What is perspective? It is the science of painting and drawing so that objects represented have apparent depth and distance.
Perspective is a complex subject. However, for still life drawing it is necessary to know just a few basic rules and vocabulary:
The horizon line is the eye level of the artist/viewer. This line changes as the viewpoint is raised or lowered which allows the viewer to see more or less of the plane depicted.
The vanishing point is the point on the horizon line at which parallel lines seem to meet. In a still life, it is very rare that the vanishing point is actually on the picture plane due to the fact that the objects are relatively close to the viewer.
There are two main rules of perspective: One, all straight lines are straight. Often in photography straight lines bend due to camera lens distortion. Two, all verticals are always vertical in relationship to the picture plane.
In still life there are two types of perspective: One point and two point. One point perspective occurs when all parallel horizontal lines converge or meet at a single point. The viewer is parallel to the cube. A practical application is a drawer coming out of cabinet or a table that is parallel to the bottom of the picture plane (see example below). If a corner or leading edge is not present, it is one point perspective.
In two point perspective there are two sets of parallel lines and two vanishing points. The two vanishing lines occur not because the cube shape has changed but the viewer’s angle or vantage point has moved. The viewer can now see the leading edge or corner of the cube. This type of perspective also is vital in still life drawing.
When an object is observed from a fixed viewpoint and the eye-level is constant, the illusion of from and space is made more convincing if converging lines move away from the position of the onlooker toward a single vanishing point. This is based upon the fixed central viewpoint, which relies on the optical impression that parallel lines converge toward a singe point.
Figure 1 shows the conceptual view. The plane is larger at the top and smaller at the base, and the middle line is shorter than the sides. This is based on our common sense, that to place objects on a box top, the top must be large, and to put a box on the floor, the box must be flat at the base.
Figure 2 shows the actual view. The planes are equal at the top and base and the middle line is the same size as the sides. This is based on the way a box is made by machine with equal sides.
Figure 3 is the perceptual view. The planes are smaller at the top and larger at the base and the middle line is taller than the sides. This is based on a static viewpoint in which the eye level is fixed and constant. The perceptual view ties up with the way that planes get larger away from the eye level. Also, it coincides with the evidence observed when viewing the open box. It means that this view comes the closest to the truth of seeing. The middle line is taller, so will appear nearer to the onlooker, with angles seeming to converge back from the picture plane to give perspective.