Often when we zoom in or out all we are thinking about is how much of a scene we are capturing - or how "close" our shot is going to be. But zooming has another, very important, effect on our images.
Zooming can greatly alter the perspective of an image by compressing or expanding a scene. As we zoom in, the distance between objects in our picture seems less and less. Conversely, as we zoom out, the distance between objects in our picture seems greater and greater. Consider the following two images:
Notice the tree in the foreground (red arrow) is basically the same size. However, the tree marked with the blue arrow seems much farther away in the second image than it does in the first. You can see that all the elements in the two pictures are affected in a similar manner. The fist image was taken at 180mm and the second at 17mm. I ended up with two substantially different images because of the focal length.
