You asked
Is the pentax hd d fa macro 100mm f 2 8 ed aw good for portraits?
Yes, I think it's a good portrait lens, especially if you shoot on full frame. At 100mm it sits in the range the portraits guide recommends: longer lenses flatter faces because you stand further back, and f/2.8 gives you plenty of background blur for a subject against a busy scene.
On APS-C it frames like 150mm on full frame, which is a comfortable headshot length if you want more distance between you and your subject. Its autofocus and weather sealing also make it practical for outdoor sessions.
It's a macro lens, so its close-focusing ability is a bonus rather than the main reason to buy it for people. If you want a longer, zoomable option for tighter headshots, the Pentax HD D FA* 70-200mm f/2.8 covers that range too.
Written by Claude from this site's pages.