Visual perspective, very simply put, is the way objects appear to our eyes, based on their size and their proximity to us. Whether or not we are familiar with the science and mathematics of perspective, we intuitively understand some of the basics simply from seeing and navigating our world. We know that objects that are closer to us appear larger than objects that are farther away from us. This is how we know that very tiny people and cars are far away, and that a dog's nose has grown to mammoth proportions because he is up close and personal, about to lick our face. And of course there's the classic example we learned in science class, that perspective is why railroad tracks disappear into nothingness at the horizon.
Understanding perspective in photography can be quite a complicated matter, but a few basic concepts will help us understand how to use perspective to our creative advantage. First, we need to know what a "normal" lens is. A normal lens is one that produces an image that looks natural to our eye, that is, an image where things look the way we are used to seeing them. The focal length of a "normal" lens depends on the sensor in the camera to which it is attached. Generally, the focal length of a normal lens is roughly equal to the diagonal of the camera sensor. For example, for an APS-C format sensor, where the sensor diagonal is about 27mm, a 27mm focal length lens (give or take a few millimeters) will produce an image that looks natural to us when viewed under normal conditions. A wide-angle lens is one with a shorter than normal focal length, and a long-focus (telephoto) lens has a longer than normal focal length.
When perspective is distorted, rather than normal, we can use it as a creative tool. Extension distortion, also called wide angle distortion, is what happens when we shoot a subject from close up using a wide angle lens, as in the photo above. When I shot this building, I was standing very close to it, practically touching it in fact. I used an 18mm focal length on a camera with an APS-C sensor (so fairly wide-angle), and pointed the camera straight up at the building. This method creates wide angle distortion, which does a few things for us creatively. First, it makes the foreground of the building appear larger, emphasizing the massiveness of the structure. Second, it makes the top of the building appear smaller. Our brains read smaller as farther away, so the height of the building is exaggerated; it seems to go on forever. Finally, it brings into view the building across the street (on the right). This part is a matter of personal preference, but I enjoy the somewhat surreal effect created by the building that seems to be leaning into the frame. By happy coincidence, the sky that day was a nice blue, with cotton-ball clouds, which were nicely reflected by the glass of the building.
Learning and practicing the wide angle distortion technique can help a photographer create unique, stylized images. On the flip side, understanding it can also help to avoid unwanted distortion, such as when shooting a portrait (unless of course you want your subject to look surreal!).
The opposite of extension, or wide angle distortion, is the compression distortion that can be produced by telephoto lenses. But that's a topic for another day ...
Feel free to drop me a line with your thoughts about perspective, distortion, or any other creative technique or topic. As always, I wish you happy shooting, and a satisfying photographic journey!