As objects get farther from the camera their images diminish in size within the camera. Assuming a fixed focal length!
A given object twice as far as when it is near the camera will be 1/2 the size at the far distance as at the near one. This means you can determine the distance to objects as long as you know the distance to one of them (and they are all the same real size).
<
op: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">So set up a camera with the library as a background and ask Suzy to stand 15 feet from the camera so you can see her from head to toe in the viewfinder. Make a picture. Then make another picture where she is farther from the camera ... wherever she wants to go. Make another picture. Or more for various positions.
Then measure her height on a print in the photograph made when she was 15 feet away. Let's say her image is 4 inches tall. Now look at the other prints (made at same magnification!) and measure her height in those. If in one of them she measures 2 inches then at that point she was 30 feet away.
If 1 inch she was
e relationship is: Unknown Distance = Known distance multiplied by Image size at known distance divided by image size at unknown distance.
So what does this have to do with the library building which was supposed to be part of the project? The library construction serves as a nice background to the scene!
andy
