Archived posting to the Leica Users Group, 2001/07/08
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]> 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."