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.
The focal point is denoted by the letter F on the diagrams below. Note that each lens has two focal points-one on each side of the lens. Unlike mirrors, lenses can allow light to pass through either face, depending on where the incident rays are coming from. Subsequently, every lens has two possible focal points. The distance from the mirror to the focal point is known as the focal length (abbreviated by f). Technically, a lens does not have a center of curvature (at least not one that has any importance to our discussion). However a lens does have an imaginary point that we refer to as the 2F point. This is the point on the principal axis that is twice as far from the vertical axis as the focal point is.