Archived posting to the Leica Users Group, 2000/09/26
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]> from the same site: > "Angenieux invented the inverse telephoto concept with their first > Angenieux Retrofocus lens designs. This approach makes it possible > for SLR cameras to mount very wide angle lenses without having to > lockup the mirror." The statement can be seen as a bit of a stretch, since motion picture projectionists often used a negative element "magnifier" in front of their projection lens to effectively shorten the focal length of the projection lens. Angenieux was indeed the first to apply the inverse telephoto configuration on a 35mm SLR, however. Its first lenses, 28/3.5 and 35/2.8 were rather mediocre at best. One of the problems with the inverse telephoto designs of the time was that the rear group, often a Triplet, a Tessar or a double-Gauss configuration themselves did not help increase the distance between the rearmost element and the film plane. The early Angenieux used a positive-positive-negative-positive configuration in the rear group. The rear group by themselves did not help increase the back-focus, and the front negative group had to be quite strong. Nikon finally ended up with a single negative element up front with its second or third generation 35/2.8 lens, with a modified Triplet, with an extra positive element at the rear, which increases the distance between the rearmost element and the film plane in comparison to a single positive element of the same power . The configuration of a negative group up front, with four groups (each of which could consist of a single element) in the order of positive-negative-positive-positive is used in essentially all SLR inverted telephoto lenses today. At around the same time, Nikon also introduced the first commonly available inverted telephoto lens with varying spacing between groups primarily for reducing various abberations at close range, the venerable 24mm/2.8 lens.