Real images: Lighted arrow image and various lenses.

Real images: Lighted arrow image and various lenses. An illuminated arrow is placed on one side of a converging lens beyond the principal focus f, and a real image is formed on the opposite side of the lens, focused on the screen. Various lenses are used, with focal lengths from 4.5 inch to 21 inches. See Figure 1: If the illuminated arrow is moved closer to f at object distance p, then the image (which is inverted) focuses on the screen farther away, at image distance q. The image is larger than the object and is thus magnified. Or, if the illuminated arrow is moved further away from the lens, then the image is formed closer to the focal point and is smaller in size than the object. The lens formula describing this relationship is 1/p + 1/q = 1/f.