Follow two rays through the opening

This geometric model keeps a tiny opening at the center and follows straight rays from two object points to a screen. Distances are arbitrary units. It omits aperture width, diffraction, brightness and lenses.

Two rays cross at a pinholeA top object point reaches the lower screen and a bottom point reaches the upper screen.OpeningObjectScreen

Increase only screen distance: the image grows. Increase only object distance: it shrinks. Inversion remains. This ideal point model does not imply that the smallest possible physical hole is always sharpest.