Archived posting to the Leica Users Group, 2003/05/01
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Right on, Don! One correction: the Dual-range/Rigid 50/2 Summicron formula has slender air-lenses between the elements of both front pairs; the second pair of lenses is not cemented but separated by a razor-thin air lens, so thin that in some cross-section illustrations they appear to be cemented. It is those air-lenses, in creating 12 air-glass surfaces in this lens, that result in the slightly lower contrast of this lens vis-a-vis the two later formulations, the contrast differences virtually disappearing as the lenses are stopped down. The current 50/2 Summicron has only six elements and eight air-glass surfaces (no "air lenses") precisely to imrpove full-aperture contrast. Don Dory wrote: > The optical design consist of a rather large front pair of elements with a > very small air lens separating the two elements. The next pair of cemented > elements is heavily positive. After the aperture is a cemented doublet > concave, concave, slightly convex, more convex. The last element is rather > large. Three of the elements are LaK9. > > You didn't ask, but along around 1955-57 Leica redesigned the lens again, > adding another high refractive element as the rear element, and enlarging > the air lens in the first group. Also, the rear group was enlarged to > accommodate the larger throat of the M series. Properly cleaned and > assembled, this lens is the overall king of Summicrons, especially when > shooting B&W. It does not quite have the contrast of the latest one, but if > you can adjust your developing of printing, this is one wonderful lens. Seth LaK 9 - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html