I'm not even sure Firefly supports proper refraction ? TBH after using Superfly exclusively for the last half year or so, there is no way I'd ever go back to Firefly.

-50 or +50 is way too much - are you looking at the wireframe from the side to see what's going on when you turn the dial?

Optics moves the INNER surface, since moving the outer surface of the lens will intersect the outer surface of the eye.

-1.4 is pretty much the limit, since at that point it's so convex that the inner surface is nearly touching the outer.

+2 makes a huge convex lens

-50 has the inner convex lens surface protruding 2" out from her head O_o

I'm not a fan of setting limits on dials (especially on experimental stuff like this) because I figure that someone out there may want to use something in a way I didn't foresee.