1178 CHAPTE R 37 Â¥ Interference of Light W aves. source produces the original light beam and the two slits ser ve only to separate the. original beam into two parts (which, after all, is what is done to the sound signal from. the side-by-side loudspeakers at the end of the preceding section).
It was after using a camera lucida in 1833 that the the pioneer of photography William Fox Talbot began his attempts to fix images chemically. David Hockney has speculated on how great artists have used the camera lucida in his book 'Secret Knowledge: Rediscovering the Lost Techniques of the Old Masters'. (for a very brief summary of some of these ideas, see his article in RA Magazine from Summer 1999).
In the simplest form of camera lucida, the artist looks down at the drawing surface through a half-silvered mirror tilted at 45 degrees. This superimposes a direct view of the drawing surface beneath, and a reflected view of a scene horizontally in front of the artist.