Archived posting to the Leica Users Group, 2000/01/21
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Erwin's narrative, in-depth analysis of a lens' optical performance and character is a very demanding reading. In contrast to that BAS concludes with an easily understandable, two digit rating. However, there are a quite a number of performance indicators, e.g. contrast, resolution, MTF which can be measured at varying f-stops, focussing distance, distance from optical axis or, in case of zoom lenses, focal length. In addition to that there are centering, vignetting, distortion, neutral colours etc.. Even with a simplified test schedule, e.g. only three f-stops etc., you get at least 100 values which have to be aggregated. It's not easy to develop a system of weighing factors that adequately reflect a typical photographer's preferences. The one problem I have with BAS tests is the scale he using to rate the lenses. Even a cheap 28-300 zoom gets at least 8.4 whilst a new Elmar 50/2.8 or a Tri-Elmar gets 9.0. The 9.9 for the complex super wide R 19/2.8 is a big surprise. Does this mean the Elmars are only 7% better than the 28-300 and the 2.8/19 is 10% better than the Elmar? Production tolerances are another problem. Sometimes you find a comparison between third party lenses with identical designs, presumably from the same manufacturer, but with different badges. And then the rating may differ by 0.1 or 0.3 points. I even remember a comparison between a Leica and Minolta badged 70-210 zoom, with the "Leica" one being some 0.1 or 0.2 points better. Another question I have is how the lenses perform when they are used and get old, particular zoom lenses with a complex system of gears and cams to move the lens groups? Hans-Peter