Talk:Zeiss Planar
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The 2.5/105 Nikkor in its later versions (well, from 1971 on) can not really be a Planar - it has 5 lenses in 4 groups, not 6 single lenses. Source: http://www.photosynthesis.co.nz/nikon/lenses.html
Much of the information in this article is incorrect. Perhaps I will edit it later. The Planar was indeed invented by Paul Rudolph of Zeiss in 1896. Rudolph wanted a better lens than was available for speeds of around f/4.5. At the time the Double Gauss type offered the speed but had an excess of a type of aberration known as oblique spherical aberration. This leads to a smeared effect in the image away from the center. Rudolph found that by thickening the negative elements and decreasing the spacing of the elements in the Double Gauss type he could improve the correction for the oblique spherical and also improve the astigmatism. However, with the glass types available at the time he found that suitable glass was not available. Rudolph then came up with the idea of a "buried surface", that is a cemented surface between two elements of glass with the same index of refraction but different dispersion. That allowed him to obtain chromatic correction. The original Planar was a symmetrical lens with six elements in four groups, the inner, negative lens consisting of two cemented elements. The name stems from the good correction for geometrical distortion. Symmetrical lenses have the advantage of automatic correction for three transverse aberrations: coma, lateral color, and geometrical distortion. For the most part the Planar design was not much used by the optical industry until an unsymmetrical version was designed in 1920 by Horace W. Lee, of Taylor, Taylor, and Hobson, an English optical manufacturer. Lee's lens had a speed of f/2. It was called the Opic. The lens did not have wide sales because it was a stand alone. However, other designers began to use the same basic design, for instance Tronnier of Schneider for the f/2 Xenon and Willie Merte of Zeiss for the well known Biotar series. Sometime about the mid 1920s TT&H began to produce the very successful Panchro and Speed Panchro lenses for motion picture cameras. These were for many years the standard lenses used in Hollywood. There are Planar type lenses with more than six elements; the extra elements generally added to increase speed or improve corrections. In 1944 Charles G. Wynne found that he could eliminate one element from the Planar by combining two of the elements and still get excellent correction. He designed a series of lenses for Wray, a British company, called the Unilite. However, the best known of the five element Planar lenses are the f/2.8 Schneider Xenotar and the somewhat later f/2.8 Zeiss Planar, both used on Rolleiflex cameras. VEB-Zeiss also produced a lens of this type called the Biometar. The basic Opic variation on Rudolph's Planar is the bases for nearly all lenses of f/2 or faster used on 35mm still cameras and on motion picture cameras. The best source of historical information on these and other photographic lenses is:
A History of the Photographic Lens Rudolf Kingslake 1989, The Academic Press ISBN 0-12-408640-3 —Preceding unsigned comment added by Oldlens (talk • contribs) 19:28, 3 July 2009 (UTC)