(from the article `photography, technology of`) Supplementary close-up lenses or extension tubes (placed between the lens and camera body) allow the camera to focus on near distances for large ...
Found on
http://www.britannica.com/eb/a-z/s/188
Generally a simple positive (converging) lens used in front of the camera lens to enable it to focus at close range. The effect is to provide a lens of shorter focal length without altering the lens-film separation, thus giving the extra extension required for close focusing.
Found on
http://www.rodsmith.org.uk/photographic%20glossary/rods%20photographic%20gl
No exact match found.
