Autofocus is an internal mechanical system that allows a lens to focus automatically.

Image stabilization is a method of reducing the likelihood of blurred photos. Lenses with image stabilization use floating lens elements that operate independently of the lens itself to reduce the effects of camera shake.

Weather resistant lenses are equipped with a special coating to prevent moderate amounts of water and particles from damaging the lens.

A lens with a fixed max aperture will have a constant max aperture at all focal lengths.