Archived posting to the Leica Users Group, 1997/10/31
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Paul Schliesser wrote: > Dan, > > You know those little numbers after the distance scale, which tell you > what the actual focal length is? When I was photographing stuff for the > Photo Techniques article, at one point I examined two of these lenses at > the same time, (both chrome), and happened to notice that one was marked > 00 and the other 90. This means that the second one was nearly 100mm. > This made me wonder if there was not something different going on here as > far as optical formula. Both lenses looked identical. > > None of the books I've seen mention a change in formula. > > Jim Lager's books have the most detail about lenses of any books that I > am aware of. His _Leica An Illustrated History, Volume II-Lenses_ covers > all of the thread mount, M and R lenses, up until 1994. Volume I is on > cameras, volume III will be accessories, but is not out yet. You can > order it from Tamarkin, http://www.tamarkin.com > > The other books I've seen either cover lenses superficially or cover only > modern lenses in any detail. > > The one I own, in chrome, is marked 00. The serial number is 1735706. > Maybe you could poll the list and find out what is out there. > > - Paul Paul, Its a bit confusing but 00 means 90.0. 90 means 89.0. if the number is less than 50 insert a decimal point between the two digits and put a 9 in front of it, otherwise insert the decimal point and put an 8 in front. Thus the maximum variation in focal length would be 5 mm. In practice its never this far off. My recollection of the 135, 75, and 35 is that the last digit of the focal length is just replaced by the digits formed as above. So 50 on a 75mm lens would be 75.0. Not sure how the 21mm is done, if it is even marked. Dennis - -- Experience is a tough teacher. It gives the test before the lesson. - -unknown