Archived posting to the Leica Users Group, 1999/07/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]There seems to be some discussion on this list about lens design and history. This area is extremely tricky and very prone to misunderstandings if one does not define with exactitude what is being claimed. The Cooke triplet has been invented by Taylor in 1893. It's defining characteristic is a layout of a first positive meniscus, then a negative middle meniscus and a positive meniscus as the third element, positioned in such a way that symmetry exists. This symmetry is Taylor's genius, not the three lenses as such. This basic layout (including the symmetry) can be patented and is original. But the choice of glass, the radius of the surface, the distance between elements and the position of the stop can be varied at will. So in its basic layout this type of triplet (+ - +) is the genius of Taylor. What will happen when a designer changes every singlet into a cemented double. We still have a triplet, but now with six elements. Is this still contained in the Cooke -idea. The Sonnar and the Ernostar are also a triplet type. Is the Sonnar then a Cooke triplet, simply borrowed by Zeiss to make a few insignificant changes. Rudolph's Tessar has indeed three groups, but Rudolph designed this one in 1902, as a modification of the Protar, not the Cooke. Tessar is from the Greek word meaning 'four', and it designates the four lens elements. It might be called a derivative of a Cooke triplet, but so much original thinking went into the Tessar, (the additional lens surface gives the designer one more parameter to correct aberrations)that it should be counted as an original design. Which aberration to correct, what type of glass to use, which radius of curvature to take are fundamental design questions, that are not inherent in Taylor's design. The answers can not be read from Taylor's lens prescription. I think it most unfair to address this topic as a simple borrowing and reworking of an older design. The same story goes for the Double Gauss or Planar design. Almost every (near) symmetrical lens with six lenses in three groups can be called a Planar design. Even if the rear or front element or both is split (producing seven or eight glass lens elements) is still is basically a Planar. Thus almost every lens made from 1896, when Rudolph designed the lens) till today in Japan, Germany, France, Italy and America in the focal length bandwidth from 35 to 90 millimeter (in 35mm format) is a derivative of the Planar. The same goes for all lenses in the medium format in equivalent focal lengths. One could also try to make a case that every six cylinder engine is just a reworking of the first one ever designed, disregarding the enormous engineering effort that went into the several designs from other manufacturers. I am not sure what the original poster tried to prove. On a very broad perspective one can argue that all lenses (except the zoom lenses) are all based on one design, the triplet (the Planar is a triplet too! 3 lens groups,identical to the Taylor layout). But does this prove, that all designers are just borrowers of ideas of their predecessor, without adding much of themselves into a 'borrowed ' design? If it were so easy why then are so many patents granted to Planar type lenses which on surface look quite alike. Is the patent bureau nuts? Or is there much more in an optical design than counting lens elements. The answer to the question if lens A is a derivative of lens B is not particularly enlightening. Yes the Hexanon 1,2/58 mm is a direct derivative of the Planar lens built into the Hasselblad. What do we know now? Do the Konica designers play the copycat game.? Not at all! They are genuine original thinkers and designers who do what all original and thinking designers do. They formulate their demands for the new lens, look into existing promising designs or in the history or in patent literature and then add their own ideas. Or let the computer do part of the thinking. Why should you find in the literature of optics several books with thousands of design examples to work upon freely. The American Optical Society has every year a contest to improve an an existing design. The original post seems to shed a false light on the working practise of thousands of optical engineers since 1900 and Marc is right to correct this new myth that is getting space on the Lug. Erwin