I read a really interesting article by a guy who wanted to grind his own microscope lenses the way that Dutch guy with the unspellable and unpronounceable name did way back in the 17th century.

Reasoning that he had no access to special grinding grits and so forth, he started with a bucket of sand from the beach. What you do is grind this in a pestle and mortar - then use the principle called levigation. What you do is mix some of the sand up in water and let it stand for a few seconds or minutes - then pour off the liquid into another container. Only the heaviest particles sink to the bottom and stay in the first container. You then let it stand for a bit longer before pouring it off again. The lens maker repeated this six times, giving him sand graded in steps from coarse to very fine...

The primitive simplicity of this appeals to me... And yet he made some very good lenses.

Microscope lenses are TINY. These simple single lenses are, especially. The very small size means a a very small radius of curvature and therefore a very high magnification. That means a lot of problems working in miniature - but the lens maker can tolerate a lot of defects because the field of view is also tiny - you are just projecting into the human eye to focus on the fovea - which is tiny.

Camera lenses are obviously much bigger - which in some ways maybe makes them easier to make, but also they require a reasonable flat field over a relatively big area, so I suppose would require much more accurate grinding. I still like the idea of starting with a sandy beach and a broken battle, though...