The first image is of a man smoking a tobacco pipe in front of an exposed sheet of film. Shown are two focal points of light rays bouncing in all directions. Instead of producing an image onto the film, the rays will just completely expose the film.
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The second image is of the same man, but in the middle of him and the sheet of film is a convex lens. What the convex lens does differently is redirect the light path from one single point onto corresponding point on the film.
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The third image is an example of why we use convex lenses instead of other lenses. The first lens in the picture hit the lens straightforward, not refracting. The second lens is similar but at an angle so some rays are refracted but the rays are not affected and continue to go straight. The third lens is a concave lens and widens the rays apart from each other. The fourth lens is a convex lens and refracts the rays so they clearly meet at a single point.
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