See the first part of this discussion which used a resolution chart.
This page shows diffraction at work on a detailed mosaic, where the degradation in contrast can be seen in the fine edge detail of the tiles which compose the mosaic.
This series is from f/4 through f/45 using the Coastal Optics 60mm f/4 UV-VIS-IR APO macro. The high resolution of the D3x along with top optics means that as soon as f/8 is reached, the contrast-robbing effects of diffraction begin to be seen, first in the micro contrast of fine edge detail, then in overall “graying” of the image, then in obvious resolution loss.
Contrast is slightly low at f/4, peaks at f/5.6, then immediately shows a slightly decline at f/8, this accelerates at f/11 and becomes obvious by f/16.
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