The Camera Lucida is an optical device that uses mirror and semi-transparent mirror to reflect a “ghost” image of the scene in front of you down onto your canvas or paper, so you can draw right over the reflected image.
This makes drawing and painting realistically quick and easy: with correct perspective, foreshortening, proportion, position, overlap, and shape - leaving you more time to develop your art the way you want it: without being frustrated by the technical elements.
The Camera Lucida has been used by the Great Masters of fine arts since it was invented, by William Hyde Wollaston, in 1807. It was later improved by Alexander Alexander in 1830; also known as mirror type camera lucida or Graphic Mirror. Today over two centuries later, you are able to purchase this same tool fine tuned by Ancient Magic Art Tools.
Camera Lucidas are what inspired William Henry Fox Talbot to invent photography on paper, so they are great for teaching the history of art, but they are primarily very practical drawing tools.