Archived posting to the Leica Users Group, 2001/07/08
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Erwin's web site carried a different explanation that would have allowed a 0.58x M6 to squeak by with a 90/2. On Sun, 8 Jul 2001 shino@ubspainewebber.com wrote: > > From: "Michael Reichmann" <m_reichmann@hotmail.com> > > > > With concerns about the rangefinder accuracy of the Summicron and the .58 VF > > I called the product manager at Leica's Canadian distributor the other day > > with my concerns. He replied that his personal experience and information > > from the company indicated that there was no reason not to consider the f/2 > > 90mm, .58 VF combo. > > > > Of course this doesn't mean that there won't be an issue but at least it > > isn't vebotten. > > > on page 226 of leica lens compendium, puts gives a detailed exposition > of rangefinder accuracy and on page 228 gives a table showing the > "effective rangefinder bases" needed for the various M lenses. > according to this table, even at the more lenient 0.03 circle of confusion > tolerance, the 90 summicron needs en effective base of 48.5, which is barely > covered by the 0.72 (effective base 49.86) and not by the 0.58 (e.b. 40.17) > however, the "effective base" calculation does incorporate a number human > factors, so i suppose it's possible some will do better and some worse. > > regarding relative depth-of-field, using formulae i took from > http://members.home.net/gillettm/DOF.html > i put together a little spreadsheet of depth-of-field > of some current fast m lenses. the 90/2 has the second > smallest depth of field after the 135/3.4 *, about 1.86 inches > at 6 feet, which is much smaller than the noctilux at 6 feet > (3.08 inches) and practically the same as the 75/1.4 at 6 feet > (1.89 inches). i was surprised that the noctilux had over one > and a half times greater depth of field that the 90 summicron. > > > Dist (ft)-> 3 4 5 6 7 8 9 10 11 12 > Lens Depth of Field (inches) > 35/1.4 2.17 3.90 6.14 8.89 12.15 15.93 20.23 25.06 30.42 36.33 > 50/1 0.75 1.35 2.12 3.08 4.20 5.51 6.99 8.65 10.48 12.49 > 75/1.4 0.45 0.82 1.30 1.89 2.58 3.39 4.30 5.33 6.47 7.71 > 90/2 0.44 0.80 1.27 1.86 2.54 3.34 4.24 5.26 6.38 7.62 > 135/3.4 0.31 0.58 0.93 1.37 1.88 2.48 3.15 3.91 4.76 5.68 > > (Circle of confusion = 0.03) > > -rei > > * the old 135/4 also had a smaller DOF (1.61 inches at 6 feet), > as of course the 135/2.8, although the latter had the advantage > of magnifying "goggles." >