive optically (splitting hairs, but whatever).

On the flip side, sapphire has significantly higher fracture toughness than Spinel (up to 4 MPa m^(1/2) vs about 1.5 MPa m^(1/2) http://www.ceramics.nist.gov/srd/summary/ftgsaph.htm, and http://www.ceramics.nist.gov/srd/summary/ftgmgal.htm), but both are much harder than glass that is about 0.8 MPa m^(1/2).

In any case, I'd welcome either material if Canon found a way to manufacture lenses out of them, but I'm more hopeful for Spinel because there are already optical products made out of it: http://www.surmet.com/technology/spinel/


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