[Ayoh]

Depends on the portrait style. A face close up can be done with any reasonable semi-telephoto lens, however a body portrait in an environmental context is more challenging and personally to me, more interesting. Here greater depth of field control and fast lenses with limited aberrations becomes useful. To be honest I find that highly cropped head shot portrait style presented in the link to be boring and the supposed skill of some of the photographers to portray the character of the subject overrated (e.g. Annie Leibovitz - an icon due to socially integrating herself into the US celebrity club rather than unique skills). Environmental/contextual portraits are more interesting and difficult, Steve Curry is quite good at those, Also Joey L.