For example, the telephoto lens is often said to “compress” your scene and make everything look flat. But, it’s not the focal length that’s doing this. It’s actually because you’re so far from the scene you’re photographing (which is how telephoto lenses are commonly used: to photograph something far away). And, it’s because of this great distance that the scene looks “flat” in the final image.
As you move farther and farther away from something, you lose visual depth. For example, if you stare at someone’s face when you’re only a foot away from them, you’ll be able to see all the curves of their face pretty clearly, but as you step farther away from them, their face will begin to look “flat.” [Read more…] about Understanding Perspective and Focal Length