How to shoot portraits with Pentax DA 17-70 lens?

1770' s biggest highlights are SDM and practical focal length, but the picture quality is really unsatisfactory. The head with constant aperture is so soft. . Besides, what you said is that you can't adjust it above F4, because the maximum aperture of this lens is F4.

If you really want to take a portrait. . It is suggested to give priority to DA70, or find a FA24-90, 1770, which is not clear enough, and is not suitable for portraits. . Or save some money and go directly to DA*50- 135, which is a special portrait.