A lens is a transmissive optical device that affects the focus of a light beam throgh refraction. Lenses are made of transparent materials such as glass, ground and polished to a to a desired shape. A lens can focus light to form an image unlike a prism. A divergent lens is based of two thin glasses that are united together.  The image is always virtual and is located between the object and the lens. In contrast convergent lenses: as long as the object is outside of the focal point the image is real and inverted.When the object is inside the focal point the image becomes virtual and upright (see animation).  

http://www.acs.psu.edu/drussell/Demos/RayTrace/Lenses.html

Below some pictures we took when performing our experiments: