You asked
What is the pentax hd da 11 18mm f 2 8 ed dc aw good for?
The Pentax HD DA* 11-18mm f/2.8 is a wide zoom for APS-C, and it suits landscapes well. On a Pentax K body it frames roughly like 16-27mm on full frame, which gives you big skies and strong foregrounds. It's weather-sealed, so it can handle a damp hike.
The f/2.8 aperture is fast for a wide zoom, which helps in low light, but landscapes rarely need it. You'll usually shoot between f/8 and f/11 anyway, so an f/4 zoom would do the job for less weight and cost. This lens isn't stabilised, so keep shutter speeds up or use a tripod at dusk.
It fits a long list of Pentax K bodies, from the Pentax KP to the Pentax K-3 Mark III. On the full-frame Pentax K-1 it works in APS-C crop mode. For more on wide zooms, see the Landscape guide.
Written by Claude from this site's pages.