Today’s invention is sunglasses with swappable combinations of lenses.
The lenses are fitted to a vertical post at the junction of the across-the-face bridge and the over-the-ear leg (a weakness in almost all spectacles). The specs would fold up as usual.
Onto this post would slide a number of turnable collars, one for each lens (shown in different colours).
When not in use, lenses would be flat against each other, providing a ‘blinker’ design down the leg.
This would allow a combination of lenses to be superimposed on each eye, for different colour viewing effects.
For someone who needs them, prescription lenses could be used here, as could photo- or electrochromatic ones.
Similarly, when using augmented reality, a lens with display information could be incorporated and rotated out of the way when not needed.