Photo nerditry: The highest resolution current commercially available 35mm "full frame" cameras pack about 60 million pixels into the sensor, which means each photosite is a bit smaller than 4 µm. With pixels this small, "diffraction" can significantly limit sharpness.

The smaller the aperture (the higher the f-stop number), the larger the "Airy discs" (smallest focusable points) projected onto the sensor.

On a modern sensor, stopping down smaller than about f/8 will reduce maximum sharpness.