Perspective: the Picture Plane and Diminution with Distance
The perspective screen works like a sheet of glass; how sizes shrink and shift with distance
Leonardo continues the perspective section with short propositions on how apparent size depends on distance. He introduces the 'perspective screen' — a vertical plane set in front of the point where the visual pyramids meet — which functions like a sheet of glass onto which one can trace what is seen, the traced objects shrinking in proportion to the distances involved. Further propositions treat objects with right-angled edges, and note that a spherical body reveals more of itself the farther it recedes. Small diagrams of the eye with converging rays accompany the text.
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No large distant body looks bigger than a small near one
No body is so great in magnitude that, over a long distance, it will not appear smaller to the eye than a smaller object placed nearer. This is the founding statement of apparent diminution with distance.
The perspective screen as a sheet of glass
The perspective screen is a perpendicular line set in front of the common point where the pyramids meet, behaving like a pane of glass on which one may trace the things seen through it. The traced objects come out smaller than the originals in the same proportion as the eye-to-glass distance is less than the glass-to-object distance.
Right-angled planes seen closer show less of themselves
For planes whose edges meet in perpendicular lines forming right angles, and which are of equal width, the nearer the plane comes to the eye the less of it is seen, and the more it passes beyond the eye the more its true size is revealed.
A sphere shows more of itself the farther it recedes
The farther a spherical body moves away from the eye, the more of its surface you see — a proposition set apart from the rules governing flat, right-angled planes.