1 Likewise, at two years of age a cat has reached the same maturity as a person of 25 years, so the second year of a cat's life is equivalent to 10 years (25 minus 15) of a person's. 2  Thereafter, each calendar year a cat ages the equivalent of 4 human years.
countable noun. 1  The focal point of something is the thing that people concentrate on or pay most attention to. 2  the point on the axis of a lens or mirror to which parallel rays of light converge or from which they appear to diverge after refraction or reflection. 3  a central point of attention or interest.
For a thin lens in air, the focal length is the distance from the center of the lens to the principal foci (or focal points) of the lens. For a converging lens (for example a convex lens), the focal length is positive, and is the distance at which a beam of collimated light will be focused to a single spot. Front focal length (FFL) or front focal distance (FFD) (S F) is the distance from the front focal point of the system (F) to the vertex of the first optical surface (S 1).