The Kirk FR-1 Focusing Rail is a lightweight geared-track macro stage that offers precise movement for macro work. The rail provides 3.9" (10cm) of movement, and its base fits directly into any Arca Swiss-type quick release clamp. It also features a swiveling Arca-type quick release clamp on top, which can be used in combination with Kirk's plates, or any of the other Arca-type brands (Arca-Swiss, Foba, NPC, Gitzo, etc.).
Using a focusing rail saves you time and improves results when shooting precise macro work. It is especially ideal for use with lenses used in the "reversed" position, for extreme macro work.