the cook should get and have some spares in the drawers
What do you mean by that ?)
I believe the correct answer is: material that the lens is
made from.
Lenses are engineered to have
specific focal lengths, besides the curvature of the two sides of a lens. The
focal range, the distance between your optic nerve and the retins in lens, of
the lenses is determined by the material that lenses are made from.
Using all of it at times and only small parts of it at others..... not fully certain
