Actually, although astronomers mostly make mirrors - it is still possible to buy the necessary to grind your own achromatic lenses. I found another fascinating article on line about grinding an 8" achromatic. It was from about 1925. In those days it would probably have cost a years wages of a typical earner to buy such a lens. Consequently it was worth putting in the hundreds of hours needed to make one. Now it is maybe only a week or a months salary, so less incentive - but the instructions would still work for the enthusiast... There must still be enthusiasts about, because you can still buy the stuff if you shop around