I själva verket tror jag inte att daggdroppen fungerar som lins utan droppen ändrar brytningsindex i den enskilda facettens lins så att man kan se in i den enskilda facetten.


Dewdrop as an extra lens on an eye of a butterfly

Actually I doubt that the dewdrop acts as a lens. I think that it changes the refraction index and thus "opens up" the single "eyes" of the compound eye letting you look "inside"