MLA Citation: Bloomfield, Louis A. "Question 1227"
How Everything Works 12 Dec 2017. 12 Dec 2017 <http://howeverythingworks.org/print1.php?QNum=1227>.
1227. How does a projector work?
A projector is essentially a camera that's operating backward. When you take a picture of a tree, all of the light striking the camera lens from a particular leaf is bent together to one small spot on the film. Overall, light from each leaf is bent together to a corresponding spot on the film and a pattern of light that looks just like the tree—a real image of the tree—forms on the surface of the film. The film records this pattern of light through photochemical processes, and subsequent development causes the film to display this captured light pattern forever. Because of the nature of the bending process, the real image that forms on the film is upside-down and backward. Because it forms so near the camera lens, it's also much smaller than the tree itself.

A projector just reverses this process. Now light starts out from an illuminated piece of developed film—such as a slide containing an image of a tree. Now the projector lens bends all of the light striking it from a particular leaf spot on the slide together to one small spot on a distant projection screen. Again, light from each leaf on the slide is bent together to a corresponding spot on the screen and a pattern of light that looks just like the slide—a real image of the slide—forms on the surface of the projection screen. As before, this image is upside-down and backwards, which is why you must be careful how you orient a slide in a projector, lest you produce an inverted image on the screen.


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