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Leica 16-18-21mm f/4 Tri-Elmar-M ASPH

MTF: 16-18-21/4 Tri-Elmar-M ASPH

Performance is remarkably consistent at 16mm and 18mm and 21mm. Aside from minor variations in, the shape of the MTF curves at 40 lp/mm (micro contrast for fine details) changes very little. Moreover this is true at f/4, f/5.6 and f/8. One cannot even say it is significant in the sense that the MTF curves might reflect slight differences in field curvature than any real-world difference in actual performance on a 3D subject (as opposed to a planar MTF testing target).

At f/4, performance is very high centrally and to about the central 1/2 of the frame, but then plummets towards in the mid-zones and periphery. The cause is likely twofold: field curvature (sharpness in a curved zone) as well as diminishing optical performance off center.

Stopping down to f/5.6, sharpness extends out a bit farther from center, but remains at modest levels outside than central ~12mm diameter area from center. But stopping down to f/8 the performance suddenly rises to excellent levels at the edges. The explanation is field curvature: depth of field has now brought those areas into sharpness. Put another way, the lens is likely performance at high levels in the outer zones even at f/5.6 (and perhaps f/4), but it does so in a curved zone outside of the nominal plane of focus, a theory confirmed with field shots (the sharpness arcs forward in fact.

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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.
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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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