DVDs are read optically instead of mechanically.
The artefacts are dated using a method called optically stimulated luminescence.
The system uses two prisms within the lens housing to optically compensate for camera shake.
Optically, there was little to choose between the two machines in terms of image clarity and definition.
According to conspiracy theorists, CIA experts edited and optically manipulated the film to mask what had really happened.
Some of the patterns seem to vibrate optically, like the op art of the 1960s.