We have seen that for u, v, and f as in the above diagram, 1/u + 1/v = 1/f. In many cameras it is possible to replace the normal lens by a telephoto lens. Such a lens may be quite complex in its structure, but essentially its effect is to increase the focal length f. Suppose that you are photographing a given image at distance u with the normal lens. You now replace this lens with a telephoto lens. What happens to u? What happens to the size of the image? Slide the cursor over these instructions in turn to find out.
What happens if u, v and f do not satisfy the above relationship? Suppose that for given u and f, the value of v is too small. What happens in the above diagram? In the koala photo?
You now replace this lens with a telephoto lens. What happens to u? What happens to the size of the image? Slide the cursor over these instructions in turn to find out.
