Understand Perspective in Digital Photography

To understand the effects of perspective derived from using a determined type of lens, it's necessary to understand exactly the meaning of the word. Let's momentarily forget about the camera, the lenses and even about photography and let's first see in what way we are capable of perceiving space in it's three dimension. For any observer, the images formed on the retina provide information about the placement of the objects surrounding them: we can now if an object is placed to the left or right, top or bottom of the line of vision and close or far from the point of observation. On the other hand, we know that the image projected by the lens on the retina is bi-dimensional, in the sense that it can only distinguish left or right and up or down. How do we achieve depth ?

In the first place, our sight in relief depends greatly on the combination of the information sub ministered by two points of view, both eyes, which, since they are separate, provide slightly different images. The interpretation in the brain of this difference is what allows us to perceive relief (stereoscopic vision).

Nonetheless, at large distances this difference is unnoticeable; in this case, or when we count on only one point of view (when we close an eye, or when seeing a drawing or photograph), we loose, on one side, the sensation of relief, but this doesn't make us completely loose our depth perception: the information we obtain when seeing things with an eye is enough to deduce it. The interpretation process we make to perceive space in three dimensions and to represent it in a realistic way on a flat surface obeys to some mechanisms called laws of perspective .

In any bi-dimensional image there are only left-right and top-bottom dimensions; the absent dimension, the depth, can be deduced and represented by how the outline of the objects in it varies: the size of the images decreases with the distance; the outlines of closer objects superpose and cover that of object further away; the dimensions place obliquely to the axis appear to diminish in the distance toward a same exit point , etc. The laws of perspective distribute on a artist's sheet of paper the images of the different parts of the scene according to the point of view. At the same time, these laws allow a spectator to reconstruct the depth sensation in the scene from that point of view. Perspective can be defined as the shape the characteristics of a three-dimensional scene are represented by on a plane; it varies according to the point of view and can be altered by the artist deliberately.