optical sapphire

Definition: Synthetic crystal similar to ruby but colourless offering very high refractive index and extreme hardness and used in specialist optics. Well, fancy that Sapphires have also found their way onto up-market cameras, to give that exclusive touch ... and an excuse to touch your wallet for a hefty premium. And where else would you find the sapphire but under finger -- it is the shutter button.

Previous Term: optical resolution  Next Term: optical spectrum