Focal /(?)/
Fo·cal
Focal
a.
- Belonging to,or concerning, a focus; as, a focal point.
Phrases & Compounds
- Focal distance
- 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.