I don't know much about lens construction. I'm curious why a lens like the 12-35 ($1300 USD) is so much more expensive than something like the new 45-150 ($300 USD). Aside from "better construction", are the lens elements a large factor? For example, the 12-35 has 4 aspherical lenses, 1 UED lens, and 1 UHR lens. The 45-150, on the other hand, has 2 fewer aspherical lenses, and no UED lens. Also, how does aperture factor in? Novice questions, I realize.