University of Auckland/Department of Physics/Physics 102/Geometric Optics/Lenses

Focal Point
The focal point of a lens is the point to which a beam of parallel light, parellel to the principal axis, converges.

Converging Lens
A converging lens refracts incoming parellel light rays so the light converges to a single point, called the Focal Point. A converging lens is thicker in the middle.

Diverging Lens
A diverging lens refracts incoming parellel light rays so the light diverges. A diverging lens is thiner in the middle

Real Image
A real image is an image formed by light rays that converge at the location of the image. A real image, unlike a virtual image, can be displayed on a screen.

Virtual Image
A virtual image is an image formed by light rays that do not converge at the location of the image.

A useul link to help explain real and virtual images: http://www.pa.msu.edu/courses/2000spring/PHY232/lectures/lenses/images.html