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EXCERPT page containing first few paragraphs. 2023-02-08 02:47:19

Leica 16-18-21mm f/4 Tri-Elmar-M ASPH
(not to scale)

MTF vs 18/3.8

At f/4 the Tri-Elmar and 18/3.8 SEM are essentially identical within a 10mm radius from center, but the 18/3.8 SEM maintains much higher performance across the field (and it might be even a touch better at f/4 than the f/3.8 as shown). That difference might be a high priority if one shoots regularly at f/4.

At f/5.6, both lenses have improved in the outer zones, but the 18/3.8 SEM is really at a world-class level for an 18mm lens; the Tri-Elmar lags considerably in the outer zones, nothing that this might be in part field curvature, which means that the 18/3.8 SEM is far superior choice for buildings, distant landscapes, etc.

At f/8 the two lenses are very similar, but this is somewhat misleading on a planar MTF target: field shots show a zone of sharpness with less curvature; the 18/3.8 SEM has a flatter field (lower field curvature. A minor focus error isn’t so bad with the 18/3.8 SEM, but with the Tri-Elmar it can throw mid zones well into “soft” territory.

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Diglloyd Guide to LEICA contains in-depth coverage of Leica M system cameras and lenses, with additional coverage of Leica M Monochrom, Leica Q.

Special emphasis is placed on Leica M lenses and certain Zeiss ZM lenses.

  • Make better images by learning how to get the best results right away.
  • Save money by choosing the right lens for your needs the first time, particularly the Summilux/Summicron/Elmarit choice and/or Zeiss ZM.
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  • Real world examples with insights found nowhere else. Make sharper images just by understanding lens behavior you won’t read about elsewhere.
  • Aperture series from wide open through stopped down, showing the full range of lens performance and bokeh.
  • Optical quality analysis of field curvature, focus shift, sharpness, flare, distortion, and performance in the field.

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