Likewise, a converging lens makes a parallel rays that goes through it converge at a single point. The point is called focal point and is found on the other side. The lens is also known as convex lens.

Let us get familiar with certain optics terms. In the diagram, the parallel rays passing through a converging lens met at a certain point called focal point. All lenses have focal points, one on each side of the lenses. Although the focal point on the diverging lens was not so apparent in the diagram, but for sure it is located at some point where the rays appear to be coming from on the first side of the lens.

Focal length is the length of which each of the focal points lies a fixed distance from the lens. It is expressed in meters. The reciprocal of a lenses focal length is called its power. This measures how well a lens can make a light beams converge. It is measured in dioptres (D). The power of a converging lens is always expressed in a positive power. While a diverging lens, does the opposite of making beams which is a negative power.

Focal points lie on a line which goes through the middle of the lens. This line is identified as the principal axis. It is used in lens diagrams to show what will happen to an image. It is because the principal axis passes vertically to the lens, and through the center. Rays on it remains unchanged and it is therefore used as a kind of point of reference in lens diagrams.

Posted 2010-11-08 and updated on Nov 08, 2010 3:50am by imcarms