Practical Drawing Series
Perspective
By Nick Ustinov
This part of the series may seem at first complex to comprehend, but if you print out a main scheme, take it in stride, and be patient, it's all quite understandable.
In the previous lesson we learned how to draw straight lines, curves and simple geometrical objects. If you have practiced enough, this could be your next serious step in practical drawing. What we have actually learned are techniques for drawing flat and simple objects that are aligned frontally to a viewer. However, with that kind of alignment, appearance of the objects is not always correct and may give an incorrect presentation, since we only see them in 2 dimensions. To get clear 3D presentation of an object's forms you should have a very specific point of view so you can see the real volume of an object in all three dimensions. By only seeing one rectangular side of the cube, you can't say anything about its real form. Rectangles can be a side of a cube or the basement of a pyramid or prism. A view of three sides gives a clearer presentation. But even in that case each side of the cube is visually accepted in a deformed way. Parallel lines become unparallel, shapes and forms change. These shape changes are caused by optical properties of our eye--the way it receives light reflected from the surrounding objects. Perspective is a science that studies optical changes of forms, sizes and objects in nature. Perspective is also a way to reproduce 3D images in two dimensions. Following perspective rules is a necessary requirement to draw realistic forms of the surrounding world. When you look in one direction, you see just a part of the surrounding world. Light rays, reflected from a visible object are pointed to an eye and focus in pupil. So-called view rays are directed from your eye to the object. Going from pupil they form a cone. The cone's basement resembles an ellipse and defines a view field. 
We can see especially clearly only in the center of that view field, called field of clear vision (darker area on the image). The size of that field is defined by a 28-37 degree angle and OP=2AB. 
This means that if you want the paper you are drawing at to be aligned properly, it should be placed at a distance at least twice as far from your eye as the paper's height. Your natural model also should be in your field of clear vision. The main perspectival deformation of an object's forms is described by the rule that the further away the object is, the smaller it seems. Looking into a small window we can see huge area with big buildings and with just a hand we can hide not just a man that is in 10 meters from us but even a whole building located far away. To get to know why this happens, we should first learn some basics.
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This article first appeared in November, 1998.
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