Abstract: In an optical transformation drawing apparatus in which an image is projected by a projector on to a rear face of a projection screen so that a draftsman can trace on the front face of the screen the image transmitted through the screen, both the projection screen and a projector support frame supporting the projector are mounted on a fixed frame to pivot about an axis with the projector support frame and the projector thereon acting as a counterweight for the screen and with the projector support frame arranged parallel to the pivot axis, a mirror being provided to deflect the image from the projector on to the rear face of the screen.

Abstract: To produce the most pleasing display of the color patterns, the colored light, which is produced by interference of light waves from the two surfaces of a thin liquid film, is separated from the principal beam of the incident light, magnified, and projected onto a screen. Reflection from the thin liquid film is specular reflection (angle of reflection equals angle of incidence). The position of the projection lens is determined by the position of the light source. Thin liquid films, such as soap bubbles, reflect colored light by interference of light waves which reflect from the front and back surfaces of the films. The color of the light is a function of the thickness of the film.