Lenses were completely carved by hand in the 17th century. A lens could be turned on crude hand-held lathes which made the manufacture of spherical and evenly curved surfaces somewhat easier. Regardless, some opticians chose to use only hand-held tools.

It's said that the Dutch microscopist Anton van Leeuwenhoek made his tiny, spherical lenses in a completely different way -- using beads of molten glass. As he never revealed his methods, no one knows whether this is actually the case.

For a great technical explanation on lens-grinding in the 17th century, see Robert O. Woods' article in Mechanical Engineering Magazine, "Clear As Glass:" http://www.memagazine.org/oct06/features/clearas/clearas.html

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