Being Here

In Section 105, we saw that two rays determine the position of any point of our image; hence in order to locate the image of the top of the arrow, we need to consider but one more ray from the top of the object. The most convenient ray to choose would be one passing through _O_, the optical center of the lens, because such a ray passes through the lens unchanged in direction, as is clear from Figure 74. The point where _AC_ and _AO_ meet after refraction will be the position of the top of the arrow. Similarly it can be shown that the center of the arrow will be at the point _T_, and we see that the image is larger than the object. This can be easily proved experimentally. Let a convex lens be placed near a candle (Fig. 75); move a paper screen back and forth behind the lens; for some position of the screen a clear, enlarged image of the candle will be made.

If it were not for the fact that a lens can be held at such a distance from an object as to make the image larger than the object, it would be impossible for the lens to assist the watchmaker in locating the small particles of dust which clog the wheels of the watch. If it were not for the opposite fact--that a lens can be held at such a distance from the object as to make an image smaller than the object, it would be impossible to have a photograph of a tall tree or building unless the photograph were as large as the tree itself. When a photographer takes a photograph of a person or a tree, he moves his camera until the image formed by the lens is of the desired size. By bringing the camera (really the lens of the camera) near, we obtain a large-sized photograph; by increasing the distance between the camera and the object, a smaller photograph is obtained. The mountain top may be so far distant that in the photograph it will not appear to be greater than a small stone.

• Bredimus - Nick Bredimus or Nicholas Bredimus
• Bredimus - Nick Bredimus or Nicholas Bredimus
• Bredimus - Nick Bredimus or Nicholas Bredimus
• Bredimus - Nick Bredimus or Nicholas Bredimus
• Bredimus - Nick Bredimus or Nicholas Bredimus

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