Sir Joshua Reynolds’ camera obscura was disguised as a book, probably so that people shouldn’t know that he used it in his paintings. It’s now in the Science Museum in London. Painters appear to have made use of optical devices pretty extensively from 1420 till the early 19th century, when the invention of chemical photography and subsequently film making set them off in another direction. It’s not that at the start of the 15th century people suddenly became better at drawing life-like representations: a much more convincing reason is that they discovered of a tool which enabled them to do so.
Here’s David Hockney telling us about the curved mirror, the camera obscura, and the camera lucida and their use in painting. His point that images were just too important back in the early modern period for artists not to have made use of optical technology seems completely convincing. The fact that he himself is an artist and draftsman is what enables him to put two and two together in a way which nobody previously had done. At one point a scientist, Charles Falco, says “Any physical scientist knows that a curved mirror is a lens, but David didn’t”. It’s this joining together of different knowledge bases which make Hockney’s discoveries so believable. There are two videos which has some slight overlap, but, to me at least, the story is so fascinating that watching both is worth the hour and a quarter it’ll take you.
There are other videos of David Hockney describing the process at my earlier post on Camera lucida.