St. Matthew Group 3

Types of Lenses

Convex	Double Convex	Plano-convex	Positive Meniscus or Concavo-convex
Concave	Double Concave	Plano-concave	Negative Meniscus or Convexo-concave

Definition of Terms

Convex: A convex lens is a lens that bulges at the center, and is a converging lens.
Concave: A concave lens is a lens that is thinner at the center, and is a diverging lens

Parts of a Lens

Optical Center: The optical center is the point where all light rays pass without being bent, and is marked with the P in diagrams.
Principal Focus: The principal focus is where the rays intersect (in convex lenses) or appear to intersect (in concave lenses). It is symbolized with F for the primary principal focus or F’ for the secondary principal focus.
Focal Length: The focal length is the distance of the optical center to the principal focus of the lens.

Do note, that the primary principal focus and the secondary principal focus is equidistant to the optical center.

Image Formation of a Convex Lens

Object Position	Image Position	Characteristics of Image
At infinity	At F	Real, inverted, and very small
Beyond 2F’	Between F and 2F	Real, inverted, and smaller than the object
At 2F’	At 2F	Real, inverted, and the same size as the object
Between F’ and 2F’	Beyond 2F	Real, inverted, and bigger than the objectl
At F’	At infinity	No image formed because the rays are parallel
Between F’ and the lens	In front of the lens	Virtual, upright, and bigger than the object

The image formed by a concave lens is always virtual, upright, and smaller than the object, and is located at the same side of the lens as the object

References