[Leica] aspherics

[imxputs <imxputs@knoware.nl>]

Aspherics in the Leica line are of two types.
       Glass elements that are grinded by CNC machinery. This machinery has 
been developed by an
       independent commercial manufacturer who developed the instrument in 
coopertaion with Leica,
       but are free to sell it to anyone. Same arrangement goes for Leica 
developed glass that is now in
       the regular catalogues of Schott and Corning. Glass elements that can 
be heated and then
       pressed into shape by ceramic moulds. Only a few glasses can survive 
this technique. All glass
       of this type is from Hoya. Zeiss uses the same technique with glass 
from the same glass supplier.

       The aspherics technology is not new. The idea of using aspherical glass 
for corecting aberrations
       has been proposed by Huygens (18th century scholar). The first 
practical application came
       around 1930. It is not the machinery that is important but the 
computation of the curvature of the
       glass AND the creativity of the designer to know what he/she is doing.
       Production technology should be closely tied to optical design.

       It makes no sense to talk about lens designs and which lens is a 
derivative of another one. Being
       very strict only a few types exist and all the rest are variants 
thereof. Anyone ever noticed that
       almost all Japanese 50mm lenses are close copies of the Planar type. 
Still their performance
       differ widely.
       Any designer would be foolish to try to dvelop a totally new design. 
Everyone builds on proven
       designs.

       Erwin