Sometimes you don't need a lens
Conditions dark enough to see the Milky Way with the naked eye, beyond our neighboring stars, may be enough to trigger, through perspective, the conceptual leap that "the sky" is not the decorated interior surface of a sphere of some arbitrarily distant radius. I had the pleasure of watching that transforming realization emerge in a new friend a couple of weeks ago... as close to an epiphany as I may ever see in anyone other than myself.
