Amateur movie making (1928)

AMATEUR MOVIE MAKING 129 of this subject and you can then join us again for the discussion of specific accessories and lenses. Light is reflected in all directions from a point in a surface. Thus from point A rays are reflected in directions 1 to 19 inclusive. A lens placed before this surface intersects rays 9, 10 and 11 at points C, M and D. The other rays do not have any effect upon the lens or film. The rays 9 and 1 1 are bent at points C and D and come to a focus together with ray 10 at point B. Passing this point they again diverge in directions indicated by E, F and G. Light. — We have already seen that light travels in straight lines — when it doesn't travel in a crooked one. The fact is that light travels in an approximately straight line only when its path lies through some medium of uniform density and composition. As soon as light leaves one medium such as air and enters another such as glass, it is bent to some degree, but as it is bent in a reverse direction when emerging from the other side of this medium and to a corresponding degree, the displacement is hardly noticeable. However, if the two sides of this medium are not parallel, then we do have a very apparent displacement of the rays which is apparent as a distortion of the image. Prism. — Most of us know that a prism will break an ordinary beam of light into its component spectral or "rainbow" colors. If we could twist this prism into a doughnut shape without the hole in the center we would have a piece of glass which would resemble two very flat, squat cones placed base to base. The same prismatic effect would persist but in a circular rather than a linear direction. If we now allow a beam of light to pass through this circular prism and fall upon a screen