There seems to be a major misconception about this design of lens. The telephoto is a type of lens design, not just all long focal length lenses. The telephoto design is characterized by a positive lens group in front and a negative element or group in the rear. The rear group or element is used to extend the focus beyond the actual distance represented by the front element to focal plane distance. This effect is known as telephoto ratio. The effective focal length is actually longer than the front element to film distance. This is important when trying to lessen the weight of a lens. Can short focal length lenses be telephotos? Yes- Kodak used a telephoto design on one of their disk cameras. Focal length was less than 50mm. Most view camera long lenses are not telephotos but are Plasmat designs. There are a few long lenses for view cameras that are telephotos however. SR

-- Steve Rasmussen (srasmuss@flash.net), December 23, 1998