FOCAL

focal. Focal, a. belonging to a focus or point

---

Fo″cal (?), a. [[Cf. F. focal. See Focus.]] Belonging to,or concerning, a focus; as, a focal point. Focal distance, or length, of a lens or mirror (Opt.), the distance of the focus from the surface of the lens or mirror, or more exactly, in the case of a lens, from its optical center. —Focal distance of a telescope, the distance of the image of an object from the object glass.