The same field z = a·x·y, read four ways. A lens does not change the surface; it chooses what to read off it.
Why there is genuinely no store here. Open the source. You will not find a data array, a Map, or a saved field. The render function computes each pixel directly from z = a·x·y and the active lens. The pixels are a transient rendering of the definition, thrown away and regenerated whenever you move a dial. The definition is the source of truth; the picture is derived from it.