camera lucida and camera obscura
The camera lucida and camera obscura are simple optical devices which assist artists in drawing faithful reproductions of distant scenes, plans, and diagrams, or microscopic specimens.
The principle of the camera obscura was known to Aristotle; light admitted through a small hole into a darkened chamber projects a real image of the scene outside on the opposite wall. Later versions have used lenses and mirrors to give an evenly-illuminated horizontal image.
The camera lucida, invented in 1807 by William Wollaston, employs a four sided prism to allow the artist to see a virtual image of an object in the plane of the paper on which the image is to be copied. It used to be of particular use in enlarging or reducing artwork and in drawing from the microscope.