A viewer moving up or down in front of a rainbow hologram sees changing spectral colors rather than different vertical perspectives. Because perspective effects are reproduced along one axis only, the subject will appear variously stretched or squashed when the hologram is not viewed at an optimum distance; this distortion may go unnoticed when there is not much depth, but can be severe when the distance of the subject from the plane of the hologram is very substantial.
When a viewer moves up or down in front of a rainbow hologram, they see shifting spectral colors instead of different vertical views. This is because perspective effects are only reproduced along one axis, causing the subject to appear stretched or squashed when not viewed at the optimal distance. This distortion may be subtle when there's little depth but becomes severe when the viewer is far from the hologram's plane.