The 18mm has less distortion than the manual focus 20mm lenses. If you keep a straight line, like the horizon, along the top edge, it stays remarkably straight. Few if any Nikon wide angles can make the shot above without the line along the top bowing out.

Lines parallel to any of the edges stay straight.

Close Focus: 0.25m or 0.85 feet.

Sharpness: It gave the usual performance: a soft corners wide open, improving greatly a stop or two down.