There is an internet myth circulating that the only factor in perspective is object distance. Pictures taken at the same object distance display objects in them at the same relative size. So, the hypothesis goes, these picture have the same perspective. Perspective is simply relative object size under this hypothesis. So, you get your identical twin friends and you go to the gym to take some pictures. One twin stands 10ft from the camera and the other 20ft from the camera. You take the picture and lo and behold, the relative size of those two people are 2:1. You change lenses, and the same difference in relative image size. It must be true, except... Now I ask one twin to stand 20ft from the camera and the other twin 40ft from the camera. The difference in image size? The exact same, 2:1. Object distance has changed and we still have the same perspective because the object distance is not important, but the ratio between the different object distances. So if it is a problem of ratio of distance to the camera, then any two objects can be placed in the frame at any distance as long as the ratio between remains constant. Not quite the hard and fast rule that is claimed. And what does this distance hypothesis mean? Nothing. For example, would a landscape taken with a wide and telephoto lens have the same perspective? Since you cannot get closer to the horizon, I guess it would. But which two objects in the image do we use to prove the same perspective? This hypothesis requires an absolute frame, but none exist. How do we compare different photographs of different subject matter? How do we chose reference points? It is true the ratio of the camera-to-object distance is directly related to the ratio of the image size of the two objects, but as a description of perspective alone, it is wanting. For centuries, the study of perspective, as we use it in imaging, has been how the appearance of depth or three dimensions is rendered in a two-dimentional plane--it is our perception of space, rather than an absolute description of it. These factors help artist understand the perception of depth as well as how to accentuate or eliminate that quality. Here are two images that show the problem. If only object distance were the only factor describing perspective, then these two images would have the same perspective. But they certainly don't look the same. Why? The only change is focal length. First, when we look at an image, we chose relative features to give depth clues. The most common is foreground and background. The steam winding through the forest floor starts close to the bottom of the image, leading up through the forest to a far point where the water enters. The small waterfall does not have a great deal of depth. Water seems to flow over it from the background almost immediately to the foreground. The second point has to do with two-point perspective, a very old concept. With a change in focal length or cropping, we are not just cutting into an image, but we are also magnifying it. This magnification is the key factor. In two-point perspective, two vanishing points are placed the horizon and are used as linear perspective anchors. How far apart these points are determines the perspective; closer together, the stronger perspective, the further apart, the weaker. When you magnify an image, you are displacing those vanishing points further away weakening the sense of depth or perspective. So even while the relative image size of objects do not change when changing focal length or cropping, the vanishing point which are used for spacial information are being displaced. There are many image qualities that relate to simply how we perceive them, perspective is one, sharpness and depth of field are others. Perspective has many factors influencing it--object distance is only one and not that significant. BTW, the waterfall was cropped from the larger image and flipped.