1. Pinhole/Central Perspective
If the pinhole were really reduced to a point, exactly one light ray would pass through each point in the plane of the plate, the pinhole, and some scene point.
It's sometimes convenient to consider instead a virtual image (not inverted but otherwise strictly equivalent to the actual one) associated with a plane lying in front of the pinhole, at the same distance from it as the actual image plane.
a. Far objects appear smaller than close ones.
b. The images of parallel lines converge on the horizon line formed by the intersection of the image plane Π with the plane parallel to Φ and passing through the pinhole.
2. Weak Perspective/Scaled Orthography
When a scene's relief is small relative to its average distance from the camera, the magnification can be taken to be constant.
