As an engineer I find this particular prank amusing

. He had to say something plausible -- if he had told you it was solid diamond hand polished in Japan by the descendants of samurai warriors, your BS detector would have gone off. Instead he says "pure crystal".
This is believable to a non-engineer, but to an engineer, it still doesn't smell right. My next question would have been "a pure crystal made of what material, smart-ass?". ("Crystal" is a bit of a give-away, as neither plastic nor glass are technically crystalline -- and if there is one thing that distinguishes engineers from the great unwashed masses, it is precision when talking about technical matters.)
This sounds like Dan's deadpan humor. Am I Right?
-- Ian.
-- In any event, to an engineer, the lens material is not terribly meaningful. When it comes to the drive mechanism, what counts (besides mechanical reliability, robustness and serviceability) is the measured jitter and error rate, and that rate in the presence of vibration, and unbalanced discs etc .
--- To everyone thinking that the lens needs cleaning -- are you feeding sandwiches into your BCD? The mechanism in which the lens is placed is fragile, and needs to operate with extremely high mechanical precision -- unless you know exactly what you're doing, you're much more likely to damage it than successfully clean the lens. Leave it alone.