I've really been enjoying re-reading Secret Knowledge by David Hockney. Really fascinating stuff on the use of lenses in Renaissance and post-Renaissance art in Europe. It's terribly threatening to some, I suppose, to imagine that the "divinely" guided masters of that era used a little trick or two to guide their work, but hell, the use of technology doesn't cancel out sheer talent. They weren't tracing everything (how do you explain Ingres' squiddy hands, done well after the popular use of camera obscura & camera lucida?), and they still pumped quite a bit of flourish into their portraits.
There's a great online exhibit for the 2001 NYU conference on the topic here.
