Quote:
Originally Posted by Katie Boundary
the use of rack focus will cause an image to shrink vertically but expand horizontally, or vice-versa.
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It depends on the lens used by the camera. When you are shooting a professional film, the director sometimes wishes to emphasize the difference in size or distance between objects in the foreground and the background; he may wants to make nearby objects appear very large and make objects at a moderate distance appear small and far away. To shoot these scenes, specific lens that cover the angle of view between 64° and 84° are used, and they translate to 35mm lens in 35mm film format. Unfortunately, one of the "side effect" of these special lens is the apparent perspective distortion when the camera is not aligned perpendicularly to the subject, which is the "issue" you noticed. In other words, with normal lens, parallel lines converge at the same rate, but with these particular lens, they converge slightly more due to the wider total field.